Metal-containing zeolite composites with separated phases as catalysts for hydroisomerization of linear hexane

Abstract

Abstract In this work, composite catalytic systems of natural mordenite and synthetic MFI-type zeolite containing Pd and Ni nanoparticles (0.5–1.5% by weight in total) were prepared by mechanical mixing (1:1), optionally with the addition of α- or γ-Al2O3 as a binder. The samples were examined using IR spectroscopy, X-ray diffractometry, transmission electron microscopy, low-temperature nitrogen ad(de)sorption, and tested in the model reaction of n-hexane hydroisomerization in a micro-pulse mode to determine the effect of composition on the peculiarities of linear alkane transformation. It has been shown that in the obtained catalytic systems, modifications of aluminum oxide used as a binder affect the effectiveness of catalysts in the conversion of n-hexane. This is explained by the different dispersity of α- and γ-Al2O3 particles, which causes different porosity of the result composites, and possibly by the interaction of zeolite acid sites with binder acid sites, which leads to changes in their characteristics depending on the modification of aluminum oxide. In this respect, α-Al2O3 proved to be better than γ-Al2O3. Synergy between the two zeolite components in the formation of isomers has been found out, which was more effective in samples with an isotropic distribution of zeolite phases. In the applied micro-pulse reaction mode, the composite catalyst prepared without a binder was the best, showing a significantly lower temperature of the maximum yield of isomerization products and a high yield of dimethyl-branched isomers, and having selectivity for n-hexane isomers at the level of high selectivity of the Pd-containing component.