Hierarchically structured Pt/K-Beta zeolites for the catalytic conversion of n-heptane to aromatics

Abstract

The aromatization of alkanes is an important process for improving the quality of Fischer-Tropsch synthesis (FTS) gasoline and producing high-valued aromatics from naphtha; however, currently available catalysts in this regard are often deficient due to the low aromatics yield and short lifetime. In this work, a series of hierarchically structured Beta (Beta-HS) zeolites with high crystallinity and meso-porosity were synthesized by steam treatment with various organosilanes as pore-forming reagent and ethanol as solvent. The nano-sized Beta-HS zeolites were further modified with K through ion-exchange and with Pt through incipient wetness impregnation; the resultant Pt/K-Beta-HS catalysts were then used in the aromatization of n -heptane. The results indicate that the abundant mesopores present in Beta-HS are conducive to the diffusion of reactants and products, whilst the modification with K is able to passivate the strong Brønsted acid sites and the loading of Pt metal can promote the dehydrogenation of alkanes and cycloalkanes, which can effectively suppress the cracking and carbonaceous deposition reactions and enhance the dehydrogenation aromatization activity. As a result, the Pt/K-Beta-HS catalysts exhibit excellent performance in the aromatization of n -heptane, with a much longer lifetime (205 h), higher selectivity to aromatics (80%) and larger turnover number of aromatic products (Pt-based TON, 240 × 10 3 ) than conventional Beta zeolites. These results prove that the steam treatment with organosilanes as pore-forming reagent is a facile and cost-effective strategy to synthesize the hierarchically structured Beta zeolites and after loading K and Pt, the Pt/K-Beta-HS zeolites can be an efficient catalyst for the conversion of n -heptane to aromatics. Steam treatment with organosilanes as pore-forming reagent is a facile strategy to synthesize the hierarchically structured Beta zeolites and after loading K and Pt, the Pt/K-Beta-HS zeolites can be an efficient catalyst for the conversion of n -heptane to aromatics. • Hierarchically structured Beta zeolites were synthesized by steam treatment with organosilane. • Organosilane not only creates abundant mesopores, but also improves the yield of zeolite product. • Hierarchical structure is conducive to the diffusion of reactants and products for alkane aromatization. • K + -modification can passivate strong acid sites and greatly alleviate the coke deposition during reaction. • K + -modified hierarchical Pt/K-Beta-HS show excellent catalytic performance in n -heptane aromatization.