Promoting effect of Pd nanoparticles on SrTi0.8Mn0.2O3 in the reverse water-gas shift reaction via the Mars–van Krevelen mechanism

The reverse water-gas shift (RWGS) reaction serves as a critical pathway for converting CO2 into diverse chemicals. The Mars–van Krevelen (MvK) mechanism, which leverages lattice oxygen as the oxidant and oxygen vacancies as reductants, offers an alternative catalytic strategy for the selective RWGS reaction. While Mn-substituted SrTiO3 (i.e., SrTi0.8Mn0.2O3) has been shown to promote the RWGS reaction selectively via the MvK mechanism, achieving a sufficient conversion of CO2 necessitates elevated temperatures. This study investigated the effect of Pd-loaded SrTi0.8Mn0.2O3 on the activation of adsorbed H2 molecules, which generated oxygen vacancies and enhanced CO2 conversion. Notably, 1.0 wt% Pd-loaded SrTi0.8Mn0.2O3 yielded 13.4% of CO at 673 K, whereas pristine SrTi0.8Mn0.2O3 and Pd-loaded SrTiO3 yielded negligible or minimal amount of CO. Hydrogen temperature-programmed reduction and X-ray absorption spectroscopy measurements revealed that Pd promoted the formation of oxygen vacancies via both thermodynamic and kinetic mechanisms. Fourier transform infrared spectroscopy and kinetic studies revealed that the RWGS reaction over Pd-loaded SrTi0.8Mn0.2O3 proceeded primarily via the MvK mechanism with a partial contribution from the Langmuir–Hinshelwood mechanism. This study underscores the effectiveness of combining metal and MvK-type catalysts to enhance the efficiency of the RWGS reaction.