Effect of calcium addition on catalytic ethanol steam reforming of Ni/Al2O3: II. Acidity/basicity, water adsorption and catalytic activity

The effect of Ca modification to Ni/Al2O3 catalysts in ethanol steam reforming was studied by using a 5-channel micro-reactor, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and temperature-programmed desorption (TPD) of probe molecules H2O, NH3, CO2 and ethanol. Both Al2O3 and Ca-modified Al2O3 supports are not catalytically active for the ethanol reforming. But in the presence of the active metal Ni, the catalytic performance of Ni/Ca-Al2O3 is far more superior to Ni/Al2O3 for low temperature H2 production. The introduction of Ca greatly reduces the acidity of Al2O3, depressing ethanol dehydration and ethylene formation. It brings about positive attributes such as increasing water adsorption, providing Ni catalyst the proximity and abundance of adsorbed OH groups. The involvement of OH groups in the reactions in turn enhances the ethanol adsorption, stabilizes its adsorbate intermediates for further conversions to H2, CH4 and CO2 at relatively low temperatures. This paper therefore serves to illustrate the importance of acidity and steam adsorption capacity in the design of the catalysts for ethanol steam reforming.

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► Ni/Ca-Al2O3 suitable for low temperature ethanol steam reforming (ESR).
► Ca diminishes the acidic OH groups on Al2O3, depressing ethylene formation.
► Ca increases water adsorption, providing abundance of adsorbed OH groups.
► The OH groups enhance ethanol adsorption, promoting conversions to H2, CH4 and CO2.