Partial Oxidation of Bio-methane over Nickel Supported on MgO-ZrO 2  Solid Solutions.

Syngas can be produced from biomethane via Partial Oxidation of Methane (POM), being an attractive route since it is ecofriendly and sustainable. In this work, catalysts of Ni supported on MgO-ZrO 2 solid solutions, prepared by a one-step polymerization method, were characterized by HRTEM/EDX, XRD, XPS, H 2 -TPR, and in situ XRD. All catalysts, including Ni/ZrO 2 and Ni/MgO as reference, were tested for POM (CH 4 :O 2 molar ratio 2, 750 ºC, 1 atm). NiO/MgO/ZrO 2 contained two solid-solutions, MgO-ZrO 2 and NiO-MgO, as revealed by XRD and XPS. Ni (30 wt%) supported on MgO-ZrO 2 solid solution exhibited high methane conversion and hydrogen selectivity. However, depending on the MgO amount (0, 4, 20, 40, 100 molar percent) major differences in NiO reducibility, growth of Ni 0 crystallite size during H 2 reduction and POM, and in carbon deposition rates were observed. Interestingly, catalysts with lower MgO content achieved the highest CH 4 conversion (~ 95%), high selectivity to H 2 (1.7) and CO (0.8), and low carbon deposition rates (0.024 g carbon .g cat -1 h -1 ) with Ni4MgZr (4 mol% MgO) turning out to be the best catalyst. In situ XRD during POM indicated metallic Ni nanoparticles (average crystallite size of 31 nm), supported by MgO-ZrO 2 solid solution, with small amounts of NiO-MgO being present as well. The presence of MgO also influenced the morphology of the carbon deposits, leading to filaments instead of amorphous carbon. A combustion-reforming mechanism is suggested and using a MgO-ZrO 2 solid solution support strongly improves catalytic performance, which is attributed to effective O 2 , CO 2 and H 2 O activation at the Ni/MgO-ZrO 2 interface.