ARTICLE | doi:10.20944/preprints202311.1820.v1
Subject: Chemistry And Materials Science, Surfaces, Coatings And Films Keywords: ceria; oxidation; oxygen; nitrogen monoxide; nitrous oxide; FTIR spectroscopy
Online: 28 November 2023 (15:42:32 CET)
The interaction between O2 and reduced ceria nanocubes was mainly investigated by FTIR spectroscopy. Nanorods and nanoparticles were also studied for comparison. Adsorption of O2 at 100 K on unreduced ceria produces only O2 molecularly adsorbed on Ce4+ sites. The Ce3+ cations in H2-reduced ceria were monitored by the 2F5/2 → 2F7/2 electronic transition band at 2133-2095 cm-1. This band possesses a fine structure well resolved at 100 K. The positions of the individual components depend on the Ce3+ environment, including the presence of nearby species such as OH groups. Even at 100 K, the interaction of O2 with reduced ceria leads to fast oxidation of about half of the Ce3+ cations, including all Ce3+ sites bound to OH groups and carbonates, and the simultaneous formation of superoxo (O2) and peroxo (O22) species. The remaining fraction of Ce3+ sites disappears upon heating up to 348 K. At higher temperatures, the peroxo species decompose directly, yielding lattice oxygen. Superoxides are converted to hydroperoxides, which then decompose to terminal OH groups. Reduced samples evacuated at T < 773 K contain sorbed H2. Part of this hydrogen is also fast oxidized to H2O even at 100 K.
Subject: Engineering, Energy And Fuel Technology Keywords: soot oxidation; catalytic; heterogeneous catalysis; oxygen vacancies; iron doped ceria catalyst; ceria
Online: 1 September 2019 (09:02:29 CEST)
This study investigates the role of oxygen vacancy on Fe-doped CeO2 catalyst activity for soot oxidation. The oxygen vacancy was assessed through Ce3+ content. The Fe content was varied between 0 and 30% for two catalyst preparation methods, co-precipitation (CP) and solution combustion synthesis (SCS). X-ray photoelectron spectroscopy indicates that ceria exists as both Ce4+ and Ce3+, while iron is present only as Fe3+. The catalyst’s activity was evaluated by ignition (T10) and combustion (T50) temperatures using thermogravimetric analysis. Optimum Fe contents yielding the highest activity were found to be 10% and 5% for CP and SCS catalysts, respectively. The surface area and morphology have shown moderate effect on catalyst activity, because catalytic soot oxidation involves solid-solid contact. More importantly, regardless of the fabrication method, it was found that Ce3+ content, which is closely related to oxygen vacancies, plays the most important role in affecting the catalyst activity.
ARTICLE | doi:10.20944/preprints202012.0573.v1
Subject: Engineering, Automotive Engineering Keywords: acetic acid; reforming; hydrogen; cobalt; ceria
Online: 23 December 2020 (09:09:34 CET)
This work focuses on the support effect on the performances of Co-based catalysts for the acetic acid steam reforming. SBA-15, a well ordered hexagonal mesoporous silica structure, and CeO2 have been selected as the supports, with the impact of chromium addition also being investigated. Better acetic acid steam reforming performances have been recorded for CeO2 compared to SBA-15 supported catalysts and, in particular, the 7Co/CeO2 catalyst showed the highest values of acetic acid conversions with enhanced H2 yields below 480°C, in comparison to the other investigated catalytic formulations. In addition, more pronounced coke depositions and acetone concentrations have been obtained with CeO2 supported catalysts, due to the tendency of ceria to catalyse the ketonization reaction. Chromium addition to Co/SBA-15 catalysts led to an enhancement in the activity towards acetic acid steam reforming, while on CeO2 supported catalysts no improvement in the catalysts activity was observed; however, on both SBA-15 and CeO2 supported catalysts, Cr addition reduced the amount of coke deposited on the catalysts surface.
ARTICLE | doi:10.20944/preprints201711.0106.v1
Subject: Chemistry And Materials Science, Chemical Engineering Keywords: ceria; zirconia; gold; sulfur; catalysts characterisation; glycerol oxidation
Online: 16 November 2017 (05:37:10 CET)
Ceria, zirconia and mixed cerium-zirconium mesoporous oxides were synthesized and used as supports for sulfur and gold species. The materials were characterised using selected advanced techniques (ICP-OES, elemental analysis, XPS, XRD, N2 adsorption and desorption isotherms, UV-vis, ATR-FTIR, TPR-H2, TG-DTA) which allowed monitoring of the oxidation state of metals (cerium and gold) and the surface properties of the catalysts, in particular the concentration of the components on the surface and in the bulk of materials. The interactions between gold, sulfur and metals from oxides were considered. The goal of this work was studied the changes in the chemical composition of materials and the oxidation states of cerium species after the modification of oxides with sulfur and gold species and the estimation of the influence of these changes on the surface properties. The chemical composition of surface affects the mobility of surface oxygen and the oxidation state of cerium, which can play the role of redox sites (e.g. Ce3+/Ce4+ species), and therefore it strongly influences on the adsorption of hydrogen sulfide and then gold loading. Additionally, gold catalysts modified with sulfur species were tested in the reaction of glycerol oxidation in the liquid phase at basic conditions as the test reaction of the catalytic oxidation of organic pollutants from water.
ARTICLE | doi:10.20944/preprints202305.0617.v1
Subject: Chemistry And Materials Science, Nanotechnology Keywords: dry reforming; methane; ceria-zirconia; supercritical synthesis; oxygen vacancies; stability
Online: 9 May 2023 (08:53:37 CEST)
This work is devoted to the study of active and stable nickel catalysts for methane dry reforming based on Pr-doped ceria-zirconia obtained by solvothermal continuous method. The studies of physicochemical and catalytic properties of the 5%Ni\Ce0.75Zr0.25-xPrxO2 series showed that Pr introduction leads to an increase in the amount of highly reactive oxygen of the oxide lattice. Praseodymium-based catalysts showed significantly higher reactant conversions. In addition to the nature of support, the method of nickel introduction was also studied - Ni was added both by impregnation and one-pot with mixed oxide preparation. The method of Ni addition was shown to have significant effect on the morphology of the supported active component and, respectively, on the catalytic activity. The 5%Ni/Ce0.75Zr0.15Pr0.1O2 catalyst prepared by one-pot method showed stable operation in the MDR reaction for 30 hours at CO2 and CH4 conversions of ~40% and an H2 yield of ~18% (Т=700°С, τ=10ms).
COMMUNICATION | doi:10.20944/preprints202310.0537.v1
Subject: Engineering, Chemical Engineering Keywords: the ostwald process; nitric acid; fertilizer; nitric oxide; ruthenium; ceria; manganese; catalysis
Online: 10 October 2023 (03:41:50 CEST)
Nitric acid is a key component in the production of nitrate fertilisers and is industrially produced using the Ostwald process. The Ostwald process can be further intensified by oxidising nitric oxide to nitrogen dioxide using heterogeneous catalysts. We have explored various monometallic and bimetallic catalysts for NO to NO2 oxidation and found ruthenium supported on ceria, containing 10 wt.% manganese to be a promising catalyst for oxidising NO to NO2 at low temperatures at industrially relevant conditions. For a feed comprising 10% NO, 6% O2, 15% H2O and rest Ar, and 8% NO, 2% NO2 5% O2, 15% H2O and rest Ar, the ruthenium-manganese catalysts attained NO-NO2 equilibrium below 400∘C. For the 5wt.% ruthenium and 10 wt.% manganese on ceria catalyst, an apparent activation energy of 39.4 kJ/mol and 85.4 kJ/mol were observed in the absence and presence of NO2, respectively. These findings demonstrate the potential of supported bimetallic ruthenium-manganese catalysts for efficient oxidation of NO to NO2 at low temperatures which can lead to significant process intensification of nitric acid plants.
ARTICLE | doi:10.20944/preprints202105.0608.v3
Subject: Chemistry And Materials Science, Biomaterials Keywords: nanocomposites; bacterial cellulose; ceria nanoparticles; thermal properties; swelling; mechanical behavior; biomedical applications; stem cells proliferation; gene expression
Online: 17 June 2021 (10:02:24 CEST)
A technique for fabrication of bacterial cellulose-based films with CeO2 nanofiller has been developed. The structural and morphological characteristics of the materials have been studied, their thermal and mechanical properties in dry and swollen states having been determined. The preparation methodology makes it possible to obtain composites with a uniform distribution of nanoparticles. The catalytic effect of ceria regarding the thermal oxidative destruction of cellulose has been confirmed by TGA and DTA methods. An increase in CeO2 content led to an increase in the elastic modulus (a 1.27-fold increase caused by the introduction of 5 wt.% of the nanofiller into the polymer) and strength of the films. This effect is explained by the formation of additional links between polymer macro-chains via the nanoparticles’ surface. The materials fabricated were characterised by a limited ability to swell in water. Swelling caused a 20- to 30-fold reduction in the stiffness of the material, the mechanical properties of the films in a swollen state remaining germane to their practical use. The application of the composite films in cell engineering as substrates for the stem cells’ proliferation has been studied. The increase in CeO2 content in the films enhanced the proliferative activity of embryonic mouse stem cells. The cells cultured on the scaffold containing 5 wt.% of ceria demonstrated increased cell survival and migration activity. An analysis of gene expression confirmed improved cultivation conditions on CeO2-containing scaffolds.