Efficient photocatalytic propane oxidative dehydrogenation with ultralow loading of PdAg intermetallic nanoparticle catalyst.

Propane oxidative dehydrogenation (ODH) is a promising route for propylene production; however, the conventional thermal catalysts suffer from carbon deposit induced by harsh reaction conditions at high temperature. Developing a highly efficient light-driven photocatalytic system is a benign environmentally-friendly alternative. Herein, an ultra-low loading PdAg intermetallic compound (0.1 wt% Pd and 0.05 wt% Ag) supported on TiO2 catalyst was employed via a facile photodeposition (PD) method. The introduction of Ag significantly improved the activation of oxygen driven by the unique interface of PdAg and TiO2 with swift carrier transfer under light condition while Pd sites act as active site for the activation of C-H bonds. Moreover, X-ray absorption spectroscopy (XAS) clearly reveals electron-deficient Ag sites with electron transfer from Ag to Pd, conducive to the adsorption and activation of oxygen. Operando FT-IR and EPR spectra elucidate introduced Ag species progressively improved reactive oxygen radical intermediates derived from oxygen, which is responsible for the activation of propane. As a result, the optimized Pd0.1Ag0.05-TiO2 catalyst displayed 3-fold enhancements in the propylene formation rate of 1649 μmol·gcat-1·h-1 compared to that of Pd/TiO2 at absence of Ag and O2, assigned to the synergistic effect of Ag and O2. Density functional theory results further confirm that incorporated Ag effectively reduced energy barrier (0.6 eV) for rate-determining step of proposed reaction pathway. This work provides mechanistic insights into synergistic effect of bimetallic photocatalysts and demonstrates a promising strategy for photocatalytic oxidative alkane conversion.