Synthesis, Modification, and Consequence of MCM-22 Zeolite From a Mother Liquor Recycling Procedure for Methanol to Olefins Reaction

Here, MCM-22 zeolites were synthesized by a hydrothermal synthesis method using a mother liquor recycling procedure, in which the use of organic templates was greatly reduced with a molar ratio of template to SiO 2 at 0.15 in the zeolite gel precursors. The as-prepared MCM-22 zeolites show high crystallinity and flake-like morphology with a thickness below 100 nm, possessing a high specific surface area of approximately 470 m 2 /g and substantial mesoporous volume of 0.49 cm 3 /g. The oxalic acid treatment was applied to adjust the textural properties of MCM-22 zeolite as well as the acid sites concentration from 0.43 to 0.22 mmol/g. The selective extraction of extra-framework aluminum via oxalic acid treatment leads to an increase in the ratio of Brønsted acid site amount to Lewis acid site amount (B/L ratio) from 0.59 to 1. The as-modified MCM-22 zeolite shows an enhanced propylene selectivity (44.7%) relative to the MCM-22 zeolite (35.6%). The eco-friendly synthesis strategy combined with an effective acid modification method is anticipated to expand the application of MCM-22 zeolite for designing high-performance catalysts for methanol to olefins (MTO) reaction. Graphical This work offers an eco-friendly route for the synthesis of MCM-22 zeolite via a mother liquor recycling strategy. Oxalic acid treatment enables precise control of acid sites by removing extra-framework Al, thereby suppressing the aromatic-based cycle in the MTO reaction and yielding high selectivity toward target olefins (e.g., propylene).