Leveraging and understanding exotherms in tandem catalysts with in situ luminescence thermometry

Abstract

Leveraging thermal gradients on catalyst surfaces remains largely underexplored despite their profound effects on reaction kinetics. In this work, we use upconverting nanoparticle (UCNP)-based luminescence thermometry to directly measure catalyst surface temperatures under in situ conditions during thermally coupled tandem reactions. Using UCNPs loaded on a model dual-functional material (DFM), Pt–CaO/CeO₂, we observe hot spots of ∼10−100 °C above the bulk bed temperature during exothermic CO oxidation. Isotopically labeled ¹³CO₂ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) supports our hypothesis that reaction-generated heat drives endothermic CO₂ desorption from CaO. Proximity studies show that nanoscale co-localization of Pt and CaO improves thermal coupling relative to dual-bed configurations, highlighting the importance of spatial organization. Comparison of UCNP thermometry with thermocouple readings further demonstrates that bulk temperature measurements underestimate true surface temperatures during exothermic reactions, underscoring the critical role of probe placement for accurate kinetic evaluation. Our methodology opens new avenues for accurate kinetic analysis, in situ thermal profiling, and rational design of thermally integrated tandem catalysts and DFMs, with direct implications for more complex transformations such as CO₂ hydrogenation.