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The theoretical calculation about the catalytic mechanism of MCM-41 supported phosphoric acid (SPAM) in the alkylation desulfurization of fluid catalytic cracking (FCC) gasoline demonstrated that properly reducing the amount of effective acid on the surface was beneficial to further enhancing the catalyst performance. Based on the previously optimized preparation of SPAM (weight ratio of total acid/MCM-41 6:1, calcination temperature 773 K and weigh ratio of H 3 PO 4 /H 4 P 2 O 7 1:2.5), an improvement by diluting the concentration of mixed phosphoric acids in the impregnating solution was carried out in this work. The surface structure and catalytic behavior of improved SPAM were investigated by structural characterization and experimental verification, respectively. The results proved that decreasing the concentration of mixed phosphoric acids in the impregnating solution in the preparation of SPAM could effectively reduce the existing acid amount on the catalyst surface by increasing the catalyst crystallinity, and both the surface acid strength and the total acids amount of SPAM were reduced. Moreover, the catalytic activity and selectivity of improved SPAM for thiophenic sulfurs alkylation in the alkylation desulfurization were enhanced and the olefins polymerization reactions were suppressed to a lower extent. Besides, the theoretical calculation was verified by this study, which opened a particularly appealing opportunity for the application of SPAM in the industrial alkylation desulfurization of gasoline. [ABSTRACT FROM AUTHOR]