- Catalytic hydrogenation of carbon dioxide using Ir(III)-pincer complexes
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(Chemical Equation Presented) Catalytic hydrogenation of carbon dioxide in aqueous potassium hydroxide was performed using a newly synthesized isopropyl-substituted PNP-pincer iridium trihydride complex as a catalyst. Potassium formate was obtained with t
- Tanaka, Ryo,Yamashita, Makoto,Nozaki, Kyoko
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- Heavy-atom isotope effects on the alkaline hydrolysis of methyl formate: The role of hydroxide ion in ester hydrolysis
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Carbonyl carbon, carbonyl oxygen, and nucleophile oxygen isotope effects were measured for the alkaline hydrolysis of methyl formate in water at 25 °C. The carbonyl carbon isotope effect is k12/k13 = 1.0338, the isotope effect for the carbonyl oxygen is k16/k18 = 0.999, and that for the oxygen nucleophile is k16/k18 = 1.023. These isotope effects are consistent with a stepwise mechanism in which the formation of the tetrahedral intermediate is largely rate-determining. The isotope effect on the oxygen nucleophile suggests that the attacking nucleophile in aqueous alkali is water with general base assistance from hydroxide.
- Marlier, John F.
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- Arene ruthenium oxinato complexes: Synthesis, molecular structure and catalytic activity for the hydrogenation of carbon dioxide in aqueous solution
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Two families of arene ruthenium oxinato complexes of the types [(η6-arene)Ru(η2-N,O-L)Cl] and [(η6-arene)Ru(η2-N,O-L)(OH2)]+ have been synthesized from the dinuclear precursors [(η6/s
- Thai, Trieu-Tien,Therrien, Bruno,Süss-Fink, Georg
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- Hydrogenation of CO2 to Formate with H2: Transition Metal Free Catalyst Based on a Lewis Pair
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Hydrogenation of CO2 to formate with H2 in the absence of transition metal is a long-standing challenge in catalysis. The reactions between tris(pentafluorophenyl)borane (BCF) and K2CO3 (or KHCO3) are found to form a Lewis pair (K2[(BCF)2?CO3]) which can react with both H2 and CO2 to produce formate. Based on these stoichiometric reactions, the first catalytic hydrogenation process of CO2 to formate using transition metal free catalyst (BCF/M2CO3, M=Na, K, and Cs) is reported. The highest TON value of this catalytic process is up to 3941. Further research revealed the reaction mechanism in which the Lewis pair enables the splitting of H2 and the insertion of CO2 into the B?H bond.
- Zhao, Tianxiang,Hu, Xingbang,Wu, Youting,Zhang, Zhibing
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- Synthetic routes to a coordinatively unsaturated ruthenium complex supported by a tripodal, protic bis(N-heterocyclic carbene) phosphine ligand
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A facile, one pot synthesis of a coordinatively unsaturated ruthenium complex supported by a tripodal, protic bis(N-heterocyclic carbene) phosphine ligand is presented. A number of coordination complexes were discovered en route during this synthesis, revealing some of the unique aspects of complexes ligated by this type of tridentate, protic bis(NHC) ligand. Through a combination of 1D and 2D NMR spectroscopic analysis and single crystal X-ray diffraction, we reveal the intermediacy of phosphine-ligated bisimidazole complexes and show that abstraction of inner-sphere halide ions facilitates conversion to the desired tridentate bis(NHC) coordination mode. Ultimately the use of N-methyl-2-pyrrolidone is shown to enable the use of the extreme temperatures needed to facilitate the direct, thermally activated tautomerization reaction that gives rise to the bis(NHC) motif.
- Flowers,Johnson,Pitre,Cossairt
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- Highly efficient hydrogenation of carbon dioxide to formate catalyzed by iridium(iii) complexes of imine-diphosphine ligands
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A new iridium catalyst containing an imine-diphosphine ligand has been developed, which showed high efficiency for the hydrogenation of CO2 to formate (yield up to 99%, TON up to 450000). A possible catalytic mechanism is proposed, in which the imine group of the catalyst plays a key role in the cleavage of H2 and the activation of CO2.
- Liu, Chong,Xie, Jian-Hua,Tian, Gui-Long,Li, Wei,Zhou, Qi-Lin
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- Enhanced CO2 electroreduction efficiency through secondary coordination effects on a pincer iridium catalyst
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An iridium(iii) trihydride complex supported by a pincer ligand with a hydrogen bond donor in the secondary coordination sphere promotes the electrocatalytic reduction of CO2 to formate in water/acetonitrile with excellent Faradaic efficiency and low overpotential. Preliminary mechanistic experiments indicate formate formation is facile while product release is a kinetically difficult step.
- Ahn, Steven T.,Bielinski, Elizabeth A.,Lane, Elizabeth M.,Chen, Yanqiao,Bernskoetter, Wesley H.,Hazari, Nilay,Palmore, G. Tayhas R.
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- Cobalt-Catalyzed Synthesis of Unsymmetrically N, N-Disubstituted Formamides via Reductive Coupling of Primary Amines and Aldehydes with CO2 and H2
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Herein, a novel route to synthesize unsymmetrically N,N-disubstituted formamides is reported, which is achieved via reductive coupling of primary amine and aldehyde with CO2/H2 over a cobalt-based catalytic system composed of CoF2, P(CH2CH2PPh2)3 and K2CO3. The mechanism investigation indicates that a secondary amine is formed via hydrogenation of the imine originated from aldehyde and primary amine, which further reacts with HCOOH generated from CO2 hydrogenation, resulting in the formation of NNFA finally.
- Ke, Zhengang,Yang, Zhenzhen,Liu, Zhenghui,Yu, Bo,Zhao, Yanfei,Guo, Shien,Wu, Yunyan,Liu, Zhimin
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- Transfer hydrogenation of carbon dioxide: Via bicarbonate promoted by bifunctional C-N chelating Cp?Ir complexes
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Metal-ligand cooperative Cp?Ir(iii) complexes derived from primary benzylic amines effectively promote transfer hydrogenation of atmospheric CO2 using 2-propanol at 80 °C. Isotope-labelling experiments strengthen that active Ir species can preferentially reduce bicarbonate congeners formed from CO2. The powerful transfer hydrogenation catalyst exhibits remarkable activity for the conversion of bicarbonates into formate salts with a turnover number up to 3200, even without H2 and CO2.
- Sato, Yasuhiro,Kayaki, Yoshihito,Ikariya, Takao
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- CO2Hydrogenation Catalyzed by a Ruthenium Protic N-Heterocyclic Carbene Complex
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We describe the hydrogenation of CO2 to formate catalyzed by a Ru(II) bis(protic N-heterocyclic carbene, p-NHC) phosphine complex [Ru(bpy)(MeCN)(PPh(p-NHC)2)](PF6)2 (1). Under catalytic conditions (20 μmol catalyst, 20 bar CO2, 60 bar H2, 5 mL THF, 140 °C, 16 h), the activity of 1 is limited only by the amount of K3PO4 present in the reaction, yielding a nearly 1:1 ratio of turnover number (TON) to equivalents of K3PO4 (relative to 1), with the highest TON = 8040. Additionally, analysis of the reaction solution post-run reveals the catalyst intact with no free ligand observed. Stoichiometric studies, including examination of unique carbamate and hydride complexes as relevant intermediates, were carried out to probe the operative mechanism and understand the importance of metal-ligand cooperativity in this system.
- Johnson, M. Cecilia,Rogers, Dylan,Kaminsky, Werner,Cossairt, Brandi M.
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- Catalytic CO2 hydrogenation to formate by a ruthenium pincer complex
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This paper reports the hydrogenation of carbon dioxide to formate catalyzed by the Ru pincer complex Ru(PNN)CO(H) (PNN = 6-(di-tert- butylphosphinomethylene)-2-(N,N-diethylaminomethyl)-1,6-dihydropyridine). Stoichiometric studies are presented that support the feasibility of the individual steps in a proposed catalytic cycle for this transformation. The influence of base and solvent on catalyst performance is explored. Overall, under optimized conditions (using diglyme as the solvent and potassium carbonate as the base) up to 23,000 turnovers of formate and a turnover frequency of up to 2,200 h-1 can be achieved.
- Huff, Chelsea A.,Sanford, Melanie S.
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- Interconversion between formic acid and H2/CO2 using rhodium and ruthenium catalysts for CO2 fixation and H2 storage
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The interconversion between formic acid and H2/CO2 using half-sandwich rhodium and ruthenium catalysts with 4,4'-dihydroxy-2,2'- bipyridine (DHBP) was investigated. The influence of substituents of the bipyridine ligand was studied. Chemical shifts of protons in bipyridine linearly correlated with Hammett substituent constants. In the hydrogenation of CO 2/bicarbonate to formate under basic conditions, significant activations of the catalysts were caused by the electronic effect of oxyanions generated by deprotonation of the hydroxyl group. Initial turnover frequencies of the ruthenium- and rhodium-DHBP complexes increased 65- and 8-fold, respectively, compared to the corresponding unsubstituted bipyridine complexes. In the decomposition of formic acid under acidic conditions, activity enhancement by the electronic effect of the hydroxyl group was observed for the ruthenium catalyst. The rhodium-DHBP catalyst showed high activity without CO contamination in a relatively wide pH range. Pressurized H2 can be obtained using an autoclave reactor. The highest turnover frequency and number were obtained at 80°C. The catalytic system provides valuable insight into the use of CO2 as a H2 storage material by combining CO2 hydrogenation with formic acid decomposition.
- Himeda, Yuichiro,Miyazawa, Satoru,Hirose, Takuji
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- Recyclable catalyst for conversion of carbon dioxide into formate attributable to an oxyanion on the catalyst ligand
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The catalyst recycling in the conversion of CO2 into formate using the iridium complex with 4,7-dihydroxy-1,10-phenanthroline as a catalyst precursor is described. The catalyst precursor was dissolved in an aqueous KOH solution under CO2 pressure prior to the reaction, but was precipitated spontaneously at the end of the reaction. The acidification by the generation of formate caused the transformation from the water-soluble deprotonated form into the water-insoluble protonated form. When the reaction was carried out at 60 °C for 20 h using 0.1 M KOH solution under 6 MPa of H2:CO2 (1:1), the catalyst precursor was precipitated spontaneously and the added KOH was consumed completely. The catalyst was recovered by filtration, and the product was obtained by the evaporation of the filtrate. Iridium leaching into the filtrate was found to be 0.11 ppm (2 conversion using the complex is an environmentally benign process, whose significant features are as follows: (i) catalyst recycling by self-precipitation/filtration, (ii) waste-free process, (iii) the easy isolation of the product, (iv) high efficiency under relatively mild conditions, and (v) aqueous catalysis without the use of organic materials. Furthermore, we have demonstrated the significant roles of the oxyanion generated from the acidic phenolic hydroxyl on the catalyst ligand, which are the catalyst recovery by acid-base equilibrium, as well as the water-solubility by its polarity and the catalyst activation by its electron-donating ability. Copyright
- Himeda, Yuichiro,Onozawa-Komatsuzaki, Nobuko,Sugihara, Hideki,Kasuga, Kazuyuki
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- Role of ligand-bound CO2in the hydrogenation of CO2to formate with a (PNP)Mn catalyst
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Herein, we describe the catalytic hydrogenation of CO2 to formate with (PNP)Mn-H (PNP = 2,6-bis(di-tert-butylphosphinomethyl)- pyridine; Mn = Mn(CO)2). Contrary to the established mechanism for CO2 hydrogenation, mechanistic studies indicate that CO2 does not insert into the Mn-H bond of (PNP)Mn-H to give the formate species, (PNP)Mn- OCHO. The lack of reactivity is confirmed by thermochemical studies that show that (PNP)Mn-H is not sufficiently hydridic to reduce CO2. Deprotonation of the hydride to give [(?PNP)Mn-H]- ((? indicates the deprotonated ligand) enhances the hydricity by ~17 kcal·mol-1 and hence should be sufficiently hydridic to hydrogenate CO2. This reactivity is not observed, and CO2 instead binds to the backbone to generate another anionic hydride species [(CO2-PNP)Mn-H]. The formate is lost only from this species, through hydride transfer to an external CO2. These findings are unexpected because substrate binding to the backbone of catalysts that can undergo metal-ligand cooperativity (MLC) is thought to be detrimental to catalysis; this work suggests that alternative mechanisms should be considered. The enhanced hydricity observed upon deprotonation may be broadly applicable to systems capable of undergoing MLC. Moreover, this work shows an example of how thermochemical analysis can be used to advance mechanistic understanding in (de)hydrogenation catalysis.
- Christensen, Elizabeth G.,Lutz, Kevin T.,McDonald, Gabriel R.,Saouma, Caroline T.,Schlenker, Kevin,Steele, Ryan P.,VanderLinden, Ryan T.,Yang, Emily L.,Zhanserkeev, Asylbek A.
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- Mechanistic insight through factors controlling effective hydrogenation of CO2 catalyzed by bioinspired proton-responsive iridium(III) complexes
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Reversible H2 storage near room temperature and pressure with pH as the switch for controlling the direction of the reaction has been demonstrated (Nat. Chem., 2012, 4, 383-388). Several bioinspired proton-responsive mononuclear Ir(III) catalysts for CO2 hydrogenation were prepared to gain mechanistic insight through investigation of the factors that control the effective generation of formate. These factors include (1) kinetic isotope effects by water, hydrogen, and bicarbonate; (2) position and number of hydroxyl groups on bpy-type ligands; and (3) mono- vs dinuclear iridium complexes. We have, for the first time, obtained clear evidence from kinetic isotope effects and computational studies of the involvement of a water molecule in the rate-determining heterolysis of H 2 and accelerated proton transfer by formation of a water bridge in CO2 hydrogenation catalyzed by bioinspired complexes bearing a pendent base. Furthermore, contrary to expectations, a more significant enhancement of the catalytic activity was observed from electron donation by the ligand than on the number of the active metal centers.
- Wang, Wan-Hui,Muckerman, James T.,Fujita, Etsuko,Himeda, Yuichiro
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- Hydrogenation of CO2 to Formate over Ruthenium Immobilized on Solid Molecular Phosphines
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Formic acid is a promising hydrogen storage medium and can be produced by catalytic hydrogenation of CO2. Molecular ruthenium complexes immobilized on phosphine polymers have been found to exhibit excellent productivity and selectivity in the catalytic hydrogenation of CO2 under mild conditions. The polymeric analog of 1,2-bis(diphenylphosphino)ethane exhibited the highest activity and turnover numbers up to 13 170 were obtained in a single run. This catalyst was already active at 40 °C and with a catalyst loading of only 0.0006 mol %. Recycling experiments revealed a loss of activity after the first run, followed by a gradual decrease during the subsequent runs. This is attributed to a change in the catalytically active complex during the hydrogenation reaction. High selectivity towards formate and low leaching were maintained in the absence of CO formation. Based on the catalyst characterization, a mechanism for the CO2 hydrogenation is proposed.
- Kann, Anna,Hartmann, Heinrich,Besmehn, Astrid,Hausoul, Peter J. C.,Palkovits, Regina
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- In situ observation of a formate intermediate during CO hydrogenation over alkali-promoted Ru(001) at high pressures
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In situ Fourier transform infrared reflection absorption spectroscopy reveals the formation of a formate intermediate during the CO hydrogenation reaction at high pressures over a potassium promoted Ru(001) surface. The vibrational data indicate bond formation between potassium and formate. The present results suggest a dual function of alkali promoters in this reaction -- promotion of CO bond dissociation and direct participation in the formation of reaction intermediates.
- Hoffmann, F. M.,Weisel, M. D.
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- CO2 activation by manganese pincer complexes through different modes of metal-ligand cooperation
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We report here the activation of CO2 using two Mn-PNN pincer complexes that can exhibit different modes of metal-ligand cooperation amido/amino mode that involves [1,2]-activation of CO2 and dearomatization/aromatization mode that in
- Kumar, Amit,Daw, Prosenjit,Espinosa-Jalapa, Noel Angel,Leitus, Gregory,Shimon, Linda J. W.,Ben-David, Yehoshoa,Milstein, David
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- In-Situ FT-IRAS Study of the Hydrogenation of CO on Ru(001): Potassium-Promoted Synthesis of Formate
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Utilizing in-situ Fourier transform infrared reflection absorption spectroscopy, we have characterized potassium-promoted Ru(001) surfaces under CO hydrogenation conditions at elevated temperature and pressure (1-50 Torr).Interaction of the 3x3-R30 deg-K-Ru(001) surface with CO at 300 K resulted in the formation of carbonate, which was hydrogenated to formate via the reaction K2CO3 + CO + H2 ->/-3 molecules site-1 s-1 at 500 K.Isotope transient measurements resulted in a comparable synthesis rate under equilibrium conditions and hence demonstrate the reactivity of the formate.The isotope transient data and the formate to carbonate conversion in excess hydrogen are consistent with two possible mechanisms: (i) Decomposition of the formate to carbonate, i.e., the reverse of the formate synthesis reaction, or (ii) further hydrogenation of the formate to methanol or methane.Characteristic vibrational features show that both formate and carbonate are directly bound to the potassium.This compound formation leads to a contraction of the potassium layer and to island formation.The formate observed under reaction conditions was shown to be more stable than model compounds produced under UHV conditions.This enhanced stability under reaction conditions is attributed to two factors: (i) The bond formation between potassium and the formate and (ii) physical site blocking due to coadsorbed CO.The results demonstrate a dual promoter mechanism of the potassium in the CO hydrogenation reaction over Ru(001)-(i) promotion of CO dissociation resulting in the formation of carbonate and (ii) direct participation of the potassium in the synthesis of formate via compound formation.
- Weisel, M. D.,Robbins, J. L.,Hoffmann, F. M.
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- Communication—CO2 reduction to formate: An electro-enzymatic approach using a formate dehydrogenase from rhodobacter capsulatus
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CO2 utilization for producing value-added chemicals has recently emerged as a strategy to mitigate atmospheric CO2 levels. Given that (i) certain formate dehydrogenases are capable of interconverting CO2 and formate, and (ii) formate is versatile in various industries, we, herein, aimed to demonstrate FDH-driven formate production from CO2. Because of its O2 stability, we selected FDH from Rhodobacter capsulatus (RcFDH) and then constructed a mediated electro-enzymatic system. The mediated electro-enzymatic kinetic parameters (kred and kox) were calculated to optimize the reaction conditions favorable for CO2 reduction. Finally, a RcFDH-driven electro-enzymatic system successfully produced 6 mM of formate in 5 hours.
- Choi, Eun-Gyu,Yeon, Young Joo,Min, Kyoungseon,Kim, Yong Hwan
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- Sulfonate-functionalized NHC-based ruthenium catalysts for the isomerization of allylic alcohols in water. recyclability studies
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Two new complexes of the type [Ru(CO3)(η6-arene) (NHC)]Cs, in which the NHC ligand incorporates a sulfonate functionality, have been prepared and fully characterized. The two water-soluble complexes have been tested in the catalytic isomerization of allylic alcohols in water. The p-cymene compound (labeled as 1) was shown to be an excellent catalyst when compared to other related Ru catalysts. This catalyst can be recycled by simple liquid-liquid extractions several times without detected loss of activity.
- Azua, Arturo,Sanz, Sergio,Peris, Eduardo
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- Palladium(II) Immobilized on Metal-Organic Frameworks for Catalytic Conversion of Carbon Dioxide to Formate
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In this work, we report the design of a two-dimensional (2D) isostructural metal-organic framework containing Pd(II) active sites, using a bipyridyl dicarboxylate linker (Mg(bpdc)(DMF)2PdCl2]n (Pd?Mg:JMS-2) and [Mn(bpdc)(DMF)2PdCl2]n(Pd?Mn:JMS-2)). The activated MOFs Pd?Mg:JMS-2a and Pd?Mn:JMS-2a were evaluated as heterogeneous catalysts for the hydrogenation of carbon dioxide (CO2) to formate. Under optimal conditions, the MOFs exhibited impressive catalytic activity with formate turnover numbers of 7272 and 9808 for Pd?Mg:JMS-2a and Pd?Mn:JMS-2a, respectively, after 24 h. These catalysts exhibited higher catalytic activity when compared to its homogeneous counterpart that was used as a linker during MOF synthesis. Post-experimental characterization showed that the structural integrity of the MOFs was not altered after catalysis. This work demonstrates that the catalytic activity of homogeneous systems can be enhanced under heterogeneous conditions by anchoring them on MOFs.
- Bingwa, Ndzondelelo,Makhubela, Banothile C. E.,Mehlana, Gift,Tshuma, Piwai
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- The alkaline anthraquinone-2-sulfonate-H2O2-catalyzed oxidative degradation of lactose: An improved Spengler-Pfannenstiel oxidation
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The alkali-catalyzed oxidative degradation of lactose (1) to potassium O-β-D-galactopyranosyl-(1→3)-D-arabinonate (2) has been studied and compared with that of D-glucose to D-arabinonate and D-galactose to D-lyxonate. A mechanism for the degradation of 1 catalyzed by alkali only is presented and discussed, taking into consideration the main reactionproducts. Increasing the reaction temperature from 293 to 318 K resulted in a drastic decrease of the selectivity for 2. Increasing the oxygen pressure from 1 to 5 bar did not significantly influence the selectivity. The overall reaction kinetics followed first-order behavior with respect to lactose, D-glucose, or D-galactose. The simultaneous addition of catalytic, equimolar amounts of sodium 2-anthraquinonemonosulfonate and H2O2 showed a pronounced effect on the selectivity. A reaction mechanism for this type of alkali-catalyzed oxidative degradation of carbohydrates is presented and discussed. Lactose could be oxidized up to almost complete conversion with a selectivity of 90-95% (mol/mol), whereas D-glucose was oxidized to D-arabinonate with a selectivity of 98%. This increased selectivity was maintained at temperatures from 293 up to 323 K, allowing a reduction of the batch time necessary for almost complete conversion from 50 to 1.5 h. The overall reaction kinetics still followed first-order behavior with respect to lactose, D-glucose or D-galactose. The apparent activation energy amounted to 114 ± 2 kJ mol-1 for lactose, to 109 ± 2 kJ mol-1 for D-glucose, and to 104 ± 9 kJ mol-1 for D-galactose. The alkali-catalyzed oxidative degradation of lactose (1) to potassium O-β-D-galactopyranosyl-(1→3)-D-arabinonate (2) has been studied and compared with that of D-glucose to D-arabinonate and D-galactose to D-lyxonate. A mechanism for the degradation of 1 catalyzed by alkali only is presented and discussed, taking into consideration the main reactionproducts. Increasing the reaction temperature from 293 to 318 K resulted in a drastic decrease of the selectivity for 2. Increasing the oxygen pressure from 1 to 5 bar did not significantly influence the selectivity. The overall reaction kinetics followed first-order behavior with respect to lactose, D-glucose, or D-galactose. The simultaneous addition of catalytic, equimolar amounts of sodium 2-anthraquinonemonosulfonate and H2O2 showed a pronounced effect on the selectivity. A reaction mechanism for this type of alkali-catalyzed oxidative degradation of carbohydrates is presented and discussed. Lactose could be oxidized up to almost complete conversion with a selectivity of 90-95% (mol/mol), whereas D-glucose was oxidized to D-arabinoate with a selectivity of 98%. This increased selectivity was maintained at temperatures from 293 up to 323 K, allowing a reduction of the batch time necessary for almost complete conversion from 50 to 1.5 h. The overall reaction kinetics still followed first-order behavior with respect to lactose, D-glucose or D-galactose. The apparent activation energy amounted to 114 ± 2 kJ mol-1 for lactose, to 109 ± 2 kJ mol-1 for D-glucose, and to 104 ± 9 kJ mol-1 for D-galactose.
- Hendriks,Kuster,Marin
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- CO2 Conversion to formates catalyzed by iridium(III) catalysts precursors with proton responsive OH and NH electron-rich tetrazole ligands
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Recent efforts in addressing the environmental problems have involved using CO2 as a cheap and nontoxic C1 source. Iridium catalysts with bidentate ligands are excellent catalysts for CO2, especially if these complexes possess proton-responsive OH or NH groups. Here-in we report the synthesis of novel Ir half-sandwich complexes with N^N bidentate tetrazolyl ligands. Serendipitous deprotection of methoxy groups resulted in N^N bidentate ligands bearing OH groups. The complexes were evaluated for CO2 hydrogenation, for which the roles of steric bulk or the presence of electronic effects influence their catalytic activity in CO2 hydrogenation. The complexes are highly active for CO2 hydrogenations with around 4.3 mmol of formate produced. The presence of proton responsive groups on the catalysts was found to steer the mechanistic cycle away from using a bridged Ir-H-Ir intermediate before forming catalytically active species. In addition, these catalysts were found to hydrogenate CO2 in the presence of bicarbonate ions selectively.
- Ocansey, Edward,Darkwa, James,Makhubela, Banothile C.E.
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- Low-temperature hydrogen production from methanol over a ruthenium catalyst in water
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Traditionally, methanol reforming at a very high temperature (>200 °C) has been explored for hydrogen production. Here, we show that in situ generated ruthenium nanoparticles (ca. 1.5 nm) from an organometallic precursor promote hydrogen production from methanol in water at low temperature (90-130 °C), which leads to a practical and efficient approach for low-temperature hydrogen production from methanol in water. The reactivity of ruthenium nanoparticles is tuned to achieve a high rate of hydrogen gas production from methanol. Notably, the use of a pyridine-2-ol ligand significantly accelerated the hydrogen production rate by 80% to 49 mol H2 per mol Ru per hour at 130 °C. Moreover, the studied ruthenium catalyst exhibits appreciably long-term stability to achieve a turnover number of 762 mol H2 per mol Ru generating 186 L of H2 per gram of Ru. This journal is
- Awasthi, Mahendra K.,Rai, Rohit K.,Behrens, Silke,Singh, Sanjay K.
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p. 136 - 142
(2021/01/29)
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- Homogeneous hydrogenation of saturated bicarbonate slurry to formates using multiphase catalysis
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Formic acid and formate salts are key intermediates along the pathways for CO2utilization and hydrogen storage. Herein we report a highly efficient multiphase catalytic system utilizing a ruthenium PNP pincer catalyst for converting supersaturated bicarbonate solutions and slurries to aqueous formate solutions up to 12 M in molarity. The biphasic catalytic system delivers turnover frequencies up to 73?000 h?1and remains stable for up to 474?000 turnovers once reaction conditions are optimized.
- Filonenko, Georgy A.,Pidko, Evgeny A.,Rebreyend, Christophe
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supporting information
p. 8848 - 8852
(2021/11/23)
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- Degradation of Organic Cations under Alkaline Conditions
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Understanding the degradation mechanisms of organic cations under basic conditions is extremely important for the development of durable alkaline energy conversion devices. Cations are key functional groups in alkaline anion exchange membranes (AAEMs), and AAEMs are critical components to conduct hydroxide anions in alkaline fuel cells. Previously, we have established a standard protocol to evaluate cation alkaline stability within KOH/CD3OH solution at 80 °C. Herein, we are using the protocol to compare 26 model compounds, including benzylammonium, tetraalkylammonium, spirocyclicammonium, imidazolium, benzimidazolium, triazolium, pyridinium, guanidinium, and phosphonium cations. The goal is not only to evaluate their degradation rate, but also to identify their degradation pathways and lead to the advancement of cations with improved alkaline stabilities.
- You, Wei,Hugar, Kristina M.,Selhorst, Ryan C.,Treichel, Megan,Peltier, Cheyenne R.,Noonan, Kevin J. T.,Coates, Geoffrey W.
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supporting information
p. 254 - 263
(2020/12/23)
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- Facile hydrogenation of bicarbonate to formate in aqueous medium by highly stable nickel-azatrane complex
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Molecular catalyst-based direct hydrogenation of bicarbonate to formate in aqueous medium is a challenging research topic for the H2 storage. Finding a green and effective method for the bicarbonate to formate conversion with non-precious metal-based catalyst is vital to the practical application. We report the direct hydrogenation of bicarbonate to formate using a water soluble nickel-azatrane complex. Catalysts 1–5, designed and synthesized, were screened for the hydrogenation of bicarbonate to formate in aqueous medium; the best TON of 121 was obtained for catalyst 4 at 120 °C (60 bar). Introduction of isopropyl (2) and methyl (3 and 4) groups in the coordination environment of the metal center enhances the production of formate. Further, the hydrogenation of bicarbonate with CO2 promoted the formate production for catalyst 4 with a TON of 92 (3 h). The use of green solvent and non-precious metal catalyst makes this catalytic method environmentally sustainable.
- Sivanesan, Dharmalingam,Seo, Bongkuk,Lim, Choong-Sun,Kim, Hyeon-Gook
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p. 121 - 128
(2020/01/03)
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- Hydroxide Based Integrated CO2 Capture from Air and Conversion to Methanol
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The first example of an alkali hydroxide-based system for CO2 capture and conversion to methanol has been established. Bicarbonate and formate salts were hydrogenated to methanol with high yields in a solution of ethylene glycol. In an integrated one-pot system, CO2 was efficiently captured by an ethylene glycol solution of the base and subsequently hydrogenated to CH3OH at relatively mild temperatures (100-140 °C) using Ru-PNP catalysts. The produced methanol can be easily separated by distillation. Hydroxide base regeneration at low temperatures was observed for the first time. Finally, CO2 capture from ambient air and hydrogenation to CH3OH was demonstrated. We postulate that the high capture efficiency and stability of hydroxide bases make them superior to existing amine-based routes for direct air capture and conversion to methanol in a scalable process.
- Sen, Raktim,Goeppert, Alain,Kar, Sayan,Prakash, G. K. Surya
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p. 4544 - 4549
(2020/02/27)
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- Effect of Ligand Electronics on the Reversible Catalytic Hydrogenation of CO2 to Formic Acid Using Ruthenium Polyhydride Complexes: A Thermodynamic and Kinetic Study
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Hydrogenation of CO2 to formic acid or formates is often carried out using catalysts of the type H4Ru(PR3)3 (1). These catalysts are also active for the reverse reaction, i.e., the decomposition of formic acid to H2 and CO2. While numerous catalysts have been synthesized for reactions in both directions, the factors controlling the elementary steps of the catalytic cycle remain poorly understood. In this work, we synthesize a series of compounds of type H4Ru(P(C6H4R)3)3 containing both electron-donating and electron-withdrawing groups and analyze their influence on the kinetic and thermodynamic parameters of CO2 insertion and deinsertion. The data are correlated with the catalytic performance of the complexes through linear free-energy relationships. The results show that formic acid dissociation from the catalyst is rate-determining during CO2 hydrogenation, while deinsertion is critical for the decomposition reaction.
- Bordet, Alexis,Estes, Deven P.,Leitner, Walter,Leutzsch, Markus,Schubert, Lukas
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p. 2990 - 2998
(2020/03/23)
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- Enhanced Stability and CO/Formate Selectivity of Plasma-Treated SnOx/AgOx Catalysts during CO2 Electroreduction
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CO2 electroreduction into useful chemicals and fuels is a promising technology that might be used to minimize the impact that the increasing industrial CO2 emissions are having on the environment. Although plasma-oxidized silver surfaces were found to display a considerably decreased overpotential for the production of CO, the hydrogen evolution reaction (HER), a competing reaction against CO2 reduction, was found to increase over time. More stable and C1-product-selective SnOx/AgOx catalysts were obtained by electrodepositing Sn on O2-plasma-pretreated Ag surfaces. In particular, a strong suppression of HER (below 5% Faradaic efficiency (FE) at a0.8 V vs the reversible hydrogen electrode, RHE) during 20 h was observed. Ex situ scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS), quasi in situ X-ray photoelectron spectroscopy (XPS), and operando X-ray absorption near-edge structure spectroscopy (XANES) measurements showed that our synthesis led to a highly roughened surface containing stable Sn?+/Sn species that were found to be key in the enhanced activity and stable CO/formate (HCOO-) selectivity. Our study highlights the importance of roughness, composition, and chemical state effects in CO2 electrocatalysis.
- Choi, Yong-Wook,Scholten, Fabian,Sinev, Ilya,Cuenya, Beatriz Roldan
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p. 5261 - 5266
(2019/03/26)
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- Carbon nanofibers?NiSe core/sheath nanostructures as efficient electrocatalysts for integrating highly selective methanol conversion and less-energy intensive hydrogen production
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H2 generation from water electrolysis is a key enabling technology for a clean and sustainable future but is still restricted by the sluggish oxygen evolution reaction (OER). So exploring an ideal electrocatalytic valorization reaction to replace the sluggish OER and boost H2 production is desirable. Methanol, as the most important liquid C1 resource with huge production capacity, is rather inexpensive and practical for utilization. In this work, in situ synthesized carbon nanofibers?NiSe (CNFs?NiSe) core/sheath nanostructures act as robust and stable electrocatalysts for highly selective methanol conversion to value-added formate with a high production rate and faradaic efficiency. Notably, the methanol conversion replaces the sluggish OER to boost H2 production at a high generation rate that is 7.5 times that in the absence of methanol, thus lowering the energy consumption. Density functional theory (DFT) calculations reveal that the high electrocatalytic selectivity is attributed to the unique exposed NiSe (102) facets, which facilitate the methanol conversion to formate by suppressing further oxidation to the greenhouse gas CO2.
- Zhao, Bin,Liu, Jian-Wen,Yin, Ya-Ru,Wu, Dan,Luo, Jing-Li,Fu, Xian-Zhu
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supporting information
p. 25878 - 25886
(2019/11/28)
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- Benzimidazoles as Metal-Free and Recyclable Hydrides for CO2 Reduction to Formate
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We report a novel metal-free chemical reduction of CO2 by a recyclable benzimidazole-based organo-hydride, whose choice was guided by quantum chemical calculations. Notably, benzimidazole-based hydride donors rival the hydride-donating abilities of noble-metal-based hydrides such as [Ru(tpy)(bpy)H]+ and [Pt(depe)2H]+. Chemical CO2 reduction to the formate anion (HCOO-) was carried out in the absence of biological enzymes, a sacrificial Lewis acid, or a base to activate the substrate or reductant. 13CO2 experiments confirmed the formation of H13COO- by CO2 reduction with the formate product characterized by 1H NMR and 13C NMR spectroscopy and ESI-MS. The highest formate yield of 66% was obtained in the presence of potassium tetrafluoroborate under mild conditions. The likely role of exogenous salt additives in this reaction is to stabilize and shift the equilibrium toward the ionic products. After CO2 reduction, the benzimidazole-based hydride donor was quantitatively oxidized to its aromatic benzimidazolium cation, establishing its recyclability. In addition, we electrochemically reduced the benzimidazolium cation to its organo-hydride form in quantitative yield, demonstrating its potential for electrocatalytic CO2 reduction. These results serve as a proof of concept for the electrocatalytic reduction of CO2 by sustainable, recyclable, and metal-free organo-hydrides.
- Lim, Chern-Hooi,Ilic, Stefan,Alherz, Abdulaziz,Worrell, Brady T.,Bacon, Samuel S.,Hynes, James T.,Glusac, Ksenija D.,Musgrave, Charles B.
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supporting information
p. 272 - 280
(2019/01/04)
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- A ruthenium porphyrin-based porous organic polymer for the hydrosilylative reduction of CO2 to formate
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A ruthenium porphyrin-based porous organic polymer (POP) was synthesized, characterized, and used to reduce CO2 to a formate salt. We demonstrate that Ru-BBT-POP can be utilized to reduce CO2 to a silyl formate and then converted to potassium formate with a respectable turnover number and frequency.
- Eder, Grace M.,Pyles, David A.,Wolfson, Eric R.,McGrier, Psaras L.
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supporting information
p. 7195 - 7198
(2019/07/02)
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- Hydrogenation of CO2, carbonyl and imine substrates catalyzed by [IrH3(PhPNHP)] complex
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A series of iridium and rhodium complexes [M(COD)(PhPNHP)]Cl {M = Ir (1), Rh (2)}, [MH2Cl(PhPNHP)] {M = Ir (3), Rh (4)} and [IrH3(PhPNHP)] (6) supported by pincer ligand H–N(CH2CH2PPh2)2 {PhPNHP} have been synthesized and characterized. All complexes were isolated in good yields. The iridium trihydride complex [IrH3(PhPNHP)] (6) was found to be an active catalyst for the hydrogenation of CO2 in 1 M aqueous KOH solution. It also acts as a catalyst for the base-free hydrogenation of carbonyl and imine substrates in MeOH. Under similar hydrogenation conditions, 2-cyclohexen-1-one undergoes solvent assisted tandem Michael addition-reduction mediated by bifunctional Lewis-acid-catalyst [IrH3(PhPNHP)] in ROH (R = Me, Et) at room temperature. The complexes 1, 3, 4, and 6 were characterized by X-ray crystallography. Extensive hydrogen bonding interactions N–H?H–Ir (2.15 ?), N–H?Cl (2.370 ?) were noted in the crystal structures of these complexes.
- Ramaraj, Ayyappan,Nethaji, Munirathinam,Jagirdar, Balaji R.
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supporting information
p. 25 - 34
(2019/01/24)
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- Direct Synthesis of Methyl Formate from CO2 With Phosphine-Based Polymer-Bound Ru Catalysts
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Methyl formate was produced in one pot through the hydrogenation of CO2 to formic acid/formate followed by an esterification step. The route offers the possibility to integrate renewable energy into the fossil-based chemical value chain. In this work, a phosphine-polymer-anchored Ru complex was shown to be an efficient solid catalyst for the direct hydrogenation of CO2 to methyl formate. The 1,2-bis(diphenylphosphino)ethane-like polymer presented the highest activity with a turnover number (TON) of up to 3401 at 160 °C. The reaction parameters were systemically investigated to optimize the reaction towards the formation of methyl formate. This catalyst could be reused seven times without a significant decrease in activity. Evolution of the catalytic Ru center during the reaction was revealed, and a possible reaction mechanism was proposed.
- Sun, Ruiyan,Kann, Anna,Hartmann, Heinrich,Besmehn, Astrid,Hausoul, Peter J. C.,Palkovits, Regina
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p. 3278 - 3285
(2019/06/13)
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- A Carbon-Neutral CO2 Capture, Conversion, and Utilization Cycle with Low-Temperature Regeneration of Sodium Hydroxide
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A highly efficient recyclable system for capture and subsequent conversion of CO2 to formate salts is reported that utilizes aqueous inorganic hydroxide solutions for CO2 capture along with homogeneous pincer catalysts for hydrogenation. The produced aqueous solutions of formate salts are directly utilized, without any purification, in a direct formate fuel cell to produce electricity and regenerate the hydroxide base, achieving an overall carbon-neutral cycle. The catalysts and organic solvent are recycled by employing a biphasic solvent system (2-MTHF/H2O) with no significant decrease in turnover frequency (TOF) over five cycles. Among different hydroxides, NaOH and KOH performed best in tandem CO2 capture and conversion due to their rapid rate of capture, high formate conversion yield, and high catalytic TOF to their corresponding formate salts. Among various catalysts, Ru- and Fe-based PNP complexes were the most active for hydrogenation. The extremely low vapor pressure, nontoxic nature, easy regenerability, and high reactivity of NaOH/KOH toward CO2 make them ideal for scrubbing CO2 even from low-concentration sources - such as ambient air - and converting it to value-added products.
- Kar, Sayan,Goeppert, Alain,Galvan, Vicente,Chowdhury, Ryan,Olah, Justin,Prakash, G. K. Surya
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supporting information
p. 16873 - 16876
(2018/11/06)
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- Versatile Rh- and Ir-Based Catalysts for CO2 Hydrogenation, Formic Acid Dehydrogenation, and Transfer Hydrogenation of Quinolines
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Considering the interest in processes related to hydrogen storage such as CO2 hydrogenation and formic acid (FA) decomposition, we have synthesized a set of Ir, Rh, or Ru complexes to be tested as versatile precatalysts in these reactions. In relation with the formation of H2 from FA, the possible applicability of these complexes in the transfer hydrogenation (TH) of challenging substrates as quinoline derivatives using FA/formate as hydrogen donor has also been addressed. Bearing in mind the importance of secondary coordination sphere interactions, N,N′ ligands containing NH2 groups, coordinated or not to the metal center, were used. The general formula of the new complexes are [(p-cymene)RuCl(N,N′)]X, X = Cl-, BF4- and [Cp?MCl(N,N′)]Cl, M = Rh, Ir, where the N,N′ ligands are 8-aminoquinoline (HL1), 6-pyridyl-2,4-diamine-1,3,5-triazine (L2) and 5-amino-1,10-phenanthroline (L3). Some complexes are not active or catalyze only one process. However, the complexes [Cp?MCl(HL1)]Cl with M = Rh, Ir are versatile catalysts that are active in hydrogenation of quinolines, FA decomposition, and also in CO2 hydrogenation with the iridium derivative being more active and robust. The CO2 hydrogenation takes place in mild conditions using only 5 bar of pressure of each gas (CO2 and H2). The behavior of some precatalysts in D2O and after the addition of 9 equiv of HCO2Na (pseudocatalytic conditions) has been studied in detail and mechanisms for the FA decomposition and the hydrogenation of CO2 have been proposed. For the Ru, Ir, or Rh complexes with ligand HL1, the amido species with the deprotonated ligand are observed. In the case of ruthenium, the formate complex is also detected. For the iridium derivative, both the amido intermediate and the hydrido species have been observed. This hydrido complex undergoes a process of umpolung D+a?" Ir-D. All in all, the results of this work reflect the active role of aNH2 in the transfer of H+.
- Fidalgo, Jairo,Ruiz-Castaneda, Margarita,García-Herbosa, Gabriel,Carbayo, Arancha,Jalón, Félix A.,Rodríguez, Ana M.,Manzano, Blanca R.,Espino, Gustavo
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p. 14186 - 14198
(2018/11/23)
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- Electrochemical Reduction of CO2 at Functionalized Au Electrodes
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Electrochemical reduction of CO2 provides an opportunity to store renewable energy as fuels with much greater energy densities than batteries. Product selectivity of the reduction reaction is known to be a function of the electrolyte and electrode; however, electrodes modified with functional ligands may offer new methods to control selectivity. Here, we report the electrochemical reduction of CO2 at functionalized Au surfaces with three thiol-tethered ligands: 2-mercaptopropionic acid, 4-pyridinylethanemercaptan, and cysteamine. Remarkably, Au electrodes modified with 4-pyridinylethanemercaptan show a 2-fold increase in Faradaic efficiency and 3-fold increase in formate production relative to Au foil. Conversely, electrodes with 2-mercaptopropionic acid ligands show nearly 100% Faradaic efficiency toward the hydrogen evolution reaction, while cystemine-modified electrodes show 2-fold increases in both CO and H2 production. We propose a proton-induced desorption mechanism associated with pKa of the functionalized ligand as responsible for the dramatic selectivity changes.
- Fang, Yuxin,Flake, John C.
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p. 3399 - 3405
(2017/03/15)
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- A nanoporous nickel catalyst for selective hydrogenation of carbonates into formic acid in water
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An efficient unsupported nanoporous nickel (NiNPore) material for the hydrogenation of carbonates to formic acid (FA) in water was investigated for the first time. NiNPore is an environmentally benign catalyst and it exhibited remarkable catalytic activity in the reduction of a wide range of carbonates to afford formic acid in excellent yields with high selectivity, and maximum values of 86.6% from NaHCO3 and even up to 92.1% from KHCO3 were obtained. The hydrogen pressure and pKa of the carbonates had a significant influence on the formation of FA. The catalyst was easily recovered and could be recycled at least five times without leaching and loss of activity. The present study demonstrated a potential application for the synthesis of FA from CO2 or carbonate compounds.
- Wang, Tian,Ren, Dezhang,Huo, Zhibao,Song, Zhiyuan,Jin, Fangming,Chen, Mingwei,Chen, Luyang
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p. 716 - 721
(2017/08/17)
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- New Ru(ii) N′NN′-type pincer complexes: synthesis, characterization and the catalytic hydrogenation of CO2 or bicarbonates to formate salts
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[RuCl(L1)(MeCN)2]Cl (1) and [RuCl(L2)(MeCN)2]Cl (2) complexes were prepared through the reaction of [RuCl2(p-cymene)]2 with 2,6-bis(benzimidazole-2-yl)-4-hydroxy-pyridine (L1) or 2,6-bis(benzimidazole-2-yl) pyridine (L2) in acetonitrile, respectively. The treatment of [Ru(OTf)(L2)(MeCN)2]OTf (3) with 1 equivalent of PPh3 in ethanol resulted in the formation of [Ru(L2-1)(MeCN)(PPh3)2]OTf (4), in which one of the N-H moieties of L2 is deprotonated to give an anionic ligand (L2-1). It was found that complex 1 can catalyze the hydrogenation of CO2 to formate salts, producing sodium formate in 34.0% yield with a turnover number (TON) of 407 under the optimized conditions. Further investigations revealed that complexes 1-4 can efficiently catalyze the hydrogenation of sodium bicarbonate to sodium formate, and the catalytic activity follows the order 4 > 1 > 2 ≈ 3. In particular, sodium formate was obtained in good yield (77%) with a high TON (1530) when complex 4 was used as the catalyst. The present results illustrate a new example of Ru(ii) complexes bearing a rigid N′NN′ framework for the efficient hydrogenation of CO2 to formate salts in a homogeneous system.
- Dai, Zengjin,Luo, Qi,Cong, Hengjiang,Zhang, Jing,Peng, Tianyou
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supporting information
p. 3055 - 3060
(2017/04/14)
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- Carbon dioxide hydrogenation: Efficient catalysis by an NHC-amidate Pd(II) complex
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The utilization of carbon dioxide as a carbon source has long been a challenge in modern organic chemistry due to its low reactivity, yet high abundance. Herein we demonstrate the highly efficient hydrogenation of carbon dioxide into formic acid in the presence of an NHC-amidate Pd(II) complex. Excellent turnover number was observed when the catalyst was used under heterolytic conditions. This catalytic system provides a new and efficient carbon dioxide hydrogenation method.
- Zargari, Nima,Jung, Erica,Lee, Joo-Ho,Jung, Kyung Woon
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supporting information
p. 3330 - 3332
(2017/07/27)
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- METHODS AND CATALYST SYSTEMS FOR CARBON DIOXIDE CONVERSION
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Disclosed herein are embodiments of a heterogeneous catalyst system and methods of using the same to convert CO2-derived compounds to formate, formic acid, or a mixture thereof. The disclosed heterogeneous catalyst systems exhibit superior reactivity and stability in comparison to homogeneous catalyst systems and also can convert a variety of CO2-derived compounds to formate, formic acid, or mixtures thereof, in high yields using economical and environmentally friendly reaction conditions.
- -
-
Paragraph 0105; 0119
(2016/06/06)
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- Selected paper development of highly active IrPNP catalysts for hydrogenation of carbon dioxide with organic bases
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Methoxy-substituted PNP-iridium(III) complexes and pyrazine-based PNP-iridium(III) complexes were developed and used to hydrogenate carbon dioxide in the presence of triethanolamine as a base. The methoxy-substituted PNP-hydridodichloridoiridium complex (C-HCl2) showed the highest turnover number, 160000; this is the highest value ever reported with an organic base in an aqueous medium. The reactivities of these complexes, derived from their ligand modification, were further studied. The results were as follows. (i) The pyrazine-based PNP-trihydridoiridium complex undergoes release of dihydrogen to afford dihydridoamido complex, possibly because of easy dearomatization of the pyrazine ring. This process was reversible, i.e., B-H2amido can readily be converted back to B-H3 on exposure to dihydrogen. (ii) The p-methoxy-substituted dihydridochlorido complex showed facile disproportionation of the chloride anion on the iridium center; this is attributed to the electron-donating nature of the methoxypyridine backbone.
- Aoki, Wataru,Wattanavinin, Natdanai,Kusumoto, Shuhei,Nozaki, Kyoko
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p. 113 - 124
(2016/01/27)
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- Method for preparing formate through carbon dioxide catalytic hydrogenation
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The invention belongs to the technical field of carbon dioxide resource utilization and relevant chemistry, and relates to a method for preparing formate through carbon dioxide catalytic hydrogenation. The method is characterized by comprising the steps that carbon dioxide is used as a raw material and reacts with hydrogen under the catalysis of nano-porous palladium catalyst and the alkaline condition to obtain formate. By means of the method for preparing the formate through carbon dioxide catalytic hydrogenation, the preparation route is short, raw materials are cheap and easy to obtain, conditions are mild, operation is simple and convenient, and the reaction yield is high.
- -
-
Paragraph 0024; 0025; 0026; 0027
(2016/10/09)
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- Method for catalyzing CO2 hydrogenation reduction by using sulfur-containing iridium complex
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The invention relates to a method for catalyzing CO2 hydrogenation reduction by using a sulfur-containing iridium complex. A sulfur-containing substituent-substituted dipyridyl iridium complex is synthesized and used as a catalyst to catalyze CO2 hydrogenation. The method has the advantages as follows: the iridium complex has good water solubility, no organic solvent is required to be added to a catalytic reaction, and pollution caused by the organic solvent is avoided; besides, a sulfydryl dipyridyl ligand is synthesized successfully with a thiourea alkylation hydrolysis method for the first time, the preparation process is simple, and synthesis methods, such as a sodium hydrosulfide alkylation method and the like, which cause severe environmental pollution are avoided. The invention provides a novel efficient transition metal catalyst for catalyzing CO2 hydrogenation.
- -
-
Paragraph 0034; 0035; 0042; 0046
(2017/01/23)
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- Catalytic reduction of CO2with organo-silanes using [Ru3(CO)12]
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The reaction of carbon dioxide with Et3SiH in the presence of catalytic amounts of [Ru3(CO)12] as a catalytic precursor was achieved to produce silyl formate (Et3SiOCOH) 1s with a TON of 9000. A similar reaction in the presence of KF yielded potassium formate (8s) in a one-pot protocol with high selectivity using water or MeCN as the solvent. In the current report the complete reduction of carbon dioxide to methane was achieved, with the use of a more reactive silane (phenylsilane). A catalytically relevant species was the ruthenium cluster [H4Ru4(CO)12]. This is the second report on the hydrosilylation of carbon dioxide catalyzed by highly active and readily available ruthenium clusters and this is the first report of hydrosilylation of CO2to methane.
- Jurado-Vázquez, Tamara,Ortiz-Cervantes, Carmen,García, Juventino J.
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- Highly efficient hydrogen storage system based on ammonium bicarbonate/formate redox equilibrium over palladium nanocatalysts
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Abstract A highly efficient, reversible hydrogen storage-evolution process has been developed based on the ammonium bicarbonate/formate redox equilibrium over the same carbon-supported palladium nanocatalyst. This heterogeneously catalyzed hydrogen storage system is comparable to the counterpart homogeneous systems and has shown fast reaction kinetics of both the hydrogenation of ammonium bicarbonate and the dehydrogenation of ammonium formate under mild operating conditions. By adjusting temperature and pressure, the extent of hydrogen storage and evolution can be well controlled in the same catalytic system. Moreover, the hydrogen storage system based on aqueous-phase ammonium formate is advantageous owing to its high volumetric energy density. Revolution of H2 evolution? A highly efficient hydrogen storage-evolution process has been developed based on the ammonium bicarbonate/formate redox equilibrium over a carbon-supported palladium nanocatalyst. Ammonium ion improves the efficiencies of both the hydrogenation of bicarbonate and the dehydrogenation of formate. By adjusting the reaction temperature and pressure, the extent of chemical reaction of hydrogen storage and evolution can be well controlled within the same catalytic system.
- Su, Ji,Yang, Lisha,Lu, Mi,Lin, Hongfei
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p. 813 - 816
(2015/06/02)
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- Methanol dehydrogenation by iridium N-heterocyclic carbene complexes
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A series of homogeneous iridium bis(N-heterocyclic carbene) catalysts are active for three transformations involving dehydrogenative methanol activation: acceptorless dehydrogenation, transfer hydrogenation, and amine monoalkylation. The acceptorless dehydrogenation reaction requires base, yielding formate and carbonate, as well as 2-3 equivalents of H2. Of the few homogeneous systems known for this reaction, our catalysts tolerate air and employ simple ligands. Transfer hydrogenation of ketones and imines from methanol is also possible. Finally, N-monomethylation of anilines occurs through a borrowing hydrogen reaction. Notably, this reaction is highly selective for the monomethylated product.
- Campos, Jesús,Sharninghausen, Liam S.,Manas, Michael G.,Crabtree, Robert H.
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p. 5079 - 5084
(2015/06/16)
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- An aqueous rechargeable formate-based hydrogen battery driven by heterogeneous Pd catalysis
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The formate-based rechargeable hydrogen battery (RHB) promises high reversible capacity to meet the need for safe, reliable, and sustainable H2 storage used in fuel cell applications. Described herein is an additive-free RHB which is based on repetitive cycles operated between aqueous formate dehydrogenation (discharging) and bicarbonate hydrogenation (charging). Key to this truly efficient and durable H2 handling system is the use of highly strained Pd nanoparticles anchored on graphite oxide nanosheets as a robust and efficient solid catalyst, which can facilitate both the discharging and charging processes in a reversible and highly facile manner. Up to six repeated discharging/charging cycles can be performed without noticeable degradation in the storage capacity.
- Bi, Qing-Yuan,Lin, Jian-Dong,Liu, Yong-Mei,Du, Xian-Long,Wang, Jian-Qiang,He, He-Yong,Cao, Yong
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supporting information
p. 13583 - 13587
(2015/02/19)
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- Alcoholysis of fluoroform
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Fluoroform (CHF3) reacts with alkali metal alkoxides MOR (M = Na, K) in the corresponding alcohols ROH (R = Me, Et, i-Pr, t-Bu, and Allyl) at 80-120°C to give orthoformate esters HC(OR)3 in 55-90% yield. Particularly notable is the f
- Miloserdov, Fedor M.,Grushin, Vladimir V.
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p. 105 - 109
(2015/03/03)
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- Towards a sustainable synthesis of formate salts: Combined catalytic methanol dehydrogenation and bicarbonate hydrogenation
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Formate salts are important chemicals widely used in everyday products. The current industrial-scale manufacture of formates requires CO at high pressure and harsh reaction conditions. Herein, we describe a new process for these products without the utilization of hazardous gases and chemicals. By application of ruthenium pincer complexes, a simultaneous methanol dehydrogenation and bicarbonate hydrogenation reaction proceeds, which provides a green synthesis of formate salts with excellent TON (>18 000), TOF (>1300 h-1), and yield (>90 %). Get rid of CO and H 2: An efficient route for the industrial synthesis of formate salts without the utilization of carbon monoxide is highly desirable. A catalytic reaction combining methanol dehydrogenation and bicarbonate hydrogenation has been developed, which provides a green and cost-efficient process for the synthesis of formate salts with excellent turnover numbers and yields.
- Liu, Qiang,Wu, Lipeng,Guelak, Samet,Rockstroh, Nils,Jackstell, Ralf,Beller, Matthias
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supporting information
p. 7085 - 7088
(2014/07/08)
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- Assigning the EPR fine structure parameters of the Mn(II) centers in bacillus subtilis oxalate decarboxylase by site-directed mutagenesis and DFT/MM calculations
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Oxalate decarboxylase (OxDC) catalyzes the Mn-dependent conversion of the oxalate monoanion into CO2 and formate. EPR-based strategies for investigating the catalytic mechanism of decarboxylation are complicated by the difficulty of assigning the signals associated with the two Mn(II) centers located in the N- and C-terminal cupin domains of the enzyme. We now report a mutational strategy that has established the assignment of EPR fine structure parameters to each of these Mn(II) centers at pH 8.5. These experimental findings are also used to assess the performance of a multistep strategy for calculating the zero-field splitting parameters of protein-bound Mn(II) ions. Despite the known sensitivity of calculated D and E values to the computational approach, we demonstrate that good estimates of these parameters can be obtained using cluster models taken from carefully optimized DFT/MM structures. Overall, our results provide new insights into the strengths and limitations of theoretical methods for understanding electronic properties of protein-bound Mn(II) ions, thereby setting the stage for future EPR studies on the electronic properties of the Mn(II) centers in OxDC and site-specific variants.
- Campomanes, Pablo,Kellett, Whitney F.,Easthon, Lindsey M.,Ozarowski, Andrew,Allen, Karen N.,Angerhofer, Alexander,Rothlisberger, Ursula,Richards, Nigel G. J.
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supporting information
p. 2313 - 2323
(2014/03/21)
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- Nickel-catalyzed hydrosilylation of CO2 in the Presence of Et3B for the synthesis of formic acid and related formates
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The reaction of CO2 with Et3SiH catalyzed by the nickel complex [(dippe)Ni(μ-H)]2 (1) afforded the reduction products Et3SiOCH2OSiEt3 (12%), Et 3SiOCH3 (3%), and CO, which were characterized by standard spectroscopic methods. Part of the generated CO was found as the complex [(dippe)Ni(CO)]2 (2), which was characterized by single-crystal X-ray diffraction. When the same reaction was carried out in the presence of a Lewis acid, such as Et3B, the hydrosilylation of CO2 efficiently proceeded to give the silyl formate (Et3SiOC(O)H) in high yields (85-89%), at 80 C for 1 h. Further reactivity of the silyl formate to yield formic acid, formamides, and alkyl formates was also investigated.
- Gonzalez-Sebastian, Lucero,Flores-Alamo, Marcos,Garcia, Juventino J.
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p. 7186 - 7194
(2014/01/06)
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- Electrooxidation of ethylene glycol and glycerol on Pd-(Ni-Zn)/C anodes in direct alcohol fuel cells
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The electrooxidation of ethylene glycol (EG) and glycerol (G) has been studied: in alkaline media, in passive as well as active direct ethylene glycol fuel cells (DEGFCs), and in direct glycerol fuel cells (DGFCs) containing Pd-(Ni-Zn)/C as an anode electrocatalyst, that is, Pd nanoparticles supported on a Ni-Zn phase. For comparison, an anode electrocatalyst containing Pd nanoparticles (Pd/C) has been also investigated. The oxidation of EG and G has primarily been investigated in half cells. The results obtained have highlighted the excellent electrocatalytic activity of Pd-(Ni-Zn)/C in terms of peak current density, which is as high as 3300A g(Pd)-1 for EG and 2150A g(Pd)-1 for G. Membrane-electrode assemblies (MEA) have been fabricated using Pd-(Ni-Zn)/C anodes, proprietary Fe-Co/C cathodes, and Tokuyama A-201 anion-exchange membranes. The MEA performance has been evaluated in either passive or active cells fed with aqueous solutions of 5wt % EG and 5wt % G. In view of the peak-power densities obtained in the temperature range from 20 to 80 °C, at Pd loadings as low as 1mg cm -2 at the anode, these results show that Pd-(Ni-Zn)/C can be classified amongst the best performing electrocatalysts ever reported for EG and G oxidation. Copyright
- Marchionni, Andrea,Bevilacqua, Manuela,Bianchini, Claudio,Chen, Yan-Xin,Filippi, Jonathan,Fornasiero, Paolo,Lavacchi, Alessandro,Miller, Hamish,Wang, Lianqin,Vizza, Francesco
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p. 518 - 528
(2013/06/05)
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- CO2-"Neutral" hydrogen storage based on bicarbonates and formates
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Let the circle be unbroken! One ruthenium catalyst generated in situ facilitates the selective hydrogenation of bicarbonates and carbonates, as well as CO2 and base, to give formates and also the selective dehydrogenation of formates back to bicarbonates. The two reactions can be coupled, leading to a reversible hydrogen-storage system. dppm=1,2- bis(diphenylphosphino)methane. Copyright
- Boddien, Albert,Gaertner, Felix,Federsel, Christopher,Sponholz, Peter,Mellmann, Doerthe,Jackstell, Ralf,Junge, Henrik,Beller, Matthias
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p. 6411 - 6414
(2011/08/05)
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- Kinetic challenges facing oxalate, malonate, acetoacetate, and oxaloacetate decarboxylases
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To compare the powers of the corresponding enzymes as catalysts, the rates of uncatalyzed decarboxylation of several aliphatic acids (oxalate, malonate, acetoacetate, and oxaloacetate) were determined at elevated temperatures and extrapolated to 25 °C. In the extreme case of oxalate, the rate of the uncatalyzed reaction at pH 4.2 was 1.1 × 10-12 s-1, implying a 2.5 × 1013-fold rate enhancement by oxalate decarboxylase. Whereas the enzymatic decarboxylation of oxalate requires O 2 and MnII, the uncatalyzed reaction is unaffected by the presence of these cofactors and appears to proceed by heterolytic elimination of CO2.
- Wolfenden, Richard,Lewis, Charles A.,Yuan, Yang
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supporting information; experimental part
p. 5683 - 5685
(2011/06/18)
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- Mechanistic studies on the reversible hydrogenation of carbon dioxide catalyzed by an Ir-PNP complex
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The PNP-ligated iridium(III) trihydride complex 1 exhibited the highest catalytic activity for hydrogenation of carbon dioxide in aqueous KOH. The catalytic hydrogenation can be tuned to be a reversible process with the same catalyst at the expense of the activity, when triethanolamine was used as a base. Theoretical studies on the hydrogenation of carbon dioxide using DFT calculations suggested two competing reaction pathways: either the deprotonative dearomatization step or the hydrogenolysis step as the rate-determining step. The results nicely explain our experimental observations that the catalytic cycle is dependent on both the strength of the base and hydrogen pressure.
- Tanaka, Ryo,Yamashita, Makoto,Chung, Lung Wa,Morokuma, Keiji,Nozaki, Kyoko
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p. 6742 - 6750
(2012/02/06)
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