Evaluation of surfactant templates for one-pot hydrothermal synthesis of hierarchical SAPO-5

Abstract

Hierarchical SAPO-5 molecular sieves were synthesized with three different mesopore structure-directing agents (meso-SDAs) (cetyltrimethylammonium bromide (CTAB), myristyltrimethylammonium bromide (MTMAB) and [3-(trimethoxysilyl)propyl] dimethyloctadecylammonium chloride (TPOAC)) based on a soft-template hydrothermal synthesis procedure. To investigate the modified porosity of the hierarchical SAPO-5s, they were characterized thoroughly with the results being compared to the conventional microporous SAPO-5. Nitrogen sorption measurements revealed considerable hysteresis loops for the hierarchical SAPO-5s as well as larger mesopore volumes (�0.15 cm3 g-1) compared to the conventional SAPO-5 (0.05 cm3 g-1). The relative number of acid sites for each sample was calculated from FTIR adsorption data and was in the order of C-SAPO-5>HCTAB>H-MTMAB>H-TPOAC. The hierarchical SAPO-5s had a significantly increased lifetime (>150 h) in the methanol to hydrocarbons (MTH) model reaction compared to the conventional SAPO-5 (<10 h), with TPOAC producing the most stable catalyst and MTMAB producing the catalyst with the largest product distribution. The modified porosity of the hierarchical SAPO-5s was additionally verified by an enhanced lifetime and increased production of large products in a shape selective process as well as a lower rate of coke formation compared to the conventional SAPO-5.