A series of Mo3VOx/H4SiW12O40/Al2O3 catalysts were prepared and applied to one-step oxydehydration of glycerol to acrylic acid. The catalysts were thoroughly characterized by BET, XRD, TEM, TGA, NH3-TPD, and XAFS techniques. It was found that acetic acid was produced in parallel with acrylic acid with similar yield when adjusting Mo3VOx content in the catalysts. Increasing calcination temperature from 350 to 650°C led to structural evolution of supported active species and subsequent activity change. Crystallinity of Mo3VOx increased with calcination temperature and a large amount of (V,Mo)Ox hetero-polyoxo mixed oxides were formed above 550°C. The Keggin structure of H4SiW12O40 began to dissociate around 450°C causing the formation of various WOx species. Above 450°C, the yield of acrylic acid dropped while that of acrolein could reach its maximum value with increase of the catalyst calcination temperature. In contrast, the yield of acetic acid showed a minor change always. Based on the catalytic and characterization results, possible active centers and reaction pathways are thus proposed, and for the improvement of the bi-functional catalyst for the one-step conversion of glycerol, both the acidic and redox properties of catalysts should be finely tuned. This work provides new insight into the reaction mechanism and the catalyst design for the one-step oxydehydration of glycerol to acrylic acid.
- Acrylic acid
- Bifunctional catalyst