Integrating experiments and theory: In-situ spectroscopic and DFT study of propane oxidation over AuCu/TiO2 catalysts

In this study, we evaluated a series of bimetallic gold‑copper catalysts, synthesized by the sequential deposition–precipitation with urea method, for their performance in the total oxidation of propane. From the tested variables (bimetallic ratio, activation protocol, and support type) the most active catalyst was found to be Au 1 Cu 3 /TiO 2 (Au:Cu =1:3), which was activated in air atmosphere and exhibited the temperature at which the propane conversion reached 50% (T 50% ) of 328 °C, surpassing the performance of its monometallic counterparts. The characterization using various techniques revealed that the Au 1 Cu 3 /TiO 2 catalyst comprises highly dispersed nanoparticles predominantly exposing Au 0 and Cu δ+ active sites in close interaction. Surface analysis via XPS showed that copper species are mainly in the 1+ oxidation state. An increase in Cu 2+ species and Lewis's acid sites were also determined in the bimetallic sample, compared to the copper-only catalyst, thus probably accounting for the observed improvement in the catalytic performance. Through operando DRIFTS-MS analysis we identified various predominant intermediate species, depending on the metal present in the catalyst: enolate for gold, formate and carbonate for copper, and a combination of these intermediates in the bimetallic sample, which probably enhances propane oxidation efficiency. Based on the theoretical results we found that gold incorporation into Cu/TiO 2 catalyst enhances copper's oxyphilicity and Lewis's acidity, boosting the propane oxidation by enabling electron-assisted activation of stable propyl sites, which form majorly enolate and fully oxidized products. A cascade charge-reservoir effect is proposed to explain differences in chemical reactivity of gold‑copper and copper catalysts. Cu preferentially binds to reduced TiO 2 , preserving direct contact with the support even in the Au Cu bimetallic catalyst. • Au 1 Cu 3 /TiO 2 shows superior propane oxidation with T 50% = 328 °C. • Highly dispersed Au 0 –Cu δ+ sites drive efficient propane oxidation. • Operando DRIFTS-MS reveals enolate, formate, and carbonate intermediates. • DFT shows that bimetallic Au Cu synergy enhances Cu oxyphilicity and Lewis acidity.