Intensification of solar photocatalysis with immobilised TiO2 by using micro-structured reaction spaces

The main disadvantage of immobilised catalytic systems is the loss of efficiency with respect to slurry systems. This is mostly due to the introduction of mass-transport limitations, and to the reduction of catalytic area. As a means of overcoming these issues, and building up on our previous studies, we investigated the merits of micro-structurisation of a tubular reactor by using glass micro-spheres as structurisation element and catalyst support. Two different reactor configurations were proposed and compared against dispersed slurry systems operating under similar conditions for the oxidation of a simulated wastewater containing phenol. The results show that catalyst immobilisation promoted an increase in the reaction rate constant, with respect to the slurry systems, of 29% when operating with an annular configuration, and 55% when employing a tubular configuration. The effect of a secondary feed of air or oxygen on the performance of immobilised systems was also investigated. The co-feeding of air promoted increases of 2.6 and 1.13 times in the reaction rate constant with respect to a single phase feed, for the annular and tubular configurations respectively; whereas the addition of pure oxygen enhanced the reaction rate to an even greater extent: 8.6 times for the annular and 4.3 times for the tubular configuration. These results reinforce our previous observations that micro-structured systems offer superior transport properties and increased contact between the catalyst and the reactants, thereby constituting an attractive alternative to suspended slurry photocatalysis.