Potassium-Doped Ni-MgO-ZrO2 Catalysts for Dry Reforming of Methane to Synthesis Gas

Ni/K-MgO-ZrO2 catalysts for dry reforming of methane, with a range of Mg/Zr ratios and each containing about 10 wt% Ni, were prepared via Ni nitrate impregnation on MgO-ZrO2 supports synthesized by co-precipitation using K2CO3. It was found that a proportion of the potassium of the precipitant remained in the samples and improved the stability of the catalysts in the reaction. It was also shown that reduction of the catalysts at 1,023 K without calcination in air is necessary for stable and high activity; calcination in air at 1,073 K gives a deterioration of the catalytic properties, leading to rapid deactivation during the reaction. The order of the CH4 conversions of the reduced catalysts after 14 h on stream was as follows: Ni/K-Mg5Zr2 similar to Ni/K-Mg a parts per thousand yen Ni/K-Mg2Zr5 a parts per thousand << Ni/K-Zr. A catalyst with 0.95 wt% K on MgO-ZrO2 with a Mg:Zr mole ratio of 5:2 showed the best resistance to deactivation. Experiments in a microbalance system showed that there was only negligible coke deposition on the surface of this sample. This behaviour was attributed to the presence of Ni nanoparticles with a diameter of less than 10 nm located on a MgO/NiO solid solution shell doped by K ions; this in turn covers a core of tetragonal ZrO2 and/or a MgO/ZrO2 solid solution. This conclusion was supported by EDS/TEM, XPS, XRD and H-2 chemisorption measurements.