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 s ites, 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 o r 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 stre ngth decreased, total acid amount increased, Bronsted acid sites increased and Lewis acid sites remained unvaried. The citric acid treatment of zeolit e beta may have functions of dealumination at a Si(2Al) site and realuminat ion at a Si(OAl) site.