(522c) Exploiting Heat Transfer Limitations in Carbon Capture with Microthermometry Via Upconverting Nanoparticles

Dual functional materials (DFMs) are an attractive option for increasing the energy efficiency of carbon capture, as their design couples endothermic desorption with an exothermic reaction. However, a central challenge is that traditional thermocouple measurements do not have the spatial resolution to resolve localized hot spots in the adsorbent-catalyst bed, which is necessary for efficiently desorbing and converting bound CO₂ into value-added products. To address this challenge, we have developed a custom-designed quartz capillary reactor technique for microscale temperature measurements that integrates Yb³⁺/Er³⁺ co-doped NaYF₄ luminescent upconverting nanoparticles (UCNPs) into a Pt‑CaO/γ‑Al₂O₃ DFM.

Our in situ microthermometry technique overcomes the averaging effects of conventional temperature sensors and enables measurement of localized thermal gradients by exciting the UCNPs with near-infrared light and measuring the intensity ratio of a pair of closely spaced green bands for reliable temperature readings, Figure. Under external heating, UCNP ratio closely tracks the thermocouple reading, confirming minimal formation of thermal gradients. We then use CO oxidation as a probe reaction to generate heat on the catalyst surface to differentiate between localized and bulk heating. Upon running CO oxidation, we observe a sharp spike in the measured UCNP ratio, above the bulk thermocouple reading, indicating that the exotherm of CO oxidation creates localized hot spots at the Pt-based active sites. We observe that the localized hot spots accelerate CO₂ desorption, supporting our hypothesis that exothermic CO oxidation drives CO₂ desorption at faster rates than bulk heating.

Our findings highlight how microscale thermal gradients can be harnessed to accelerate CO₂ desorption in DFMs, providing insight into the complex mechanism of combined reaction and desorption. By correlating localized temperatures with real-time CO₂ adsorption and desorption, we establish a framework for engineering future catalytic reactors that strategically couple active sites and adsorbents to enable more energy efficient carbon capture and utilization.