We investigate the influence of Taylor-Gortler vortices on the conversion in a photochemical reactor. This flow regime is realized in a fluid flowing along the gap between two concentric vertical cylinders, when the inner cylinder rotates with a velocity exceeding a certain critical value. A first-order photochemical reaction is activated in the system by a light source (uv lamp) placed within the inner cylinder. By numerical simulations, we prove that, in most cases, this flow regime leads to a higher conversion than the laminar flow regime. The influence of the amplitude of the vortices on the velocity profile, the outlet concentration profile and the overall conversion is determined at given reaction rates and attenuation coefficients. A significant improvement of the conversion has been found for fast reactions and strong attenuations.