In situ FTIR spectroscopic study of 2-propanol adsorptive and catalytic interactions on metal-modified aluminas

Pure alumina was modified by additives of Ni, Ph, and Pt metal particles by impregnation from aqueous solutions of corresponding precursor compounds sand subsequent reduction in a stream of hydrogen at 400 degreesC for 2 h. The catalysts thus obtained were subjected to N-2, H-2, and O-2 sorptometry, high-resolution electron microscopy, and X-ray photoelectron spectroscopy. Accordingly, the metal reducibility, surface area, dispersion, and particle size were determined. Thin wafers of the catalysts, pretreated in situ in a specially designed IR reactor/cell, were exposed to 2-propanol vapor at various temperatures (room temperature to 400 degreesC) for 10 min, and IR spectra of the gas-phase and adsorbed species were measured. The results indicated that the metal additives provided the surface with dehydrogenation/hydrogenation and cracking (hydrogenolysis) sites. Consequently, the initial alcohol dehydration selectivity of alumina (to give pure propene at 300-400 degreesC) was successfully challenged by a strong activity toward formation of major products of acetone, propane, and methane in the gas phase. A range of relevant adsorbed species were characterized and found to result predominantly from adsorptive interactions of 2-propanol and acetone molecules. Surface reaction pathways were suggested, assuming concerted and sequential interactions of the alcohol (and product) molecules with acid-base and metal sites. It was believed that gas-phase migration of alkene molecules and surface diffusion of hydrogen adatoms facilitate the sequential interactions.