Catalytic Oxidation Of Benzene Over ?-Fe₂O₃ Supported Metal Oxides

In recent years,the air pollution has become more serious with the increasing emissions of the volatile organic pollutants?VOCs?,and many countries have set stricter standards for VOCs emissions.Therefore,it is urgent to eliminate the emission of VOCS in the air and develop appropriate treatment technologies that can meet more stringent standards.In this paper,the goethite was used as the carrier to synthesize three kind of?-Fe₂O₃loaded metallic oxide?CeO₂,Co₃O₄ and NiO?composite catalysts.The mineral phase,morphology and redox potential of the as-prepared composite catalyst were characterized by the ways of XRD,BET,SEM,XPS and H₂-TPR.And the effects of different factors?molar ratio of active component,calcined temperature,initial concentration of benzene and gas hourly space velocity?on the performance of catalytic oxidation of benzene over composite catalyst were investigated by experiments.Important conclusions were shown as follows:?1?CeO₂/?-Fe₂O₃ composite composite catalyst possessed a good catalytic oxidation activity,which was synthesized by using goethite as a precursor through impregnation-calcination method.When the mass ratio of Ce and Fe was 0.3,the calcinations temperature was 500°C,1000 mg/m³ benzene in air and reaction temperature at 450°C,the selectivity of CO₂ could reach 86.7%.The improved catalytic properties of the CeO₂/?-Fe₂O₃ catalysts were mainly related to the high concentration of surface oxygen species and the better redox properties which were attributed to the strong interaction between Ce and Fe.?2?Co₃O₄/?-Fe₂O₃ composites exhibited excellent catalyst activity for benzene oxidation and were synthesized by using goethite as precursor via impregnation-calcination method.The composite catalyst with the Co/Fe molar ratio of 0.6 and calcinated at the temperature of 500 ^oC displayed the superior catalytic activity,on which the lowest complete oxidation was 400 ^oC and the high selectivity to CO₂ could even reached 91.7%.Moreover,Co₃O₄/?-Fe₂O₃ composite also exhibited a great stability that had no significant decrease in the catalytic activity for 144 h.The characterization results showed that the best Co₃O₄/?-Fe₂O₃ composite catalyst has large specific surface area,high concentration of surface oxygen species and strong redox properties which were all beneficial to benzene oxidation.?3?NiO/?-Fe₂O₃ composites were synthesized by using goethite as precursor via impregnation-calcination method and were evaluated of their catalytic activity for benzene oxidation.The composite catalyst with the Ni/Fe molar ratio of 0.4 and calcinated at the temperature of 550 ^oC displayed the best catalytic activity.The surface adsorbed oxygen species played a crucial role in the catalytic oxidation according to the characterization results of composites.