Xiaoli Zheng

Theoretical study on the reaction mechanism of reverse water–gas shift reaction using a Rh–Mo6S8 cluster

The reverse water gas shift (RWGS) reaction catalyzed by a Rh–Mo6S8 cluster is investigated using density functional theory calculations. The reaction is explored along four possible mechanisms: one is the redox mechanism, another is the carboxyl mechanism, the third refers to the formic acid directly decomposing to CO, and the fourth involves the formation of a CHO intermediate. Thermodynamic and kinetic data are calculated to consider the catalysis cycle efficiency. Here, we perform the energetic span model (ESM) to investigate the kinetic behavior of the four catalytic cycles. Interestingly, it is shown that the direct decomposition of formic acid is the most suitable pathway for RWGS with the highest TOF value and lowest rate-determining energy barrier. We hope that our work will be beneficial to the development of RWGS.

Mechanisms of the Water-Gas Shift Reaction Catalyzed by Ruthenium Carbonyl Complexes.

Density functional theory (DFT) is employed to study the water-gas shift (WGS) reaction in the gas phase for two complexes, Ru3(CO)12 and Ru(CO)5. Here we report four mechanisms of ruthenium carbonyl complexes catalyzed for WGS reaction. The energetic span model is applied to evaluate efficiency of the four catalytic pathways. Our results indicate that mechanism C and D show a good catalytic behavior, which is in agreement with results from the literature. The mechanism C and D not only include the important intermediate Ru3(CO)11H(-) but also exclude the energy-demanding OH(-) desorption and revise an unfavorable factor of the previous mechanism. Two complexes along mechanisms B have the highest turnover frequency (TOF) values. The trinuclear carbonyl complexes-Ru3(CO)12 is preferred over mononuclear carbonyl Ru(CO)5 by comparing TOF due to the fact that metal-metal cooperativity can enhance activity to the WGS reaction. In this work, the nature of interaction between transition states and intermediates is also analyzed by the detailed electronic densities of states, and we further clarify high catalytic activity of ruthenium carbonyl complexes as well. Our conclusions provide a guide to design catalysts for the WGS reaction.

The catalytic mechanism of CO oxidation in AlAu6 clusters determined by density functional theory

We present density functional calculations of O2 and CO adsorption on an AlAu6 cluster. It is found that in the AlAu6 cluster the active sites would be first occupied by coming O2 rather than CO due to a more negative binding energy of the former. Furthermore, the catalytic mechanisms of CO oxidation in AlAu6 clusters, which are based on a single CO molecule and double CO molecules, are discussed. This investigation reveals that the reaction of a single CO molecule with the AlAu6O2 complex has the lowest activation barrier (0.27 eV), which is 0.51 eV lower than that of the pure Au6− cluster. For the AlAu6O2(CO)2 complex, due to the structural distortion of the AlAu6 cluster, the activation barrier of the determination rate is higher by 0.53 eV than that of the AlAu6O2CO complex, which shows that the cooperation effect of the second CO molecule can go against CO oxidation. For the Al@Au6O2(CO)2 complex, the activation barrier of the determination rate is lower by 0.07 eV than the path of one CO molecule, which demonstrates that the cooperation effect of the second CO molecule can prompt CO oxidation.

Insight into the reaction mechanism of ethanol steam reforming catalysed by Co–Mo6S8

ABSTRACT The production of hydrogen via steam reforming of ethanol (SRE) is favourable for the use of hydrogen as an alternative fuel. Co–Mo6S8 possesses high activity and stability for SRE to sustainably produce hydrogen. The competition among reaction pathways related to C–H, O–H, C–C, C–O cleavage and H2 formation was studied. The adsorption and reaction of related intermediates in the ESR reaction pathway are described. The results indicated that the most feasible route for the decomposition of ethanol catalysed by Co–Mo6S8 is CH3CH2OH*→CH3CH2O*→CH3CHO*→CH2CHO*→CHCHO*→CHCO*→CH*+CO*. The CH* can be decomposed into C*+H*, and CO* can be oxidised via the redox mechanism of the water gas shift (WGS) reaction. Thus the final products are CO2 and H2. The present result may help people to design an SRE catalyst, which has the ability to break C–C to form CO and H2, then CO react with H2O in the WGS reaction generating CO2 and H2. GRAPHICAL ABSTRACT

Theoretical investigation of water-gas shift reaction catalyzed by water-soluble Rh(III)–EDTA complex

Abstract We systematically investigate the mechanisms of water-gas shift reaction (WGSR) on [Rh(EDTA)CO]− complex on the basis of density functional theory calculations. Two different reaction pathways have been considered: One is the synthesis of HCOOH, and the other is the direct formation of H2 from H2O and CO. The former offers new insights into the fundamental direct mechanism for WGSR. In this study, we combine with the energetic span model to study the catalytic activity of different active sites and two different reaction pathways. Our calculation results indicate that the formation of HCOOH mechanism is the energetically favorable pathway for the water-gas shift reaction on [Rh(EDTA)CO]− catalyst. Moreover, the Oc site acts as the most active site for the formation of HCOOH due to the highest value of TOF. NPA charges are calculated to shed further light on the properties leading up to the formation of HCOOH. Our work will be useful for developing the WGSR mechanism and designing better catalysts for WGSR.

Theoretical investigation of water gas shift reaction catalyzed by [Ru(CO) 3 Cl 3 ] – in solution

Mononuclear Ru halogen carbonyl complex was the exclusive to catalyze the water-gas reaction (WGR) according to Ken-ichi Tominaga et al. Density functional theory (DFT) is employed to study the water-gas shift reaction (WGSR) in basic solution for [RuCl3(CO)3]−. Four different mechanistic pathways have been considered. The calculations indicate that formic acid mechanism to be competitive. The energetic span model (ESM) proposed by Shaik et al. has been applied to reveal the kinetic behavior of the four catalytic cycles. The one with the highest efficiency usually gives the highest TOF. The formic acid mechanism exhibits high catalytic activity towards water gas shift reaction due to the highest value of the calculated turnover frequency (1.89 × 10–14 s–1), which is higher than the value of TOF (1.74 × 10–16 s–1, Ru(CO)5; 1.88 × 10–15 s–1, Fe(CO)5). It turned out that [Ru(CO)3Cl3]– is a promising candidate for an improved WGSR catalyst and a better catalyst for the industrially important reaction.

The Dopant Aluminum Enhances CO Oxidation Catalyzed by Subnanometer Small Palladium Clusters: A DFT Study

We have elucidated the mechanism of CO oxidation catalyzed by AlPdn (n = 1–3) clusters through first-principle density-functional theory (DFT) calculation. It is found that these subnanometer species transfer into reaction complexes which catalyzes CO oxidation through two different mechanisms, occurring via Langmuir-Hinshelwood paths. It is shown that mixing two different metals (Al and Pd) can have more beneficial effects than pure palladium on the catalytic activity and the alloyed AlPd2 cluster is proposed as the best effective nanocatalysts.