Generally, reaction profiles typical for consecutive reactions were measured, which is in line with the reaction network shown in Figure . All experiments have in common that nitrobenzene is not converted completely, and conversion stagnates after a certain time. EtO-4H-Qui is the major intermediate. Beside this, Iso-EtO-4H-Qui is formed, especially when triflate is used as acid catalyst. Furthermore, small quantities of 4H-Qui were detected. After 5 h reaction time, a water content of about 0.1 wt% was measured by Karl-Fischer-titration, which is formed as a coupled product of several reaction steps. Hence, an ongoing degradation of the TiO2-PP composite due to the formation of hydroxyl radicals is likely, which might contribute to the stagnation of the photocatalytic step. Furthermore, a competitive adsorption of these substances at TiO2 might decrease the efficiency of the nitrobenzene reduction. The adsorption of colored products to the reactor components was also visually observable as the color of e.g. photocatalytic insert changed (see SI, Figure ) which leads to reduced photon flux at the photocatalyst and thereby lower reaction rates.