Modulating acid site distribution in MTT channels for controllable hydroisomerization of long-chain n-alkanes

Abstract

Bifunctional catalysts with high isomerization activity and mono-branched isomer selectivity are urgently demanded for dewaxing long-chain n-alkanes. In particular, branching location of mono-branched isomer is difficult to control by current techniques. In this study, SSZ-32 zeolite with tunable distribution depth of acid sites in micropore channels is successfully prepared by ion exchange under partial template protection. Loaded with similar Pt nanoparticles, these SSZ-32 catalysts exhibit tunable activity and selectivity for hydroisomerization of n-hexadecane. Characterization results show that the adsorption model and insertion depth of n-alkane is altered by changing the distribution depth of acid sites in SSZ-32 micropore channels. When acid sites distribute in a moderate depth (∼ 4.5 nm) of the micropore channels, high yield of center-position mono-branched isomers (46.85%) is achieved, cracking reaction is significantly inhibited. The mole ratio of 6−/7−/8-methyl isomers to 2−/3-methyl isomers was increased to at least 1.3 times of the traditional catalyst with acid sites distributed throughout the micropores. The cold flow properties of lube base oils in isomerized dewaxing of Fischer-Tropsch wax are improved significantly by achieving an optimal and effective diffusion depth of reaction intermediates in the MTT micropore channels. Efficient and selective hydroisomerization of long-chain n-alkane is realized on Pt/SSZ-32 prepared by the facile partial-detemplation method.