Effects of Synthetic Parameters on the Structure and Catalytic Performance of Cu−Cr Catalysts Prepared by a Non-Alkoxide Sol−Gel Route

Abstract

The surface areas of Cu−Cr xerogels prepared by an epoxide assisted route are highly dependent on synthetic conditions like gelation temperature, amount of water in the solvent, and gel aging time. Gelation temperature affects the relative rates of hydrolysis and condensation, the amount of water in solution adjusts the solution pH, and the aging process influences the microstructural properties of the xerogels. These factors affect the stability of the sol particles in solution and the final structure of the gel. Thermogravimetric and differential thermogravimetric analysis, specific surface area measurement through nitrogen adsorption, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy are employed to determine particle size distribution and morphology of the different particulate products (i.e., gels, powders) obtained via different synthesis conditions, both before and after thermal treatments. The xerogel surface area can reach up to 230 m2/g by adjusting the operating parameters. Moreover, the results show that the Cu−Cr catalysts with CuCr2O4 and Cr2O3 phases obtained by calcining the as-prepared xerogels in 20% O2 in Ar have better activity for glycerol catalytic conversion than catalysts with Cu and Cr2O3 phases that were obtained by calcination in Ar. In addition, the activity of catalysts increased with the surface areas of xerogels. It is noteworthy that the catalysts have significant selectivity to 1,2-propanediol (54%) and 1-propanol (36%) at 32% conversion of glycerol at 210 °C and 4.1 MPa H2 pressure.