Characterization and Syngas Production at Low Temperature via Dry Reforming of Methane over Ni-M (M = Fe, Cr) Catalysts Tailored from LDH Structure

Bimetallic layered double oxide (LDO) NiM (M = Cr, Fe) catalysts with nominal compositions of Ni/M = 2 or 3 were tailored from layered double hydroxides (LDH) using a coprecipitation method to investigate the effects of the trivalent metal (Cr or Fe) and the amount of Ni species on the structural, textural, reducibility, and catalytic properties for CH4/CO2 reforming. The solids before (LDH) and after (LDO) thermal treatment at 500 degrees C were characterized using TGA-TD-SM, HT-XRD, XRD, Raman, and IR-ATR spectroscopies; N-2 physical adsorption; XPS; and H-2-TPR. According to the XRD and Raman analysis, a hydrotalcite structure was present at room temperature and stable up to 250 degrees C. The interlayer space decreased when the temperature increased, with a lattice parameter and interlayer space of 3.018 angstrom and 7.017 angstrom, respectively. The solids fully decomposed into oxide after calcination at 500 degrees C. NiO and spinel phases (NiM2O4, M = Cr or Fe) were observed in the NiM (M = Cr, Fe) catalysts, and Cr2O3 was detected in the case of NiCr. The NiFe catalysts show low activity and selectivity for DRM in the temperature range explored. In contrast, the chromium compound demonstrated interesting CH4 and CO2 conversions and generally excellent H-2 selectivity at low reaction temperatures. CH4 and CO2 conversions of 18-20% with H-2/CO of approx. 0.7 could be reached at temperatures as low as 500 degrees C, but transient behavior and deactivation were observed at higher temperatures or long reaction times. The excellent activity observed during this transient sequence was attributed to the stabilization of the metallic Ni particles formed during the reduction of the NiO phase due to the presence of NiCr2O4, opening the path for the use of these materials in periodic or looping processes for methane reforming at low temperature.