Study On Preparation And Structure-Performance Relationship Of Copper-Ceria Catalysts For Water-Gas Shift Reaction

Water gas shift (WGS) reaction catalysts need to be developed and improved tomeet the requirements of polymer electrolyte membrane fuel cell (PEMFC).CuO/CeO2catalysts have been given extensive attention, due to their excellentperformance and low cost as compared with precious metal catalyst. The activity andstability of CuO/CeO2catalysts are still required further betterment in order to fitpractical applications of fuel cell system. In the present dissertation, effects ofpreparation methods and synthesis parameters on the catalytic properties wereinvestigated. Catalyst characterization was done using XRD, N2physisorption,H2-TPR, TPD, Raman spectroscopy and SEM-EDS techniques. PEG is firstly chosenas surfactant for copper-ceria catalysts used in WGS reaction under optimumpreparation conditions, effects of the concentration and molecular weight on WGSactivity of the catalysts were systematically examined, and the mechanism of actionto improve dispersive property of catalyst precursors was illustrated. In addition,effect of operation condition on WGS activity of CuO/CeO2-Al2O3was alsoillustrated, which can offer reference data in practical application. The results are asfollows:(1) The effect of preparation methods on catalytic performance of CuO/CeO2catalysts was investigated. The results show that co-precipitation is the primarymethod; the catalyst prepared by co-precipitation method is facile to form smallerCuO and CeO2crystal, larger BET surface area, pore volume and pore radius andbetter reduction properties, thus enhancing its catalytic activity and stability.(2) The effect of the preparation parameters is deeply investigated on theCuO/CeO2catalyst performance under various conditions such as precipitationtemperature, calcination condition and the washing method of precipitate. Theoptimal preparation parameters are determined as follows: precipitationtemperature=80℃, precipitateunder water washing before drying, calcinated at450℃for4h.(3) The structure-activity relationship of CuO/CeO2catalysts synthesized via a PEG-assisted route was systematically studied, for the first time. It is considered thatPEG concentration is weight factor. Dispersive property of catalyst precursors isimproved by means of steric hindrance of PEG. Best dispersive property and theminimum of agglomeration degree of catalyst precursors will be obtained at theapproximate critical micelle concentration, which makes the optimal WGS activity.The optimal PEG and related concentration used for synthesis of catalyst areproposed as follows: PEG-6000(3.0g·L-1), PEG-10000(5.0g·L-1) or PEG-20000(10.0g·L-1).(4) The influence of cerium sources with different valence states on the WGScatalytic activity of CuO/CeO2catalysts was preliminarily investigated. It was foundthat the catalyst synthesized by trivalent cerium exhibited higher WGS activity thanthe one prepared with quadrivalent cerium, which can be attributed to a highersurface area, larger pore volume, superior reduction performance and strongercopper-ceria interaction presented by the former.(5) Influence of reaction parameters on WGS activity of CuO/CeO2-Al2O3catalyst was also investigated. Better operation conditions were acquired as follows:Space velocity:3000h-1, Steam/Carbon=2.4~4, reaction temperature range=250~350℃.