Mesopore modification of beta zeolites by sequential alkali and acid treatments: Composition-dependent T-atoms removal behavior back donating to hierarchical structure and catalytic activity in benzene alkylation

Acidic zeolites beta with wider Si/Al ratios were desilicated and dealuminated using the alkali acid treatment approach involving hydrothermal alkali pre etching. Zeolites beta subjected to mesopore modification were characterized by the techniques of XRD, N-2 physisorption, SEM, TEM, EDX, ICP-AES, NH3-TPD, pyridine FTIR adsorption, and immersion porosimetry to examine changes of structural/ textural and acidic properties with initial Si/Al ratio. Benzene alkylation with 1-dodecene was used as a model reaction to elucidate the influence of mediated acidity and texturally mesoporous structure on bulky hydrocarbon transformations. The resulting zeolites beta were shown to have hierarchical porous structures and regular mesoporous size distributions. Initial Si/Al ratios appeared to dominate significant mesoporosity development though no clear threshold of initial Si/Al ratio was identified to be more instrumental in forming mesopores. A volumetric fraction of intraparticle to total BJH mesopores proved to reduce with increasing initial Si/Al ratio. The modified zeolites showed more than 95% desilication selectivity whereas less than 5.0% dealumination selectivity upon overall treating processes. T-atoms removal efficiencies relative to areal, volumetric and diametrical factors revealed the coherent characteristics to T-atoms removal selectivities. Moreover, the dependency of benzene alkylation activity on mesopore size distribution was observed from changes of 1-dodecene conversion and LAB selectivity, both of which were promoted by the hierarchical zeolites. Despite both with comparable acidic properties, the typical sample subjected to the combined alkali acid treatments was shown to have narrowing mesopore size distribution and hence to exhibit the enhanced catalytic performance for selective production of linear alkylbenzenes compared with the purely desilicated sample with broadening mesopore size distribution. (C) 2017 Elsevier Inc. All rights reserved.