(513f) Catalysis Science of Bulk Mixed Metal Oxide Catalysts: An Operando IR-TPSR Spectroscopic Study

In the present investigation, the catalytic science of bulk mixed metal oxides have been studied (with FeVO₄ model) by employing Operando temperature programmed surface reaction-Infrared spectroscopy (TPSR-IR) with well defined V₂O₅, Fe₂O₃, FeVO₄, and supported V₂O₅/Fe₂O₃ catalysts. Raman spectroscopy confirmed the phase purity of bulk metal oxides and the exclusive presence of a surface V₂O₅ monolayer on the Fe₂O₃ support. The Operando IR-TPSR spectroscopes showed the presence of CH₃O* and Lewis methanol intermediate species on bulk Fe₂O₃ surface and their subsequent conversion to dimethyl ether and methanol/HCHO products respectively. However, predominantly CH₃O* intermediate species were observed for V₂O₅, FeVO₄ and monolayer V₂O₅/Fe₂O₃ catalysts. They exclusively form HCHO product from exposed surface VOx sites. The TEM images also confirmed the presence of an amorphous surface layer for FeVO₄ catalyst. The selectivity and activity of FeVO₄ are comparable with that of industrial Fe₂(MoO₄)₃-MoO₃ catalyst, which has a problem of MoO₃ volatilization at high reaction temperatures. Therefore, the surface of bulk mixed metal oxide catalyst FeVO₄ is enriched with active and stable VOx species, responsible for methanol oxidation to formaldehyde.