Applied Surface Science, Vol.474, 42-56, 2019
Investigating the correlation between deactivation and the carbon deposited on the surface of Ni/Al2O3 and Ni/La2O3-Al2O3 catalysts during the biogas reforming reaction
Ni/Al2O3 and Ni/La2O-Al2O3 catalysts were investigated for the biogas reforming reaction using CH4/CO2 mixtures with minimal dilution. Stability tests at various reaction temperatures were conducted and TGA/DTG, Raman, STEM-HAADF, HR-TEM, XPS techniques were used to characterize the spent samples. Graphitized carbon allotrope structures, carbon nanotubes (CNTs) and amorphous carbon were formed on all samples. Metallic Ni-0 was recorded for all (XPS), whereas a strong peak corresponding to Ni2O3/NiAl2O4, was observed for the Ni/Al sample (650-750 degrees C). Stability tests confirm that the Ni/LaAl catalyst deactivates at a more gradual rate and is more active and selective in comparison to the Ni/Al for all temperatures. The Ni/LaAl exhibits good durability in terms of conversion and selectivity, whereas the Ni/Al gradually loses its activity in CH4 and CO2 conversion, with a concomitant decrease of the H-2 and CO yield. It can be concluded that doping Al2O3 with La2O3 stabilizes the catalyst by (a) maintaining the Ni-0 phase during the reaction, due to higher dispersion and stronger active phase-support interactions, (b) leading to a less graphitic and more defective type of deposited carbon and (c) facilitating the deposited carbon gasification due to the enhanced CO2 adsorption on its increased surface basic sites.