Porous Nickel-Alumina Derived from Metal-Organic Framework (MIL-53): A New Approach to Achieve Active and Stable Catalysts in Methane Dry Reforming

An Al-containing MIL-53 metal-organic framework with very high surface area (S-BET=1130 m(2).g(-1), N-2 sorption) was used as sacrificial template to prepare a nickel-alumina-based catalyst ((NiAlMIL)-Al-0) highly active and stable in the reaction of dry reforming of methane (DRM). The procedure consisted in impregnating the activated (solvent free) MIL-53 sample with a nickel precursor solution, then calcining the material to remove the organic linkers and subsequently reducing it to form the reduced nickel active phase. At the step of calcination, this procedure results in the formation of a porous uniform spinel phase with Ni nanospecies embedded in the alumina-based matrix, as deduced from XRD, TPR and TEM analyses. This leads after reduction to a porous lamellar gamma-Al2O3 material with small Ni-0 nanoparticles homogeneously dispersed and stabilized within the support. The performances of this catalyst in DRM are better than those of two reference Ni/alumina catalysts prepared for comparison by conventional nickel impregnation of two preformed alumina supports: a first one obtained by calcination of MIL-53 (Al-MIL) and a second one consisting of a commercial gamma-Al2O3 batch (Al-COM). Under steady state conditions at a temperature of 650 degrees C and a pressure of 1 bar, the higher CH4 and CO2 conversions (till 3 times higher than on Ni-0/Al-COM), high catalytic stability (no loss of activity after 13-100 h) and higher selectivity towards DRM (H-2:CO products ratio remaining at 1) on (NiAlMIL)-Al-0 compared to the other catalysts is believed to come from the particularly strong interaction between the nickel and alumina phases generated by using the unique high specific surface of the parent MOF support to deposit nickel. This creates an intimate mixing favorable to a persisting interaction of the nickel nanoparticles with the alumina support in the reduced material. The lamellar shape of the gamma-Al2O3 composing the catalyst and its remaining high specific surface may also contribute to the excellent Ni resistance to sintering and in turn to the inhibition of carbon nanotubes formation during the reaction.