Catalytic partial oxidation and CO2-reforming on Rh- and Ni-based catalysts obtained from hydrotalcite-type precursors

The catalytic activity of two catalysts (Ni10Mg61Al29 and Rh1Mg71Al28, as atomic ratio percent) obtained by calcination and reduction of hydrotalcite-type (HT) precursors were investigated in catalytic partial oxidation (CPO) and CO2-reforming of methane at low contact times. Characterization of the samples after different thermal treatments showed that the preparation via HT precursors represents a simple and reproducible way to obtain catalysts, characterized by highly dispersed metallic crystallites stabilized inside an inert matrix at high surface area. The CPO tests were carried out at various feed compositions, reaction temperatures and contact times, with, however relevant differences between the oven temperature and those measured. The best catalytic performances were found at high temperature, approaching thermodynamic equilibrium. When the amount of reaction heat was decreased by using a diluted mixture, the specific effect of contact time was observed and attributed to the role of steam- and CO2-refonning consecutive reactions. CO2-reforming tests at low contact times confirmed the high activity of the catalysts obtained from HT precursors, with a higher activity of nickel towards CO2 and of rhodium towards methane, the latter associated with a higher selectivity in H-2 due to a lower tendency to form water. These results help to explain the CPO data, that suggest a higher activity of rhodium in selective CPO of methane. Finally, it is worth noting that both catalysts did not show any structural and/or physical modifications after the catalytic tests, with, furthermore, no deactivation phenomena due to coke formation in the CO2-reforming reaction. (C) 1998 Elsevier Science B.V. All rights reserved.