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H-ZSM-5 zeolite was treated with phosphorus acid by impregnating H-ZSM-5 with aqueous solutions of phosphoric acid at various concentrations. H-ZSM-5 (P-HZSM-5) modified with phosphoric acid was used as a catalyst for the methanol-to-olefin reaction. The molar ratios of P/Si and Si/Al in H-ZSM-5 and P-HZSM-5 were measured by EDX analysis. The Si/Al molar ratios of P-HZSM-5 increased with higher concentration of H3PO4 in the solution, which might be caused by partial dealumination of H-ZSM-5 by the H3PO4 treatment. The P/Si molar ratio of P-HZSM-5 after washing was proportional to the H3PO4 concentrations in the aqueous solutions. The remaining phosphorus species after the washing must be strongly adsorbed by interaction with the pore surface of H-ZSM-5 zeolite. The P-HZSM-5 catalyst showed very high propylene selectivity up to 57% with methanol conversion of 100%. Furthermore, catalyst stability was significantly improved for the P-HZSM-5 catalysts. Ammonia TPD spectra showed that the strong acid sites of H-ZSM-5 disappeared after the phosphoric acid treatment. Consequently, the formation of aromatics and coke was inhibited, resulting in higher light olefin selectivity and catalyst stability.

Single-and poly-crystalline silicalite/HZSM-5 core-shell composite catalysts were synthesized by optimizing the silicalite coating conditions. At low molar ratios of SiO 2 (fumed silica) and TPAOH in the coating solutions, a crystal growth of silicalite layer on the HZSM-5 surface was dominant instead of a homogeneous nucleation in the solution. The mass gain after the coating was also inhibited at low molar ratios of silica source and TPAOH. High para-selectivities of silicalite/HZSM-5 composites in the toluene alkylation with methanol were obtained over the single crystal-like silicalite/H-ZSM-5 composite catalyst prepared by one coating process.