RETRACTED: Solar photothermochemical alkane reverse combustion

Abstract

A one-step, gas-phase photothermocatalytic process for the synthesis of hydrocarbons, including liquid alkanes, aromatics, and oxygenates, with carbon numbers (Cn) up to C13, from CO2 and water is demonstrated in a flow photoreactor operating at elevated temperatures (180–200 °C) and pressures (1–6 bar) using a 5% cobalt on TiO2 catalyst and under UV irradiation. A parametric study of temperature, pressure, and partial pressure ratio revealed that temperatures in excess of 160 °C are needed to obtain the higher Cn products in quantity and that the product distribution shifts toward higher Cn products with increasing pressure. In the best run so far, over 13% by mass of the products were C5+ hydrocarbons and some of these, i.e., octane, are drop-in replacements for existing liquid hydrocarbons fuels. Dioxygen was detected in yields ranging between 64% and 150%. In principle, this tandem photochemical–thermochemical process, fitted with a photocatalyst better matched to the solar spectrum, could provide a cheap and direct method to produce liquid hydrocarbons from CO2 and water via a solar process which uses concentrated sunlight for both photochemical excitation to generate high-energy intermediates and heat to drive important thermochemical carbon-chain-forming reactions.

Elemental Boron for Efficient Carbon Dioxide Reduction under Light Irradiation

“…Thep hotothermal effect can be described as the conversion of photon energy into heat and has been considered as an emerging technology of great interest for solar energy harvesting. [4] As this technology can enable aremarkable and prompt increase in the local temperature at the nanometer scale,i th as found ab road range of applications in various fields,i ncluding solar power generation, localized water heating, seawater desalination, and catalysis. [4a,b,5] It is well known that thermodynamically stable CO 2 molecules are more reactive at high temperatures.…”

Direct Coupling of Thermo‐ and Photocatalysis for Conversion of CO2–H2O into Fuels

“…directly combined Fe‐based or Cu/ZnO catalysts for thermocatalytic hydrogenation of CO 2 with photocatalytic water splitting . Recently, MacDonnell and co‐workers reported a one‐step, gas‐phase photothermocatalytic process for the synthesis of hydrocarbons from CO 2 –H 2 O in a flow photo reactor with a Co/TiO 2 catalyst under UV illumination . These preliminary and encouraging results show that the photothermocatalytic process is efficient in enhancing the conversion of CO 2 –H 2 O into fuels by using solar energy and is worthy of further extensive study.…”

“…Rapid consumption of the generated hydrogen by direct thermocatalytic hydrogenation of CO 2 to produce alkanes greatly accelerates the migration of photogenerated electrons and thus lowers the recombination rate of photogenerated electrons and holes, providing a synergistic effect between photocatalysis and thermocatalysis in the direct thermophotocatalytic reduction of CO 2 –H 2 O. Recently, MacDonnell and co‐workers reported a similar photothermochemical process that used Co/TiO 2 for both photocatalytic water splitting and Fischer—Tropsch synthesis . They suggested that the products of photocatalysis could be consumed in thermal reactions.…”

“…[8] Recently, MacDonnell and co-workersr eportedaone-step, gas-phase photothermocatalytic process for the synthesis of hydrocarbons from CO 2 -H 2 Oi naflow photo reactor with aC o/TiO 2 catalyst under UV illumination. [9] These preliminarya nd encouraging resultss how that the photothermocatalytic processi se fficient in enhancing the conversion of CO 2 -H 2 Oi nto fuels by using solar energy and is worthy of furtherextensive study.We note that thermocatalytic hydrogenation of CO 2 to alkanes, known as the Sabatier reaction, is am aturetechnology for energy storage, [10] which can be readily realized under mild conditions. For example, CO 2 conversion and CH 4 selectivity can both reach approximately 100 %, over Ni- [11] or Ru-based [12] catalysts at atmospheric pressure and low reaction temperature (ca.…”

“…Although the detailed mechanismso nh ow the reactive intermediates react with photocatalytically generated hydrogen atoms are still not clear,w eb elieve that the photocatalytically generated hydrogen could directly react with CO 2 ,o wing to the highlye fficient thermocatalytic hydrogenation of CO 2 over AuÀRu/TiO 2 .R apid consumptiono ft he generated hydrogen by direct thermocatalytic hydrogenationo fC O 2 to produce alkanes greatlya ccelerates the migration of photogenerated electrons and thus lowerst he recombination rate of photogenerated electrons and holes, providing as ynergistic effect between photocatalysis and thermocatalysis in the directthermophotocatalytic reductiono fC O 2 -H 2 O. Recently,M acDonnell and co-workersr eported as imilarp hotothermochemical process that used Co/TiO 2 for both photocatalytic water splitting and Fischer-Tropsch synthesis. [9] They suggested that the products of photocatalysis could be consumed in thermalreactions.…”