THE ACTIVE SURFACE OF SILICA-SUPPORTED COPPER IN THE HYDROGENATIVE TRANSFORMATIONS OF CYCLOHEXENE - THE ROLE AND STATE OF CARBONACEOUS DEPOSITS

The evolution of the catalytic surface and its main characteristics ar e investigated in the hydrogenative transformations of cyclohexene ove r a silica-supported copper catalyst for the first time in a static ci rculation system and in a flow reactor. The main tools were: (i) resta rt reactions when aging was studied, (ii) competitive hydrogenation re action with the cyclopropane molecule known to require very different surface features to be present and (iii) the removal of weakly as well as strongly held carbonaceous species. It was found that in hydrogena tive transformations of cyclohexene the presence of hydrogen-rich carb onaceous residues are necessary. Without their formation there is no r eaction. As their quantity grows the catalyst becomes more active. The y are product precursors and unreacted cyclohexane covering the surfac e to such an extent that the remaining metal ensembles are not enough for cyclopropane hydrogenation to occur. In restart reactions the cata lyst undergoes coking but only to a small extent at 443 K. (C) 1998 El sevier Science B.V.