Silicon-Tuned Acidity in Nanoporous SAPO-34 for Enhanced Copper Dispersion and Methane-to-Methanol Conversion

Low-concentration coalbed methane, an underused energy resource, poses environmental risks due to its potent greenhouse effect upon direct atmospheric release, creating an urgent need for efficient utilization. Converting methane to methanol offers a viable solution to this challenge. This research examines how the silicon content affects the catalytic activity of Cu/SAPO-34 in the continuous direct oxidation of methane into methanol. Yield and selectivity of methanol exhibit a distinct volcano-shaped dependence on silicon content, among which Cu/SA2 showed excellent activity and selectivity, achieving a space-time yield of methanol 293.6 ± 5.9 μmol/(gcat·h) and selectivity 78.9% ± 1.5%. Silicon content tunes SAPO-34’s acid site distribution and silicon coordination environment, which govern copper species anchoring during solid-state ion exchange. Moderate silicon content promotes the optimized dispersion of copper species, effectively enhancing the content of isolated Cu2+ active sites. In situ DRIFTS elucidates the methane activation mechanism involving Cu(I)-methyl intermediates, along with the critical role of trace oxygen (1000 pm) and water vapor in promoting the catalytic redox cycle of the active sites. This work clarifies the zeolite composition–activity relationship, guiding rational design of high-performance catalysts for methane valorization.