Noble metal-free heterogeneous catalysts are highly desired for selective and solvent-free oxidation reactions. However, their practical application has been greatly restricted by their moderate activity. Herein, the scalable synthesis of a noble metal-free (Fe,Co,Ni,Cu)₃O₄ medium entropy oxide (MEO) catalyst and its grafting on reduced graphene oxide (rGO) is detailed. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses confirm the formation of a high entropy spinel oxide phase with inclusions of CuO particles as a secondary phase. This MEO@rGO catalyst exhibits excellent performance for solvent-free aerobic oxidation of toluene, with 18.2% conversion after 4 hours and over 90% selectivity for benzaldehyde, outperforming all previously reported catalysts, including those based on noble metals. A thorough analytical investigation reveals that the outstanding MEO@rGO activity is related to a synergistic effect between the multiple different cations in the MEO, its abundant oxygen vacancies and the active sites on rGO. In addition, four robust machine learning models including adaptive boosting–support vector regression (SVR), Random Forest, K-nearest neighbor and Extra tree are applied to predict selectivity. The Adaboost–SVR model best fits all the experimental data with an average absolute relative error of 0.09%. The proposed model is reliable as an effective predictor for selectivity and has great potential to be used in the chemical and petrochemical industries.

In this study, Nickel oxide-based catalysts (Ni_xO_x) were synthesized and used for the in-situ upgrading process of heavy crude oil (viscosity 2157 mPa·s, and API gravity of 14.1° at 25 °C) in aquathermolysis conditions for viscosity reduction and heavy oil recovery. All characterizations of the obtained nanoparticles catalysts (Ni_xO_x) were performed through Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), X-Ray and Diffraction (XRD), and ASAP 2400 analyzer from Micromeritics (USA), methods. Experiments of catalytic and non-catalytic upgrading processes were carried out in a discontinuous reactor at a temperature of 300 °C and 72 bars for 24 h and 2% of catalyst ratio to the total weight of heavy crude oil. XRD analysis revealed that the use of nanoparticles of NiO significantly participated in the upgrading processes (by desulfurization) where different activated form catalysts were observed, such as α-NiS, β-NiS, Ni₃S₄, Ni₉S₈, and NiO. The results of viscosity analysis, elemental analysis, and ¹³C NMR analysis revealed that the viscosity of heavy crude oil decreased from 2157 to 800 mPa·s, heteroatoms removal from heavy oil ranged from S—4.28% to 3.32% and N—0.40% to 0.37%, and total content of fractions (ΣC₈–C₂₅) increased from 59.56% to a maximum of 72.21%, with catalyst-3 thank to isomerization of normal and cyclo-alkanes and dealkylation of lateral chains of aromatics structures, respectively. Moreover, the obtained nanoparticles showed good selectivity, promoting in-situ hydrogenation-dehydrogenation reactions, and hydrogen redistribution over carbons (H/C) is improved, ranging from 1.48 to a maximum of 1.77 in sample catalyst-3. On the other hand, the use of nanoparticle catalysts have also impacted the hydrogen production, where the H₂/CO provided from the water gas shift reaction has increased. Nickel oxide catalysts have the potential for in-situ hydrothermal upgrading of heavy crude oil because of their great potential to catalyze the aquathermolysis reactions in the presence of steam.

FeBO3 and Fe3BO6 are antiferromagnets with TN≈ 348 K and 508 K respectively. This work presents the results of the study of the thermal expansion and phase transitions occurring in these borates by...