Effect of hydrogen spillover on acidic properties of silica-supported tungsten oxide catalysts: in situ DRIFTS study

Abstract

The knowledge and understanding about hydrogen spillover on the acidic property over surface metal and metal oxide catalysts are beneficial information in catalytic reactions with hydrogen. The perception of the nature of the surface acidity is a key role in catalytic properties and surface chemistry. However, metal oxide catalyst is still not widely studied on this issue. Therefore, the aim of this work is to investigate the effect of hydrogen spillover on their acidic property over silica-supported W catalysts by in situ DRIFTS. The results of in situ DRIFTS experiments have confirmed that the acidic property of silica-supported W catalysts was affected by hydrogen spillover. The Lewis acid site can be changed to the Brønsted acid site upon hydrogen exposure of activated catalysts (i.e., W/HY-500, W/SiO2, W/HY-15, W/MCM-22, W/Al2O3, W/SSP, and W-SSP). The Lewis acid transformation performance correlates with oxygen vacancy and tungstate W5+ active species. This active site could be generated by catalyst preparations and activating the process of H2 and N2 pretreatments. Additionally, molecular hydrogen can be dissociated to form hydrogen spillover onto surface catalysts leads to form the new Si−OH species. It was postulated that the Si−O−W species is a major importance for new Si−OH formation. Some H atoms should be adsorbed around the Lewis acid site of Si−O−W species leads to the Si−OH formation.