One-step synthesis of P-HZSM-5 zeolite and its catalytic performance in MTP reaction

P-HZSM-5 zeolite was successfully synthesized in one step under conventional hydrothermal conditions by using tetraethyl orthosilicate (TEOS), sodium metaaluminate, phosphoric acid (85%), and tetrapropylammonium hydroxide (TPAOH, 25%) as raw materials. The influence of phosphate acid content on the structure, acidity, particle size, and catalytic performance in methanol conversion to propene (MTP) of P-HZSM-5 obtained was investigated. The results indicated that the crystallinity, acidity and particle size of PZSM-5 zeolites are decreased with the increase of phosphoric acid amount used in the synthesis; meanwhile, the crystal symmetry is changed from orthorhombic to monoclinic and the morphology is transformed from spherical into strip. When P-HZSM-5 is used as the catalyst in MTP, these changes exhibited evident influence on the product selectivity. Over the P-HZSM-5 samples obtained with a molar ratio of H₃PO₄/Al₂O₃ being 2 and 4, the total yields of ethylene and propylene are close (52.30% and 52.63%, respectively), but the ratio of propene/ethene in the product are quite different (7.02 and 4.12, respectively); it suggests that the product selectivity of MTP can be adjusted by the phosphoric acid content.