IR spectroscopy of NH4-clinoptilolite after deammoniation at 400 °C shows a single hydroxyl band at 3620 cm-1, slightly asymmetric to the lower wave numbers. The deammoniation is reversible and stoichiometric: for each NH4+ ion that decomposes an acidic hydroxyl group is formed in the lattice. At temperatures higher than 400 °C dehydroxylation occurs: two lattice hydroxyls condense, water is evacuated, and Lewis acid sites are created. Comparison of the adsorption of NH3 and pyridine on the H-clinoptilolite, shows that about 10% of the lattice hydroxyl groups are on the external surface. The catalyst is active for the isomerization of 1-butene. The isomerization activity changes with the amount of hydroxyl groups on the external surface. Lewis acid sites are created at elevated temperatures, but have no secondary influence on the catalytically active Brønsted sites.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry