Bronsted acid property of alumina-based mixed-oxides-supported tungsten oxide

The effect of alumina-based supports (Al2O3, Al2O3-TiO2, Al2O3-ZrO2, SiO2-Al2O3, and SiO2) on the structure and acid properties of supported tungsten oxide catalysts was investigated. Among the tested supported tungsten oxide catalysts, WO3/Al2O3-TiO2 (Al2O3/TiO2 = 9, Al-Ti9) showed the highest activity for reactions catalyzed by Bronsted acid sites and the largest Bronsted acidity. Structural characterization revealed that Bronsted acid sites on WO3/Al-Ti9 were generated at the boundaries between domains of amorphous monolayer WO3 and Al2O3-TiO2 support and WO3/Al2O3 reported previously, and that Al2O3 and Al-Ti9 with a high density of Lewis acid and surface hydroxyl groups resulted in the formation of Bronsted acid sites. Crystalline WO3 species formed mainly on SiO2-Al2O3 and SiO2 with a low density of Lewis acid sites and a high density of surface hydroxyl groups. These results suggested that a high density of Lewis acid sites and surface hydroxyl groups are important factors to form amorphous WO3 monolayer domains and to generate Bronsted acid sites on alumina-based supports.

Automated summary

The study found that WO3 supported catalysts on Al2O3-TiO2 supports exhibited the highest activity and Bronsted acidity. Crystalline WO3 mainly formed on SiO2-Al2O3 and SiO2, while a high density of Lewis acid sites and surface hydroxyl groups on alumina-based supports played an important role in forming amorphous WO3 monolayer domains and generating Bronsted acid sites.