Insights into the Morphology Effect of Ceria on the Catalytic Performance of NiO–PdO/CeO₂ Nanoparticles for Thermo-oxidation of n-C₇ Asphaltenes under Isothermal Heating at Different Pressures

Abstract

The overall objective of this study is to evaluate the effect of morphologies (C, cubic; O, orthorhombic; and S, spherical) of ceria in the catalytic activity for n-C7 asphaltene thermo-oxidation. In this way, cubic (C-CeO2), orthorhombic (O-CeO2), and spherical (S-CeO2) ceria nanoparticles were synthesized using the hydrothermal method and doped with 1.0% in a mass fraction of Ni and Pd oxides by incipient wetness impregnation. The catalytic activity of the systems was evaluated through non-isothermal and isothermal thermogravimetric analyses at different pressures. The non-isothermal thermogravimetric results evidenced an increase in the n-C7 asphaltene mass as the temperature increases between 100 and 230 °C for all systems and operating conditions. At 3.0 MPa, n-C7 asphaltene gains 3.6, 5.8, and 3.2% for O-CeO2, C-CeO2, and S-CeO2, respectively, while at 6.0 MPa, there is an increase of 7.3, 10.4, and 5.9% for the same systems, respectively. The Ni and Pd phases increase the amount of oxygen chemisorbed in all systems in the order S-NiPdCe < O-NiPdCe < C-NiPdCe and reduce the temperature required for the total n-C7 asphaltene decomposition at temperatures lower than 200 °C at 6.0 MPa in the same order. Also, isothermal thermogravimetric analysis demonstrates that the asphaltene conversion increased with ceria-based nanocatalysts in the increasing order S-CeO2 < O-CeO2 < C-CeO2. Cubic CeO2 doped with Ni and Pd presents the highest yield, reaching 100% conversion at 170 °C and 6.0 MPa at 60 min. The data confirm that the presence of Ni and Pd facilitate the transference oxygen vacancies between the bulk and surface of the nanocatalyst, and therefore, the catalytic activity is enhanced. The catalytic activity, in turn, is improved by the presence of {110}, {100}, and {111}, oxygen vacancies, and Ce3+ and NiO–Ce species. This work reveals the benefits of structured cubic ceria nanocatalysts as a promising support for nickel- and palladium-containing materials for n-C7 asphaltene decomposition.

Catalytic Decomposition of n-C7 Asphaltenes Using Tungsten Oxides–Functionalized SiO2 Nanoparticles in Steam/Air Atmospheres

“…These results agree with literature reports for the adsorption of different asphaltene types onto different solid surfaces [36,37,42,43,73]. The adsorption isotherms follow a type Ib behavior according to the IUPAC classification [87], indicating that there is a strong affinity between the n-C 7 asphaltenes and the synthesized materials [31,90]. On another side, considering the acidic character of tungsten oxide, this behavior suggests the basicity of the asphaltenes in addition the presence of heteroatoms such as nitrogen and oxygen in the asphaltene molecules, which favor the interaction with the nanoparticle surface [91,92].…”

“…During this process, different reactions occur simultaneously, generating physicochemical changes in the heavy oil, even leading to upgrading through viscosity reduction and API gravity increase. Nevertheless, the conversion of heavy and refractory fractions such as asphaltenes into lighter compounds struggles to occur behind the combustion zone, as the decomposition temperature could be higher than 400 • C [28][29][30][31].…”

Structural-Compositional Effect of Polycyclic Aromatic Hydrocarbons on Thermal-Oxidative Decomposition at High-Pressure: A Molecular Dynamics and Machine Learning Approach

“…This was primarily because the PAHs tended to adsorb on the surface of the nanoparticles. − Mazloom et al reported that PAH structures with higher aromaticity and polarity tended to adsorb more readily onto the surface of nanoparticles. The influence of the geometry of the nanocomposites (cubic, orthorhombic, and spherical) on the thermo-oxidate process has also been evaluated; Medina et al demonstrated that the conversion rates of PAHS were highest for cubic cerium nanoparticles, followed by orthorhombic and spherical nanoparticles. Despite the valuable contributions of these studies, they do not consider the effect of the structural and compositional characteristics of PAHs on the thermal-oxidative process.…”

“…One potential solution is the transformation of these PAHs into a less hazardous or nonhazardous compound by catalytic procedures, ,, with thermal-oxidative processes being a highly promising solution . Thermogravimetric analysis is one of the most commonly used techniques for studying the thermo-oxidation process of PAHs. ,− It allows researchers to obtain thermo-oxidation profiles that can be used to evaluate the impact of different catalysts used during the process, including nanotechnology. − Nassar et al evaluated three species of metal oxide nanoparticles and found that the activation energy required to oxidize PAHs was reduced, leading to more favorable reaction pathways and oxidation kinetics. This was primarily because the PAHs tended to adsorb on the surface of the nanoparticles. − Mazloom et al reported that PAH structures with higher aromaticity and polarity tended to adsorb more readily onto the surface of nanoparticles.…”

2021 Pioneers in Energy Research: Alan Marshall

“…These authors demonstrated the combination of ultrahigh-resolution FT-ICR and cyclic ion mobility mass spectrometry as an effective tool to overcome the limitation on structural determination of asphaltene molecules to shed important insights into hydrotreating mechanisms. The article of Medina, Cortés, Franco, and co-workers reports the effect of morphologies of ceria nanoparticles on the catalytic conversion of asphaltenes using multiple complementary characterizations. Friederici, Rüger, and co-workers from the University of Rostock reported the characterization of plastic pyrolysis chars using thermal analysis hyphenated with mass spectrometric approaches.…”