This book gives an overview on Photo-catalytic reactor design, 3D Modeling and simulation using some software's, its application in degradation of Rhodamine-B (Dye) using two catalysts (TiO2 & Nb2O5). The main objective of this work is to describe relevant aspects of degradation process recollecting material published in scientific literature as well as comparing it with practical experience. The influence of process variables such as Effect of amount of catalyst, Effect of Concentration of Rhodamine-B (Dye), Effect of pH on Percentage degradation was studied.