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 CuO_x 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 CuO_x species dispersion, acting as anchoring sites to effectively stabilize and disperse CuO_x 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 CuO_x 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.