Effects of NaOH solution treatment on the catalytic performances of MCM-49 in liquid alkylation of benzene with ethylene

MCM-49 zeolite was alkali-treated with NaOH solutions under mild and severe conditions. The samples before and after alkali-treatment were both used as catalysts in liquid alkylation reaction of benzene with ethylene. XRD, XRF, TPD, TPO, IR, SEM, 29Si NMR, N2 adsorption and desorption techniques were employed to characterize the samples. The mildly alkali-treated samples exhibited higher catalytic stability than the parent HMCM-49, as the amorphous particles on the MCM-49 crystal surface were cleaned and the diffusion of the reactant and product was enhanced. The severe alkali-treatment condition resulted in the selective extraction of silicon atoms and the introduction of extra mesopores. The catalytic stability of the catalysts that had been severely alkali-treated was not as good as that of mildly treated ones, but was still better than that of the parent HMCM-49 catalyst if the alkali-treatment conditions were not too severe.

The crystallinity of MCM-49 can be increased by mild alkali-treatment and mesopores can be introduced by severe alkali-treatment. The increased catalytic stability of the alkali-treated samples in the liquid alkylation of benzene with ethylene is mainly attributed to purification of zeolite crystals of the mild alkali-treated samples, and to the facilitated diffusion for substances in the case of severe alkali-treatment.Figure optionsDownload high-quality image (115 K)Download as PowerPoint slide