Study On The Selective Oxidation Of CO With Tin-doped Copper-cerium-based Catalysts In Hydrogen-rich Gas

In the current situation of energy shortage in the world,proton exchange membrane fuel cell(PEMFC)has been developing rapidly in the past decade,which has been applied and popularized in the applications worldwide.In general,H2 is the ideal fuel for PEMFC as the only reaction product is H2O.Due to the distribution and storage of pure hydrogen,the H2-rich streams made from the reforming of hydrocarbon or bioethanol become the primary fuel source of PEMFC.Nevertheless,H2-rich streams generated by such way always contains small quantity of CO approximately 0.5-1.0vol %,which would poison the Pt anode and reduce the surface Pt sites for H2 adsorption/dissociation and oxidation,further decrease the efficiency of PEMFCs.Thus,it is of most importance to remove CO to avoid poisoning the anode of fuel cells.As well documented,selective oxidation of CO in the hydrogen rich gas(CO-PROX)is regarded as an efficient and convenient method to eliminate the CO trace less than 100 ppm.In the past decades,CuO-CeO2 catalysts have attracted much attention and have been widely studied for CO-PROX due to its unique oxygen storage ability for ceria,comparable reducibility,and its properties to firmly anchor Cu,which encourages the outstanding activity,selectivity for CO-PROX.Meanwhile,CuO-CeO2 generally sustains the defects of low catalytic performance at relatively lower temperature range and narrow temperature window(5-20 ℃)for the complete CO conversion of CO.Also,the addition of Sn could promote the catalytic activities of CuO-CeO2 catalyst for CO-PROX as it can reversibly undergo the Sn4+ ?Sn2+ reaction at relatively low temperature.Therefore,a series of Sn doped in CuO-CeO2 catalysts were prepared by a rapid,convenient,green and free-solvent grinding combustion method.The catalysts were testsd by catalytic activity evaluation of catalysts for CO-PROX in H2-rich streams and characterization by various characteriazation techniques such as N2-adsorption-desorption,XRD,XPS,Raman and DRIFTs,and the corresponding results are demonstrated as follows:1.Sn doped in Cu O-CeO2 catalysts can improve the catalycitc performance,and when the ratio of Sn/Ce was 5% the catalyst has the best CO conversion.On the one hand,the Sn-Cu-Ce catalyst activity was Substantial improvement at the low temperature range compared to that of Cu-CeO2 catalyst.On the other hand,the window of the completely CO conversion was broaden for Sn-Cu-Ce catalyst compared to that of Cu-CeO2 catalyst.The high performance is due to the Sn-Cu-Ce-[Ox] that formed in Sn-Cu-Ce catalyst,and the presence of more oxygen vacancy.2.The chloride ions within catalysts has an inhibition for Sn-Cu-Ce catalytsts.Consequently,even extremely small amounts of chloride provide the species necessary for a sintering mechanism of Cu via surface migration1.These may indicate that chloride ions are easier to combine with copper ions and cause bulk copper chloride during its manufacture through the surface migration and further cause inhibiting interaction between copper ions and ceria support.3.The calcination temperature have a certain influence for the catalytic catativity for Sn-Cu-Ce.Calcined at the low temperature such as 300 ℃ or 400 ℃ has an inhibition for catalyst to form the stable solid solution strutrue.However,the higher catalytic performance of the Sn-Cu-Ce calcined at the relatively higher calcination temperature500 ℃ and 600 ℃ is assigned to stable Sn-Cu-Ce interaction,more tin incorporated in the lattice of ceria,the more laatice distortion,resulting the more oxygen vacancies.4.The presence of H2O and CO2 in the H2-rich streams has a certain influence for catalysts.In the presence of CO2 or both H2O and CO2,Cu-Ce catalyst has a better catalytic performance compared to that of Sn-Cu-Ce.And in the presence of H2O,the CO conversion has a better catalytic performance compared to that of Cu-Ce.5.Sn-Cu-Ce shows a good stability in the H2-rich streams for 200 h.The CO conversion of catalyst slightly decrease when in the presence of the H2O and CO2 during 48 h.However,the catalyst still remains to the former stability until 350 h when remove the H2O and CO2 in the reaction streams.