1520-21-4Relevant articles and documents
Origin and Abatement of Heterogeneity at the Support Granule Scale of Silver on Silica Catalysts
Plessers, Eva,van den Reijen, Jeroen E.,de Jongh, Petra E.,de Jong, Krijn P.,Roeffaers, Maarten B. J.
, p. 4562 - 4569 (2017)
Incipient wetness impregnation is used commonly to form supported metal nanoparticle catalysts. Recently, it has been revealed that this approach may induce severe heterogeneity between catalyst granules of the same batch. At least a 10-fold variation in metal loading was observed, which affect the catalytic performance of individual catalyst granules severely. However, the origin of this heterogeneity is still unclear. Here we show that every elementary step in the preparation procedure of a Ag on silica catalyst has an effect on the resulting interparticle heterogeneity, but the influence of the drying step is the most important. This is because drying by capillary force results in a heterogeneous sample. Specifically, the position of a granule in the stagnant drying bed influences the resulting color and, thus, Ag loading significantly. This is further demonstrated by varying the drying conditions: freeze-drying and fluidized-bed drying led to a more homogeneous Ag loading. An investigation of the fluidized-bed-dried sample by using optical microscopy revealed a large fraction of transparent granules (94 %), which indicates that almost all the Ag nanoparticles in this sample are confined within the 6 nm pores. The optimized supported Ag on silica catalyst shows a good catalytic performance. This adaptation of the drying step can be implemented easily on a laboratory scale, is scalable, and does not require the use of expensive solvents or metal precursors.
Robust Synthesis of Gold-Based Multishell Structures as Plasmonic Catalysts for Selective Hydrogenation of 4-Nitrostyrene
Li, Jian,Long, Yan,Liu, Yu,Zhang, Lingling,Wang, Qishun,Wang, Xiao,Song, Shuyan,Zhang, Hongjie
, p. 1103 - 1107 (2020)
A robust self-template strategy is used for facile and large-scale synthesis of porous multishell gold with controllable shell number, sphere size, and in situ surface modification. The process involved the rapid reduction of novel Au-melamine colloidal templates with a great amount of NaBH4 in presence of poly(sodium-p-styrenesulfonate) (PSS). After soaking the templates in other metal salt solution, the obtained bimetallic templates could also be generally converted into bimetallic multishell structures by same reduction process. In the hydrogenation of 4-nitrostyrene using NH3BH3 as a reducing agent, the porous triple-shell Au with surface modification (S-PTSAu) exhibited excellent selectivity (97 %) for 4-aminostyrene in contrast with unmodified triple-shell Au. Furthermore, it also showed higher enhancement of catalytic activity under irradiation of visible light as compared to similar catalysts with fewer shells.
Base-free chemoselective transfer hydrogenation of nitroarenes to anilines with formic acid as hydrogen source by a reusable heterogeneous Pd/ZrP catalyst
Tuteja, Jaya,Nishimura, Shun,Ebitani, Kohki
, p. 38241 - 38249 (2014)
A highly efficient, chemoselective, environmentally-benign method is developed for the catalytic transfer hydrogenation (CTH) of nitroarenes using FA as a hydrogen source. Various supported Pd catalysts were examined for this transformation, and Pd supported ZrP (Pd/ZrP) proved to be the best catalyst for CTH of nitrobenzene. Applicability of the Pd/ZrP catalyst is also explored for hydrogenation of various substituted nitroarenes. The Pd/ZrP catalyst showed high specificity for hydrogenation of nitro groups even in the presence of other reducible functional groups such as -CC, -COOCH3, and -CN. To investigate the reaction mechanism, a Hammett plot was obtained for CTH of p-substituted nitroarenes. The active site is thought to be in situ generated Pd(0) species as seen from XRD and TEM data. The Pd/ZrP catalyst is reusable at least up to 4 times while maintaining the same activity and selectivity. To the best of our knowledge, this is one of the best methodologies for CTH of nitroarenes under base-free conditions with high activity and chemoselectivity over heterogeneous Pd-based catalysts. the Partner Organisations 2014.
Selective Liquid-Phase Hydrogenation of a Nitro Group in Substituted Nitrobenzenes over Au/Al2O3 Catalyst in a Packed-Bed Flow Reactor
Nuzhdin, Alexey L.,Moroz, Boris L.,Bukhtiyarova, Galina A.,Reshetnikov, Sergey I.,Pyrjaev, Pavel A.,Aleksandrov, Pavel V.,Bukhtiyarov, Valerii I.
, p. 1741 - 1749 (2015)
A series of substituted nitrobenzenes with the general formula XC6H4NO2 (X=Cl, CH=CH2, or C(O)CH3) dissolved in toluene were reduced with hydrogen over the 1.9 % Au/Al2O3 catalyst at 60-110 C and 10-20 bar in a three-phase packed-bed reactor operating in up-flow mode. Under these conditions, hydrogenation of isomeric ClC6H4NO2 gives exclusively chloroanilines. Hydrogenation of 3-CH2CHC6H4NO2 and 4-CH3C(O)C6H4NO2 leads to the formation of 3-CH2CHC6H4NH2 and 4-CH3C(O)C6H4NH2 with selectivities of up to 93 and 97 % at substrate conversions of 98 and 100 %, respectively. Smooth catalyst deactivation was observed regardless of which substituted nitrobenzene was taken for hydrogenation. According to the results obtained by temperature-programmed oxidation of the spent catalyst, a carbonaceous deposit formed that might block the catalyst surface. Almost complete regeneration of the supported gold catalyst with retention of its high selectivity to hydrogenation of a nitro group was achieved in a flow of air at temperatures up to 400 C to eliminate carbonaceous deposits.
Bimetallic Platinum-Tin Nanoparticles on Hydrogenated Molybdenum Oxide for the Selective Hydrogenation of Functionalized Nitroarenes
Shu, Yijin,Chan, Hang Cheong,Xie, Lifang,Shi, Zhangping,Tang, Yi,Gao, Qingsheng
, p. 4199 - 4205 (2017)
The hydrogenation of functionalized nitroarenes to the corresponding anilines is of great importance in the fine chemical industry and requires high-performance catalysts with a good activity and selectivity. Herein, hydrogenated MoOx (H-MoOx) supported bimetallic Pt-Sn (Pt-Sn/H-MoOx) was developed to accomplish selective and efficient hydrogenation. In the case of 4-nitrostyrene, an outstanding selectivity to 4-vinylaniline (≈93 %) with a high turnover frequency (0.094 s?1) was achieved under mild conditions (T=30 °C, PH2 =1 atm). The metal–support interactions contributed to the efficient turnover on the ultrafine nanoparticles, and the atom-rearranged bimetallic Pt-Sn surface promoted the selectivity because of the preferred adsorption of the nitro group. The good efficiency for various functionalized nitroarenes further verified the promise of Pt-Sn/H-MoOx in chemoselective hydrogenation.
Boronate self-assemblies with embedded Au nanoparticles: Preparation, characterization and their catalytic activities for the reduction of nitroaromatic compounds
Matsushima, Yusuke,Nishiyabu, Ryuhei,Takanashi, Naoto,Haruta, Masatake,Kimura, Hideaki,Kubo, Yuji
, p. 24124 - 24131 (2012)
Sequential boronate esterification of benzene-1,4-diboronic acid with pentaerythritol induced hierarchical molecular self-assembly to produce mono-dispersed flower-like microparticles. ATR-FT-IR, PXRD, 13C-CP- MAS and 11B-DD-MAS NMR spectra indicate that the particles consist of zigzag-shaped packing structures of polymeric 2,4,8,10-tetraoxa-3,9- diboraspiro[5.5]undecane. Au nanoparticles (Au NPs) with a mean diameter of 2.7 nm were successfully deposited on the microparticles by the deposition reduction (DR) method. It is noteworthy that the resulting novel hybrids exhibited an efficient catalytic activity for the reduction of nitroaromatic compounds; in particular, high chemoselectivity in the hydrogenation of 4-nitrostyrene to the corresponding aniline was attained without reduction of the vinyl bond. Careful investigation of the catalyst suggested a synergistic effect between Au NPs and the boronate support in the selective hydrogenation. These findings strongly suggest that boronate self-assemblies are advantageous as support materials for preparation of heterogeneous catalysts based on polymer-Au hybrids. The Royal Society of Chemistry 2012.
Co/N-codoped porous carbons derived from poly(Schiff base)/Co(II) complex as ultrahighly efficient catalysts for CTH of nitroarenes
Chen, Hongbiao,Li, Huaming,Liu, Bei,Liu, Yijiang,Xie, Weichao,Yang, Mei
, (2021)
Herein we report the scalable synthesis of Co/N-codoped porous carbon (Co/N-C) catalysts by pyrolyzing poly(Schiff base)/Co(II) complex. The strong Co(II)-binding affinity of poly(Schiff base) leads to the formation of uniformly distributed Co(0) nanoparticles, Co-Nx species, and N–C configurations, in which their catalytic contributions are confirmed and estimated by ligand-poisoning and acid-etching experiments and the Co-Nx species has been proved to be highly active for catalytic transfer hydrogenation (CTH) reaction. Consequently, the as-prepared Co-N/C-950 catalyst exhibits an ultrahigh activity for the CTH of 4-nitrophenol (4-NP) with a TOF of 226 mol4-NP molCo?1 min?1 (13560 h?1) together with an excellent selectivity for CTH of challenging nitroarenes. Moreover, the Co(0) nanoparticles embedded in the Co-N/C-950 catalyst can be further transformed to Co4N phase by a facile nitridation reaction, yielding Co4N-N/C-950 catalyst with even higher activity for the CTH of 4-NP (TOF up to 310 mol4-NP molCo?1 min?1).
Reduction of 4-nitrostyrene to 4-aminostyrene
Shul'Tsev
, p. 694 - 697 (2013)
Reduction of 4-nitrostyrene with Fe0, Fe2+, and S2O 4 2- was studied. A new method of 4-aminostyrene synthesis was developed.
Half-Sandwich Ruthenium Complexes of Amide-Phosphine Based Ligands: H-Bonding Cavity Assisted Binding and Reduction of Nitro-substrates
Pachisia, Sanya,Kishan, Ram,Yadav, Samanta,Gupta, Rajeev
, p. 2009 - 2022 (2021)
We present synthesis and characterization of two half-sandwich Ru(II) complexes supported with amide-phosphine based ligands. These complexes presented a pyridine-2,6-dicarboxamide based pincer cavity, decorated with hydrogen bonds, that participated in the binding of nitro-substrates closer to the Ru(II) centers, which is further supported with binding and docking studies. These ruthenium complexes functioned as the noteworthy catalysts for the borohydride mediated reduction of assorted nitro-substrates. Mechanistic studies not only confirmed the intermediacy of [Ru-H] in the reduction but also asserted the involvement of several organic intermediates during the course of the catalysis. A similar Ru(II) complex that lacked pyridine-2,6-dicarboxamide based pincer cavity substantiated its unique role both in the substrate binding and the subsequent catalysis.
Size- and support-dependent silver cluster catalysis for chemoselective hydrogenation of nitroaromatics
Shimizu, Ken-ichi,Miyamoto, Yuji,Satsuma, Atsushi
, p. 86 - 94 (2010)
Silver clusters on θ-Al2O3 support catalyze highly chemoselective reduction of a nitro group for the reduction of substituted nitroaromatics such as nitrostyrene. These catalysts show higher selectivity than conventional platinum-group metal-based heterogeneous catalysts. Systematic studies on the influence of the metal particle size and support oxides show that the intrinsic activity increases with decrease in the silver particle size, and acid-base bifunctional supports such as Al2O3 give higher activity than acidic or basic supports. Kinetic and in situ infrared studies provide a reaction mechanism which explains fundamental reasons of these tendencies. Cooperation of the acid-base pair site on Al2O3 and the coordinatively unsaturated Ag sites on the silver cluster is responsible for the rate-limiting H2 dissociation to yield a H+/H- pair at metal/support interface, while the basic site on oxides acts as an adsorption site of nitroaromatics. High chemoselectivity could be attributed to a preferential transfer of the H+/H- pair to the polar bonds in the nitro group.
Cyclic (Alkyl)(amino)carbene Ligand-Promoted Nitro Deoxygenative Hydroboration with Chromium Catalysis: Scope, Mechanism, and Applications
Zhao, Lixing,Hu, Chenyang,Cong, Xuefeng,Deng, Gongda,Liu, Liu Leo,Luo, Meiming,Zeng, Xiaoming
supporting information, p. 1618 - 1629 (2021/01/25)
Transition metal catalysis that utilizes N-heterocyclic carbenes as noninnocent ligands in promoting transformations has not been well studied. We report here a cyclic (alkyl)(amino)carbene (CAAC) ligand-promoted nitro deoxygenative hydroboration with cost-effective chromium catalysis. Using 1 mol % of CAAC-Cr precatalyst, the addition of HBpin to nitro scaffolds leads to deoxygenation, allowing for the retention of various reducible functionalities and the compatibility of sensitive groups toward hydroboration, thereby providing a mild, chemoselective, and facile strategy to form anilines, as well as heteroaryl and aliphatic amine derivatives, with broad scope and particularly high turnover numbers (up to 1.8 × 106). Mechanistic studies, based on theoretical calculations, indicate that the CAAC ligand plays an important role in promoting polarity reversal of hydride of HBpin; it serves as an H-shuttle to facilitate deoxygenative hydroboration. The preparation of several commercially available pharmaceuticals by means of this strategy highlights its potential application in medicinal chemistry.
