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

Abstract

An Al‐containing MIL‐53 metal‐organic framework with very high surface area (SBET=1130 m2.g−1, N2 sorption) was used as sacrificial template to prepare a nickel‐alumina‐based catalyst (Ni0AlMIL) 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 γ‐Al2O3 material with small Ni0 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 (AlMIL) and a second one consisting of a commercial γ‐Al2O3 batch (AlCOM). Under steady state conditions at a temperature of 650 °C and a pressure of 1 bar, the higher CH4 and CO2 conversions (till 3 times higher than on Ni0/AlCOM), high catalytic stability (no loss of activity after 13–100 h) and higher selectivity towards DRM (H2:CO products ratio remaining at 1) on Ni0AlMIL 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 γ‐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.

Nanostructured Nickel Aluminate as a Key Intermediate for the Production of Highly Dispersed and Stable Nickel Nanoparticles Supported within Mesoporous Alumina for Dry Reforming of Methane

“…The performance of the reduced catalysts in dry reforming of methane carried out at atmospheric pressure, 650 °C and under a high space velocity (GHSV = 72 L·g −1 ·h −1 ) are given in Table 1 as reactants conversions (CH 4 and CO 2 ) and H 2 /CO products ratio. With both catalysts, conversions were remarkable, close to thermodynamic equilibrium, and higher by approximately 3 times than on a reference Ni-alumina catalyst prepared by a conventional wetness impregnation method and tested for comparison in the same conditions [12]. This is not only due to the excellent Ni 0 dispersion providing a high number of active sites within the mesoporous Ni-alumina-based catalysts (as also confirmed by H 2 -TPD, data not shown) but also to the high accessibility to the active sites provided by their high specific surfaces.…”

“…Scanning Electron Microscopy (SEM) images were registered in mixed mode (70% secondary electrons and 30% retro-diffused signals) on a Hitachi SU-70 SEM-FEG microscope with an electron acceleration tension of 7 kV. High-Resolution transmission electron microscopy observations were done on 50–70 nm sections of the samples prepared by microtomic cutting as detailed elsewhere [12,13]. The TEM micrographs and EDS elemental mappings were registered on a JEOL-JEM 2020 electron microscope with LaB6 gun.…”

“…To this end, we recently developed two distinct synthesis routes of mesoporous nickel alumina DRM catalysts. In the first approach (Scheme 1A), a metal-organic-framework (MOF) of high surface area was used as sacrificial precursor (step a); it contained aluminum-hydroxyl nods bridged by organic linkers able to act as anchorage sites for nickel ions after impregnation (step b); after decomposing the linkers by thermal oxidation (step c) and then reducing the sample (step d), a porous nickel alumina catalyst with very small and highly stable Ni nanoparticles dispersed on thin γ-Al 2 O 3 layers was obtained [12]. The second approach (Scheme 1B) consisted of the direct addition of nickel within the synthesis medium of the alumina matrix (one-pot procedure, step a’) combined to an evaporation-induced self-assembly (EISA) method (step b’), leading after thermal oxidative decomposition of the organic structuring agent (assemblies of block copolymers) to a hexagonally structured mesoporous Ni-alumina material with Ni 2+ species occluded inside the Al 2 O 3 walls (step c’) and remaining strongly attached to the support after reduction (step d’) [13].…”

Investigation of new routes for the preparation of mesoporous calcium oxide supported nickel materials used as catalysts for the methane dry reforming reaction

“…Catalytic performances were measured after reduction of the prepared materials, using a Microactivity catalytic reactor (MAR from PID ENG & TECH Spain) and applying reaction conditions chosen from our previous works. [10][11][12][13] 100 mg of each calcined sample was loaded between 2 layers of quartz wool in the reactor. A leak test was first accomplished in the presence of an inert gas (argon), then reduction of the sample was operated at atmospheric pressure under flowing 5%H 2 /Ar (30 mL min -1 ) and increasing the temperature from room temperature up to 700 °C and keeping this temperature for 2 h to ensure full nickel oxide reduction into Ni 0 .…”

“…As well established in the literature, deactivation can be prevented by (i) synthesizing very small and well dispersed metallic active sites, (ii) establishing a strong metal-support interaction and (iii) introducing an element with a high capability of carbon removal. [8][9][10][11][12][13][14][15] To this respect, using alkaline earth metal oxides as catalytic supports in DRM allows to benefit from their high oxygen storage capacities. Hence, such basic oxides are able to decrease carbon buildup on active metal surface by providing kinetically larger concentration of labile oxygen that is known to contribute to the removal of carbonaceous deposits by initiating their oxidation.…”