Abstract
Nickel-containing hydrotalcite-derived materials have been recently proposed as promising materials for methane dry reforming (DRM). Based on a literature review and on the experience of the authors, this review focuses on presenting past and recent achievements on increasing activity and stability of hydrotalcite-based materials for DRM. The use of different NiMgAl and NiAl hydrotalcite (HT) precursors, various methods for nickel introduction into HT structure, calcination conditions and promoters are discussed. HT-derived materials containing nickel generally exhibit high activity in DRM; however, the problem of preventing catalyst deactivation by coking, especially below 700 °C, is still an open question. The proposed solutions in the literature include: catalyst regeneration either in oxygen atmosphere or via hydrogasification; or application of various promoters, such as Zr, Ce or La, which was proven to enhance catalytic stability.
Highlights
Our worldwide natural gas consumption increases yearly, i.e., in 2014, 12.9 Gtoe were consumed, which is 22.5% higher with the respect to the year 2004
The results presented in ref. [25,26,47,48] evince that CO2 conversions were higher than CH4 conversions at every stage within the whole temperature range considered i.e., 600–850 ◦ C, pointing to the occurrence of the reverse water-gas shift (RWGS) reaction in the presence of MgO-supported catalysts
Ni/Mg/Al mixed oxides for combined dry/steam reforming. They compared the catalytic activity of these hydrotalcite-derived materials to commercial NiO-supported catalysts, proving that the use of both Ni/Al and Ni/Mg/Al catalysts resulted in very similar yields and conversions than those obtained in the presence of the commercial catalyst
Summary
Our worldwide natural gas consumption increases yearly, i.e., in 2014, 12.9 Gtoe were consumed, which is 22.5% higher with the respect to the year 2004. Another advantage of using MgO as a support for the preparation of DRM catalysts arises from the possibility of forming a NiO-MgO solid solution at any molar ratio due to the similar anion radii of Mg and Ni cations (Mg2+ 0.065 nm, Ni2+ 0.072 nm [26]) and the particular lattice parameters of this mixed oxide structure The formation of this mixed oxide phase results in increased metal-support interaction, and prevents catalyst deactivation via sintering. The best performance was registered for 10 wt % Ni/MgO catalysts, which was attributed to the higher basicity of the studied materials, together with the formation of small nickel crystallites leading to stronger metal-support interaction It must be mentioned, that in both studies the most active catalysts still exhibited the presence of carbon deposits after reaction. The influence of Ni content, Mg/Al ratio, preparation method and pre-treatment conditions will be carefully compared and evaluated
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