Ni–Sr/TiZr for H2 from methane via POM: Sr loading & optimization

Abstract

Achieving remarkable H₂ yield with significantly high H₂/CO over Ni-based catalysts through partial oxidation of methane (POM) is a realistic approach to depleting the concentration of CH₄ and using H₂ and CO as synthetic feedstock. This study examined Ni catalysts on titania–zirconia for methane conversion via POM at 600 °C and atmospheric pressure. The addition of strontium to the catalyst was explored to improve its performance. Catalysts were characterized by X-ray diffraction, Raman-infrared-UV-vis spectroscopy, and Temperature-programmed reduction-desorption techniques (TPR, TPD). 2.5 wt% Sr addition induced the formation of the highest concentration of extreme basic sites. Interestingly, over the unpromoted catalyst, active sites are majorly generated by hardly reducible NiO species whereas upon 2.5 wt% promoted Sr promotional addition, most of active sites are derived by easily reducible NiO species. 45% CH₄ conversion and 47% H₂ yield with H₂/CO = 3.5 were achieved over 2.5 wt% Sr promoted 5Ni/30TiO₂ + ZrO₂ catalyst. These results provide insight into the role of basic sites in enhancing activity through switching indirect pathways over direct pathways for POM. Further process optimization was carried out in the range of 10 000–22 000 SV, 0.35–0.75 O₂/CH_4, and 600–800 °C reaction temperature over 5Ni2.5Sr/30TiO₂ + ZrO₂ by using central composite design under response surface methodology. The optimum activity as high as ∼88% CH₄ conversion, 86–87% yield of H₂, and 2.92H₂/CO were predicted and experimentally validated at 800 °C reaction temperature, 0.35O₂/CH₄ ratio, and 10 000 space velocity.