The acidity of H,Na mordenites prepared from Na mordenite by ion exchange with ammonium to different degrees followed by deammoniation at various temperatures has been studied by microcalorimetry and i.r. spectroscopy. The differential molar adsorption heat and the amount of NH3 molecules adsorbed were considered as measures of acid strength and the number of acid sites, respectively. Heat of adsorption as a function of coverage shows a stepwise decrease. Sites with adsorption heats of ammonia of 100 and 170-185 kJ mol-1 proved to be Lewis acid centers, and those of 110-160 kJ mol-1 are Brönsted acid centers. Half of the latter are not accessible for m-xylene. The strong Lewis sites are active for m-xylene disproportionation and isomerization, while Brönsted acid sites of medium strength catalyse only m-xylene isomerization.
- catalytic selectivity
- isomerization and disproportionation of m-xylene
ASJC Scopus subject areas
- Environmental Science(all)