AUTHOR=Puello-Polo Esneyder , Arias Dana , Márquez Edgar 

TITLE=Al2O3-MgO Supported Ni, Mo, and NiMo Mixed Phosphidic-Sulphidic Phase for Hydrotreating of Stearic and Oleic Acids Into Green Diesel

JOURNAL=Frontiers in Chemistry

VOLUME=10

YEAR=2022

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2022.880051

DOI=10.3389/fchem.2022.880051

ISSN=2296-2646

ABSTRACT=<p>The effect of the sulfur and metal-type content of MoP-S/<italic>γ</italic>-Al<sub>2</sub>O<sub>3</sub>-MgO, NiMoP-S/<italic>γ</italic>-Al<sub>2</sub>O<sub>3</sub>-MgO, and NiP-S/<italic>γ</italic>-Al<sub>2</sub>O<sub>3</sub>-MgO phosphide on hydroprocessing (HDO, HDCx-HDCn, HCK, HYD, and HYG) of fatty acids was studied. The catalysts were characterized by XRF, XRD, textural properties, XPS, Raman, Py-TPD, and EDS elemental mapping. The chemical analyses by X-ray fluorescence (XRF), EDS elemental mapping, and CHNS-O elemental analysis showed stoichiometric values Al/Mg = 38–40, Mo:Ni:P ∼ 1, and S ≤ 4.5 wt % (this value means that the molar ratio Mo:S ∼ 1.0:1.6, i.e., MoS<sub>2</sub>); also EDS elemental mapping confirmed the presence of Mo, Ni, Al, O, P, Mg, and S with good distribution on Al<sub>2</sub>O<sub>3</sub>-MgO. The impregnation of metals leads to a decrease in the surface area and pore volume as follows NiMoP-S/<italic>γ</italic>-Al<sub>2</sub>O<sub>3</sub>-MgO &lt; MoP-S/<italic>γ</italic>-Al<sub>2</sub>O<sub>3</sub>-MgO &lt; NiP-S/<italic>γ</italic>-Al<sub>2</sub>O<sub>3</sub>-MgO &lt; Al<sub>2</sub>O<sub>3</sub>-MgO &lt; Al<sub>2</sub>O<sub>3</sub> (unimodal pore size distribution), propitiating a pseudo bimodal pore size distribution with Dp-BJH between ∼5–7 nm and 11.8–14.2 nm for the presence of MgO. XRD confirmed differences between metallic phosphates and phosphides, and XPS confirmed the presence at the surface of Mo<sup>δ+</sup>(0 &lt; δ+ &lt; 2), Mo<sup>4+</sup>, Mo<sup>6+</sup>, Ni<sup>δ+</sup>(0 &lt; δ+ &lt; 2), Ni<sup>2+</sup>, S<sup>2−</sup>, SO<sub>4</sub><sup>2−</sup>, P<sup>δ+</sup>, and P<sup>5+</sup> species. Raman revealed the presence of MoS<sub>2</sub> only in MoP-S/<italic>γ</italic>-Al<sub>2</sub>O<sub>3</sub>-MgO and NiMoP-S/<italic>γ</italic>-Al<sub>2</sub>O<sub>3</sub>-MgO, while the NiMoP-S/γ-Al<sub>2</sub>O<sub>3</sub>-MgO catalyst had a more significant number of Brønsted and Lewis sites, although the increasing temperature decreased the Lewis sites. MoP-S/<italic>γ</italic>-Al<sub>2</sub>O<sub>3</sub>-MgO was more active at HDO showing the highest production rate for octadecane of 53 mol/(g<sub>cat</sub>·h), whereas NiP-S/<italic>γ</italic>-Al<sub>2</sub>O<sub>3</sub>-MgO was more active at HDCx-HDCn [45 mol/(g<sub>cat</sub>·h)] and HCK [6 mol/(g<sub>cat</sub>·h)]; meanwhile, NiMoP-S/<italic>γ</italic>-Al<sub>2</sub>O<sub>3</sub>-MgO had a mix of HDO [47 mol/(g<sub>cat</sub>·h)] and HDCx-HDCn [41 mol/(g<sub>cat</sub>·h)]. This showed production towards octadecane, heptadecane, and light hydrocarbons, meaning that the fatty acids were deoxygenated through bifunctional sites for hydrogenation (HYD) and hydrogenolysis (HYG) as follows: MoP-S/<italic>γ</italic>-Al<sub>2</sub>O<sub>3</sub>-MgO (K<sub>1</sub> = 0.08 and K<sub>2</sub> = 0.03 L/mol) &lt; NiMoP-S/<italic>γ</italic>-Al<sub>2</sub>O<sub>3</sub>-MgO (K<sub>1</sub> = 0.25 and K<sub>2</sub> = 0.45 L/mol) &lt; NiP-S/<italic>γ</italic>-Al<sub>2</sub>O<sub>3</sub>-MgO (K<sub>1</sub> = 2.5 and K<sub>2</sub> = 6.5 L/mol). For this reason, we considered that phosphide acts as a structural promoter with sulfur on its surface as a “mixed phosphidic-sulphidic species”, allowing the largest generation of heptadecane and octadecane by the presence of BRIM sites for HYD and CUS sites for HYG.</p>