Mapping Operating Temperature at the Confinement within Thermochromic-Zeolite Catalysts

Exploring the temperature at the confinement of heterogeneous catalysts is highly desired to understand catalytic activity under real operating conditions. However, the additional introduction of external nanothermometers has significantly limited the implementation of nanothermometry for catalysts. Here, we propose an in situ synthesis strategy for luminescent temperature-sensitive carbon dots as nanothermometers using the inherent carbon sources in nanoporous zeolite catalysts. Using spatiotemporally resolved band-shape luminescence thermometry as active site nanothermometers, the evolution of operating temperature within the nanoconfined pores of individual zeolites can be visualized. Using the exothermic dehydrogenation of liquid hydrogen storage media by zeolite-supported catalysts based on active Rh species as a model, our results show that the zeolite framework is a poor thermal conductor. We find that, for exothermic reactions, uniform dispersion of active species, decoration of additional adsorption sites, and shorter distances between active species in zeolites with low thermal conductivity can effectively accelerate the heat release within the catalyst. Such a synergistic effect on enhancing the heat release rate of catalysts can significantly facilitate catalytic activity by more than 30 times. The visualizations of operating temperature in zeolites demonstrate that thermal-controlled catalytic fundamentals need to be taken into consideration when designing nanopore-supported catalysts.