Methanol Catalytic Oxidation over Cu-Modified SSZ-13 Catalysts: Performance and Mechanism

Methanol (CH₃OH) is increasingly used as an alternative marine fuel due to its ability to reduce emissions of CO₂ and particulate matter. However, its application often leads to elevated levels of unburned methanol in the exhaust. Catalytic oxidation is widely considered an effective strategy for eliminating methanol slip. In this article, a series of Cu/SSZ-13 catalysts with different Cu loadings are prepared by the impregnation method. Methanol conversion increased markedly as the Cu loading increased from 2.5 to 10 wt%. The Cu₁₀/SSZ-13 catalyst achieved complete CH₃OH conversion at 225 °C with minimal byproduct formation throughout the tested temperature range. Further increasing the Cu loading to 12.5 wt% resulted in no significant change in either CH₃OH conversion or byproduct yields. Characterization results indicated that the Cu species predominantly existed as CuO nanoparticles dispersed on the external surface of SSZ-13, rather than as framework-incorporated isolated Cu²⁺ ions. CuO is identified as the primary active phase for CH₃OH oxidation. The superior performance of Cu₁₀/SSZ-13 is attributed to its abundant surface-adsorbed oxygen species and high density of basic sites. In situ DRIFTS measurements further revealed that methoxy and formate species are the key intermediates during methanol oxidation over the Cu₁₀/SSZ-13 catalyst.