Photocatalyst: To Be Dispersed or To Be Immobilized? The Crucial Role of Electron Transport in Photocatalytic Fixed Bed Reaction

Abstract

Photocatalytic fixed bed reactors allow a straightforward separation from the process stream and simplify the installation and operation in practical application. However, it is widely believed that the restriction on mass transport and volume activation severely slows the reaction. Here, we demonstrate that photocatalytic fixed bed reactors can deliver a superior reaction rate to the slurry suspension by rationally modulating the electronic process and the most concerning issue of mass transport occurring on a decisecond time scale does not retard the reaction. Although the long-distance transport of photogenerated electrons in porous semiconductor films toward catalytic sites encounters boundary scattering, this electronic process can be far faster than semiconductor−cocatalyst interfacial electron transfer occurring on the decisecond−second time scale. Besides, the fixed bed reaction can be freely amplified without losing photon utilization. Under irradiation provided by a 320 W Hg lamp, we realize a reaction rate of 0.262 mol/h with 65.2% quantum yield for anaerobic dehydrogenation of ethanol.

Asymmetric Potential Barrier Lowering Promotes Photocatalytic Nonoxidative Dehydrogenation of Anhydrous Methanol

“…Therefore, the rate and photon utilization of photocatalytic reaction that includes the efficient hole extraction (methanol dehydrogenation) and HE half-reactions can be enhanced (Figure 4b). Since adjusting pH values can evidently promote the photocatalytic reaction, to make a step further, we here investigate the photocatalytic HE coupled with nonoxidative dehydrogenation of anhydrous methanol in a circular flow system [14]. This reaction configuration formed by immobilizing photocatalyst onto the smooth wall of light incidence side can be easily amplified by connecting reaction units for practical application (Figure 5a) [14].…”

“…Photocatalytic HE mainly contains interfacial transfer of photogenerated electrons from semiconductor to cocatalyst and electrochemical transfer of these chargers to solution that are connected in series [12][13][14]. To realize efficient photocatalysis, it is desired to facilitate semiconductor-cocatalyst (SC) interfacial electron transfer that suffers from high energy dissipation and occurs on decisecond-second timescale [9,[14][15][16]. Besides, electron leakage that inherently influences photon utilization should be minimized [9,14].…”

“…To realize efficient photocatalysis, it is desired to facilitate semiconductor-cocatalyst (SC) interfacial electron transfer that suffers from high energy dissipation and occurs on decisecond-second timescale [9,[14][15][16]. Besides, electron leakage that inherently influences photon utilization should be minimized [9,14]. Regarding this end, many approaches such as nanostructuring confinement [13,17], contact bridging [16], and surface electronic modification [9,15,18] that are related to band bending modulation of semiconductor have been proposed.…”

Self-Promoted H2 Formation for Photoinduced Removal of CO to ≤1 ppm in H2 Stream

“…Unlike the conventional slurry suspension, we here immobilize the semiconductor (TiO2) to form photocatalytic fixed bed reactor to remove CO in the H2 stream (Figure S3). 23 Prior to performing photoinduced radical reaction, cocatalyst was deposited onto TiO2 film by photoinduced reduction of Cu 2+ ions to form TiO2|Cu immobilized photocatalyst. 23 The required moisture (H2O) for the photocatalytic removal of CO can be supplied by vaporizing water in the reaction chamber at the operation temperature (~35 º C).…”

“…23 Prior to performing photoinduced radical reaction, cocatalyst was deposited onto TiO2 film by photoinduced reduction of Cu 2+ ions to form TiO2|Cu immobilized photocatalyst. 23 The required moisture (H2O) for the photocatalytic removal of CO can be supplied by vaporizing water in the reaction chamber at the operation temperature (~35 º C).…”