Morphology-driven catalytic performance of H-ZSM-5 in benzene alkylation with syngas

Benzene alkylation with syngas is attractive for alkylbenzene production, which use metals/metal oxides combining H-ZSM-5 zeolites as the catalyst. Herein, the H-ZSM-5 zeolites with three different morphologies—spindle-, flake-, and nano-sized—were synthesized. Subsequently, crystal structural, textural and acidic properties of three H-ZSM-5 zeolites and their corresponding bifunctional catalysts were characterized and the catalytic reaction activity and stability of the benzene alkylation with syngas were investigated. The bifunctional catalyst derived from nano-sized zeolites demonstrates an initial benzene conversion rate of 46.7% and reduces by 71.78% after 51 h of continuous operation, owing to abundant acid sites, large surface area and mesopores diameters, and balanced acidity to promote reactant and product diffusion. The spindle-shaped zeolite catalyst delivers the highest initial benzene conversion rate (53.77%) due to abundant acid sites. However, the benzene conversion rate drops to 12.12% of the initial value after 39 h due to limited micropore volume and relatively small mesopore diameters of the catalyst. The flake-shaped zeolite catalyst exhibits the lowest initial conversion rate and the shortest lifetime (30 h) owing to the fewest accessible acid sites and the peculiar pore structure. Three cases indicate that increasing mesopore volume is conducive to improve ratio of Brønsted to Lewis acid sites (B/L), resulting in enhancement of the catalytic activity. Meanwhile, the huge micropore volume and increased mesopore diameter are positive to alleviate pore blockage and coverage of active sites due to high mass-transfer efficiency within the zeolitic channels. These textural advantages collectively contribute to a delayed catalyst deactivation process and sustained catalytic activity. This work highlights the pivotal role of the H-ZSM-5 morphology in the benzene alkylation process with syngas and facilitates the efficient development of production process for non-oil alkylbenzene.