Oscillatory Behaviour of Ni Supported on ZrO in the Catalytic Partial Oxidation of Methane as Determined by Activation Procedure.

Ni/ZrO catalysts, active and selective for the catalytic partial oxidation of methane to syngas (CH-CPO), were prepared by the dry impregnation of zirconium oxyhydroxide (Z) or monoclinic ZrO (Z), calcination at 1173 K and activation by different procedures: oxidation-reduction () or direct reduction (). The characterization included XRD, FESEM, in situ FTIR and Raman spectroscopies, TPR, and specific surface area measurements. Catalytic activity experiments were carried out in a flow apparatus with a mixture of CH:O = 2:1 in a short contact time. Compared to Z, Z favoured the formation of smaller NiO particles, implying a higher number of Ni sites strongly interacting with the support. In all the activated Ni/ZrO catalysts, the Ni-ZrO interaction was strong enough to limit Ni aggregation during the catalytic runs. The catalytic activity depended on the activation procedures; the treatment yielded very active and stable catalysts, whereas the treatment yielded catalysts with oscillating activity, ascribed to the formation of Ni carbide-like species. The results suggested that Ni dispersion was not the main factor affecting the activity, and that active sites for CH-CPO could be Ni species at the boundary of the metal particles in a specific configuration and nuclearity.