Synthesis of Low Silica SAPO‐34 by In Situ Pretreatment and Its Catalytic Performance in the Methanol‐to‐Olefins (MTO) Reaction

A series of low‐silica SAPO‐34 molecular sieves with a tunable silica content were synthesized through a facile in situ pretreatment strategy under different pretreatment condition. The effects of the pretreatment condition on the crystal phases, chemical composition, morphology and acidity of SAPO‐34 were characterized by XRD, XRF, SEM, N2 adsorption‐desorption, NH3‐TPD and 29Si MAS NMR. The obtained low‐silica SAPO‐34 exhibits higher catalytic performance in the MTO reaction than conventional SAPO‐34 due to the moderate acidity and larger surface areas. Sample S4 with a Si content of Si/(Si+Al+P)=0.053 showed the prolonged catalytic lifetime of 204 min and remarkably improved selectivity for ethylene and propylene reaching up to 86.58 %, which was 34 % and 4.16 % higher than the reference sample. The in situ pretreatment strategy has been developed to synthesize low‐silica SAPO‐34 with excellent catalytic performance in the MTO reaction.