The Preparation Of Copper-cerium-based Catalysts And The Study Of CO Selective Oxidation In Hydrogen-rich Gas

Hydrogen as fuel of proton exchange membrane fuel cells(PEMFC),whether reforming production or partial oxidation reaction,the obtained H2-rich gas will contain 0.5-2%CO.However,the electrode of PEMFC can be poisoned because of the strong adsorption of trace amount of CO(100 ppm).Therefore,selective removal of CO in the hydrogen-rich gas is needed to be resolved for the development of PEMFC urgently.Copper-cerium catalysts,because of high catalytic performances and is cheaper than precious metal catalysts,as one of the most popular catalyst for CO preferential oxidation.The preparation process of traditional preparation methods of catalysts,such as sol-gel,coprecipitation,impregnation,etc.,is complex and time consuming.Therefore,the improvement of preparation method of catalyst,such as simplify producing process and shorten manufacturing time,has very important practical applications.A series of copper-cerium catalysts were prepared by a simple and rapid urea grinding combustion(UGC)method within 30 minutes.Various characterization techniques(XRD,H2-TPR,X-ray photoelectron spectroscopy(XPS)and catalytic activity test evaluation of catalysts for CO preferential oxidation in hydrogen-rich gas were studied,the main conclusions are as follows:1.Different calcination temperature and copper loading has great influence on the catalytic performances of CuCe catalysts.The catalyst,which was 7.5 wt.%copper content and calcined at 700 ?,not only has a wide full CO conversion temperature window(about 50 ?)and the 100%CO conversion has been got at 120 ?.2.The catalytic activities of CuCe catalysts prepared with different copper source for CO preferential oxidation in H2-rich gas displayed significantly differences.The catalyst,prepared with copper nitrate as copper source showed highest catalytic activity for CO preferential oxidation because of the existence of high dispersion copper species and strong interaction with ceria as well as more oxygen vacancies.The CuCe catalyst,prepared with copper sulfate as the copper source,showed a very poor catalytic activity,which is attributed to the existence of the incomplete decomposition of sulfate.3.Compare with that prepared by surfactant-template,sol-gel and urea combustion method,the CuCe catalyst prepared by UGC method displays the better catalytic activity for CO oxidation.The temperature of 100%CO conversion is lower at least 20 ?.4.The calcination temperature and adding amount of Fe all has certain influence on the catalytic activity of CuCe-Fe catalysts for CO preferential oxidation.The influence of calcination temperature on the catalytic activity is more significant than that of iron amount.The CuCe-Fe0.025 catalyst has a better catalytic activity than that of CuCe catalyst for low temperature CO oxidation.In addition,the addition of other transition metals(Zn,Mn and Co)cannot be improved on the catalytic performance of CuO-CeO2 catalyst.Even the addition of Zn significantly inhibited the catalytic activity of the CuO-CeO2 catalyst.5.The addition of different rare earth metals has different impacts on the performance of CuCe catalyst.However,although the low temperature oxidation activities of CuCe-R catalysts are worse than that of CuCe catalyst for CO preferential oxidation in hydrogen-rich gas,the selectivity of CuCe-R is better.6.The presence of water and carbon dioxide in the H2-rich reaction gas can obviously inhibit the catalytic activity of CuCe,CuCe-Fe and CuCe-Sm catalysts.In the presence of water and carbon dioxide in the reaction gas,both the CO conversion and the selectivity of the CuCe-Fe catalyst are higher than those of the CuCe catalyst.The addition of Fe has a significant enhancement effect on the tolerance to water and carbon dioxide.7.In the presence of water and carbon dioxide in the hydrogen-rich gas,the catalytic activity of CuCe catalyst shows a good stability in 55 h.Moreover,after reaction 200 h,CO conversion was reduced about 7.7%.The stability of catalytic activity of CuCe-Fe catalyst is better than that of CuCe catalyst.The former maintain basic stability after 68 h and the CO conversion was decreased about 5%after reaction 400 h.In all,the addition of Fe not only improves the tolerance to water and carbon dioxide and also enhances the stability of the catalyst.In time-on-stream test,the experiment time of CuCe-Fe(400 h)takes twice as long than that of CuCe when CO conversions drop to the similar extent.The stability test of CuCe-Sm only in 34 h remained relatively stable,but CO conversion was decreased about 6.5%after reaction 200 h.The addition of Sm into CuCe catalyst could not improve the stability of the catalyst,but enhances the CO2 selectivity of the catalyst.