Copper-Based Water Gas Shift Catalysts for Hydrogen Rich Syngas Production from Biomass Steam Gasification

Copper-based catalysts deposited on foams were developed to perform the water gas shift reaction at low temperature (150-300 degrees C) at the outlet of a biomass gasifier with limited pressure drop. Different synthesis methods were used such as wet impregnation and urea-nitrates combustion methods for the preparation of copper/ceria/foam catalysts containing 4.5-7.0 wt % of copper as the active phase and 7.0-9.0 wt % of ceria as the wash coat. The latter were characterized in order to evaluate present phases, their crystallite size, and ceria lattice parameter by X-ray diffraction (XRD) analysis, specific surface area by N-2 adsorption technique (BET method), and reducibility by temperature programed reduction (TPR). The activity of the catalysts was studied in the water gas shift reaction at low temperature (150-300 degrees C) and at a high gas hourly space velocity (between 3600 and 9500 h(-1)) as a function of preparation parameters (synthesis method and catalyst composition) and operating parameters (temperature and prereduction step). It appeared that the wet impregnation method is the optimized studied method because it led to similar activity to those obtained with a more complex synthesis method (urea-nitrate combustion). The optimized copper and ceria contents are 5.5 and 9.0 wt %, respectively, 30 ppi foam. The study of the temperature effect highlighted the optimum at 300 degrees C without the sintering of metallic copper nor ceria crystallites. Catalytic tests showed in situ activation of the catalyst at 300 degrees C. So, the prereduction step was unnecessary at this temperature. Finally, the more promising catalyst (5.5 wt % of Cu and 9.0 wt % of CeO2) was tested at the outlet of a high temperature water gas shift reactor, and the conditions of the two coupled reactors (high and low reaction temperatures and steam to carbon (S/C) molar ratio) were optimized permitting the reaching of thermodynamic values for methane conversion with 500 degrees C in the high temperature reactor and 350 degrees C and a S/C of 3 in the low temperature reactor.