The efficient utilization of the Sun’s energy through artificial photosynthesis is a Grand Challenge goal. Broad utilization of the solar spectrum will require integrating thermo- and photo- catalytic approaches to create a photothermal catalysis process, offering the potential for better utilization of solar energy, which is considered the ultimate inexhaustible power source for human civilization. The photochemical CO2&nbsp;conversion into commodity chemicals and fuels offers the potential double benefit of generating economic benefits while simultaneously mitigating CO2&nbsp;emission-related climate change. Although natural photosynthesis has been optimized through natural evolution over millions of years, photothermocatalytic CO2 reduction offers vast opportunities to reduce CO2 under conditions (i.e., elevated temperature and pressure) and with materials (e.g., emerging nanostructured inorganic catalysts) that nature has not had the opportunity to work with. Despite this immense promise, the conversion of CO2&nbsp;into solar fuels has a low yield and is not yet economically feasible on a larger scale.Herein, we present the HI-Light reactor – a solar-thermocatalytic “reverse combustion” technology that enables the reduction of CO2, increasing its value as a commodity. The unique feature of our reactor is the simultaneous light and reactant delivery technique that maximizes the utilization of catalyst in the reactor. This is accomplished through a novel variant on the traditional “shell-and-tube” reactor design where the tubes are internal light-guiding rods with specially designed scattering surfaces that enable deep and efficient penetration of the solar energy into the reactor, and the reagents and products flow through the shell outside the rods. Using reverse water–gas shift (RWGS) as a pilot reaction, we examined the effect of temperature, light irradiation, and residence time on its photo-thermocatalytic performance for CO2&nbsp;hydrogenation to form CO, with a cubic phase defect-laden indium oxide, In2O3-x(OH)y, catalyst. We demonstrated the light enhancement effect under a variety of reaction conditions. Notably, the light-on performance for the cubic nanocrystal photocatalyst exhibited a CO evolution rate at 15.40&nbsp;mmol gcat−1&nbsp;hr−1&nbsp;at 300°C and atmospheric pressure. This is 20 times higher conversion rate per unit catalyst mass per unit time beyond previously reported In2O3-x(OH)y catalyst in the cubic form under comparable operation conditions and more than 5 times higher than that of its rhombohedral polymorph. We also presented an evaluation of current photocatalytic reactors for solar fuel production from an optofluidic perspective. Optofluidics offers precision in controlling both the fluidic and optical environment and can solve long-standing challenges in photocatalysis. We evaluated pathways for improving the light scattering, heat and mass transfer inside the current photocatalytic reactors, and offered upscaling considerations for reactor design to facilitate real-world deployment.

Solar-Driven Photothermal Catalytic Reactor Design for Scalable Artificial Photosynthesis

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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