Plasmonic photocatalysis represents the synergetic union of two active fields of research: plasmonic effects in illuminated metallic nanoparticles and catalytic effects in tailored metallic nanoparticles. Traditionally, metallic nanoparticles that excel for one application are limited for the other, but recent developments have shown that desirable catalytic behaviors, such as reduced activation barriers and improved product selectivity, derive from nonthermal behaviors uniquely produced by this synergy. After examining such findings, this review will address a specific debate that has recently surfaced: what is the relative degree of contributions of thermal and nonthermal effects in plasmonic photocatalysis? We demonstrate the importance of correctly accounting for thermal effects before characterizing nonthermal contributions. We show that another synergy occurs: these desirable nonthermal behaviors have a temperature dependence, and the resulting temperature-dependent reaction rates far exceed what can be explained from purely thermal effects alone. Thus, the synergy of plasmonic photocatalysis offers an exciting new contribution to the quest for efficient, selective, sustainable methods for chemical synthesis and energy conversion.

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 ℃. 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.