Methanol Activation Catalyzed by Small Earth-Alkali Mixed Silicon Clusters Sim–nMn with M = Be, Mg, Ca and m = 3–4, n = 0–1

Abstract

The methanol activation pathways occurring on small pure and mixed silicon clusters Sim–nMn with M = Be, Mg, Ca and m = 3–4, n = 0–1 were investigated using quantum chemical computations (density functional theory B3LYP/aug-cc-pVTZ and coupled-cluster theory CCSD(T)/CBS extrapolated from energies with the aug-cc-pVnZ basis sets, n = D, T, Q) to examine their thermodynamic and kinetic feasibilities. In all cases considered, the cleavage of the O–H bond is favored over that of the C–H bond. The O–H bond cleavage in the presence of the singlet Si3 cluster is thermodynamically less preferred than on mixed Si2M clusters, even though it becomes more kinetically favored. Most importantly, the energy barriers for the O–H bond breaking on the singlet Si3, Si2Ca, and Si3Ca clusters are found to be lower than the previously reported results for metal clusters, catalytic metal surfaces, metal oxides, etc. The small mixed Si clusters thus appear to be good catalysts for methanol activation and most probably in other d...