Stability of Ni/SiO2-ZrO2 catalysts towards steaming and coking in the dry reforming of methane with carbon dioxide

Ni/SiO2-ZrO2 catalysts with Ni loadings of 1 to 13 wt-% were prepared, characterized by elemental analysis, X-ray diffraction, N-2 sorption, temperature programmed oxidation, temperature programmed reduction, and tested for their activity and stability in the dry reforming of methane with carbon dioxide at 850 degrees C, gas hourly space velocity of 6000 and 1800 h(-1) and atmospheric pressure. The SiO2-ZrO2 support as obtained through a simple and efficient sol-gel synthesis is highly porous (A(BET) = 90 m(2).g(-1), d(P) = 4.4 nm) with a homogeneously distributed Si-content of 3 wt-%. No loss of Si or formation of monoclinic ZrO2, even after steaming at 850 degrees C for 160 h, was detectable. The catalyst with 5 wt-% Ni loading in its fully reduced state is stable over 15 h on-stream in the dry reforming reaction. If the catalyst was not fully reduced, a reduction during the early stages of dry reforming is accompanied by the deposition of up to 44 mg.g(-1) carbon as shown by experiments in a magnetic suspension balance. Rapid coking occurs for increased residence times and times-on-stream starting at 50 h. The Ni loading of 5 wt-% on SiO2-ZrO2 was shown to provide an optimal balance between activity and coking tendency.