Structure-property-performance relationship of transition metal doped WO3 mixed oxides for catalytic degradation of organic pollutants.

Transition metal doped WO3 mixed oxides (named as W-M-O, M = Nb, Fe, Cr, Cu, Ti or Sn, respectively) with high structure stability were synthesized by modified sol-gel method using citric acid as organic crosslinking agent, and were evaluated for catalytic elimination of low-concentration toluene, monochlorobenzene and 1,2-dichloroethance with high toxicity and relatively stable molecule structure, as the typical examples for the pollutants of various volatile organic compounds (VOCs). Results of the structure-property-performance relationship research showed that mesoporous structure and nanocrystalline/amorphous state were formed, and binary metal components were dispersed into each other, which contributed to promoting the metal/metal electron interaction and adjusting the physicochemical properties of mixed metal oxides. The sequence of apparent catalytic activity for toluene degradation was: W-Nb-O＞W-Fe-O＞W-Cr-O, W-Cu-O＞W-Ti-O＞W-Sn-O＞WO3, and the sequence for monochlorobenzene degradation was: W-Nb-O＞W-Fe-O＞W-Cr-O, W-Ti-O＞W-Cu-O＞W-Sn-O＞WO3. There existed cooperative catalytic effect: mesopore and surface acid sites of catalysts facilitated adsorption, activation and breakage of the C-X bond, and then redox sites of catalysts promoted deep oxidation of a series of reaction intermediates to transform into CO2 and H2O. Especially, the optimized W-Nb-O catalyst deserved more attention, since it represented remarkable catalytic activity, selectivity and durability for three typical VOCs degradation along with good resistance to water vapor and corrosion of HCl.