The photocatalytic synthesis of C2+ hydrocarbons and oxygenates from CO2 and H2O is a truly sustainable route to fuels and building block chemicals production. Our combined computational/experimental investigations of photocatalytic CO2 reduction by H2O in organic-free, concentrated solar photoreaction (CSPR) conditions at elevated temperatures (gas phase reaction at ~ 100-400oC) have shed light upon several chemical and physical phenomena at the mechanistic level that drive elementary reaction steps on the surface. Significant insights from these studies include the isolation of new H-transfer mechanisms and variation in surface chemistry under a range of experimental environment. A deeper understanding of the role of surface chemistry and the development of new H-transfer mechanisms have enabled the tunability in the selectivity between hydrogenation and H2 – a critical efficiency aspect of the system. Based on our investigations in a high energy environment at elevated reaction temperatures, we found that semiconductors with a high Debye temperature, robust bulk bonding, and elevated surface chemical reactivity could directly promote new reaction intermediates produced via thermal/vibrational routes that further enhance the selectivity towards hydrocarbon synthesis. Kinetic isotope studies employing heavy water coupled with solid state NMR (SSNMR) have been utilized to experimentally probe the nature of hydrogenation — whether it is vibrationally/thermally or electrochemically driven. Further studies aimed at understanding the carbon-carbon coupling elementary reaction steps have isolated some potential key intermediates for the production of C2+ compounds. Insights derived from our investigation on photocatalytic synthesis mechanisms and electronic properties is already paving the way towards the ultimate aim of producing higher hydrocarbons and oxygenates photocatalytically from simple thermodynamic-minimum reactants.

Understanding the chemical and physical mechanisms active in elevated temperature photocatalytic synthesis of hydrocarbons

255th National Meeting (2018)

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