Confirming nonthermal plasmonic effects enhance CO₂ methanation on Rh/TiO₂ catalysts

In some cases, illumination of traditional thermal catalysts and tailored plasmonic photocatalysts may synergistically combine thermal and nonthermal mechanisms to enhance reaction rates and improve product selectivity at reduced temperatures. To understand how these attributes are achieved in plasmon-driven catalysis, these intertwined thermal and nonthermal effects must be untangled. Here, we show how a novel indirect illumination technique, in conjunction with precisely monitored thermal profiles of the catalyst, can confirm and clarify the role of nonthermal effects in plasmon-enhanced carbon dioxide methanation on a Rh/TiO₂ photocatalyst. We find that the extracted nonthermal methane production rate has a linear dependence on the top surface temperature, distinctly different from an exponential dependence for thermal catalysis. We also find that the apparent quantum efficiency from the nonthermal contribution has no dependence on light intensity but maintains a linear dependence on top surface temperatures between 200 and 350 °C. The clear exposition of nonthermal effects in the Rh/TiO₂ plasmonic photocatalyst illustrates how this methodology may be applied for the quantitative evaluation of thermal and nonthermal light effects in other plasmon-enhanced catalytic reactions.[Figure not available: see fulltext.].