Catalytic oxidation of volatile organic compounds (n-hexane, benzene, toluene, o-xylene) promoted by cobalt catalysts supported on γ-Al2O3-CeO2

Gold-Based Catalysts for Complete Formaldehyde Oxidation: Insights into the Role of Support Composition

Formaldehyde (HCHO) is recognized as one of the most emitted indoor air pollutants with high detrimental effect on human health. Significant research efforts are focused on HCHO removal to meet emission regulations in an effective and economically profitable way. For over three decades, the unique electronic properties and catalytic abilities of nano-gold catalysts continue to be an attractive research area for the catalytic community. Recently, we reported that mechanochemical mixing is a relevant approach to the preparation of Co-Ce mixed oxides with high activity in complete benzene oxidation. A trend of higher surface defectiveness, in particular, oxygen vacancies, caused by close interaction between cobalt oxide and cerium oxide phases, was observed for a mixed oxide composition of 70 wt.% Co3O4 and 30 wt.% CeO2. These results directed further improvement by promotion with gold and optimization of mixed oxide composition, aiming for the development of an efficient catalyst for room temperature HCHO abatement. Support modification with potassium was studied; however, the K addition caused less enhancement of HCHO oxidation activity than expected. This motivated the preparation of new carrier material. In addition to Co3O4-CeO2 mixed metal oxides with preset ratio, γ-Al2O3 intentionally containing 33% boehmite and shortly named Al2O3-b was used for synthesis. Analysis of the role of support composition in HCHO oxidation was based on the characterization of nano-gold catalysts by textural measurements, XRD, HRTEM, XPS, and TPR techniques. Gold supported on mechanochemically treated Co3O4-CeO2-Al2O3-b (50 wt.% Al2O3-b) exhibited superior activity owing to high Ce3+ and Co3+ surface amounts and the most abundant oxygen containing species with enhanced mobility. This catalyst achieved oxidation to CO2 and H2O by 95% HCHO conversion at room temperature and 100% at 40 °C, thus implying the potential of this composition in developing efficient catalytic materials for indoor air purification.

Mechanochemically Prepared Co3O4-CeO2 Catalysts for Complete Benzene Oxidation

Considerable efforts to reduce the harmful emissions of volatile organic compounds (VOCs) have been directed towards the development of highly active and economically viable catalytic materials for complete hydrocarbon oxidation. The present study is focused on the complete benzene oxidation as a probe reaction for VOCs abatement over Co3O4-CeO2 mixed oxides (20, 30, and 40 wt.% of ceria) synthesized by the more sustainable, in terms of less waste, less energy and less hazard, mechanochemical mixing of cerium hydroxide and cobalt hydroxycarbonate precursors. The catalysts were characterized by BET, powder XRD, H2-TPR, UV resonance Raman spectroscopy, and XPS techniques. The mixed oxides exhibited superior catalytic activity in comparison with Co3O4, thus, confirming the promotional role of ceria. The close interaction between Co3O4 and CeO2 phases, induced by mechanochemical treatment, led to strained Co3O4 and CeO2 surface structures. The most significant surface defectiveness was attained for 70 wt.% Co3O4-30 wt.% CeO2. A trend of the highest surface amount of Co3+, Ce3+ and adsorbed oxygen species was evidenced for the sample with this optimal composition. The catalyst exhibited the best performance and 100% benzene conversion was reached at 200 °C (relatively low temperature for noble metal-free oxide catalysts). The catalytic activity at 200 °C was stable without any products of incomplete benzene oxidation. The results showed promising catalytic properties for effective VOCs elimination over low-cost Co3O4-CeO2 mixed oxides synthesized by simple and eco-friendly mechanochemical mixing.

The relevance of Lewis acid sites on the gas phase reaction of levulinic acid into ethyl valerate using CoSBA-xAl bifunctional catalysts

CoSBA-xAl catalysts show a high yield in the levulinic acid conversion into ethyl valerate. This is due to the presence of weak Lewis acid sites associated with Co²⁺ species that have been stabilized by incorporation of Al into the support.

CuO and CeO2-doped catalytic material synthesized from red mud and rice husk ash for p-xylene deep oxidation

CuO-CeO₂ catalysts supported on material synthesized from red mud and rice husk ash (CuO-CeO₂/ZRM) were prepared by co-impregnation method. The role of CeO₂ additive in the improvement of physicochemical properties and catalytic activity of CuO-CeO₂/ZRM catalysts were emphasized. Several techniques, including Brunauer-Emmett-Teller Nitrogen physisorption measurements, X-ray powder diffraction, hydrogen temperature programed reduction, scanning electron microscopy and transmission electron microscopy (TEM) were used to investigate the properties of catalysts. Crystallite size calculated by Scherrer' equation was 17.4 - 21.8 nm. Modification of 5 wt% CuO/ZRM catalyst with CeO₂ had reduced the size of the nanoparticles leading to a significant enhancement of the catalytic activity in p-xylene deep oxidation at temperature range of 275 - 400 °C. The 5 wt% CuO/ZRM sample promoted by 3 wt% of nanoparticle CeO₂ with the average size of 17.5 nm and BET surface area of 31.3 m² g^-1 exhibited the best activity for p-xylene deep oxidation. In this sample, the conversion of p-xylene reaches to 90% at 350 °C.

Plasma-catalyst hybrid reactor with CeO2/γ-Al2O3 for benzene decomposition with synergetic effect and nano particle by-product reduction

A dielectric barrier discharge (DBD) catalyst hybrid reactor with CeO₂/γ-Al₂O₃ catalyst balls was investigated for benzene decomposition at atmospheric pressure and 30 °C. At an energy density of 37-40 J/L, benzene decomposition was as high as 92.5% when using the hybrid reactor with 5.0wt%CeO₂/γ-Al₂O₃; while it was 10%-20% when using a normal DBD reactor without a catalyst. Benzene decomposition using the hybrid reactor was almost the same as that using an O₃ catalyst reactor with the same CeO₂/γ-Al₂O₃ catalyst, indicating that O₃ plays a key role in the benzene decomposition. Fourier transform infrared spectroscopy analysis showed that O₃ adsorption on CeO₂/γ-Al₂O₃ promotes the production of adsorbed O₂^- and O₂^2‒, which contribute benzene decomposition over heterogeneous catalysts. Nano particles as by-products (phenol and 1,4-benzoquinone) from benzene decomposition can be significantly reduced using the CeO₂/γ-Al₂O₃ catalyst. H₂O inhibits benzene decomposition; however, it improves CO₂ selectivity. The deactivated CeO₂/γ-Al₂O₃ catalyst can be regenerated by performing discharges at 100 °C and 192-204 J/L. The decomposition mechanism of benzene over CeO₂/γ-Al₂O₃ catalyst was proposed.

A Co3O4–CeO2 functionalized SBA-15 monolith with a three-dimensional framework improves NOx-assisted soot combustion

Co₃O₄–CeO₂/SBA-15 monolith can efficiently filter and catalyze the soot particles. The optimized one exhibited a low T₁₀ (293 °C) and T₉₀ (378 °C).