Huang, K; Zhu, C; Shi, N; Wen, F; Wang, S; Wu, L; Liu, D
Hydroisomerization of the low carbon straight chain alkanes in the products of F-T synthesis, which could be used in high quality gasoline with high octane number, is promising to realize clean utilization of coal resources. Herein, a series of MOR/MCM-41 micro-mesoporous composites are prepared by in-situ recrystallization method, with the degree of alkali dissolution of MOR zeolite crystals being controlled and the mesoporous MCM-41 being synthesized by using zeolite solution as Si and Al sources. A series of Pt-loaded catalysts are obtained by ion exchange and impregnation of metal active components, and n-hexane is selected as the model compound of F-T low carbon n-alkanes for hydroisomerization performance evaluation. TEM, SEM, XRD, BET, Pyridine-IR, and N2 adsorption-desorption isotherms measurements are introduced to characterize the morphologies, structures and chemical and physical properties of the hybrids. After in-situ recrystallization modification, the grain size of MOR crystals decrease, the outer surface of MOR is coated with MCM-41, and the adsorption performance of MOR is improved, which indicates that appropriate alkali treatment could reduce the particle aggregation of MOR zeolite and adjust the ratio of Brönsted acid to Lewis acid. In catalytic performance evaluation, the conversion rate of n-hexane increases when the reaction temperature is increased from 200â to 280â. With the increasing of the alkali treatment concentration, the selectivity of isomer products is improved, and the degree of cracking is reduced, mainly due to the composite alkali treatment effect on MOR particle dispersion. Additionally, the synthesis method of MCM-41 could expand the channels through adjusting the catalyst pore structure and shorten the mass transfer path between the reactant molecules and the active center, also contributes to the selectivity improvement. The selectivity of n-hexane hydroisomerization can be improved by preparing micro-mesoporous composites and setting up a modified system. This study will provide reference for more efficient conversion of low carbon n-alkanes hydroisomerization. © 2020, Editorial Office of Journal of China Coal Society. All right reserved.