Catalytic performance of titanium subgroup metal oxides for syngas conversion

Titanium subgroup nanometallic oxides (TiO₂, ZrO₂ and HfO₂), prepared via supercritical method, were combined with ZSM-5 and quartz to obtain bifunctional catalysts (Ti/HZ, Zr/HZ, Hf/HZ) and metal oxide catalysts (Ti/Si, Zr/Si, Hf/Si) respectively. The effect of crystal structure, surface oxygen vacancy and syngas adsorption of metal oxides on the catalytic CO hydrogenation was investigated. The results show that the bifunctional catalysts could directly catalyze the syngas to aromatics. The oxygen vacancy concentration, oxygen electron properties and the H/C ratios (the adsorption ratio of CO to H₂) of the metal oxides synergistically determine the type of intermediates on the metal oxide surface. The CH_xO* species generated on the surface of ZrO₂ is beneficial for Zr/HZ catalyst to obtain higher aromatic selectivity (71.15%), while CH₃* on TiO₂ and HfO₂ leads to higher CH₄ selectivity for Ti/HZ and Hf/HZ catalysts. The results of this research could provide a valuable reference for design of syngas aromatization catalyst.