Employing a Nickel-Containing Supramolecular Framework as Ni Precursor for Synthesizing Robust Supported Ni Catalysts for Dry Reforming of Methane

This work presents a facile and efficient approach for preparing well dispersed supported Ni catalyst (HMA@Ni/SBA-15) for dry reforming of methane (DRM) through the modified impregnation method by using a hexamethylenetetramine (HMA) Ni(II) complex, a three-dimensional hydrogen-bonded supramolecular framework, as Ni precursor. By employing this method, the Ni-II cation was discretely impregnated into the mesoporous channels of SBA-15 support by the "obstacle effect" of the HMA coordination shell of the Ni complex; and then the Ni nanoparticles were stabilized inside the mesoporous channels of SBA-15 by the confinement effect. The developed HMA@Ni/SBA-15 catalyst demonstrated much higher catalytic activity and much better catalytic stability than the traditional Ni/SBA15 towards this reaction. The superior catalytic activity was suggested to be associated with the enhanced Ni dispersion and the improved reduction degree of NiO. In addition, the confinement effect of mesopore channels and strengthened interaction between Ni and support by improved Ni dispersion contributed to stabilizing Ni particles during the reduction and reaction process at high temperature. The strengthened Nisupport interaction of HMA@Ni/SBA-15 favored the formation of whisker-like carbon, which did not depress the accessibility of Ni active sites. However, owing to the weaker Ni-support interaction, the clearly observed shell-like carbon closely encapsulated on Ni nanoparticles of spent Ni/SBA-15 would significantly depress the accessibility of Ni active sites to reactants. The combination of stabilized Ni nanoparticles and well-kept Ni accessibility of HMA@Ni/SBA-15 catalyst allows it to show outstanding catalytic stability for DRM reaction. The much superior catalytic activity and stability of the developed HMA@Ni/SBA-15 catalyst to the traditional Ni/SBA-15 make it a promising candidate for producing synthesis gas through DRM reaction.