Synthesis, characterization and catalytic activity of SAPO-34 obtained with piperidine as templating agent

The synthesis of SAPO-34 in the presence of a new templating agent, namely piperidine, was investigated. The effects of the gel composition, the template concentration, the time and temperature of crystallization on the degree of crystallinity and the purity of the crystalline phase were examined. It was found that SAPO-34 and SAPO-20 are competing phases at high piperidine concentrations, whereas SAPO-34, SAPO-17 and SAPO-35 are the phases present at low template concentrations. Pure SAPO-34 with high crystallinity was obtained at a piperidine/Al₂O₃ ratio of 1.1:1.0. An optimal synthesis procedure giving an homogeneous SAPO-34 framework without Si islands, consists of heating a gel of composition 1.0Al₂O₃/0.6P₂O₅/1.1Pip./0.8SiO₂/100H₂O at 200 °C for 4–8 days. Such a reproducible procedure gives rise to an acidic catalyst active in the aldol condensation of acetaldehyde with formaldehyde.