A critical review of CO2 photoconversion: Catalysts and reactors

Photoreduction of CO2 on ZIF-8/TiO2 nanocomposites in a gaseous photoreactor under pressure swing

“…In addition, aqueous system is disadvantaged because protons compete for electrons more readily than CO2 to generate H2 gas. Common arrangements in using gaseous reactors include fixed beds, optical fibers and honeycomb monoliths, using water and hydrogen as electron and hydrogen sources [14], while these still suffer from low CO2 conversion efficiency. Herein we report a new approach achieving significant increase in photocatalytic CO2 reduction to produce CO by rationally designing composite catalysts to increase reactant loading, and by introducing a new gaseous photoreactor with tuned reactor pressure to reduce mass transfer resistance and product desorption.…”

A perspective on perovskite oxide semiconductor catalysts for gas phase photoreduction of carbon dioxide

“…The photocatalytic reduction of CO 2 into hydrocarbons using solar energy, often referred to as artificial photosynthesis, is believed to be a potential and promising approach to solve both issues. [1][2][3][4][5] Since the reduction of CO 2 by a TiO 2 photocatalyst was reported by Inoue and Fujishima's group, [6] the photocatalytic reduction of CO 2 has attracted the attention of many researchers. The key to this process is to develop an efficient photocatalyst that can properly position the valence and conduction bands for the oxidation and reduction half-reactions of water and CO 2 , respectively.…”

“…[3,4] Two major photocatalytic systems are being studied: a solid-liquid interface prepared by an aqueous dispersion of photocatalysts and a solid-gas interface. [5] Usually, both the liquid-phase (CH 3 OH, HCHO, HCOOH) and gas-phase (CH 4 ) products can be detected in a liquid photoreaction system, whereas only gas-phase (CH 4 , CO) products could be detected in a gas photoreaction system. [7] Although the solid-liquid reaction interface increases the accessible area for carriers and reactants, this approach has two drawbacks: the rather low solubility of CO 2 and the reduction of water competing with CO 2 reduction in the aqueous suspensions.…”

“…[5,21] That is, the bottom of the CB of the semiconductor photocatalysts should have a more negative potential than the reduction potential of CO 2 forming HCOOH, CO, HCHO, CH 3 OH and CH 4 ; likewise, the top of the VB should have a more positive potential than the oxidation potential of H 2 O. Equations (1)- (8) show the possible reactions involved in CO 2 photoreduction and their corresponding theoretical potentials (vs. the normal hydrogen electrode in an aqueous solution at pH 7 and 25°C, assuming unit activity). [4,5,21] …”

“…The key to this process is to develop an efficient photocatalyst that can properly position the valence and conduction bands for the oxidation and reduction half-reactions of water and CO 2 , respectively. [5,7] To date, various photocatalysts (such as TiO 2 , [8] CdS, [9] GaP, [10] Zn 2 GeO 4 , [11] etc.) have been used for photocatalytic CO 2 reduction.…”