Abstract: A metal ion doped TiO₂ photocatalyst,which was prepared by the sol-gel method,was immobilized to stainless steel screen,glass spring and porous nickel mesh by coating.Transmission electron microscopy and X-ray diffraction were applied to characterize the structures of these photocatalysts.The photocatalytic degradation performance of three different modified nano-TiO₂ photocatalysts on formaldehyde in indoor air was investigated.The catalysis efficiency of the three photocatalytic reactors,the effects of environmental factors on catalysis efficiency,and the lifetime of the supported photocatalyst were studied.It was found that the gaseous photocatalysis over the supported photocatalyst is an efficient method for formaldehyde removal;the degraded rate of 1.5% La³⁺-doped TiO₂ is excellent;and its conversion rate of formaldehyde was 91.5% in 60 min,more than that of Fe³⁺-doped and Ag⁺-doped TiO₂.The photocatalytic degradation rate of porous nickel mesh as carrier is more than that of glass spring and stainless steel screen.Changing circular wind speed and ultraviolet wavelength will not influence the photocatalytic degradation rate of formaldehyde.The deactivation of the supported photocatalyst has been observed but it is easily recovered by cleanness.