Dry reforming of methane over Ni/Al2O3 catalysts: Support morphological effect on the coke resistance

Flower-like (Al2O3-F), wire-like (Al2O3-W) and sphere-like (Al2O3-S) alumina supported nickel catalysts (designated as Ni/Al2O3-F, Ni/Al2O3-W and Ni/Al2O3-S) were prepared for catalytic dry reforming of methane (DRM). The resultant catalysts exhibited variable catalytic activities and coke resistance performances in the reaction, which was closely dependent on their various physicochemical properties from the morphological effect of Al2O3 supports. To be precise, Ni/Al2O3-W presented adequately high catalytic activity and promising anticoke behavior, which was attributed to its strong metal-support interaction, the surface dispersion of smallsized Ni nanoparticles and noticeable activation ability towards CO2. Ni/Al2O3-F possessed high anti-coke performance as well in terms of its significant CO2 activation ability. However, the encapsulation effect of Al2O3-F nanostructure resulted in insufficient abundance of metallic Ni active sites on the surface of Ni/Al2O3-F, thus giving rise to poor initial catalytic activity. The weak CO2 activation ability and the large particle size of metallic Ni on Ni/Al2O3-S induced the considerable formation of filamentous carbon after long-term DRM test. With regard to in situ DRIFTs analysis, the existence of OH* as the coke precursor scavenger and its reaction with the CHx* intermediate species from CH4 cracking were demonstrated to play crucial roles in dominating the overall anti-coke performances of Ni/Al2O3 catalysts. This work provides new insights into the development of high coke-resistance Ni-based catalysts from the perspective of support morphology modulation.