HIGH LOADING NI MGO CATALYSTS - SURFACE CHARACTERIZATION BY IR-SPECTRA OF ADSORBED CO

The influence of calcination and reduction conditions on the surface p roperties of high loading Ni/MgO catalysts (18 wt% Ni) was studied. IR spectra of adsorbed CO show that the increase of the calcination temp erature decreases the reducibilty of the Ni phase as diffusion of Ni2 into the bulk of MgO particles is enhanced. CO adsorption (I 0 Torr) produces various carbonyls (mono- and polycarbonyls, linear and bridge d), the distribution of the different types depending on pretreatment conditions. Disruption of metal Ni particles by CO attack on edge and comer sites produces tetra-carbonyl species subsequently stabilized on Mg2+O2- sites. Disproportionation of CO is also observed, monitored b y the appearance of bands due to carbonate-like species as a consequen ce of the adsorption Of CO2 on the basic matrix. The activity for the Boudouard reaction decreases upon pretreatments at the highest tempera ture as the smoothing of metal particles reduces the concentration of Ni sites in the lowest coordination, which promote CO dissociation.