Removing low-concentration methane via thermo-catalytic oxidation on CuOx/zeolite

Abstract

Methane (CH4) is the second most potent greenhouse gas that exists largely in low concentrations. This fact, coupled with its inert nature, brings both urgency and challenge for any mitigations (including thermo-catalytic oxidation). In this study, we address this challenge by synthesizing highly dispersed CuOx species (∼6 wt%) loaded on mordenite zeolite (MOR), and enhancing the catalytic performance for the thermal oxidation of low-concentration CH4. The optimized sample, Cu-MOR-11, demonstrates exceptional catalytic properties, including high activity with 100 % CH4 total oxidation to CO2 at 400 °C, low reaction temperature with a T10 at 230 °C and T90 at 350 °C, as well as excellent long-term stability and reusability over a 100-hour reaction period. These attributes make it a promising candidate for large scale CH4 oxidation applications. To elucidate the mechanisms behind the enhanced catalytic performance of Cu-MOR-11, we conclude, 1) the generation of more Brønsted acid sites which facilitated the absorption and dissociation of CH4; 2) the presence of Al3+ as acid sites in the MOR supports played a crucial role in achieving high CuOx species dispersion, acting as anchoring sites to effectively stabilize and disperse CuOx species, which provides more active sites; 3) variation in preparation environments (e.g., pH) led to different oxidation states of the catalysts, with alkaline conditions facilitating the deoxidation of CuOx species, resulting in more Cu+&Cu0 compared to CuO; 4) the presence of Brønsted acid sites which mitigated coking at low temperatures and prevented the loss of structural stability at high temperatures.