Preparation And Catalytic Performance For Dichloroethane Combustion Of Cr-based Catalysts

Chlorinated volatile organic compounds （CVOCs） are one of the major air pollutants.Among all the removal techniques, Catalytic combustion is one of the most promisingtechniques as it is an effective and energy saving process. Though this technology is widelyused in CVOCs treatment, it is faced with a lot of challenges. First, the temperature ofcatalytic combustion for CVOCs was relatively high. Second, the activity of catalysts wouldbe decreased when high water vapor concentration was present in industry waste gas. The keyto solve the problem is to develop novel catalyst with both high activity and durability towater vapor. The major objective of this work is to study the effect of surface chemicalproperties of the Cr-based catalysts on its activity at high humidity.In this work, five Cr-based catalysts with different doping of transitional metal wereprepared. The influence of transitional metal doping on the reaction activity was analyzed.The results showd that,doping of Fe, Mn and Ce didn’t change the reation activity of thecatalyst. Meanwhile, the doping of Cu largely decreased the reaction activity. The XRD testsshowed that the crystal size of Chromium of the tested catalysts was very small and alsodispersed very uniformly on the surface. The XPS results showed that the CrOx/Al₂O₃and Fedoped catalyst Cr₄FeO_x/Al₂O₃had more Cr³⁺content, resulting in higher catalytic activity fordichloroethane. As Cr³⁺was present with higher redox activity other than Cr6+, the catalyticactivity for copper doped catalyst Cr4CuOx/Al₂O₃was slightly lower.The effect of water vapor on the catalytic activity of Cr-based catalysts was investigated inthis work. The results showed that, under RH90%initial concentration of humidity, thehinder effects of water vapor on the catalytic activity of Cr4MnOx/Al₂O₃and Cr₄CeO_x/Al₂O₃catalysts were relatively smaller than that on CrOx/Al₂O₃and Cr₄FeO_x/Al₂O₃, with the activitydecrease amount of8%and20%, respectively. In other words, Cr4MnOx/Al₂O₃andCr₄CeO_x/Al₂O₃catalysts showed stronger durability to the negative effect of water vapor ascompared to the CrOx/Al₂O₃and Cr₄FeO_x/Al₂O₃catalysts. The DCE-TPD results showed that,with pre-adsorption under different different humidity, the amount of desorption area decreaseof dichloroethane over CrOx/Al₂O₃and Cr₄FeO_x/Al₂O₃catalysts were relatively larger than that of Cr4MnOx/Al₂O₃and Cr₄CeO_x/Al₂O₃, which indicated stronger interaction betweenH2O and the catalyst surfaces on the former two catalysts, and weaker interaction betweendichloroethane and catalyst surface.The effect of Ce doping amount on the catalytic activity and durability to the negativeeffect of water vapor for Cr₄MnCe_nO_x/Cord （n=0¹ï¼‰ catalysts were inverstigated. The resultsshowed that the doping of Ce into Cr4MnOx/Cord catalyst improved the reaction actibity anddurability to hinder effect of water vapor. Among them, Cr₄MnCe_0.6O_x/Cord had the bestactivity to convert dichloroethane in this work whether in dry or highly humid circumstance.Also, the reaction activity of this catalyst was minorly changed after stored for a month,which indicated the most promising application of Cr₄MnCe_0.6O_x/Al₂O₃/Cord catalyst fordichlroethane catalytic combustion in real chemical industry.