Cluster model studies on catalytic sulfidation of MoO3

MoS2-based catalysts, initially prepared from MoO3, are known to yield high activity and selectivity for the production of mixed alcohols. This makes research on the sulfidation of MoO3 quite important. Here we apply density-functional theory (DFT) together with large surface clusters (cluster code StoBe) to study the sulfidation of the MoO3(010) surface as well as hydrogen adsorption at an atomic level. Surface oxygen is always found to bind more strongly with its substrate than its sulfur substitute with binding distances that are shorter for oxygen than for sulfur. Sulfur-oxygen exchange reactions are energetically preferred over sulfur adsorption at MoO3(010). Further, sulfur binding is found to be facilitated by the existence of surface oxygen vacancies where sulfur substitution takes place preferentially at the singly coordinated O(1) site. Hydrogen adsorption at the perfect and sulfidic surface leads to stable OH, H2O and SH, H2S groups which are quite weakly bound and may easily adsorb. Thus, the presence of pre-adsorbed hydrogen facilitates oxygen and sulfur removal from the MoO3(010) surface which is in qualitative agreement with earlier findings.