The impact of heat transfer in packed plasmonic catalyst beds on light-driven CO2 hydrogenation

Abstract

Fiber Bragg based - fiber optic sensors were applied in operando to monitor the temperature of illuminated plasmonic catalysts at various depths inside the catalyst bed during light-driven CO2 hydrogenation. Multipoint temperature measurements showed that single-sided illumination induced a pronounced vertical temperature gradient, which remained stable throughout the reaction. This behaviour was observed in two light driven reactions: the exothermic Sabatier reaction catalysed by Ru/Al2O3 and the endothermic reverse water gas shift reaction catalysed by Au/TiO2. The temperature gradient, attributed to a combination of limited light penetration depth and poor thermal conductivity of the catalyst bed, must be taken into account in kinetic studies. Metal loading and gas composition had a strong influence on the temperature gradient, while gas flow rate and reaction heat had a negligible effect. For catalyst temperatures up to 250 & ring;C, radiative heat loss accounted for approximately 15 % of the incident light power. Our study demonstrates that accurate in operando temperature monitoring at multiple positions inside the catalyst bed is essential to distinguish between thermal and nonthermal contributors in plasmon catalysis.