Intrinsic kinetics of plasmon-enhanced reverse water gas shift on Au and Au-Mo interfacial sites supported on silica

Well characterized AuMo_x catalysts were synthesized by controlled surface reactions (CSR) and studied in reverse water gas shift (RWGS) reaction with and without visible light addition. The numbers of Au and Au-Mo interfacial sites on these catalysts were quantified using low temperature (173 K) CO adsorption with Fourier transform infrared spectroscopy (FT-IR) and electron microscopy. Due to the localized surface plasmon resonance (LSPR) effect, visible light irradiation of the catalyst caused a decrease in the apparent activation energy from 80.2 ± 3.9 kJ/mol to 55.5 ± 3.1 kJ/mol and 67.5 ± 1.3 kJ/mol to 38.7 ± 1.9 kJ/mol with visible light irradiation over Au/SiO₂ and Au₁Mo_0.1/SiO₂, respectively. The catalytic activity went through a maximum upon addition of Mo, with Au₁Mo_0.1/SiO₂ being the most active catalyst. The Au₁Mo_0.1 catalyst with LSPR was 30 times more active than the reference Au catalyst under dark conditions. Visible light irradiation increased the reaction rate 4.7-4.8 times at 573 K for all catalysts. The turnover rates (CO mole produced per mole of Au or AuMo_x site per min) on the Au and AuMo_x interfacial sites were measured to be 0.98 min^-1 and 14 min^-1 in the dark conditions and 4.4 min^-1 and 63 min^-1 under the light conditions at 573 K. The rate per AuMo_x interfacial site is 14 times greater than the rate per Au site under both dark and light conditions. These results indicate that the LSPR has the same enhancement effect on both Au and AuMo_x catalytic sites.