PET waste as organic linker source for the sustainable preparation of MOF-derived methane dry reforming catalysts

A catalyst made of Ni0 nanoparticles highly dispersed on a lamellar alumina support was prepared by an environmentally-friendly route. The latter involved the synthesis of an aluminum-containing metalorganic framework (MOF) MIL-53(Al) in which the linkers were derived from the depolymerization of polyethylene terephthalate (PET) originating from plastic wastes. After demonstrating the purity and structure integrity of the PET-derived MIL-53(Al), this MOF was impregnated with nickel nitrate salt and then calcined to form a lamellar Ni-Al2O3 mixed metal oxide with a high surface area (SBET = 1276 m2 g-1, N2 sorption). This mixed oxide consisted of nickel aluminate nanodomains dispersed within amorphous alumina, as revealed by PXRD and TPR analyses. Subsequent reduction under H2 resulted in the formation of well-dispersed 5 nm Ni0 nanoparticles homogeneously occluded within the interlamellar porosity of the γ-alumina matrix, as attested by electron microscopy. This waste-derived catalyst displayed catalytic performances in the reaction of dry reforming of methane (DRM) as good as its counterpart made from a MOF obtained from commercial benzene-1,4-dicarboxylic acid (BDC). Thus, under similar steady state conditions, at 650 °C and 1 bar, the PET-derived catalyst led to CH4 and CO2 conversions as high as those on the BDC-derived catalyst, and its catalytic stability and selectivity towards DRM were excellent as well (no loss of activity after 13 h and H2:CO products ratio remaining at 1). Moreover, both catalysts were much better than those of a reference nickel alumina catalyst prepared by conventional impregnation route. This work therefore demonstrates the possibility of using plastic wastes instead of commercial chemicals to prepare efficient porous nickel-alumina DRM catalysts from MOFs, fostering the concept of circular economy.