Activity and stability of Mo/ZSM-5 catalysts with a hierarchical pore system in the non-oxidative conversion of methane
A. A. STEPANOV1, E. V. MIKUBAEVA1, L. N. VOSMERIKOVA1, YA. E. BARBASHIN1, V. G. BONDALETOV2, A. V. VOSMERIKOV1
1Institute of Petroleum Chemistry, Siberian Branch of the Russian Academy of Sciences, Tomsk, Russia
2National Research Tomsk Polytechnic University, Tomsk, Russia
Keywords: zeolite ZSM-5, polyaniline, non-oxidative conversion of methane, benzene, hierarchical catalysts
Abstract
Results of studies on the activity and stability of Mo/ZSM-5 catalysts with a hierarchical pore system in the process of non-oxidative conversion of methane into aromatic hydrocarbons are presented. ZSM-5 zeolites were synthesised by hydrothermal synthesis with the addition of different amounts of polyaniline (3 %, 6 % and 12 %) as the second structure-forming agent (template), along with hexamethylenediamine (HMDA). The Mo/ZSM-5 catalysts were prepared from the zeolites and nano-sized Mo powder by solid-phase synthesis. According to IR spectroscopic data, all the synthesised zeolites belong to the ZSM-5 type and have 100 % crystallinity. It is shown that the addition of the second template (polyaniline) at synthesis stage improves the textural characteristics of the zeolite: increased specific surface area and mesopore volume, with an insignificant change of micropore volume, in comparison with ZSM-5 synthesised using only HMDA. With an increase in the amount of polyaniline added at the synthesis stage, the average pore size in the zeolite is observed to increase to 3.1 nm. The addition of polyaniline also causes changes in their acidic properties. The strength and concentration of strong acid centres of zeolite, related to Brønsted acid centres, are observed to decrease, which is probably due to changes in the distribution of Al atoms in zeolite structure and, as a consequence, to the redistribution of Brønsted and Lewis acidity. Non-oxidative methane conversion was carried out at a temperature of 750 °C and atmospheric pressure in a quartz reactor with a fixed catalyst bed. Catalytic tests have shown that the addition of polyaniline leads to the production of samples characterised by higher activity and selectivity for benzene formation. The best activity and stability are observed for Mo/ZSM-5 catalyst based on the zeolite synthesised with the addition of 6 % polyaniline, methane conversion was 11.5 %, and benzene yield was 6.7 %.
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