Higher Bronsted acidity of WOx,/ZrO2 catalysts prepared using a high-surface-area zirconium oxyhydroxide

Abstract

The precipitated zirconium oxyhydroxide, ZrOH(H), was used as a support for tungstate loading, where its specific surface area was 1.5-fold higher than that of the analogous sample obtained commercially, ZrOH(L). Due to this difference, crystalline WO3 and ZrO2 (tetragonal and monoclinic) were formed at a higher calcination temperature by 150 K for WZrOH(H) than for WZrOH(L) when tungstate was loaded. For WOx/ZrO2 with different W surface densities produced by calcination at 723-1173 K, pyridine-IR experiment and Raman spectroscopy revealed that more Bronsted acid sites were present for WZrOH(H) calcined at 1023 and 1073 K than for WZrOH(L) calcined at 873 K while distorted Zr-stabilized WO3 nanoparticles were found for these samples. Thus, the former samples showed the superior activity to the latter in the dehydration of formic acid. The linear relationship between the catalytic performance and Bronsted acidity was observed, explaining that WOx/ZrO2 with more Bronsted acid sites is more active in the dehydration reaction. Consequently, the enhanced Bronsted acidity and catalytic activity of WZrOH(H) resulted from the use of zirconium oxyhydroxide with a high surface area for tungstate loading.