CO₂ reforming of CH₄ over Ni supported on SiO₂ modified by TiO₂ and ZrO₂: Effect of the support synthesis procedure

Two series of catalysts containing nickel supported on silica modified by TiO2 and ZrO2 were tested in the dry (CO2) reforming of methane (DRM). The two series of catalysts with 10 wt% Ni and with Ti(Zr)/Si = 1 were obtained by using two different support preparation procedures. One series had the support synthesized by sol-gel and the other series the support obtained by grafting a home-made SiO(2 )with zirconium and titanium alkoxides. According to XRD, TPR, NH3-TPD and XPS analyses, the two series of catalysts and supports had different structural, acidic, and surface chemistry properties. The promoter effect was evaluated with respect to the nickel supported on bare silica. DRM reaction was conducted in a fixed-bed reactor at atmospheric pressure in the low temperature range of 450-650 degrees C with a feed gas mixture containing CH4 and CO2 in a 1:1 ratio in He. As compared to the unpromoted nickel catalyst, doping silica with titanium oxide increased the methane conversion in the entire range of the tested temperature, and the catalytic stability at 650 degrees C during 24 h of time on stream. The effect was quite remarkable in the case of the nickel on the sol-gel prepared support exhibiting at 650 degrees C a stable 65 % CH4 conversion during 24 h. On the contrary, regardless the support preparation method, the presence of zirconium affected only slightly the methane conversion and the catalytic stability. After catalytic test, all the catalysts formed carbon but to a less extent the ones with the grafted supports. The structural characterizations before and after the reaction confirmed a better structural stability of the nickel particles supported on the sol-gel doped silica, explaining the improvement of the catalytic stability during the DRM reaction.