Methane Dissociation on Bimetallic AuNi₃, Au₂Ni₂ and Au₃Ni Clusters‐A DFT Study

Abstract

The effect of gold atom for the dissociation of methane on tetrahedral bimetallic Au x Ni y (x + y = 4; x,y = 1-3) clusters are introduced using density functional theory method. The binding energy and HOMO-LUMO gap fluctuate with odd-even number of gold atoms. The clusters, AuNi 3 and Au 3 Ni, containing odd number of doped gold atoms, which causes open shell configuration, are exceptionally stable and highly resistance to carbon deposition, whereas closed shell Au 2 Ni 2 cluster is less stable. As the number of doped Au atom increases in the clusters, adsorption or binding energy of methane increases. The dissociation of methane is a four elementary steps process, and first step of dissociation, CH 4 ! CH 3 , is not the rate determining step, and thermodynamically favorable at room temperature and pressure for the clusters due to adsorption. Whereas, the dissociation of CH!C, coke formation step 4, is the rate determining step due to highest energy barrier for all the clusters. The calculated activation energies for the rate determining step are 0.92 eV, 0.41 eV and 1.64 eV for AuNi 3 , Au 2 Ni 2 and Au 3 Ni clusters, respectively. In addition, the dissociation temperature for all the intermediates, e. g., CH 3 , CH 2 and CH are 450 K(CH 3 and CH 2 ) and 650 K(CH) on AuNi 3 cluster; 450 K(CH 3 ) and 550 K(CH 2 and CH) on Au 2 Ni 2 cluster; and 650 K(CH 3 ), 750 K(CH 2 ) and 950 K(CH) on Au 3 Ni cluster. Thus, the coke resistivity decreases as Au 3 Ni > AuNi 3 > Au 2 Ni 2 and corresponding coke resistance temperatures are 950 K, 650 K and 550 K, respectively. The charge tranfer to the clusters during adsorption is negative, and is positive in the dissociation steps. Thus, the number of doped gold atom not only influences the stability of bimetallic AuÀNi clusters, but also their reactivity towards methane, which can provide some new insight for the design of coke resistant catalysts for methane reforming.[a] Prof.

Dissociation of hydrazine on tetrahedral Ni4 cluster by density functional theory

“…From natural population analysis during adsorption, charge transfer to the cluster is − 0.17 eV, indicating dissociation of N 2 H 4 is favourable at standard conditions. This result is similar to what was found in an earlier study [75]. NBO analysis for adsorption system (Fig.…”