Hydrogenation of CO2 to CO or CH4 typically proceeds at high temperature (300°C - 500°C) using supported metal nanoparticles as catalysts. Alternatively, semiconductor metal oxide photocatalysts can be applied, but they require high intensity UV light. Here, we report supported plasmonic metal nanocatalysts that facilitate CO2 hydrogenation at low temperature (&lt; 250°C) using sunlight as energy source. We demonstrate an unrivalled high photon to product efficiency (PTP) of 55% over the entire solar spectrum. To determine the cause of this high PTP and provide guidelines for design of future metal catalysts for photoconversions, we studied the underlying physical effects that rule this process. We attributed the excellent sunlight harvesting ability of our supported metal nanocatalysts to the strong broadband localized surface plasmon resonance (LSPR) spanning the entire solar spectrum. We based this conclusion on UV-vis-NIR spectrophotometric characterization of the catalysts and optical modelling based on the boundary element method. Based on studies of the reaction kinetics upon solar illumination and in dark, we were capable of distinguishing between thermal (photothermal heating) and non-thermal effects contributing to the photohydrogenation reactions. Whilst at low solar intensity (1 sun) the activity of the catalyst was mainly attributed to thermal effects, we identified a large non-thermal contribution at slightly elevated intensities (5 - 10 suns) resulting in the high PTP of up to 55% over the whole solar spectrum. In addition to elucidating the cause of the high PTP, we demonstrated that the conversion of CO2 to CH4 proceeds with sunlight as sole energy source. External heating is not required to promote the reaction, which makes the process sustainable as a whole. Based on the presented results, we are convinced that our highly efficient conversion of CO2 and H2 to CO or CH4 is a disruptive technology that can simultaneously accelerate the energy transition and reduce CO2 emissions, thereby addressing a major societal challenge.

Plasmonic metal nanocatalysts for photohydrogenation of CO2 to CO or CH4 with unrivaled high photon to product efficiency

2019 Fall National Meeting

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