Perovskite-type Composite Oxide Used As Catalyst For Degradation Of The Pollutant From Exhaust Gas And Organic Dyes And For Selective Hydrogenation Reaction

This work aims to investigate the role of silica support in the catalytic oxidation of rhodamine B?RhB?over LaFeO₃-Silica composites.Four LaFeO₃-Silica composites using mesoporous silica?SBA-15,SBA-16,MCF?and nano-sized silica powder?NSP?as supports are prepared.XRD,N₂ physisorption isotherms and TEM results show that pure LaFeO₃ phase,with particle size of 15-20 nm,is prepared and the texture of supports remains unchanged after the deposition of LaFeO₃.Catalytic results show that,besides the function to disperse LaFeO₃ on the surface,the support plays two important roles in the reaction: one is to absorb RhB from solution to the pores of support,and the other is to transport RhB from the pores to the active site,both influence the catalytic efficiency.Thus the non-porous NSP with negligible capacity for RhB adsorption is the worst,and the MCF with considerable capacity for RhB adsorption and the strongest ability to transport RhB to the active site is the best support of LaFeO₃ for RhB oxidation.SBA-15 and SBA-16,although show considerable or even higher capacity for RhB adsorption relative to MCF,their contribution to the reaction is less due to the low efficiency of transporting RhB to the active site.On these bases,the role of silica support in RhB oxidation conducted over LaFeO₃-Silica composite is proposed.Effect of nickel on the catalytic performances of LaCoO₃ for CO oxidation is investigated,by partial substitution of Co with Ni atoms in the framework or by deposition of NiO on the surface of LaCoO₃.Catalytic tests show that the activity is in order of 10%Ni/LaCoO₃ > LaCoO₃ > LaCo_0.8Ni0.2O₃,with the CO ignition temperature of 60,110 and 140 ? for 10%Ni/LaCoO₃,LaCoO₃ and LaCo_0.8Ni_0.2O₃,respectively.Based on the characterizations such as XPS,H₂-TPR,O₂-TPD and CV measurements,it is inferred that the improved activity of 10%Ni/LaCoO₃ is due to a synergistic effect induced by NiO and LaCoO₃,and the decreased activity of LaCo_0.8Ni_0.2O₃ is to the enrichment of La atoms on the surface,caused by the Ni incorporation.Long-time stability test indicates that 10%Ni/LaCoO₃ is stable in the reaction,with no appreciable loss of activity after running for 32 h.The highly active and stable activity of 10%Ni/LaCoO₃ suggests that impregnation of metal oxides on the surface of perovskite can be a feasible strategy for the preparation of industrial catalyst for CO oxidation.Selective hydrogenation is one class of important reactions in the industry for the synthesis of chemical intermediates and/or for the removal of unwanted heteroatom?e.g.,hydrodesulfurization?.The application of perovskite oxide as catalyst for hydrogenation is rarely reported?we show that Pd containing perovskite oxide,LaFe_0.95Pd_0.05O₃,also is an exciting material for selective hydrogenation reactions conducted in liquid phase with atmospheric H₂ pressure and reaction temperature of 50 ?,and can be reused for at least five cycles without appreciable loss in the activity,giving new options in the selection of catalyst for selective hydrogenation reactions.