Jianchao Liu,Hong Xu,Jinxiang Dong,Ligong Zhou,Xuekuan Li,Hui Ge
The synthesis of alkylbenzenes produced from syngas and benzene over a ZnCrOx/beta bifunctional catalyst has been studied. Our characterization results showed that in the mixed catalyst the beta-zeolite crystallites were dispersed on the surface of the ZnCr oxides. The close contact facilitated the methanol intermediate formed on ZnCrOx to diffuse to the acidic sites of the beta-zeolite crystallites, reacting with benzene to produce alkylbenzenes. The competitive side reactions, which lead to by-products such as CO2 and hydrocarbons, were suppressed. The medium strong acidity and mesopores of the beta-zeolite crystallites contributed to the high activity and selectivity. The optimized ZnCrOx/beta-11 = 1 : 3 (w/w) afforded 40.72% benzene and 62.40% CO conversion with high alkylbenzene selectivity during the initial stage of the reaction, which then underwent quick deactivation, and maintained a benzene conversion of ∼27%. Coke formation on the beta-zeolite crystallites was proposed to be the main cause of deactivation.
The pore architecture and acidity of zeolite materials play crucial roles in the activity and selectivity of catalytic reactions. Herein, hierarchical SAPO-11 molecular sieve microspheres with uniform intercrystalline mesoporosity (ca. 4.3 nm) and tunable acidity were synthesized via dry-gel conversion (DGC) of a silicoaluminophosphate–organosilane composite. The products were comprehensively characterized using multiple techniques, including XRD, SEM, TEM, N2 adsorption–desorption, NH3-TPD, pyridine-adsorbed IR (Py-IR), TG and 29Si MAS NMR measurements. It is revealed that the products' acidity can be precisely tuned in a wide range by simply adjusting the water content used in the synthesis. The growth of such hierarchical SAPO-11 underwent a rearrangement of the mesopores: the original mesopores (ca. 17 nm) of the precursor were collapsed at the initial stage of crystallization and the final mesopores of the products were directed by the organosilane. More importantly, the Pt/hierarchical SAPO-11 catalysts exhibited enhanced isomerization selectivity in the hydroisomerization of n-dodecane, attributed to their excellent diffusion properties resulting from the hierarchical pore network. This work demonstrates a facile approach to synthesize hierarchical zeolites with tunable acidity, which is beneficial for catalytic reactions involving bulky molecules.
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