Mechanochemically Prepared Co3O4-CeO2 Catalysts for Complete Benzene Oxidation

Abstract

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.

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

“…This effect caused by potassium could be explained by the possible incorporation of K+ ions having a radius of 1.38 Å as compared to Ce 4+ , Co 2+ , and Co 3+ radii of 1.01, 0.79, and 0.64 Å, respectively. The Co-Ce mixed oxide preparation by grinding procedure determined the surface structural disorder characterized by Co lattice contraction as the magnified patterns in 2θ range of 36-38° showed a shift of Co3O4 (311) plane position toward higher degree values [29,34]. The slight expansion of the Co3O4 and CeO2 lattice could be related to decreased lattice defectiveness determined by gold deposition.…”

“…The mixture was subjected to grinding in an electric mortar (Mortar Grinder RM 200, Retsch, Haan, Germany) for 1 min. The detailed procedure is described in our previous study [29]. Calcination in air at 400 • C for 2 h yielded the Co 3 O 4 -CeO 2 mixed oxide, which is denoted as Co-Ce.…”

“…The chosen carrier for gold deposition was a mechanochemically synthesized mixed oxide containing 70 wt.% Co 3 O 4 and 30 wt.% CeO 2 . The selection of this composition was made based on the best activity of the aforementioned catalytic material manifested in complete benzene oxidation [29]. K + doping effect on HCHO oxidation activity was also evaluated.…”

Bulk Co3O4 for Methane Oxidation: Effect of the Synthesis Route on Physico-Chemical Properties and Catalytic Performance

“…Finally, the signals located at 785.5 and 789.5 eV were identified as the shake-up satellite signals from the Co 2+ and Co 3+ ions, respectively [26]. On the other hand, the O1s spectra of the samples was deconvoluted into four signals located at 529.5, 530.6, 531.5 and 532.6 eV, which were identified as lattice oxygen species, adsorbed oxygen species, oxygen from carbonate and hydroxyl groups and oxygen from adsorbed water, respectively [27,28].…”

“…lattice oxygen species, adsorbed oxygen species, oxygen from carbonate and hydroxyl groups and oxygen from adsorbed water, respectively [27,28]. The surface composition in terms of Co 3+ /Co 2+ and Oads/Olatt molar ratios estimated from the aforementioned deconvolutions is summarized in Table 2.…”