Catalytic Combustion For Dichloromethane Over Metal Oxide Catalysts

Chlorinated volatile organic compounds?CVOCs?was widely applied in many chemical production progresses,and become one of the main air pollutants.Among various available abatement techniques to control CVOCs pollution,catalytic oxidation is a promising method because of its low energy consumption,high efficiency,and preferred ability of converting CVOCs into harmless substance.The development of catalysts with low cost,high activity,high selectivity and good stability for CVOCs catalytic oxidation has been one of the most important topics in the research field of environmental catalysis.In this paper,some metal oxides material was selected as catalysts.The catalytic oxidation of Dichloromethane?DCM?,a reported alkyl chloride pollutant,has been investigated on these catalysts.Ni-V/M?M=Al₂O₃,ZSM-5,TiO₂,ZrO₂?catalyst were prepared by sol-gel method,and the effects of different acidic materials on the catalytic performance for DCM destruction were evaluated.The physical-chemical properties of the catalysts were characterized by XRD,BET,FTIR-Pyridine and H₂-TPR.It was found that the activity for catalytic combustion of DCM was related to the synergy between acidic role and oxidation.10%Ni-V/Al₂O₃-n?the?-Al₂O₃ prepared by precipitation method?and 10%Ni-V/TiO₂ catalysts that possess larger surface acidity and strong oxidizing ability exhibit preferable catalytic activity.Especially the former catalyst,whose T₉₀?temperature when 90%DCM conversion was obtained?at only 252?,but a certain amount of CH₃Cl is detected at the low temperature.And obvious decrease in the catalyst performance was seen during the 50 h stability test.10%Ni-V/TiO₂ catalyst exhibit a good activity,no CH₃Cl was detected in the DCM destruction as well as any obvious decrease was seen during the stability test,this may owning to the larger moderate strong acidic sites and strong oxidizing ability of the catalyst.Nine TiO₂ catalysts with different crystal phase were prepared by hydrothermal method,precipitation method and template method,and the catalytic performance for DCM destruction was evaluated.The screening tests showed that the TiO₂-HA,TiO₂-B and TiO₂-R were three best catalytic activities among three crystal phase.TiO₂-HA catalyst delivered a high catalytic activity with the T₉₀ at only 201?,which even be superior than those noble metal catalysts reported in other papers.The XRD and the morphology characterization exhibit that the TiO₂-HA catalyst is nanoparticle anatase structure with hollow spherical morphology.FTIR-pyridine was characterized the acidity on the catalysts surface,TiO₂-HA and TiO₂-B which possess more acid sites show better performance than TiO₂-R,and TiO₂-HA with strong B acid sites exhibits superior activity than TiO₂-B who has no B acid sites,which confirmed that the exposure of more B acid sites on the catalyst surface results in an enhancement of catalytic performances.The satisfactory performance of the TiO₂-HA can be contributed to the hollow texture with rich actives and the high amount of moderately strong acidic sites on the hollow TiO₂ surface.A series of Ni-V/TiO₂-HA catalysts were prepared by sol-gel method.Catalytic performances for DCM degradation over these catalysts were evalutated.The results show that 4%Ni-V/TiO₂ possess the highest catalytic activity with the T₉₀ at only 203?,and exhibit 95%,90% selectivity to CO_x and HCl,respectively.The characterization results indicate that rich acidic sites and good redox property are both conductive to improve the ability of adsorption and activation of the reactant molecules.The Ni-V metal oxide modification on the TiO₂-HA catalyst surface made the interaction between Ni-V and TiO₂-HA,which changed the surface structure and make it possess more acidity and moderately strong B sites.And the Ni-V metal oxide modification made the catalyst possess high redox property and high oxygen mobility,readily for the removal of Cl species produced during DCM decomposition in the form of HCl and CO oxidized to CO₂.And the catalyst also show good stability during the 100 h long-term test,with the DCM conversion could maintain above 95%,exhibiting high stability and resist chloride poisoning ability.