Effect of NO2 and NO3-/HNO3 adsorption on NO photocatalytic conversion

Abstract

A study was undertaken of the adsorption and photocatalytic conversion of NO, NO2 and NO3-/HNO3 using two photocatalysts (P25 and HT-ET). The HT-ET is a catalyst synthesized in our laboratory comprised only of anatase phase and with a surface area three times larger than that of the P25. In powder form, the catalyst was introduced into and extended along the length of a tube with no type of compaction on the part of the solid (pressure drops are negligible under these conditions). This tubular photoreactor arrangement operates as a continuous reactor system enabling FTIR analysis of the surface of the catalysts during the conversion process. NO adsorption was negligible, though the FTIR studies revealed the formation of nitrites on the surface after 18 h of reaction. Overall NO conversion efficiency rates were above 68% with both catalysts in that reaction time. However, selectivity to NO2 was very high with both catalysts. It was also found with both catalysts that the number of NOx moles eliminated during NO photocatalytic conversion coincided with the number of adsorbed NO2 moles observed in the adsorption studies performed with this molecule, indicating that the NO2 molecule is not efficiently converted photocatalytically.