Journal of Physical Chemistry B, Vol.104, No.13, 2853-2859, 2000
Influence of citric acid treatment on the surface acid properties of zeolite beta
A method of increasing the amount of acid sites, especially Bronsted acid sites, on the surface of H beta zeolite is reported. The H beta samples were prepared through NH4NO3 solution ion exchange, citric acid treatment, and 823 K calcination from as-synthesized zeolite beta using sodium eliminate or pseudoboehmite as the aluminum source, and were characterized by NH3-TPD, pyridine-IR, Si-29 MAS NMR, and Al-27 MAS NMR. The surface properties of H beta zeolite changed after the citric acid treatment as follows: acid strength decreased, total acid amount increased, Bronsted acid sites increased and Lewis acid sites remained unvaried. The citric acid treatment of zeolite beta may have functions of dealumination at a Si(2Al) site and realumination at a Si(OAl) site.
Keywords:NUCLEAR-MAGNETIC-RESONANCE;IR SPECTROSCOPY;DEFECT SITES;ALUMINUM;CATALYSTS;DEALUMINATION;STATE;DISPROPORTIONATION;TRANSALKYLATION;ISOMERIZATION