Enhanced coke suppression by using phosphate-zirconia supported nickel catalysts under dry methane reforming conditions

Ni based phosphate zirconium catalysts were prepared by impregnation technique and used under CH₄ dry reforming conditions. Catalysts (x%Ni/8%PO₄–Zr, where x = 5, 10, 15 or 20) were characterized by nitrogen physical adsorption-desorption, X-ray diffraction, temperature programmed reduction, CO₂ and NH₃ temperature programmed desorption, thermal gravimetric analysis and transmission electron microscopy (TEM-EDAX). Catalysts displayed a typical mesoporous structure and different reducibility grade as a function of Ni loading, diagnostic of a different extent of metal-support interaction. Activity and stability strongly depend upon Ni loading while the best performance was observed for catalyst characterized by a Ni loading of 10 wt%. The CO₂-TPD profiles of spent catalysts indicated that such catalyst had more tendency to gasify coke formed over the catalyst surface. TGA analysis of used catalysts quantitatively showed that catalysts at higher Ni loading deactivated as result of huge graphitic carbon formation on catalyst surface. On the contrary, system 10%Ni8%PO₄/ZrO₂ turns out to be an excellent candidate to conduct the methane reforming reaction with CO₂ without coke formation at high CH₄ and CO₂ conversions. Phosphate play a fundamental role in promoting Ni–ZrO₂ interaction which reflects in the stabilization of catalytic system against metal sintering and coke formation.