Pd+Al2O 3 -supported Ni-Co bimetallic catalyst for H 2 production through dry reforming of methane: effect of carbon deposition over active sites

Dry reforming of methane (DRM) is gaining global attention due to its capacity to convert two greenhouse gases together. It proceeds through CH4 decomposition over active sites (into CH4−x) followed by CH4−x oxidation by CO2 (into syngas). Furthermore, CH4−x oligomerization into coke cannot be neglected. Herein, xNi(5−x)Co/Pd+Al2O3 (x = 5, 3.75, 2.5, 1.25, 0) catalysts are prepared, investigated for DRM, and characterized with X-ray diffraction, UV-Vis, transmission electron microscopy, temperature-programmed reduction/desorption techniques, and thermogravimetry. Fine-tuning among stable active sites, graphitic carbon deposits, and catalytic activity is noticed. The total reducibility and basicity are found to decrease upon increasing the Co proportion up to 2.5 wt% in the Ni-Co bimetallic Pd+Al2O3-supported catalyst. The active sites derived from strong metal–support interaction species (NiAl2Ox or dispersed CoOx) are found to be promising in higher levels of activity. However, activity is, again, limited by graphitic carbon which is increased with an increasing Co proportion in the Ni-Co bimetallic Pd+Al2O3-supported catalyst. The incorporation of 1.25 wt% Co along with 3.75 wt% Ni over Pd+Al2O3 results in the generation of fewer such active sites, extensive oxidizable carbon deposits, and inferior catalytic activity compared to 5Ni/Pd+Al2O3. The 2.5Ni2.5Co/Pd+Al2O3 catalyst has lower crystallinity, a relatively lower coke deposit (than the 3.75Ni1.25Co/Pd+Al2O3 catalyst), and a higher number of stable active sites. It attains a 54–51% H2 yield in 430 min TOS and 0.87 H2/CO (similar to 5Ni/Pd+Al2O3)