Ni catalysts derived from Mg–Al layered double hydroxides for hydrogen production from landfill gas conversion

Abstract

A layered double hydroxide (LDH) precursor with a hydrotalcite-like structure containing Ni/Mg/Al cations was prepared. A series of Ni catalysts containing mixed-oxides and spinel phases were then obtained through thermal treatment of the LDH precursor. X-ray diffraction (XRD), transmission electron microscopy (TEM), and temperature-programmed reduction (TPR) revealed that the LDH derived Ni catalysts have well-dispersed nickel phases upon reduction. The thermal treatment temperatures have noticeable effects on the specific surface area, pore volume, phase transformation, particle size, and reducibility of the catalysts. Thermal treatment temperatures up to 700 °C promote the generation of mesopores which facilitate an increase in specific area and pore volume. Beyond 700 °C sintering occurs, mesopores collapse, and specific area and pore volume decrease. High thermal treatment temperatures favor the phase transformation to spinel solid solutions and the particle size growth. Metal-support interaction is enhanced but reducibility is hindered due to the formation of spinel solid solution phases. The LDH derived Ni catalysts were tested for landfill gas conversion at 750 °C and have shown excellent activity and stability in terms of methane conversion. At gas hourly space velocity (GHSV) of 240,000 h−1 and pressure of 1 atm, 81% methane conversion was achieved during a 48 h test period without apparent catalyst deactivation.