Approaches to the design of efficient and stable catalysts for biofuel reforming into syngas: doping the mesoporous MgAl2O4 support with transition metal cations

Abstract

The mesoporous MgAl₂O₄ support is promising for the design of efficient and stable to coking catalysts for natural gas and biofuel reforming into syngas. This work aims at doping this support with transition metal cations (Fe, Cr, Ti) to prevent the incorporation of Ni and rare-earth cations (Pr, Ce, Zr), loaded by impregnation, into its lattice along with providing additional sites for CO₂ activation required to prevent coking. Doped MgAl_1.9Me_0.1O₄ (Me = Fe, Ti, Cr) mesoporous supports prepared by the one-pot evaporation-induced self-assembly method with Pluronic P123 triblock copolymers were single-phase spinels. Their specific surface area varies in the range of 115–200 m² g⁻¹, decreasing to 90–110 m² g⁻¹ after successive addition of the supporting nanocomposite active component 10 wt% Pr_0.3Ce_0.35Zr_0.35O₂ + (5 wt% Ni + 1% Ru) by impregnation. Mössbauer spectroscopy for iron-doped spinels confirmed the spatially uniform distribution of Fe³⁺ cations in the lattice without clustering being mainly located at the octahedral positions. Fourier-transform infrared spectroscopy of the adsorbed CO molecules was performed to estimate the surface density of metal sites. In methane dry reforming, the positive effect of MgAl₂O₄ support doping was observed from both a higher turn-over frequency as compared with the catalyst on the undoped support as well as the highest efficient first-order rate constant for the Cr-doped catalyst as compared with published data for a variety of Ni-containing catalysts based on the alumina support. In the reaction of ethanol steam reforming, the efficiency of catalysts on the doped supports is comparable, while exceeding that of Ni-containing supported catalysts reported in the literature. Coking stability was provided by a high oxygen mobility in the surface layers estimated by the oxygen isotope heteroexchange with C¹⁸O₂. A high efficiency and coking stability were demonstrated in the reactions of methane dry reforming and ethanol dry and steam reforming in concentrated feeds for the honeycomb catalyst with a nanocomposite active component on the Fe-doped MgAl₂O₄ support loaded on the FeCrAl-alloy foil substrate.