Effect of acidic promoters on the titania-nanotubes supported V2O5 catalysts for the selective oxidation of methanol to dimethoxymethane

Abstract

The effect of acidic promoters on the titania-nanotubes (TNT) supported V 2 O 5 catalysts (VTNT) was investigated. The structure of TNT was quite stable after the treatment with sulfuric, phosphoric, and phosphotungstic acids, respectively. The acid-modified VTNT catalysts were tested for the selective oxidation of methanol to dimethoxymethane (DMM). It was found that only the VTNT modified with sulfuric acid followed by calcination at 673 K exhibited the significantly enhanced selectivity to DMM with high methanol conversions. The calcination created some sulfate groups strongly interacted with vanadium species, which enhanced the strengths of surface acidity without weakening the redox ability of vanadium sites. The addition of phosphoric and phosphotungstic acids might enhance the surface acidity of V 2 O 5 /TiO 2 , but weakened its redox ability, and therefore had the negative effect for the target reaction. Addition of sulfate groups followed by calcination at 673 K strengthened the surface acidity of V 2 O 5 /TiO 2 and thus promoted the selectivity to dimethoxymethane at the high methanol conversions, while the addition of phosphoric and phosphotungstic acids in any case or the addition of sulfate groups without a high temperature calcination had the negative effect because they decreased either the surface acidity or redox ability of V 2 O 5 /TiO 2 .