Surface acid properties of Nb2O5–P2O5–SiO2 gel-derived catalysts

Amorphous catalytic materials belonging to the Nb2O5-P2O5-SiO2 system were prepared through an original sustainable sol-gel procedure, and characterized by surface area, porosity and acidity measurements. Their acid properties have been investigated by FTIR spectroscopy of adsorbed pyridine, ammonia titration and TPR, as well as by titration with 2-phenylethylamine from organic solution. They present Lewis acidity attributed to niobium surface cationic centers, and Brønsted acidity sufficiently strong to protonate pyridine. The total acidity depends on the niobium content. The conversion of ethanol was investigated by vapor phase Temperature Programmed Reaction, steady-state catalytic experiments and static In Situ FTIR experiments. The samples are active in converting ethanol to ethylene with 100 % selectivity at low conversion (523-573 K), but also produce acetaldehyde by dehydrogenation at higher temperature and conversion. They show an unusually poor activity for the production of diethylether also at low ethanol conversion. Ethoxy groups act as reaction surface intermediates.