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

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.