Molten-salt Preparation Of Pt/TiO₂ Catalysts And Their Catalytic Performance For VOCs Removal

Volatile organic compounds?VOCs?cause harmful effects on the atmospheric environment and human health.Therefore,effectively controlling and reducing the emission of VOCs has great significance.Catalytic oxidation technology has high purification efficiency,low energy consumption and no secondary pollution,and the core of this technology is the development of high-performance catalysts.Molten salt method is a method for preparing nanomaterials with simple operation and moderate reaction temperature.In this paper,we used in-situ molten salt method to prepare TiO₂catalysts with low loadings of noble metal Pt and Ce-,V-,or W-doped 0.05 wt%Pt/TiO₂ catalysts.The catalytic activities of toluene?or acetone?oxidation and other properties?stability,water resistance,sulfur resistance,etc.?were investigated.The main conclusions are as follows:different molten salt systems and calcination temperatures have an impact on the catalytic activity of the catalysts.When Ti?SO₄?₂was used as titanium precursor,the sample with the best catalytic activity of toluene oxidation was calcined at 300 ^oC in NaNO₃ and NaF molten salt systems.Using H₂PtCl₆ as a platinum precursor,different Pt loading catalysts were prepared by varying the amount of solution.The obtained TiO₂ was anatase structure of tetragonal phase.Its morphology was irregular and its size was about 200 nm.Pt particles were highly dispersed on the TiO₂ support.Over the x wt%Pt/TiO₂ catalysts,the reduction peaks ascribed to the reduction of lattice oxygen species of TiO₂ shifted toward the low temperature.That is to say,the reactivity of surface lattice oxygen species was enhanced via the loading of Pt onto TiO₂.Under the reaction conditions of acetone or toluene concentration=1000 ppm,acetone/oxygen or toluene/oxygen molar ratio=1/400,and space velocity?SV?=40000 mL/?g h?,the catalytic activity increased with a rise in the loading of Pt.The catalytic activity of 4.14 wt%Pt/TiO₂ was the best,T_50%and T_90%?the reaction temperature required for 50%and 90%conversion of acetone?were 172 ^oC and 195 ^oC,respectively.While T_50%and T_90%over 0.05 wt%Pt/TiO₂ were 236 ^oC and 274 ^oC,respectively.It should be noted that the addition of Ce?V,or W?into 0.05 wt%Pt/TiO₂ could improve the catalytic activity.The catalytic activities of the Ce-doped 0.05 wt%Pt/TiO₂ catalysts first increased with a rise in the amount of CeO₂ from 0 to 0.57 wt%,and then decreased with a further increase from0.57 to 1.61 wt%.Compared to 0.54 wt%V₂O₅-0.05 wt%Pt/TiO₂ and 0.55 wt%WO₃-0.05 wt%Pt/TiO₂,0.57 wt%CeO₂-0.05 wt%Pt/TiO₂ catalyst had high surface oxygen adsorbed species concentration.T_50%and T_90%over 0.57 wt%CeO₂-0.05 wt%Pt/TiO₂ were 212 ^oC and 245 ^oC,respectively.Water resistance,CO₂ resistance and sulfur resistance had also been improved.After addition of 20 vol%water vapor,10vol%CO₂,or 100 ppm SO₂ into the reactant,more than 85%,70%,and 60%of acetone were eliminated,respectively.The improvement in SO₂-tolerance was due to?i?Ce,V,or W-doping increased the amount of surface acid sites,and then inhibited the adsorption of acidic SO₂;?ii?the generation of Ce₂?SO₄?₃ or VOSO₄ partially consumed SO₂ and then inhibited the formation of Ti?SO₄?₂ or TiOSO₄;and?iii?WO₃modified catalyst inhibited SO₂ oxidation activity.The complete oxidation of acetone over 0.57 wt%CeO₂-0.05 wt%Pt/TiO₂ involved the following procedures:gaseous acetone molecules were first adsorbed on the catalyst surface,and then partially decomposed to generate formate species at low temperature.With an increase in the reaction temperature,the formate species were changed to the carbonate species.Finally,the intermediates were totally oxidized to CO₂ and H₂O.