Alkali promotion of Ni/MgO catalysts

The effects of the alkali addition (e.g., Li, Na, K) on the physico-chemica l properties of a 19% Ni/MgO catalyst (alk(at)/Ni-at = 0.122 divided by 0.1 50) have been evaluated by TPR, TPD of H-2 (H-TPD) and CO (CO-TPD), TEM and temperature-programmed reaction measurements in toluene hydrogenation (TPT H). Lithium promotes the reduction negatively affecting the morphology and dispersion of the Ni/MgO catalyst, whereas both Na and K enhance the develo pment of the active surface area, Alkali exert a physical effect on the act ive phase which lowers both the CO chemisorption stoichiometry acid the sti cking coefficient of toluene hydrogenation, Alkalis also induce an electron ic effect on the active Ni phase resulting both in the inhibition of the Bo uduard reaction (2 CO(ads) --> C-(ads) + CO2) and in a drop (approximate to 20 kJ mol(-1)) of E-app in toluene hydrogenation. (C) 1999 Elsevier Scienc e B.V. All rights reserved.