The group of Prof. Strunk has recently received a new set-up for studying gas-phase photocatalytic CO2 reduction. The set-up will enable investigation of catalytic activity under high purity conditions. A thorough cleaning procedure before actual CO2 reduction experiment is shown to be essential. Otherwise, carbon-containing species originating from synthesis procedure or subsequent modification, might be located on the surface of sample contributing to the product formation. Therefore, the yields as well as product formation rates would be overestimated. The reactor design and choice of reaction conditions will allow performing both the photocatalytic cleaning and CO2 reduction in a consecutive manner in the same set-up. This approach will enable investigation of product formation originating exclusively from heterogeneous photocatalytic CO2 reduction.