Design and development of co methanation catalysts for a novel coal to SNG production technology

The overall purpose of this research is to design and develop Ni-based methanation catalysts with high and efficient methane production activity, selectivity, and stability for realistic feed conditions with H2/CO<3 by combining methanation and WGS reactions. Initially, preliminary tests were conducted on a conventional methanation catalyst, 15%Ni/γ-Al2O3, to evaluate the impact of experimental parameters on methanation performance. Secondly, various catalyst bed configurations using classical methanation and WGS catalysts were investigated. It was determined that using catalyst mixtures or sequential beds did not significantly enhance CH4 yield compared to a pure methanation catalyst. The third section explored bifunctionality by integrating WGS and methanation reactions within a single catalyst. New Ni-based catalysts with different promoters, supports, and pretreatment conditions were synthesized and evaluated. At 400 °C and an H2/CO ratio of 3, most catalysts exhibited high CO conversion values (93%-99%), with the highest conversion observed for 5%Ce-10%Ni/SBA-15-550. Reducing the H2/CO ratio to 2 caused a drop in CO conversion for 1%Mg-10%Ni/γ-Al2O3 (from 92.9% to 84.2%) and 15%Ni/SBA-15-750 (from 92.7% to 72.6%), while other catalysts maintained stable conversion values. Temperature decrease significantly impacted performance. At 250 °C, only six out of sixteen catalysts exhibited CO conversion, with 5%Ce-10%Ni/γ-Al2O3 demonstrating the best performance (ca. 96%). Ce-Ni catalysts were characterized using XPS, XRD, HR-TEM, SEM, and RAMAN techniques. XPS analysis revealed enhanced electronic interactions with Ce addition, XRD indicated improved NiO reduction, RAMAN showed increased carbon deposition at lower temperatures, and SEM/TEM identified distinct Ce and Ni cluster formations influenced by the support material. Kinetic studies on the 5%Ce-10%Ni/γ-Al2O3 catalyst identified different kinetic regimes between 300-350 °C and 350-400 °C. Among the evaluated power-law type and Langmuir-Hinshelwood models, although Langmuir-Hinshelwood models had better predictive capabilities, all rate equations were inadequate for modeling the reaction.