Catalytic roles of acid property in different morphologies of H-ZSM-5 zeolites for syngas-to-aromatics conversion over ZnCrO_x/H-ZSM-5 catalysts

Direct synthesis of aromatics from syngas provides a promising approach for the production of fine chemicals from non-petroleum carbon resources. In this study, direct conversion of syngas into aromatics was investigated over a serial of bifunctional catalysts coupling ZnCrO_x oxides and H-ZSM-5 zeolites with different morphologies. Detailed investigation showed that the CO conversion was positively correlated with the Brønsted acid sites, and the differences in aromatics selectivity and aromatics distribution on different bifunctional catalysts with different morphologies of H-ZSM-5 zeolites were attributed to the synergistic effects of acidity and particle size. For nano-type zeolites, changes in acidity might not have a significant effect on aromatics selectivity, while the transfer of intermediate species on coffin-type zeolites was mainly influenced by acidity. Moreover, for different morphology zeolites of nano-type n-Z5-125 and coffin-type c-Z5-100 with similar acidity, the side reactions in syngas aromatization on the former were 1.7 times higher than those on the latter. The reactants diffused more readily on TPAOH treated c-Z5-150-0.1 M, which promoted olefins cyclization and further increased the aromatics selectivity from 69.8% to 74.8%.