1664-98-8Relevant academic research and scientific papers
Stepwise photocatalytic dissociation of methanol and water on TiO 2(110)
Guo, Qing,Xu, Chenbiao,Ren, Zefeng,Yang, Wenshao,Ma, Zhibo,Dai, Dongxu,Fan, Hongjun,Minton, Timothy K.,Yang, Xueming
, p. 13366 - 13373 (2012)
We have investigated the photocatalysis of partially deuterated methanol (CD3OH) and H2O on TiO2(110) at 400 nm using a newly developed photocatalysis apparatus in combination with theoretical calculations. Photocatalyzed products, CD2O on Ti5c sites, and H and D atoms on bridge-bonded oxygen (BBO) sites from CD3OH have been clearly detected, while no evidence of H2O photocatalysis was found. The experimental results show that dissociation of CD3OH on TiO2(110) occurs in a stepwise manner in which the O-H dissociation proceeds first and is then followed by C-D dissociation. Theoretical calculations indicate that the high reverse barrier to C-D recombination and the facile desorption of CD2O make photocatalytic methanol dissociation on TiO2(110) proceed efficiently. Theoretical results also reveal that the reverse reactions, i.e, O-H recombination after H2O photocatalytic dissociation on TiO2(110), may occur easily, thus inhibiting efficient photocatalytic water splitting.
Reactivity of stoichiometric and defective TiO2 (110) surfaces toward DCOOD decomposition
Wang, Qinggen,Biener, Jurgen,Guo, Xing-Cai,Farfan-Arribas, Enrique,Madix, Robert J.
, p. 11709 - 11720 (2003)
The effect of defects on TiO2 (110) on the decomposition of DCOOD was investigated by temperature-programmed reaction spectroscopy (TPRS). Different concentrations of anion vacancy defects were created on the TiO2 (110) surface by el
C-H bond activation with Ge-oxyl complex generated by photoinduced- electron-transfer of di(hydroxo)porphyrin GeIV complex
Shiragami, Tsutomu,Kuroki, Ayano,Matsumoto, Jin,Yasuda, Masahide
, p. 529 - 534 (2014)
Visible-light irradiation of MeOH solution containing di(hydroxo) tetraphenylporphyrin atogermanium(IV) complex (tppGe(OH)2; 1a), cumene, and Fe3+ ion (Fe(NO3)3) as an electron acceptor gave cumyl alcohol as an oxidative product along with Fe2+ ion as a reductive product. The quantum yield (Φox) and turn over frequency (TOF) for the formation of cumyl alcohol was 0.033 and 111.1 h -1, respectively. The addition of KOH aqueous solution (1 mM) into reaction solution led to an increase of Φox to 0.047. The free energy change (ΔG) with electron transfer from excited triplet state (31a*) to Fe3+ was estimated as a large negative value (-1.37 eV). Furthermore, in 1a-photosensitized oxidation of MeOH in the presence of K2PtCl6 as an electron acceptor, formaldehyde (HCHO) was formed in Φox = 0.034 and TOF = 120.0 h-1. The isotope effect for the formation of HCHO (Φox(H)/ Φox(D) = 5.04) was observed when MeOH-d4 was employed as an substrate. Both formation of cumyl alcohol and formaldehyde was not observed at all in the case of photosensitized reactions by tppGe(OMe) 2 (1b) having two axial methoxo ligands. These findings indicate the photosensitized reaction was initiated by photoinduced electron transfer from 31a* to Fe3+ or K2PtCl6 to generate porphyrin radical cation (1a+?), which underwent a proton dissociation of hydroxo axial ligand to give tpp(OH)Ge-O? (Ge-oxyl complex) as key intermediate. The Ge-oxyl complex oxidized substrates through a hydrogen-atom abstraction. It is strongly suggested that 1a can act as a good sensitizer for being able to activate C-H bond of organic compounds.
Concerted Grob Fragmentation in N-Halo-α-amino Acid Decomposition
Armesto, X. L.,Canle L., M.,Losada, M.,Santaballa, J. A.
, p. 4659 - 4664 (1994)
The Grob fragmentation of N-halo-α-amino acids in aqueous solution has been studied, being first order in N-halo-α-amino acid and pH-independent.The substituents on the C2 and N atoms strongly affect the reaction rate.Structure reactivity correlations for C2 substituents provide ρ* values of -3.9 and -4.1 for N-Cl and N-Br compounds, respectively.The same correlations for N substituents lead to ρ* values of -2.1 and -1.9 for N-Cl and N-Br compounds.The transition state (TS) can be generally described as product-like, its structure and characteristics being significantly affected by the substituents on the C2 and on the N atoms.In conclusion, the reaction is a DEDN concerted and slightly nonsynchronous two-stage process.
Kinetics of Photoelectrochemical Oxidation of Methanol on Hematite Photoanodes
Mesa, Camilo A.,Kafizas, Andreas,Francàs, Laia,Pendlebury, Stephanie R.,Pastor, Ernest,Ma, Yimeng,Le Formal, Florian,Mayer, Matthew T.,Gr?tzel, Michael,Durrant, James R.
, p. 11537 - 11543 (2017)
The kinetics of photoelectrochemical (PEC) oxidation of methanol, as a model organic substrate, on α-Fe2O3 photoanodes are studied using photoinduced absorption spectroscopy and transient photocurrent measurements. Methanol is oxidized on α-Fe2O3 to formaldehyde with near unity Faradaic efficiency. A rate law analysis under quasi-steady-state conditions of PEC methanol oxidation indicates that rate of reaction is second order in the density of surface holes on hematite and independent of the applied potential. Analogous data on anatase TiO2 photoanodes indicate similar second-order kinetics for methanol oxidation with a second-order rate constant 2 orders of magnitude higher than that on α-Fe2O3. Kinetic isotope effect studies determine that the rate constant for methanol oxidation on α-Fe2O3 is retarded ～20-fold by H/D substitution. Employing these data, we propose a mechanism for methanol oxidation under 1 sun irradiation on these metal oxide surfaces and discuss the implications for the efficient PEC methanol oxidation to formaldehyde and concomitant hydrogen evolution.
Hydrogen atom abstraction reactions independent of C-H bond dissociation energies of organic substrates in water: Significance of oxidant-substrate adduct formation
Ishizuka, Tomoya,Ohzu, Shingo,Kotani, Hiroaki,Shiota, Yoshihito,Yoshizawa, Kazunari,Kojima, Takahiko
, p. 1429 - 1436 (2014)
Detailed kinetic studies on the oxidation reactions of organic substrates such as methanol with RuIVO complexes as oxidants, formed electrochemically in water, have been conducted to elucidate the reaction mechanism. The rate constants of the oxidation reactions exhibited saturation behaviours relative to the substrate concentration, regardless of the oxidants and the substrates employed. This indicates the existence of a pre-equilibrium process based on the adduct formation between the RuIVO oxidant and the substrate. Herein, we have experimentally confirmed that the driving force of the adduct formation is the hydrogen bonding between the oxidants and alcohols even in water. In addition, we have investigated the kinetic isotope effects (KIE) on the oxidation reaction using methanol and its deuterated derivatives and as a result observed moderate KIE values for the C-H bond of methanol. We have also revealed the independency of the reaction rates from the bond dissociation enthalpies of the C-H bonds of the substrates. This independency is probably derived from the tightly condensed transition state, whose energy level is strongly controlled by the activation entropy but less sensitive to the activation enthalpy.
Matrix Isolation Investigation of the Room Temperature and Pyrolytic Reactions of (CH3)2Zn with CH3OH and CH3SH
Bai, Hebi,Ault, Bruce S.
, p. 10492 - 10497 (1995)
Matrix isolation and cryogenic thin film approaches have been employed for the synthesis, isolation, and characterization of 1:1 and 1:2 complexes of (CH3)2Zn with CH3OH and CH3SH.These complexes were characterized by a shifting of certain sensitive vibrational modes of the acid and base subunits in the complex.The ratio of the 1:1 and 1:2 complexes could be altered by changing the relative amounts of the two reagents employed in a given experiment or by warming the cryogenic thin film from 14 K to as high as 200 K.Merged jet mixtures of (CH3)2Zn with either CH3OH and its isotopomers or CH3SH were also pyrolyzed at temperatures as high as 370 deg C.For the (CH3)2Zn/CH3OH pair, significant production of CH4 and CH2O was observed with minor amounts of C2H4.In the (CH3)2Zn/CH3SH experiments a substantial yield of (CH3)2S and CH4 was obtained.These pyrolytic reactions and products have not been reported previously and may have implications for the chemical vapor deposition of ZnO and ZnS.
Kinetic Studies of the Reaction of the Hydroxymethyl Radical with NO and NO2
Nesbitt, F. L.,Payne, W. A.,Stief, L. J.
, p. 5158 - 5161 (1989)
The absolute rate constant for the reaction CD2OH + NO has been measured from 230 to 373 K in a discharge-flow system.The decay of the CD2OH radical was monitored in excess NO by collision-free sampling mass spectrometry.At 298 K, k1 = (2.2 +/- 0.4) x 10-12 cm3 s-1 (2?) independent of pressure from 0.5 to 1.5 Torr.For the 230-298 K interval, an activation energy of 1.2 kcal/mol is obtained, but k1 does not appear to change within experimental error on going from 298 to 373 K.The absolute rate constant at 298 K has also been measured for the reaction CH2OH + NO2 by the same technique.The result is k2 = (8.3 +/- 4.1) x 10-12 cm3 s-1 (2?).Qualitative detection was made of D2CO and H2CO as products of these reactions, but no evidence was obtained for the expected accompanying products HNO and HNO2 nor for the CD2OHNO and CH2OHNO2 adducts.It is suggested, partially by analogy with the CH2OH + O2 reaction, that the reaction mechanism in both cases involves initial formation of a vibrationally excited complex that, depending on reaction conditions, can dissociate back to reactants or, after isomerization, dissociate to products.Collisional stabilization of the addition complex may be feasible, but we have no evidence for this under the low-pressure condition of our experiments.The rate constants for reaction of CH2OH with O2, NO, and NO2 are briefly compared.
Thermal methane conversion to formaldehyde promoted by single platinum atoms in PtAl2O4- cluster anions
Zhao, Yan-Xia,Li, Zi-Yu,Yuan, Zhen,Li, Xiao-Na,He, Sheng-Gui
, p. 9482 - 9486 (2014)
Identification and mechanistic study of thermal methane conversion mediated by gas-phase species is important for finding potentially useful routes for direct methane transformation under mild conditions. Negatively charged oxide species are usually inert with methane. This work reports an unexpected result that the bi-metallic oxide cluster anions PtAl2O4 - can transform methane into a stable organic compound, formaldehyde, with high selectivity. The clusters are prepared by laser ablation and reacted with CH4 in an ion trap reactor. The reaction is characterized by mass spectrometry and density functional theory calculations. It is found that platinum rather than oxygen activates CH4 at the beginning of the reaction. The Al2O4- moiety serves as the support of Pt atom and plays important roles in the late stage of the reaction. A new mechanism for selective methane conversion is provided and new insights into the surface chemistry of single Pt atoms may be obtained from this study. One atom is enough: The negatively charged oxide cluster PtAl2O 4- is an active species in thermal methane conversion. The single platinum atom activates methane and delivers two hydrogen atoms to the "oxide support" Al2O4-. Methane is then transformed to formaldehyde with a high selectivity.
Photodecomposition of Methyl Nitrite Trapped in Solid Argon
Jacox, Marilyn E.,Rook, Frederick L.
, p. 2899 - 2904 (1982)
The threshold wavelength for the photolysis of methyl nitrite isolated in solid argon at 14 K has been determined to be near 370 nm.Photolyzed samples show prominent infrared absorptions of H2CO and HNO, which are perturbed by the hydrogen-bonding interac
