Ethanol steam reforming over Ni/MxOyNi/MxOy–Al2O3Al2O3 (M=CeM=Ce, La, Zr and Mg) catalysts: Influence of support on the hydrogen production

Hydrogen production from ethanol reforming over alumina-supported nickel catalysts modified with Ce, Mg, Zr and La was studied. Characterization of catalysts by XRD, TPR, XRD and TPD of NH3 revealed changes in the acidity, nickel dispersion and nickel-support interaction with the type of the modifier added to Al2O3. The acidity of catalysts containing Mg, Ce, La and Zr additives decreased with respect to that supported on bare Al2O3. The trend of metal dispersion as derived from XRD and H2 chemisorption results followed the order: La2O3–Al2O3>MgOAl2O3>MgO–Al2O3>CeO2Al2O3>CeO2–Al2O3>Al2O3>ZrO2Al2O3>Al2O3>ZrO2–Al2O3. TPR and XPS analyses indicate the development of strong interactions between nickel species and ZrO2, La2O3 and CeO2 oxides added to supports. The activity measurements coupled with the physicochemical characterization data indicated the different catalysts functionality that influences on their reforming activity. Thus, the higher reforming activity for Mg-modified catalyst respect to bare Al2O3 was explained in terms of the lower acidity and better dispersion achieved in the former, while for Ce- and Zr-promoted catalysts the improvement in intrinsic activity was ascribed to the enhancement of water adsorption/dissociation on the Ni–Ce and Ni–Zr interfaces developed on these catalysts. On the other hand, the lower intrinsic activity of La-added catalyst was explained in terms of the dilution effect caused by the presence of lanthanum on Ni surfaces. Characterization of catalysts after reaction showed differences on the amount and type of coke deposited on catalysts surfaces. La and Ce additives were found to prevent the formation of carbon filaments on nickel surfaces, which is responsible of the changes in product selectivities with reaction time observed on Ni/Al2O3, Ni/ZrO2–Al2O3 and Ni/MgO–Al2O3.