The Modification Of TiO₂Photocatalyst And Its Photocatalytic Performance Toward NO Abatement

With the global economic integration process accelerating, thetransportation industry has been developing rapidly, exhaust gas pollutionis being more and more serious. As one of the main pollutants produced bymotor vehicles，nitrogen oxides （NOx） harm both the environment and thebody seriously. Due to its strong mobility, NOxis easy to form surfacesource pollution such as city roads and local diffusion pollution, such asthe sealed tunnel and parking lot. What’s more, it will affect the indoor airquality along with the atmospheric movement. This kind of NOxhas thecharacteristics of low concentration, long duration and wide influence,traditional NOxpollution control technologies such as SCR, SNCR, NSRcannot fully meet the current demands. Photocatalytic technology with thecharacteristics of fast speed, high efficiency and complete reaction has abroad prospect in the environmental pollution control.In this work, preliminary study was taken on TiO₂photocatalyticoxidation removal of low concentration NO. On the basis of this, themodification of TiO₂-based photocatalyst was done through nitrogendoping and Pt noble metal deposition, and the methods of XRD, TEM,DRS were used to characterize the modified catalysts. Through thecomparison of photocatalytic activity of the modified catalysts at roomtemperature, the mechanism of TiO₂and its modified catalysts forphotocatalytic oxidation removal of low concentration NO waspreliminarily discussed. The main contents and results of this paper are asfollows: 1. Study the effect of heat treatment on the crystal structure of TiO₂.With the increase of heat treatment temperature, TiO₂changed fromamorphous titania to anatase TiO₂and then converted into rutile TiO₂. Bycomparing the photocatalytic oxidation activity of NO on different crystaltype TiO₂catalysts,500℃was found to be the best calcinationstemperature because the anatase TiO₂in this temperature had the highestphotocatalytic activity due to the good crystallinity and particle size. Theoxidation rate of NO and NOxremoval rates were15%and15.2%respectively;2. The absorption edge of nitrogen doped TiO₂was obviouslyred-shifted, larger than420nm. The experiments proved that the N-TiO₂catalyst not only improved the photocatalytic efficiency under UV light,but also showed a photocatalytic removal activity of low concentration NOunder visible light compared with TiO₂. During the samples with the N/Timolar ratio of5%,10%,20%,30%,50%and100%, the100%sample hadthe highest activity: the oxidation rate of NO and removal efficiency were46.4%and16.8%under UV light; the oxidation rate of NO and theremoval efficiency were19.8%and12.8%respectively under visible light.At the same time, the nitrogen doping lowered the transformationtemperature of anatase to rutile （decreased from600℃to500℃）;3. The Pt/TiO₂catalyst synthetized through wet impregnation hadmuch higher photocatalytic activity than that of pure anatase TiO₂towardNO abatement in spite of different load ratio, different initial concentrationand different velocity. Among the samples, the Pt load ratio of0.5%hadthe highest activity, the NO oxidation rate and removal efficiency were45%and38.1%respectively. Through the photocatalytic activitycomparison of three kinds of0.5%Pt/TiO₂synthetized in differentmethods, platinum oxides on the surface of TiO₂were found to play a keyrole in the reaction;4. The molecular sieve SBA-15with the characteristic of orderedpore structure and good adsorption properties is a suitable catalyst support. Supported catalyst Pt-TiO₂/SBA-15was made by mixing Pt/TiO₂andSBA-15together. The NO oxidation rate on this catalyst is more than70%,much higher than that of Pt-SBA-15/TiO₂, Pt/TiO₂and TiO₂; but on theremoval efficiency, it showed lower activity than that of Pt/TiO₂and TiO₂.