Mechanistic insights into methane total oxidation over Cu/Hydroxyapatite catalyst synthesized with β-Cyclodextrin assistance

Abstract

The total oxidation of methane (CH4), a highly stable alkane volatile organic compound (VOC), using low-cost Cu-based catalysts, has garnered considerable attention. Nonetheless, challenges such as Cu particle agglomeration and the lack of consensus on mechanism of CH4 total oxidation over Cu-based catalysts remain. In this work, β-cyclodextrin (βCD) was introduced during Cu/hydroxyapatite catalyst (βCD-Cu/HAP) preparation, and its catalytic performance in CH4 total oxidation was compared with the Cu/HAP catalyst. Both materials were prepared using the wet impregnation method and thoroughly characterized. It was found that utilization of βCD, which decomposed during calcination, led to smaller Cu particle size (from 61 to 34 nm) and better Cu dispersion (from 1.9 to 3.5 %), resulting in an enhancement of the catalyst reduction properties. Additionally, the βCD-Cu/HAP catalyst possessed a higher oxygen storage capacity, demonstrating its superior ability to replenish the oxygen vacancies. The βCD-Cu/HAP catalyst activity was double that of the original Cu/HAP catalyst with a 20kJmol-1 lower activation energy, as determined by fitting the initial reaction rate to a power-law model. Further, Langmuir–Hinshelwood (LH), Eley–Rideal (ER), and Mars–van Krevelen (MVK) type rate expressions were regressed to the experimental data. After statistical and physico-chemical assessments, the MVK mechanism involving two oxidized sites and one reduced site with H2O adsorption on oxidized sites was identified as the most appropriate model for describing the experimental data. These findings offer an enhanced understanding of CH4 total oxidation, guiding the development of efficient, low-cost catalysts for this reaction. Environmental ImplicationVolatile organic compounds (VOCs) pose significant environmental and health issues due to their toxicity and widespread sources. Among VOCs, alkane contribute to a large proportion of the VOCs emitted, with light alkanes being particularly challenging to mitigate due to their high stability. Methane, the most stable light alkanes, is the focus of this study. Catalytic oxidation technology offers a promising solution for VOC mitigation. In our work, we conducted a mechanistic investigation of methane total oxidation, aiming at deepening our understanding of catalytic oxidation of light alkanes, thereby contributing to substantial environmental benefits.