Aixia Li

CO oxidation catalyzed by Al n Pt (n = 1–11) clusters: A density functional theory simulations

We have elucidated the details of mechanism of CO oxidation catalyzed by AlnPt (n = 1–11) clusters through first-principle density-functional theory (DFT) calculations. These subnanometer species transform into reaction complexes which catalyze CO oxidation through a kind of mechanism, occurring via Langmuir-Hinshelwood path. It is shown that mixing two different metals (Al and Pt) can have beneficial effects on the catalytic activity. The alloyed AlnPt clusters are proposed as effective nanocatalysts at lower temperatures (equal to room temperature). The adsorption of O2, CO, and their coadsorption at various sites of neutral AlnPt (n = 1–11) clusters have been modeled. It was found that in all situations, Pt sites are the catalytically active centers for CO but that for O2 molecule is not the same result.

Density functional theory study of water-gas shift reaction on TM@Cu12 core-shell nanoclusters

The mechanism of water-gas shift reaction on the transition metal of Co, Ni, Cu (from the 3d row), Rh, Pd, Ag (from the 4d row), Ir, Pt, and Au (from the 5d row) @Cu12 bimetallic clusters have been studied using density functional theory (DFT) calculations. Three reaction mechanisms including redox, carboxyl, and formate mechanisms, which are equal to CO* + O* → CO2 (g), CO* + OH* → COOH* → CO2 (g) + H*, and CO* + H* + O* → CHO* + O* → HCOO** → CO2 (g) + H*, respectively, have been studied. The result revealed that the WGSR prefer to follow the carboxyl mechanism on the TM@Cu12 surfaces. The rate-controlling step of WGS reaction is H2O dissociation into OH and H or COOH decomposition into CO and OH. The transition metal additive in Cu cluster could enhance the activity of water dissociation, which is beneficial for WGS reaction. Especially, doping Ni has the largest promotion effect in reducing the active barrier, the reason is electronic effect. The calculation indicates that Ni@Cu12 is thus the promising candidates for improved WGSR catalysts. In addition, The TOF values are studied to estimate effectively activity of the TM@Cu12 cluster. To get insight into conclusion, reaction mechanism and structure of cluster was elucidated by the relative energy profiles and detailed electronic local density of states (LDOS).

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.

Theoretical study of water gas shift reaction on Cu n Ni ( n = 1–12) clusters

Density functional theory has been used to study the water-gas-shift reaction on CunNi (n = 1–12) clusters. The reaction mechanism of carboxyl has been examined. Using the energetic span model (ESM), we find that the turnover frequency-determining transition state (TDTS) is the carboxyl dissociation (COOH → CO2 + H) for CunNi (n = 1–12) and the turnover frequency-determining intermediate (TDI) is the co-adsorptions of CO and H2O on CunNi clusters for CunNi (n = 2–6, 11, 12). When it comes to CunNi (n = 1, 7–10), the turnover frequency-determining intermediate (TDI) is the co-adsorption of OH and H on CunNi clusters. Our calculation shows that the Cu8Ni cluster with the highest value of the calculated turnover frequence (TOF) exhibits high catalytic activity towards water gas shift reaction.

Theoretical investigation of the CO oxidation on Al12Zr Cluster

Equilibrium geometries of Al12Zr cluster were systematically studied on the basis of density functional theory with generalized gradient approximation. To gain insights into high catalytic activity we use the CO oxidation as a benchmark probe. In Al–Zr bimetallic clusters, Zr site is the catalytically active centre, the adsorption of CO and O2 on the same site respectively (single-site mechanism), a Langmuir-Hinshelwood (LH) mechanism is proposed, which proceed via two steps, CO + O2 → CO2 + O and CO + O → CO2. Two CO oxidation mechanisms of two CO2 molecules as product have been simulated. For the later mechanism, the key step is the O–O bond scission in the OCOO* intermediate, which is significantly accelerated due to the attack of the neighboring CO molecule. The calculated barriers for the later reactions are lower compared with the former reaction. Detailed reaction paths corresponding to this case are calculated. Our study suggests that the CO oxidation catalyzed by Al12Zr cluster is likely to occur at the room temperature.

Density Functional Study of Catalytic Activity of Cu12TM for Water Gas Shift Reaction

Based on density functional theory calculations, we have systematically studied the WGS reaction on various nanosized Cu12TM of Co, Ni, Cu (from the 3d row), Rh, Pd, Ag (from the 4d row), Ir, Pt, Au (from the 5d row). The reaction mechanism proposed by Langmuir–Hinshelwood has been followed, which corresponds to

A DFT Study of the CO Oxidation Mechanism on AlnAu (n = 1–12) Clusters

{\text{CO* + OH* }} \to {\text{COOH*}} \to {\text{CO}}_{2} {\text{ + H*}}

Theoretical Study of the Water-Gas Shift Reaction Catalyzed by Tungsten Carbonyls

CO* + OH*→COOH*→CO2+ H*. The comparison of the Gibbs free energy profiles of carboxyl mechanism on different Cu12TM systems concludes that WGS reaction is determined by the steps of H2 forming and OH* reacting with CO* to form COOH*. BEP relationship between activation barriers (Ea) and reaction energies (ΔH) on a series of Cu12TM clusters is very good. What’s more, the activation barrier of rate-determining step of Cu12Au is the smallest. TOF, with the aid of An Energetic Span Model (ESM), is used to estimate the efficiency of the different Cu12TM clusters. The results show that the values of TOFs in doping Cu12Rh, Cu12Ir and Cu12Pt are smaller than that in pure Cu. Moreover, the values of TOFs in doping Cu12Co, Cu12Ni, Cu12Pd, Cu12Ag, and Cu12Au are higher than that in Cu13. The higher value of TOF, the more favorable catalysts they are. This results shoud be helpful in developing efficient catalysts for WGS reaction. Finally, d-band center is used to explain the binding energy of CO and H2O. It shows that there is a good liner relationship between d-band center and binding energy of CO but not for H2O.