The performance of two photocatalytic reactors for air decontamination- designated Photo-CREC-air reactors-is analyzed using computational fluid dynamics (CFD). Simulations of the original Photo-CREC-air revealed that the occurrence of a dead volume renders ∼68% of the available photocatalyst surface area inactive, resulting in poor air-photocatalyst contact. Moreover, the square cross section of the reactor geometry introduces regions of low ultraviolet (UV) irradiation. These issues are successfully addressed in a modified Photo-CREC-air design, which presents a uniform flow distribution over the photocatalyst surface and, therefore, good air-photocatalyst contact. In addition, the redesigned reactor geometry results in uniform UV irradiation over the photocatalyst. Simulations of reactor operation in continuous mode, with acetone as a model pollutant, revealed that negligible conversions are attained in the original Photo-CREC-air design, whereas conversions of 7.8% are predicted by simulations of the modified reactor. A simulation considering 10 modified Photo-CREC-air reactors in series showed that acetone conversions of 61% could be achieved in such a system.