Preparation Of Porous Transition Metal Oxide-supported Noble Metal Or Alloy Catalysts And Their Catalytic Performance For Oxidation Of Toluene,Benzene Or Methanol

There are many kinds of volatile organic compounds?VOCs?,most of which are the precursors of photochemical smog and haze and are harmful to the atmospheric environment and human health.With appearance of the increasing environmental problems in China,the government has promulgated a series of strict regulations for VOCs emissions,and it is necessary to control the emissions of VOCs.Catalytic oxidation is currently considered as one of the most effective technologies in the elimination of VOCs.Catalytic oxidation of VOCs can be carried out at lower temperatures,leading to low energy consumption and no secondary pollution.Therefore,catalytic oxidation has attracted much attention.The key issue of such a technology is the availability of highly efficient catalysts.Hence,the development of novel catalysts with high performance and low cost is of practical significance,whereas the finding of new catalyst preparation strategies and elucidating of catalytic reaction mechanisms are of scientific importance.Transition-metal oxide catalysts are widely used for catalytic removal of various VOCs due to their good redox properties,but their low-temperature catalytic performance is poorer.Noble metals show good catalytic activities for VOCs oxidation at low temperatures,but the high cost limits their wide applications in industry.Au is a cheaper noble metal and exhibits better catalytic activity for some reactions.If transition-metal oxides were made to be macroporous or mesoporous structures and used to load noble metal nanoparticles?NPs?,surface areas and noble metal dispersion of such materials would be enhanced and more amounts of active sites would be generated.Among transition-metal oxides,iron,manganese,and cobalt oxides show better catalytic performance,rendering them to be good supports.In chapter 3,catalytic performance of three-dimensionally ordered macroporous?3DOM?Fe₂O₃-supported gold nanocatalysts for toluene oxidation was studied.In chapter 4,catalytic properties of three-dimensionally ordered mesoporous CoO-supported Pt nanocatalysts for benzene oxidation were investigated.Doping of base metals or cheaper noble metals to Pt or Pd can not only improve catalytic activity,stability,and poison-resistant behavior of a noble metal catalyst,but also enhance the utilization of noble metals and reduce the cost of noble metal catalysts,thus making the catalysts possess practical applications.Chapter 5was focused on the preparation,characterization,and catalytic performance of Pt-Co alloy nanoparticles supported on three-dimensionally ordered mesoporous manganese oxide for methanol oxidation.Catalytic behaviors of three-dimensionally ordered mesoporous Co₃O₄-supported AgAuPd alloy nanocatalysts for methanol oxidation were studied in chapter 6.In the meanwhile,physicochemical properties of the catalysts were characterized in detail,thermal stability and water-or carbon dioxide-resistant performance were examined,catalytic reaction mechanisms were probed,structure-performance relationships between physicochemical properties and catalytic activities for typical VOCs oxidation of the catalysts were clarified.By so doing,one can generate catalysts with lower cost,high performance,high stability,and good anti-poisoning ability.The main results obtained in the present dissertation are as follows:?1?3DOM Fe₂O₃ and 0.48-1.95 wt%Au/3DOM Fe₂O₃ catalysts were prepared using the polymethyl methacrylate?PMMA?-templating and polyvinyl alcohol?PVA?-protected reduction methods,respectively.It is found that the 3DOM Fe₂O₃and 0.48-1.95 wt%Au/3DOM Fe₂O₃ catalysts possessed a surface area of 45-46m²/g,in which the 3DOM Fe₂O₃ was rhombohedral in crystal structure.Au NPs with a size of 4-6 nm were highly dispersed on the surface of 3DOM Fe₂O₃.Catalytic activity for toluene oxidation increased with the loading of Au NPs,with the1.95Au/3DOM Fe₂O₃ catalyst showing the highest activity(the temperatures T_50%and T_90%required for achieving toluene conversions of 50 and 90%were 162 and 204 ^oC at a space velocity?SV?=20,000 mL/?g h?,respectively).It is concluded that the good catalytic performance of 1.95Au/3DOM Fe₂O₃ was associated with its highly dispersed Au NPs and better low-temperature reducibility as well as the strong interaction between Au NPs and 3DOM Fe₂O₃.?2?The three-dimensionally ordered mesoporous Co₃O₄?meso-Co₃O₄?support was synthesized via the three-dimensionally ordered mesoporous silica?KIT-6?-templating route,the three-dimensionally ordered mesoporous CoO?meso-CoO?support was obtained via reduction of meso-Co₃O₄ by glycerol,and the Pt NPs were highly dispersed on the surface of meso-Co₃O₄ and meso-CoO using the PVA-protected reduction method.The supported Pt catalysts performed much better than their supports for benzene oxidation,in which the 0.56 wt%Pt/meso-CoO catalyst exhibited the highest activity(T_50%=156 ^oC and T_90%=186 ^oC).It is concluded that meso-CoO possessed good oxygen activation ability,and the loading of Pt NPs was beneficial for benzene adsorption.Therefore,the excellent catalytic performance of0.56 wt%Pt/meso-CoO was related to its good ability of oxygen activation and benzene adsorption.?3?The three-dimensionally ordered mesoporous manganese oxide?meso-MnO_y?and its supported Pt_xCo catalysts were prepared using the KIT-6-templating and PVA-protected NaBH₄ reduction methods,respectively.The meso-MnO_y in the catalysts was composed of MnO₂?in majority?and Mn₂O₃?in minority?.The meso-MnO_y-supported metal catalysts displayed a three-dimensionally ordered mesoporous structure and a high surface area?94-110 m²/g?,and the Pt and Pt_xCo NPs with a particle size of 2.2-3.1 nm were well dispersed on the surface of meso-MnO_y.The supported Pt and Pt_xCo catalysts exhibited high performance for methanol combustion,in which 0.70Pt_2.42Co/meso-MnO_y performed the best(T_50%=50 ^oC and T_90%=86 ^oC at SV=80,000 mL/?g h?).Partial deactivation of the0.70Pt_2.42Co/meso-MnO_y catalyst due to H₂O or CO₂ addition was reversible.It is concluded that the excellent performance of 0.70Pt_2.42Co/meso-MnO_y was associated with the highly dispersed Pt_2.42Co alloy NPs,high O_ads species concentration,good low-temperature reducibility,and strong interaction between Pt_2.42Co alloy NPs and meso-MnO_y.?4?The cubically crystallized meso-Co₃O₄ and its supported Ag_xAu_yPd,Ag,Au,and Pd catalysts were prepared using the KIT-6-templating and PVA-protected NaBH₄ reduction methods,respectively.The as-prepared catalysts possessed a three-dimensionally ordered mesoporous structure and a high surface area of115-125 m²/g,and the noble metal NPs with an average size of 2.8-4.5 nm were highly dispersed on the meso-Co₃O₄ surface.The supported Ag_xAu_yPd catalysts outperformed the supported Ag,Au or Pd catalyst,with the0.68Ag_0.75Au_1.14Pd/meso-Co₃O₄ catalyst showing the highest activity(T_50%=100 ^oC and T_90%=112 ^oC at SV=80,000 mL/?g h?)for methanol combustion.Partial deactivation due to H₂O or CO₂ addition of the 0.68Ag_0.75Au_1.14Pd/meso-Co₃O₄catalyst was reversible.It is believed that the highly dispersed Ag_0.75Au_1.14Pd alloy NPs,high O_ads species concentration,good low-temperature reducibility,and strong interaction between Ag_0.75Au_1.14Pd alloy NPs and meso-Co₃O₄ were responsible for the good catalytic performance of 0.68Ag_0.75Au_1.14Pd/meso-Co₃O₄.