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Influence of the Ce4+/Ce3+ Redox-Couple on the Cyclic Regeneration for Adsorptive and Catalytic Performance of NiO-PdO/CeO2±δ Nanoparticles for n-C7 Asphaltene Steam Gasification

1
Grupo de Investigación en Fenómenos de Superficie—Michael Polanyi, Departamento de Procesos y Energía, Facultad de Minas, Universidad Nacional de Colombia, Sede Medellín, Medellín 050034, Colombia
2
Química de Recursos Energéticos y Medio Ambiente, Instituto de Química, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín 050010, Colombia
*
Authors to whom correspondence should be addressed.
Nanomaterials 2019, 9(5), 734; https://doi.org/10.3390/nano9050734
Received: 31 March 2019 / Revised: 2 May 2019 / Accepted: 7 May 2019 / Published: 13 May 2019
(This article belongs to the Special Issue Application of Nano-Technology for Oil Recovery)
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Abstract

The main objective of this study is to evaluate the regenerative effect of functionalized CeO2±δ nanoparticles with a mass fraction of 0.89% of NiO and 1.1% of PdO in adsorption and subsequent decomposition of n-C7 asphaltenes in steam gasification processes. During each regeneration cycle, the adsorption capacity and the catalytic activity of the nanoparticles were evaluated. To estimate the adsorption capacity of the nanoparticles, adsorption kinetics were studied at a fixed concentration of n-C7 asphaltenes of 10 mg·L−1 as well as adsorption isotherms at three different temperatures at 25 °C, 55 °C, and 75 °C. To evaluate the catalytic activity, the loss of mass of the nanoparticles was evaluated by isothermal conversions with a thermogravimetric analyzer at 230 °C, 240 °C, and 250 °C, and at non-isothermal conditions involving a heating from 100 °C to 600 °C at a 20 °C·min−1 heating rate. The asphaltenes showed a high affinity for being adsorbed over the nanoparticles surface, due to the nanoparticles-asphaltene interactions are stronger than those that occur between asphaltene-asphaltene, and this was maintained during nine evaluated regeneration cycles as observed in the Henry’s constant that increased slightly, with changes of 21%, 26% and 31% for 25 °C, 55 °C and 75 °C. Polanyi’s adsorption potential decreases by 2.6% for the same amount adsorbed from the first cycle to the ninth. In addition, the catalytic activity of the nanoparticles did not change significantly, showing that they decompose 100% of the n-C7 asphaltenes in all cycles. However, the small decrease in the adsorption capacity and catalytic activity of the nanoparticles is mainly due to the presence and change in concentration and ratio of certain elements such as oxygen, iron or others at the surface of the nanoparticle as shown by X-ray photoelectron spectroscopy (XPS) analyses. Thermodynamic parameters of adsorption such as Δ H a d s o , Δ S a d s o , and Δ G a d s o and the effective activation energy (Ea) were calculated to compare adsorptive and catalytic performance during each cycle. There is an increase of 9.3% and 2.6% in the case of entropy and enthalpy, respectively, and a decrease of 0.5%, 3.1% and 6.5% for 25 °C, 55 °C and 75 °C respectively for the Gibss free energy from cycle 1 to cycle 9. It was found that these parameters are correlated with the Ce concentration and oxidation state ratios (Ce3+/Ce4+ couple) at the surface. View Full-Text
Keywords: adsorption; asphaltene; catalytic steam gasification; cerium redox cycle; thermal EOR regeneration cycles; nanoparticles adsorption; asphaltene; catalytic steam gasification; cerium redox cycle; thermal EOR regeneration cycles; nanoparticles
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Medina, O.E.; Gallego, J.; Restrepo, L.G.; Cortés, F.B.; Franco, C.A. Influence of the Ce4+/Ce3+ Redox-Couple on the Cyclic Regeneration for Adsorptive and Catalytic Performance of NiO-PdO/CeO2±δ Nanoparticles for n-C7 Asphaltene Steam Gasification. Nanomaterials 2019, 9, 734.

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