CO₂ addition on the non-oxidative dehydro-aromatization of methane over MoMCM-22

Abstract

This work aims at studying the effect of CO₂ addition in the non-oxidative conversion of methane over a Mo-containing MCM-22 zeolite. Catalyst characterization made use of X-ray fluorescence, textural analysis, X-ray diffraction and diffuse reflectance spectroscopy. Molybdenum was present as highly condensed species with octahedral coordination, such as (Mo₇O₂₄)₆ and MoO₃ species. Catalytic tests were carried out at atmospheric pressure and 700 °C, with WHSV of 90g_CH4 · g ⁻¹_Mo  h⁻¹. Coke species were studied by thermogravimetric analysis and thermoprogrammed oxidation. Besides the carbidic carbon, two other types of coke were observed: one associated to molybdenum and the other associated to Brönsted acid sites located both on the catalyst surface and inside zeolite pores. The species associated to acid sites, known to be responsible for polyaromatics formation and catalyst deactivation, were reduced in a more significant way by the use of CO₂, increasing the catalyst stability.