Jinghui Lyu

The effect of Si/Al ratio on the catalytic performance of hierarchical porous ZSM-5 for catalyzing benzene alkylation with methanol

Ethylbenzene is the major side product in benzene alkylation with methanol and it is difficult to be suppressed over hierarchical porous ZSM-5. Moreover, the separation of ethylbenzene from xylene still remains a great challenge. Our research indicated that ethylbenzene formation could be highly suppressed by changing the Si/Al ratio of the catalyst. Hierarchical porous ZSM-5 catalysts with different Si/Al ratios were prepared via reducing the amount of Al in the solvent evaporation assisted dry gel conversion method. In this method, tetra-n-propylammonium hydroxide was used as the direct agent to create micropores, and hexadecyltrimethoxysilane was added to create additional porosities by forming organic assemblies which occupied a certain space between zeolitic walls. The catalyst with a Si/Al ratio of 1800 could achieve high benzene conversion (59.5%) and high xylene selectivity (39.0%) as well as excellent suppression of ethylbenzene formation (<0.1%).

Alkylation of benzene with methanol over hierarchical porous ZSM-5: synergy effects of hydrogen atmosphere and zinc modification

The competitive reaction of methanol to olefins is difficult to be suppressed in benzene alkylation with methanol over hierarchical porous ZSM-5. The influence of ZnO content and different atmospheres on the catalytic performance of hierarchical porous ZSM-5 catalyst was investigated. The results indicated that the introduction of ZnO could form the Lewis acid sites of zinc species (ZnOH+) at the expense of the Bronsted acid sites, and the reduction of strong Bronsted acid would help to suppress the side reaction of methanol to olefins. However, the presence of ZnOH+ could catalyze the dehydrogenation reaction of light hydrocarbons to olefins which would result in the formation of coke under the nitrogen atmosphere, while the hydrogen atmosphere could inhibit the dehydrogenation ability of ZnOH+.

Promoting effects of MgO and Pd modification on the catalytic performance of hierarchical porous ZSM-5 for catalyzing benzene alkylation with methanol

The effect of MgO and Pd modification on the catalytic performance of hierarchical porous ZSM-5 for benzene alkylation with methanol was investigated. The results indicated that the introduction of MgO could reduce the Bronsted acid sites which suppressed the side reaction of methanol to olefins and in turn effectively promoted the alkylation of benzene. However, the single modification of MgO could not completely suppress the formation of ethylbenzene and coke. Doping a small amount of Pd had a positive effect on inhibiting the generation of ethylbenzene and coke, which could be attributed to the hydrogenation of ethylene into ethane on Pd. The dual modified catalyst (MgO and Pd) exhibited high benzene conversion (56%) and xylene selectivity (39.1%), and the lowest ethylbenzene selectivity (0.13%) and coke content (0.4 wt%).

In situ encapsulation of platinum clusters within H-ZSM-5 zeolite for highly stable benzene methylation catalysis

The catalytic conversion of benzene and methanol to alkyl aromatic products is a promising way of converting nonpetroleum sources to fine chemicals. Ethylbenzene is the major by-product, which is still difficult to suppress. Besides, coke deposition on ZSM-5 catalysts is of serious concern on account of its impact on the catalyst deactivation and consequent loss in the production yield. In this study, Pt@ZSM-5 catalysts were synthesized using in situ hydrothermal synthesis techniques. The resultant catalysts exhibit a higher activity (60.1%) in comparison with impregnated Pt/ZSM-5 catalysts (56.3%), which is ascribed to the preservation of the pore volume and surface area in the resulting material. Notably, thanks to the high dispersion of Pt particles within the ZSM-5 nanocrystals, the Pt@ZSM-5 catalysts show superior anti-coking performance without deactivation after 300 h on stream, along with a high suppression ability towards the formation of ethylbenzene (<0.01%). Meanwhile, the confinement within the ZSM-5 crystals protects the Pt clusters from sintering and coalescence during thermal regeneration treatments. Such novel Pt@ZSM-5 catalysts exhibit excellent activity, remarkable stability and outstanding recyclability, thus providing an opportunity for benzene alkylation with methanol towards industrial production.