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1.
The non‐CO‐involved oxidation of methanol (NCOIOM) on a Pt(111) surface is investigated by using density functional theory. Relative energy diagrams for the NCOIOM are established in which the reaction mechanisms for a catalytic cycle—including the associated barriers, the reactive energies, the intermediates, and the transient states—are shown. The results indicate that the reaction proceeds via the kinetically favored pathways: A) HCOH→HC(OH)2→HCOOH→HCOO‐ [‐COOH]→CO2 and B) CHO→HCOOH→HCOO‐ [‐COOH]→CO2, with OH playing a key role in the entire process. The vibrational frequencies of the intermediate states derived from the calculations are in agreement with the experimental measurements.  相似文献   

2.
Pyrolysis and oxidation of acetaldehyde were studied behind reflected shock waves in the temperature range 1000–1700 K at total pressures between 1.2 and 2.8 atm. The study was carried out using the following methods, (1) time‐resolved IR‐laser absorption at 3.39 μm for acetaldehyde decay and CH‐compound formation rates, (2) time‐resolved UV absorption at 200 nm for CH2CO and C2H4 product formation rates, (3) time‐resolved UV absorption at 216 nm for CH3 formation rates, (4) time‐resolved UV absorption at 306.7 nm for OH radical formation rate, (5) time‐resolved IR emission at 4.24 μm for the CO2 formation rate, (6) time‐resolved IR emission at 4.68 μm for the CO and CH2CO formation rate, and (7) a single‐pulse technique for product yields. From a computer‐simulation study, a 178‐reaction mechanism that could satisfactorily model all of our data was constructed using new reactions, CH3CHO (+M) → CH4 + CO (+M), CH3CHO (+M) → CH2CO + H2(+M), H + CH3CHO → CH2CHO + H2, CH3 + CH3CHO → CH2CHO + CH4, O2 + CH3CHO → CH2CHO + HO2, O + CH3CHO → CH2CHO + OH, OH + CH3CHO → CH2CHO + H2O, HO2 + CH3CHO → CH2CHO + H2O2, having assumed or evaluated rate constants. The submechanisms of methane, ethylene, ethane, formaldehyde, and ketene were found to play an important role in acetaldehyde oxidation. © 2007 Wiley Periodicals, Inc. 40: 73–102, 2008  相似文献   

3.
The gamma ray induced oxidation of Sb(III) in sulfuric acid solutions was studied. A simplified method depending on selective extraction of the different valency states and radiometric counting was elaborated for oxidation yield determination. The effect of increasing amounts of HCOOH, CH3COOH, NH2CH2COOH, CH3CHOH COOH and H2C2O4 on G[-Sb(III)] was examined. The study enabled a determination of rate constant values for reactions of the used additives with the OH radical in the working solutions.  相似文献   

4.
Electrochemical reduction of CO2 to ethanol, a clean and renewable liquid fuel with high heating value, is an attractive strategy for global warming mitigation and resource utilization. However, converting CO2 to ethanol remains great challenge due to the low activity, poor product selectivity and stability of electrocatalysts. Here, the B‐ and N‐co‐doped nanodiamond (BND) was reported as an efficient and stable electrode for selective reduction of CO2 to ethanol. Good ethanol selectivity was achieved on the BND with high Faradaic efficiency of 93.2 % (−1.0 V vs. RHE), which overcame the limitation of low selectivity for multicarbon or high heating value fuels. Its superior performance was mainly originated from the synergistic effect of B and N co‐doping, high N content and overpotential for hydrogen evolution. The possible pathway for CO2 reduction revealed by DFT computation was CO2→*COOH→*CO→*COCO→*COCH2OH→*CH2OCH2OH→CH3CH2OH.  相似文献   

5.
H2‐promoted catalytic activity of oxide‐supported metal catalysts in low‐temperature CO oxidation is of great interest but its origin remains unknown. Employing an FeO(111)/Pt(111) inverse model catalyst, we herewith report direct experimental evidence for the spillover of H(a) adatoms on the Pt surface formed by H2 dissociation to the Pt?FeO interface to form hydroxyl groups that facilely oxidize CO(a) on the neighboring Pt surface to produce CO2. Hydroxyl groups and coadsorbed water play a crucial role in the occurrence of hydrogen spillover. These results unambiguously identify the occurrence of hydrogen spillover from the metal surface to the noble metal/metal oxide interface and the resultant enhanced catalytic activity of the metal/oxide interface in low‐temperature CO oxidation, which provides a molecular‐level understanding of both H2‐promoted catalytic activity of metal/oxide ensembles in low‐temperature CO oxidation and hydrogen spillover.  相似文献   

6.
《中国化学快报》2023,34(7):107809
Comprehensive fundamental understanding of CO hydrogenation reactions over Cu and ZnCu alloy surfaces is of great importance. Herein, we report a comparative DFT calculation study of elementary surface reaction network of CO hydrogenation reactions on stepped Cu(211), Cu(611), ZnCu(211) and ZnCu(611) surfaces. On ZnCu(211) and ZnCu(611) surfaces, the energetic favorable reaction path of CO hydrogenation reaction follows CO* → HCO* → H2CO* → H3CO* → CH3OH* → CH3OH with H3CO* hydrogenation as the rate-limiting step and proceeds more facilely on ZnCu(611) surface than on ZnCu(211) surface. On Cu(211) and Cu(611) surfaces, the energetic favorable reaction path of CO hydrogenation reaction follows CO* → HCO* → HCOH* → H2COH* → H3COH* → CH3* → CH4* → CH4 with H2COH* hydrogenation as the rate-limiting step and proceeds more facilely on Cu(611) than on Cu(211). The key difference of CO hydrogenation reaction on ZnCu alloy surface and Cu is that the resulting CH3OH* species desorbs to produce CH3OH on ZnCu alloy but undergoes H*-assisted decomposition to CH3* and eventually to CH4 on Cu surface. These results successfully unveil elementary surface reaction networks and structure sensitivity of Cu and ZnCu alloy-catalyzed CO hydrogenation reactions.  相似文献   

7.
The electrocatalytic CO2 reduction reaction (CO2RR) can dynamise the carbon cycle by lowering anthropogenic CO2 emissions and sustainably producing valuable fuels and chemical feedstocks. Methanol is arguably the most desirable C1 product of CO2RR, although it typically forms in negligible amounts. In our search for efficient methanol‐producing CO2RR catalysts, we have engineered Ag‐Zn catalysts by pulse‐depositing Zn dendrites onto Ag foams (PD‐Zn/Ag foam). By themselves, Zn and Ag cannot effectively reduce CO2 to CH3OH, while their alloys produce CH3OH with Faradaic efficiencies of approximately 1 %. Interestingly, with nanostructuring PD‐Zn/Ag foam reduces CO2 to CH3OH with Faradaic efficiency and current density values reaching as high as 10.5 % and ?2.7 mA cm?2, respectively. Control experiments and DFT calculations pinpoint strained undercoordinated Zn atoms as the active sites for CO2RR to CH3OH in a reaction pathway mediated by adsorbed CO and formaldehyde. Surprisingly, the stability of the *CHO intermediate does not influence the activity.  相似文献   

8.
Restrained molecular dynamics simulations were performed to study the binding affinity of the peptide with alkanethiols of different tail-groups, S(CH2)7CH3, S(CH2)7OH and S(CH2)7COOH, which self-assembled on Au(111) surface in the presence of water molecules. The curves of binding affinity were calculated by fixing the center of mass of the peptide at various distances from the assembling surface. Simulation results show that the binding affin- ity is in the order as COOH-SAMs〉OH-SAMs〉CH3-SAMs, while 100% COOH-SAMs〉5% COOH-SAMS in concentration. The effects on binding affinity by different tail-groups were also studied. Results show that the binding affinity between COOH-SAMs and the peptide is bigger than those of the others and increasing the acidity of COOH-SAMs will result in stronger attractive power.  相似文献   

9.
The unimolecular decomposition of two radical isomers of C2H5O (CH3CH2O/ethoxy, CH3CHOH/α‐hydroxyethyl) are investigated by means of Rice–Ramsperger–Kassel–Marcus/master equation simulations in helium and nitrogen bath gases on an accurate one‐dimensional potential energy surface. For ethoxy, simulations are carried out between temperatures of 406 and 1200 K and pressures of 0.001 and 100 atm. For CH3CHOH, simulations are carried out between temperatures of 800 and 1500 K and pressures of 0.001 and 100 atm. Results are compared with available experimental data, with good agreement. The dominant product of α‐hydroxyethyl decomposition is CH3CHO + H, with C2H3OH + H and CH3 + CH2O, being minor channels. Rate coefficients are strongly dependent on temperature and pressure and are recommended with attendant uncertainty factor estimates. The relative roles of vinyl alcohol and acetaldehyde in the context of combustion chemistry are also discussed.  相似文献   

10.
In aqueous acidic acetonitrilc solution cerium(IV) oxidizes diphenylmethane (Ph2CH2) to produce diphenylmethanol (Ph2CHOH) first and then benzophenone (Ph2CO). With the organic reductant in great excess, both the Ce(IV)-Ph2CH2 and Ce(IV)-Ph2CHOH rcactions follow second-order kinetics. The rates of both reactions increase nonlinearly with increasing [H+] or with decreasing [H2O]. Both kinetic and spectrophotometrc results indicate that replacement of water molecules by complex formation through the phenyl or hydroxyl group plays an important role in activating the reaction. Under similar conditions, the order of relative reactivities toward Ce(IV) oxidation is PhCH2OH > CH3CH2OH > Ph2CHOH > Ph2CH2 > PhCH3> (Ph2CO, C6H6). Mechanistic interpretations of the kinetic results are presented.  相似文献   

11.
  • 1. The anions CH3O‐CO and CH3OCO‐CO are both methoxide anion donors. The processes CH3O‐CO → CH3O + CO and CH3OCO—CO → CH3O + 2CO have ΔG values of +8 and ?68 kJ mol?1, respectively, at the CCSD(T)/6‐311++G(2d, 2p)//B3LYP/6‐311++G(2d,2p) level of theory.
  • 2. The reactions CH3OCOCO → CH3OCO + CO (ΔG = ?22 kJ mol?1) and CH3COCH(O)CO2CH3 → CH3COCH(O)OCH3 + CO (ΔG = +19 kJ mol?1) proceed directly from the precursor anions via the transition states (CH3OCO…CO2) and (CH3COCHO…CH3OCO), respectively.
  • 3. Anion CH3COCH(O)CO2CH3 undergoes methoxide anion transfer and loss of two molecules of CO in the reaction sequence CH3COCH(O)CO2CH3 → CH3CH(O)COCO2CH3 → [CH3CHO (CH3OCO‐CO)] → CH3CH(O)OCH3 + 2CO (ΔG = +9 kJ mol?1). The hydride ion transfer in the first step is a key feature of the reaction sequence.
Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

12.
This study revisits the stability of the possible conformations and the decomposition reactions of ethyl formate in the S0 state using the (U)MP2, MP4SDTQ, CCSD(T), and (U)B3LYP methods with various basis sets. The transition states of the decomposition channels to HCOOH + C2H4, CO + CH3CH2OH, CH2O + CH3CHO, HCOH + CH3CHO, C2H6 + CO2, and H2 + CH2CHOCHO are determined. The microcanonical rate constants derived from the RRKM theory are calculated for each of the decomposition reactions. The high‐pressure limit rate constants are calculated for the decomposition channels to HCOOH + C2H4, CO + CH3CH2OH, and CH2O + CH3CHO.  相似文献   

13.
Direct synthesis of CH3COOH from CH4 and CO2 is an appealing approach for the utilization of two potent greenhouse gases that are notoriously difficult to activate. In this Communication, we report an integrated route to enable this reaction. Recognizing the thermodynamic stability of CO2, our strategy sought to first activate CO2 to produce CO (through electrochemical CO2 reduction) and O2 (through water oxidation), followed by oxidative CH4 carbonylation catalyzed by Rh single atom catalysts supported on zeolite. The net result was CH4 carboxylation with 100 % atom economy. CH3COOH was obtained at a high selectivity (>80 %) and good yield (ca. 3.2 mmol g−1cat in 3 h). Isotope labelling experiments confirmed that CH3COOH is produced through the coupling of CH4 and CO2. This work represents the first successful integration of CO/O2 production with oxidative carbonylation reaction. The result is expected to inspire more carboxylation reactions utilizing preactivated CO2 that take advantage of both products from the reduction and oxidation processes, thus achieving high atom efficiency in the synthesis.  相似文献   

14.
The electronic energy barriers of surface reactions pertaining to the mechanism of the electrooxidation of methane on Pt (111) were estimated with density functional theory calculations on a 10-atom Pt cluster, using both the B3LYP and PW91 functionals. Optimizations of initial and transition states were performed for elementary steps that involve the conversion of CH(4) to adsorbed CO at the Pt/vacuum interface. As a first approximation we do not include electrolyte effects in our model. The reactions include the dissociative chemisorption of CH(4) on Pt, dehydrogenation reactions of adsorbed intermediates (*CH(x) --> *CH(x-1) + *H and *CH(x)O --> *CH(x-1)O + *H), and oxygenation reactions of adsorbed CH(x) species (*CH(x) + *OH --> *CH(x)OH). Many pathways were investigated and it was found that the main reaction pathway is CH(4) --> *CH(3) --> *CH(2) --> *CH --> *CHOH --> *CHO --> *CO. Frequency analysis and transition-state theory were employed to show that the methane chemisorption elementary step is rate-limiting in the above mechanism. This conclusion is in agreement with published experimental electrochemical studies of methane oxidation on platinum catalysts that have shown the absence of an organic adlayer at electrode potentials that allow the oxidation of adsorbed CO. The mechanism of the electrooxidation of methane on Pt is discussed.  相似文献   

15.
Details on the reactions of: (1) Pd+ + CH3CHO → PdCO+ + CH4 and (2) Pd+ + CH3CHO → PdH + CH3CO+ in the gas phase were investigated using density functional theory (B3LYP), in conjunction with the LANL2DZ+6‐311+G(d) basis set. Three encounter complexes were located on the potential energy surfaces and the calculations indicated that both the C? C and aldehyde C? H bond activation of acetaldehyde could lead to the dominant demethanation reaction. The charge transfer process for PdH abstraction was caused by an intramolecular PdH rearrangement of the newly found η1‐aldehyde attached complex. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011  相似文献   

16.
Using the rotating ring (platinum)—disk (glassy carbon) electrode methodology, electrocatalytic activity of the microstructured copper centers (imbedded within the polyvinylpyrrolidone polymer matrix and deposited onto the glassy carbon disk electrode) has been monitored during electroreduction of carbon dioxide both in acid (HClO4) and neutral (KHCO3) media as well as diagnosed (at Pt ring) with respect to formation of the electroactive products. Combination of the stripping-type and rotating ring-disk voltammetric approaches has led to the observation that, regardless the overlapping reduction phenomena, the reduction of carbon dioxide at copper catalyst is, indeed, operative and coexists with hydrogen evolution reaction. Using the fundamental concepts of surface electrochemistry and analytical voltammetry, the reaction products (thrown onto the platinum ring electrode) could be considered and identified as adsorbates (on Pt) under conditions of the stripping-type oxidation experiment. Judging from the potentials at which the stripping voltammetric peaks appear in neutral CO2-saturated KHCO3 (pH 6.8), formic acid or carbon monoxide seem to be the most likely reaction products or intermediates. The proposed methodology also permits correlation between the CO2 electroreduction products and the potentials applied to the disk electrode. By performing the comparative stripping-type voltammetric experiments in acid medium (HClO4 at pH 1) with the adsorbates of formic acid, ethanol and acetaldehyde (on Pt ring), it can be rationalized that, although C2H5OH or CH3CHO are very likely CO2-reduction electroactive products, formation of some HCOOH, CH3OH or even CO cannot be excluded.  相似文献   

17.
Rate constants for the reactions of OH radicals and Cl atoms with 1‐propanol (1‐C3H7OH) have been determined over the temperature range 273–343 K by the use of a relative rate technique. The value of k(Cl + 1‐C3H7OH) = (1.69 ± 0.19) × 10?12 cm3 molecule?1 s?1 at 298 K and shows a small increase of 10% between 273 and 342 K. The value of k(OH + 1‐C3H7OH) increases by 14% between 273 and 343 K with a value of (5.50 ± 0.55) × 10?12 cm3 molecule?1 s?1 at 298 K, and further when combined with a single independent experimentally determined value at 753 K gives k(OH + 1‐C3H7OH) = 4.69 × 10?17T1.8 exp(422/T) cm3 molecule?1 s?1, which fits each data point to better than 2%. Two well‐established structure–activity relationships for H abstraction by OH radicals give accurate predictions of the rate constant for OH + 1‐C3H7OH, provided the β‐CH2 group is given an increased reactivity of a factor of about 2 over that for the structurally equivalent CH2 group in alkanes at 298 K. A quantitative product analysis was carried out at 298 K for the Cl‐initiated photooxidation of 1‐C3H7OH, using both FTIR and gas chromatography. HCHO, CH3CHO, and C2H5CHO were the only major organic primary products observed, although HCOOH was found in much smaller amounts as a secondary product. A key characteristic of the analysis was that the initial values of the product ratio [CH3CHO]/[C2H5CHO] were effectively constant for NO pressures between 0.15 and 0.3 Torr, but fell by about 35% as the pressure fell to 0.0375 Torr. From a detailed consideration of the mechanism for the oxidation, it is suggested that C2H5CHO, CH3CHO (+HCHO), and 3 molecules of HCHO are formed uniquely from CH3CH2CHOH, CH3CHCH2OH, and CH2CH2CH2OH radicals, respectively. On this basis, use of the product yields gives the branching ratios of 56, 30, and 14% for Cl atom reaction at the α‐, β‐, and γ‐C? H positions in 1‐C3H7OH at 298 K. Given the very low temperature coefficients involved, little change will occur over tropospheric temperature ranges. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 110–121, 2002  相似文献   

18.
The direct methanol fuel cell (DMFC) is considered as a promising power source, because of its abundant fuel source, high energy density and environmental friendliness. Among DMFC anode materials, Pt and Pt group metals are considered to be the best electrocatalysts. The combination of Pt with some specific transition metal can reduce the cost and improve the tolerance toward CO poisoning of pure Pt catalysts. In this paper, the geometric stabilities of PtFe/PdFe atoms anchored in graphene sheet and catalytic CO oxidation properties were investigated using the density functional theory method. The results show that the Pt (Pd) and Fe atoms can replace C atoms in graphene sheet. The CO oxidation reaction by molecular O2 on PtFe–graphene and PdFe–graphene was studied. The results show that the Eley–Rideal (ER) mechanism is expected over the Langmuir–Hinshelwood mechanism for CO oxidation on both PtFe–graphene and PdFe–graphene. Further, complete CO oxidation on PtFe–graphene and PdFe–graphene proceeds via a two‐step ER reaction: CO(gas) + O2(ads) → CO2(ads) + O(ads) and CO(gas) + O(ads) → CO2(ads). Our results reveal that PtFe/PdFe commonly embedded in graphene can be used as a catalyst for CO oxidation. The microscopic mechanism of the CO oxidation reaction on the atomic catalysts was explored.  相似文献   

19.
New experimental results were obtained for the mutual sensitization of the oxidation of NO and methane in a fused silica jet‐stirred reactor operating at 105 Pa, over the temperature range 800–1150 K. The effect of the addition of sulfur dioxide was studied. Probe sampling followed by online FTIR analyses and off‐line GC‐TCD/FID analyses allowed the measurement of concentration profiles for the reactants, stable intermediates, and final products. A detailed chemical kinetic modeling of the present experiments was performed. An overall reasonable agreement between the present data and modeling was obtained. According to the present modeling, the mutual sensitization of the oxidation of methane and NO proceeds via the NO to NO2 conversion by HO2 and CH3O2. The conversion of NO to NO2 by CH3O2 is more important at low temperatures (800 K) than at higher temperatures (850–900 K) where the production of NO2 is mostly due to the reaction of NO with HO2. The NO to NO2 conversion is favored by the production of the HO2 and CH3O2 radicals yielded from the oxidation of the fuel. The production of OH resulting from the oxidation of NO accelerates the oxidation of the fuel: NO + HO2 → OH+ NO2 followed by OH + CH4→ CH3. In the lower temperature range of this study, the reaction further proceeds via CH3 + O2→ CH3O2; CH3O2+ NO → CH3O + NO2. At higher temperatures, the production of CH3O involves NO2: CH3+ NO2→ CH3O. This sequence of reactions is followed by CH3O → CH2O + H; CH2O +OH → HCO; HCO + O2 → HO2 and H + O2 → HO2 → CH2O + H; CH2O +OH → HCO; HCO + O2 → HO2 and H + O2 → HO2. The data and the modeling show that unexpectedly, SO2 has no measurable effect on the kinetics of the mutual sensitization of the oxidation of NO and methane in the present conditions, whereas it frequently acts as an inhibitor in combustion. This result was rationalized via a detailed kinetic analysis indicating that the inhibiting effect of SO2 via the sequence of reactions SO2+H → HOSO, HOSO+O2 → SO2+HO2, equivalent to H+O2?HO2, is balanced by the reaction promoting step NO+HO2 → NO2+OH. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 406–413, 2005  相似文献   

20.
We report a new strategy to prepare a composite catalyst for highly efficient electrochemical CO2 reduction reaction (CO2RR). The composite catalyst is made by anchoring Au nanoparticles on Cu nanowires via 4,4′‐bipyridine (bipy). The Au‐bipy‐Cu composite catalyzes the CO2RR in 0.1 m KHCO3 with a total Faradaic efficiency (FE) reaching 90.6 % at ?0.9 V to provide C‐products, among which CH3CHO (25 % FE) dominates the liquid product (HCOO?, CH3CHO, and CH3COO?) distribution (75 %). The enhanced CO2RR catalysis demonstrated by Au‐bipy‐Cu originates from its synergistic Au (CO2 to CO) and Cu (CO to C‐products) catalysis which is further promoted by bipy. The Au‐bipy‐Cu composite represents a new catalyst system for effective CO2RR conversion to C‐products.  相似文献   

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