Impact\nof Potassium Addition on the Performance of\nNi/MgAl<sub>2</sub>O<sub>4</sub> Catalysts in Steam Reforming of Bio-Oil\nModel Compounds

Ni/MgAl<sub>2</sub>O<sub>4</sub> catalysts with and without\nK promotion\nwere tested in steam reforming of phenol (SRP), ethanol (SRE), and\nbutanol (SRB), to evaluate the effect of K on catalytic activity and\nmethane formation. The catalysts were prepared by a wet impregnation\nmethod and were characterized using nitrogen adsorption, in situ XRD,\nH<sub>2</sub>-TPR, TEM, XPS, and XANES techniques. Catalytic evaluations\nwere performed at temperatures ranging from 250 to 650 °C. DFT\ncalculations were employed to study the hydrogenation of CH<sub><i>x</i></sub> species on Ni modified by K. The addition of K to\nthe Ni catalysts weakened the NiO-support interaction, causing NiO\nagglomeration and an increase in Ni particle size. The effect of K\non CH<sub>4</sub> formation was strongly influenced by the structure\nof the reformed molecule, leading to the formation of different CH<sub><i>x</i></sub> species during the reaction. The introduction\nof K into the Ni catalyst suppressed formation of CH<sub>4</sub> by\nhydrogenation of CH, with this effect diminishing for CH<sub>2</sub> and being absent for CH<sub>3</sub> species. DFT calculations of\nthe interaction between CH<sub><i>x</i></sub> species absorbed\nin an Ni<sub>4</sub> cluster (CH<sub><i>x</i></sub>-Ni<sub>4</sub>) and K, particularly KOH, indicated that species such as\nHOKH<sub><i>x</i></sub>C–Ni<sub>4</sub> were stabilized,\nwith decreased energies of −291.5, −242.4, and −27.7\nkJ/mol for CH, CH<sub>2</sub>, and CH<sub>3</sub>, respectively. The\nincreased heat of adsorption for CH and CH<sub>2</sub> species reduced\ntheir hydrogenation activity toward methane.