Pyridine and ammonia as probes for FTIR analysis of solid acid catalysts

Pyridine and ammonia have been used as probe molecules for the quantitative analysis of surface acidity of some solid catalysts by FTIR spectroscopy. For pyridine, a scale of acidity and an evaluation of the relative acid strength at different temperatures (373-773 K) were obtained for both Bronsted- and Lewis-acid sites. Correlation was verified between the concentration of Bronsted sites and the catalytic activity of the catalysts examined for the dehydration of 2-(2-hydroxyethyl)pyridine to 2-vinylpyridine. In contrast, ammonia was a much less reliable probe, mainly due to the overlapping of the resulting IR absorption bands. Moreover, it decomposed even at rather low temperatures, when adsorbed onto the catalysts

FT-IR and EPR spectroscopic analysis of La1-xCexCoO3 perovskite-like catalysts for NO reduction by CO

A FT-IR and EPR spectroscopic investigation has been carried out on a series of La1-xCexCoO3 (x=0-0.15) perovskite-type catalysts, which are quite active for the reduction of NO by CO, and a mechanism has been proposed for this reaction. The first step involves the oxidation of CO by the catalyst, followed by the dissociative adsorption of NO onto the catalyst surface. Finally, adsorbed nitrogen (N-ads) yields N2O, N-2 and NCOads along three parallel paths. Thus, oxygen exchange between NO and CO seems to occur indirectly and involves a surface oxygen vacancy. The catalytic activity is decreased by the substitution of Ce4+ for La3+ in the perovskite-type structure, which reduces the mobility of bulk oxygen. Activity is partially restored for x greater than or equal to 0.05 due to the presence of a segregated cerium oxide phase