Sonication-assisted dealumination of zeolite A with thionyl chloride

Dealumination of as-synthesized zeolites is an important step in adjusting the Si/Al ratio and hence their acidities and catalytic properties. The dealumination of zeolite 4A by thionyl chloride treatment was investigated near room temperature in the liquid phase with and without the assistance of sonication. The structural changes observed by Si-29 and Al-27 solid-state NMR showed that the experimental condition, that is, in the presence and absence of sonication, significantly affected the efficiency of the dealumination process of zeolite 4A. Successful dealumination was achieved with the assistance of sonication at room temperature, while simple stirring led to negligible changes. It was also found that the degree of dealumination could be tailored by the duration of sonication to generate zeolites with various Si/Al ratios. XPS surface elementary analysis detected chlorine rich sieve surfaces after the sonication treatment, which is attributed to AlCl3 and NaCl, the byproducts of the dealumination reaction. These results confirmed that sonication accelerated dealumination reaction under ambient conditions. XRD tests, unit cell calculation, and nitrogen physisorption analysis revealed partial loss in framework integrity after the treatment. This new procedure allows convenient preparation of alumina-deficient zeolites of a wide range of Si/Al ratios under ambient conditions. The dramatic local heating resulted from ultrasound is proposed to explain the unusual observation of dealumination by thionyl chloride near room temperature.