Preparation And Performance Of Cu-based Composite Nanostructure Catalysts For CO Oxidation

Carbon monoxide?CO?is a kind of flammable,explosive and toxic gas pollutants.It is strongly inclined to combine with the hemoglobin in the human body,which can cause difficulty in breathing in some humans exposed at elevated levels.Therefore,it is necessary to eliminate the CO pollutants in the human environment.Currently,it is recognized that catalytic oxidation technology is one of the most effective ways to reduce the CO emission,due to its highly effective characteristic?below 300 ??and low use of energy?without additional fuel?compared to a thermal process.Many kinds of catalysts,including noble metal catalysts and copper-based catalysts,have been reported to be active for the catalytic oxidation of CO.Noble metal catalysts,which offer excellent catalytic properties at low temperatures,have been widely investigated for CO oxidation.However,due to the cost and limited availability of precious metals,considerable attention has been paid to transition metal oxide catalysts as substitute catalysts.For comparison,copper-based catalysts have been explored as a possible substitute for precious metals for its remarkable ability toward CO oxidation.CeO₂ has been extensively employed as the support of the catalysts because of its excellent oxygen storage/release capacity.CuO-CeO₂ catalysts have captured tremendous attentions recently because of their low costs,high catalytic activities,and wide applications in CO oxidation.In this paper,a series of supported copper-based catalysts were synthesized to explore the the catalytic performance in the CO oxidation.The influence of the copper loading amount on the redox and catalytic properties over CuO-CeO₂ sheets catalysts was studied and the active copper species were also identified.Meanwhile,CuO-CeO₂ mixed oxides were also loaded on other functional materials to investigate the relationship between structure and activity.The structure and properties of the catalysts were systematically characterized with various structural and textural detections,including XRD,TEM/HRTEM,Raman,BET,H₂-TPR,XAFS and in-situ DRIFTS.The main contents of the research are as follows:1.Copper-ceria catalysts with different loadings of copper?2,5 and 10 wt.%?supported on ceria nanosheets were prepared via a deposition-precipitation?DP?method,and then the catalytic activities were tested for the CO oxidation.Notably,the sample containing 5 wt.%of Cu exhibited the best catalytic performance as a result of the highest number of active CuO species on the catalyst surface.Further increase of copper content strongly affected the dispersion of copper and thus leads to the formation of less active bulk CuO phase,which was verified by XRD and H₂-TPR analysis.Moreover,on the basis of in-situ DRIIFTS results,the surface Cu⁺ species,which were mostly derived from the reduction of CuO_x cluster,are likely to play a crucial role in the CO oxidation.Consequently,the superior catalytic performance of the copper-ceria sheets is mainly attributed to the highly dispersed CuO_x cluster rather than Cu-[O_x]-Ce structure,while the bulk CuO phase is adverse to the catalytic activity of CO oxidation.2.A series of Cu-SiO₂@CeO₂ composite catalysts with different CeO₂ coatings and copper loadings were prepared by two-step method.The results of catalytic tests shows that the catalytic activity of the studied catalysts increased with the increase of CeO₂ coating.In comparison,the catalytic performance increased first and then decreased with the increase of copper loading.And the high temperature stability test of 5Cu-SiO₂@50CeO₂ catalysts with the optimal catalytic activity were performed over 24 h under a condition of 600 0C,1448,000 mL.gcat^-1·h^-1.An enhanced activity and good stability of 5Cu-SiO₂@50CeO₂ were demonstrated compared to 5Cu25Ce-SiO₂ catalysts,which were synthesized by one-step co-impregnation method.