Correlation between structure, acidity and catalytic performance of WOx/Al2O3 catalysts

The relationship between acidity, surface structure and catalytic activity for a series of WOx/Al2O3 catalysts was investigated. The catalysts, containing up to 4.1 atom W/nm2, were prepared by incipient wetness impregnation and studied by N2 physisorption, XRD, in situ Raman and infrared spectroscopy. The W phase was essentially present as surface species. Polymeric W surface species appeared above 1.4 atom W/nm2; their abundance increased with W surface density. Lutidine and CO adsorption measurements, followed by infrared spectroscopy, evidenced the presence of relatively strong Brønsted acid sites. The development of these acid sites was similar to that of the abundance of polymeric W surface species. Similar evolution with W surface density was also observed for the activity for 2-propanol dehydration, an acid-catalyzed reaction, indicating a direct relationship between the abundance of polymeric W surface species, that of relatively strong Brønsted acid sites and the catalytic activity of WOx/Al2O3 catalysts.