The active surface of silica-supported copper in the hydrogenative transformations of cyclohexene: The role and state of carbonaceous deposits Original Research Article

The evolution of the catalytic surface and its main characteristics are investigated in the hydrogenative transformations of cyclohexene over a silica-supported copper catalyst for the first time in a static circulation system and in a flow reactor. The main tools were: (i) restart reactions when aging was studied, (ii) competitive hydrogenation reaction 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 hydrogenative transformations of cyclohexene the presence of hydrogen-rich carbonaceous residues are necessary. Without their formation there is no reaction. As their quantity grows the catalyst becomes more active. They are product precursors and unreacted cyclohexane covering the surface to such an extent that the remaining metal ensembles are not enough for cyclopropane hydrogenation to occur. In restart reactions the catalyst undergoes coking but only to a small extent at 443 K.