FT-IR characterization of supported Ni-catalysts: Influence of different supports on the metal phase properties

Supported Ni catalysts (2 wt.% Ni) were investigated by FT-IR and UV–vis-NIR spectroscopy, using CO2, CH3CN and CO as probe molecules. The supports studied range from acidic (SiO2), via amphoteric (Al2O3, Mg(Al)O) to basic oxides (MgO, CaO). CO2 adsorption experiments allowed to obtain the following qualitative scale for the basic strength of O2− sites and Mn+O2− pairs: Ni/CaO > Ni/MgO ≥ Ni/Mg(Al)O ≫ Ni/Al2O3. On Ni/SiO2 these sites are absent. CH3CN adsorption allowed to reveal acidic and strong basic Lewis sites with the following results: Ni/SiO2 does not contain basic or acidic Lewis sites. Ni/Al2O3 contains acidic Lewis sites but no strong basic Lewis sites. The ratio between the strong basic and the acidic Lewis sites decreases in the order: Ni/MgO > Ni/CaO > Ni/Mg(Al)O. The strength of Lewis acid sites decreases in the order Ni/Al2O3 ≫ Ni/Mg(Al)O > Ni/MgO > Ni/CaO. Interaction of CO at room temperature results into formation of Ni(CO)4 and/or Ni(CO)y