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One of the promising solutions to both global climate warming and increasing energy demands is artificial photosynthesis, which can be implemented via the photoreduction of CO2 to produce fuel. A monolith photoreactor was used to increase the amount of catalyst loading due to its multiple channels. The photocatalyst was dip coated using NiO/InTaO4 sol and then calcined at 1100 °C. A uniform NiO/InTaO4 layer was obtained on the top of pre-coated SiO2 sublayer on the internal channels of the monolith. The polymethylmethacrylate (PMMA) optical fibers, after being carved on their surface, could transmit and scatter light to effectively illuminate the catalyst inside the channels of the monolith. Vapor-phase CO2 with H2O was photocatalytically reduced to hydrocarbons by UV or visible-light in a steady-state flow mode. The maximum methanol conversion rate achieved was 0.16 µmol g−1 h−1 with visible-light of 290 klx at 25 °C. The highest rate of acetaldehyde was 0.3 µmol g−1 h−1 which was obtained with a loading of 2.6% NiO by simulated sunlight AM1.5G at 70 °C. More importantly, the quantum efficiency was significantly improved indicating that photon energy was effectively utilized in the monolith reactor, compared with previous optical-fiber reactor.
Liou et al. (Sat,) studied this question.