No abstract

No abstract

Important modifications to the reactivity of metallic nickel highly dispersed on various oxide supports have been observed. These vary according to the acidity of the support and the presence of Ce3+ additives. The loss or attenuation of hydrogen chemisorption properties and catalytic activity in butane hydrogenolysis seems to be correlated to the acidity of the support, which leads to a total or partial coverage of the metallic surface during the reduction process by hydrogen, which remains strongly chemisorbed up to high temperatures.The presence of Ce3+ additives causes an increase in the catalytic activity in the CO/H, reaction and a significant shift of the selectivities in favour of the formation of heavier hydrocarbons from both the hydrogenation of CO and the hydrogenolysis of butane.These results are discussed in terms of strong metal-support interactions and concomitant modifications of the electronic environment of the metal.

The nature of hydroxyl groups formed during deammoniation of three NH4-X zeolites has been investigated in terms of their stability during dehydroxylation and their acidity towards bases like pyridine. It appears that besides the two principal bands at 3660 and 3560 cm-' always observed in spectra of decationated X and Y zeolites, a third band is present at 3625 cm-l, the intensity of which depends on the percentage of Na+ ions exchanged and, for a given sample, on the outgassing temperature. This band is attributed to hydroxy1 groups which show acidic properties, are very accessible to large molecules, and are therefore probably located inside the large cavities of the network, but which are very sensitive to dehyroxylation at relatively low outgassing temperatures.