Promotional Role of Pd Over Ni Catalyst Dispersed Over Sc-ZrO₂ for Methane Partial Oxidation: Crystallinity and Reducibility Effects

Abstract

Natural emissions of the highly potent greenhouse gas methane cannot be completely prevented, but in the presence of O₂, methane can be catalytically converted to hydrogen-rich syngas. This reaction is specified as partial oxidation of methane (POM). Herein, Ni dispersed over “scandia-stabilized-zirconia” (5Ni/DSZ) and the promotional effect of Pd (0.01 to 0.1 wt%) are investigated for POM and characterized with surface area and porosity measurements, X-ray diffraction, Raman spectroscopy, temperature-programmed studies, and thermogravimetry. During the POM, the initial population of active Ni sites decreases in non-promoted catalysts due to oxidation under oxygen, upon loading of 0.02 wt.% Pd over 5Ni/DSZ, the active site population is preserved against oxygen during the POM due to improved metal support interaction between Ni and long-range order crystallites of support (like cubic ZrO₂ and orthorhombic Sc₂Zr₅O₁₃). 5Ni0.02 Pd/DSZ catalyst acquired more than 80% catalytic activity (CH₄ conversion and H₂ yield) with 2.5 H₂/CO ratio at 600°C during 240 min on stream. The 5Ni0.02 Pd/DSZ catalyst also maintained more than 70% H₂ yield with H₂/CO ratio ~2 during 30 h time on stream. The thermostable 5Ni0.02 Pd/DSZ catalyst may be recommended for hydrogen-rich syngas production with high H₂-yield through POM.