MOR/DEA/TEA mixed-template synthesis of CHA-type SAPO with different silica and alumina sources

Abstract

We investigated the effects of different sources of alumina (pseudo-boehmite, aluminum hydroxide, aluminum tri-sec-butylate, aluminum isopropoxide, and aluminum phosphate) and silica (silica sol, silicic acid, tetraethyl orthosilicate, and sodium silicate) on the physicochemical characteristics of the CHA-type SAPO in a mixed-template system. SAPO-44 was synthesized hydrothermally in the presence of low-cost templates of morpholine, TEA, and DEA. The synthesized catalysts were characterized by XRD, FE-SEM, XRF, BET, and NH3-TPD techniques. The results showed that controlling the hydrolysis rate of the alumina source has a determining role in the phase purity and crystallinity of the samples synthesized in a mixed-template system. Compared to single-template systems, the structures fabricated using multi-template gel (high template/P₂O₅) are highly sensitive to extraneous ions or alcohols introduced into the reaction mixture through the sources. Besides, the results demonstrated the significant effect of the silica source on the nucleation mechanism and, thus, on particle size and distribution. The catalyst prepared from pseudo-boehmite and silica sol had the highest crystallinity, surface area, and micropore volume among the samples. This mixed-templated catalyst outperformed the single-templated catalysts in the MTO process, with a methanol conversion of 100%, a light olefin selectivity of 89%, and an active lifetime of around 5 h.