Tracking the Mode of Carbon Deposition During Dry Reforming of Methane over Ni/γ‐Al2O3

Abstract

Abstract Dry reforming of methane was studied over Ni/Al 2 O 3 catalyst at 600 °C with varying CO 2 /CH 4 ratios (0.2, 0.5, 1, 2, 5). 13 CO 2 as well as 12 CO 2 were used along with 12 CH 4 and resulting carbon was characterized with 13 C solid state NMR spectroscopy in order to elucidate the role of CO 2 in carbon build up. 13 C NMR results revealed that carbon in the deposited coke not only came from CH 4 , but also from CO 2 . CO 2 saturation coverage is determined by adsorption calorimetry as 0.02 mole/site at 323 K, populated on Al 2 O 3 . The critical CO 2 /CH 4 ratio for the onset of carbon growth at atmospheric pressure was determined as 1.8 in good agreement with the literature. The effect of CO 2 /CH 4 ratio on the type of carbon formation was investigated by HCTEM. Long‐term reaction tests resulted in octopus carbon structure with several fibers growing from one nickel crystal. Above the critical CO 2 /CH 4 ratio, carbon growth was inhibited, only a small amount of amorphous carbon could form. At CO 2 /CH 4 ratios below the critical value, whisker formation was clearly observed. When the steady state operation of reforming reaction was changed to a transient operation by injecting pure CO 2 flow to the reactor, coke deposition could be inhibited at the expense of hydrogen stoichiometry.