Study of the catalytic wet air oxidation of p-hydroxybenzoic acid on a fresh ruthenium catalyst supported by different oxides

Tijani Hammedi; Rahma Bensouilah; Abdelkader Ouakouak; Jordi Llorca; Francisco Medina Cabello; Zouhaier Ksibi

doi:10.1016/j.heliyon.2023.e20875

Study of the catalytic wet air oxidation of p-hydroxybenzoic acid on a fresh ruthenium catalyst supported by different oxides

Heliyon. 2023 Oct 11;9(10):e20875. doi: 10.1016/j.heliyon.2023.e20875. eCollection 2023 Oct.

Authors

Tijani Hammedi¹, Rahma Bensouilah¹, Abdelkader Ouakouak², Jordi Llorca³, Francisco Medina Cabello⁴, Zouhaier Ksibi¹

Affiliations

¹ University of Tunis ElManar, Faculty of Sciences of Tunis, Laboratory of Materials Chemistry and Catalysis LR01ES08, Tunis, 2092, Tunisia.
² Research Laboratory in Subterranean and Surface Hydraulics, University of Biskra, PO Box 145, Biskra, 07000, Algeria.
³ Universitat Politècnica de Catalunya, Institute of Energy Technologies, Catalysis and Energy Laboratory, Av. Diagonal 647, 08028, Barcelona, Spain.
⁴ Rovira i Virgili University, Chemical Engineering Department, Av/Països Catalans 26, 43007, Tarragona, Spain.

Abstract

The catalytic wet air oxidation (CWAO) of p-hydroxybenzoic acid (p-HBA) was conducted in a batch reactor at 140 °C, and at a total air pressure of 50 bar over Ru-based catalysts. Four materials were selected as supports - TiO₂, CeO₂-TiO₂, ZrO₂-TiO_2, and La₂O₃-TiO₂ - all of which had mesopores in their texture and pollutant adsorption capacities. The supports were prepared by the sol-gel method, and then impregnated with 3 wt% of Ru precursor. Such characterization techniques as N₂-sorption, XRD, XPS, H₂-TPR, NH₃-TPD, TEM, and HAADF-STEM were used to analyze the different solids. The correlation between catalytic activities and physicochemical properties was discussed. A significant specific surface area (S_BET), a large amount of surface-active oxygen, and Lewis acidity sites were observed on cerium-containing catalysts (Ru/CeTi). Fresh Ru catalysts containing cerium showed higher activity than Ru/TiO₂, Ru/ZrTi, and Ru/LaTi catalysts. It is assumed that the acidic sites and surface oxygen trap the p-HBA molecule, thus increasing the catalytic properties of the Ru particles which interact with the surface oxygen through the cerium redox process (Ce³⁺/Ce⁴⁺). As the presence of cerium increases surface-active oxygen, it inhibits the deposition of carbon on the surface of the Ru catalyst. The pseudo-second order (PSO) model adequately described the kinetic data of the p-HBA oxidation reaction using Ru catalysts.

Keywords: CWAO; P-hydroxybenzoic acid; Ru catalysts; Sol-gel processing; Support effects.