The promoting effect of magnesium on NiMgLaZr catalysts for biogas upgrading to syngas via a tri-reforming process

Abstract

The effect of partial substitution of lanthanum by magnesium on the catalytic activity of the Ni-La₂Zr₂O₇ catalyst in the biogas tri-reforming reaction was studied. Four catalysts, Ni-La_2-xMg_xZr₂O_7-δ (x = 0.25, 0.5, 0.75, and 1), were prepared using a modified polymeric precursor method, characterized using several techniques, and evaluated at 800 °C with a sub-stoichiometric molar feed composition of CH₄/CO₂/H₂O/O₂ = 1/0.33/0.33/0.08. The catalyst with x = 0.5 showed the best performance, which is attributed to its optimum properties of nickel particle size, metal-support interactions, and basicity. A stability test was performed with this catalyst using a molar feed composition of CH₄/CO₂/H₂O/O₂ = 1/0.33/0.67/0.08, previously optimized to obtain a synthesis gas with a H₂/CO ≈ 2 molar ratio for 100 h, and compared with a commercial steam reforming catalyst. The catalyst with x = 0.5 exhibited higher CH₄ and CO₂ conversions, a lower amount of carbon deposited, and a lower degree of nickel particle sintering.