CATALYTIC ACTIVITY OF LAYERED ALPHA-(TIN OR ZIRCONIUM) PHOSPHATES AND CHROMIA-PILLARED DERIVATIVES FOR ISOPROPYL-ALCOHOL DECOMPOSITION

Layered alpha-zirconium and alpha-tin phosphates (alpha-ZrP and alpha-SnP) and their chromia-pillared homologues have been evaluated from the point of view of surface acidity. The FT-IR of pyridine adsorption and the dehydration of 2-propanol at 180-degrees-C were used as chemical probes to measure acid sites. The studied materials were characterized by X-ray diffraction, surface area measurements and X-ray photoelectron spectroscopy. The latter technique was also used to reveal the chemical state of both fresh and used on-stream catalysts. Under the experimental conditions used, alpha-SnP presents a moderate Bronsted and Lewis acidity, which is absent in alpha-ZrP. In contrast, all the thermally stable porous materials, obtained by pillaring alpha-SnP and alpha-ZrP with chromium (III) oxide, show a marked enhancement of the acidity with respect to the original phosphates. These acid sites are strong enough to still retain a small proportion of pyridine upon outgassing at 500-degrees-C, but insufficient to perform methanol decomposition into hydrocarbons. Interestingly, the 2-propanol conversion in the presence of air led to both dehydration and dehydrogenation, this latter functionality being activated in an alcohol-helium stream.