Surfactant-Assisted Synthesis, Characterizations, and Catalytic Oxidation Mechanisms of the Mesoporous MnOx−CeO₂ and Pd/MnOx−CeO₂ Catalysts Used for CO and C₃H₈ Oxidation

Abstract

A series of mesoporous MnOx−CeO2 binary oxide catalysts with high specific surface areas were prepared by surfactant-assisted precipitation. The CO and C3H8 oxidation reactions were used as model reactions to evaluate their catalytic performance. The techniques of N2 adsorption/desorption, XRD, XPS, TPR, TPO, TPD, and in situ DRIFTS were employed for catalyst characterization. It is found that the activity for CO and C3H8 oxidation of the catalysts exhibits a volcano-type behavior with the increase of Mn content. The catalyst with a Mn/Ce ratio of 4/6, possessing a high specific surface area of 215 m2/g, exhibits the best catalytic activity, which is related not only to its highest reducibility and oxygen-activation ability, as revealed by TPR and TPO, but also to the formation of more active oxygen species on the MnOx−CeO2 interface as identified by TPD. After the addition of a small amount of Pd to the MnOx−CeO2 catalyst, its activity for CO oxidation is greatly enhanced, due to the acceleration of gas-phase oxygen activation and transferring via spillover. However, the activity for C3H8 oxidation is hardly promoted due to the different reaction pathways for CO and C3H8 oxidation. For CO oxidation, the gas-phase oxygen activated by Pd can directly react with the adsorbed CO to form CO2, while, for C3H8 oxidation, which takes place at a much higher temperature than CO oxidation, the C−H bond activation and cleavage may be mainly driven by the active oxygen species on the interface between MnOx and CeO2. The addition of Pd shows little effect on the active interface oxygen species, so no promotion upon C3H8 oxidation is observed.

Enhanced catalytic degradation of ciprofloxacin over Ce-doped OMS-2 microspheres

“…5A, the Mn 2p 3/2 peaks of OMS-2 and Ce(0.48)-OMS-2 were at 641.8 eV and 642.4 eV for Mn 3+ and Mn 4+ [24]. The experimental and fitted Ce 3d spectra of Ce(0.48)-OMS-2 were presented in Fig.…”

“…5B. The surface atom ratio of Ce 3+ to Ce 4+ was 1.13, where Ce 3+ = (u + u 0 + v + v 0 ) and Ce 4+ = (u + u + u + v + v + v) [24]. The surface average oxidation state (AOS) of Mn was estimated based on the formula: AOS = 8.956-1.126( E) [25], where E is the Mn 3s multiplet splitting values (Fig.…”

Facile preparation of 3D ordered mesoporous CuOx–CeO2 with notably enhanced efficiency for the low temperature oxidation of heteroatom-containing volatile organic compounds

“…6h), which can be ascribed to the reduction of the surface capping and bulk oxygen of CeO 2 , respectively. 65 The reduction peaks of the CuO x -CeO 2 mixed oxides are systematically shifted towards the lower temperature region compared with bulk-CeO 2 and bulk-CuO, implying that the reduction of copper and cerium oxide is promoted due to the interaction between the Cu and Ce oxide. The htpCCx catalysts have two to four reduction peaks below 500 uC, with the reductive peaks at around 100 and 170 uC attributed to the reduction of the well dispersed Cu species and Cu incorporated into the CeO 2 lattice, respectively.…”

Platinum supported on highly-dispersed ceria on activated carbon for the total oxidation of VOCs

“…Indeed, it is well known the ability of noble metals to facilitate the reduction of reducible oxides, such as ceria, via hydrogen spillover, where hydrogen molecules are chemically adsorbed and readily dissociated into atomic species on the surface of the metal. Then, atomic hydrogen spills over to the support surface and easily reacts with the oxide which is in the oxide-metal interface or in the proximity of the latter, promoting the reduction of the oxide at low temperature [24,34]. Finally, the broad peak appearing around 924 K is related to the bulk reduction of ceria [24,27,35].…”