Dual-Site Cooperation for High Benzyl Alcohol Oxidation Activity of MnO₂ in Biphasic MnO_x–CeO₂ Catalyst Using Aerial O₂ in the Vapor Phase

Abstract

Selective oxidation of benzyl alcohol to benzaldehyde in the vapor phase has drawn growing interest recently. In this work, MnO x –CeO2 mixed oxide compositions have been prepared by a coprecipitation method and tested for their oxidation activities of benzyl alcohol to benzaldehyde in the vapor phase. Detailed structural analyses have indicated that MnO x –CeO2 catalysts contain two phases, namely, α-MnO2 and fluorite CeO2 phases. The benzyl alcohol oxidation activity of pure MnO2 is more than 7 times higher compared to that of CeO2, indicating a much higher intrinsic oxidation ability of the MnO2 phase. Further, enhancement of the benzyl alcohol oxidation rate over MnO2 in 10%MnO x –CeO2 catalyst by 13 times is observed in relation to pure MnO2. The role of CeO2 in the MnO x –CeO2 catalyst has also been investigated, which indicates that the oxidation activity is almost independent of CeO2. However, stronger adsorption of benzyl alcohol over the MnO x –CeO2 catalysts compared to that of MnO2 points to the role of CeO2 in adsorption. Thus, both the CeO2 and the MnO2 components have different roles in the catalytic processadsorption of benzyl alcohol on the CeO2 surface and its oxidation on MnO2 at the interface. The cooperation between the two sites toward oxidation could happen due to jumping of adsorbed benzyl alcohol from the surface of the CeO2 phase to the closest Mn4+ site in the MnO2 phase at the contact surface with MnO2 by thermal motion.

Electro-oxidation Reaction of Methanol over Reducible Ce1–x–yNixSryO2−δ: A Mechanistic Probe of Participation of Lattice Oxygen

“…The crystallite sizes of the solution combustion-synthesized materials calculated using Scherrer’s method with respect to the highest intense peak of (111) were 15.19, 8.02, and 5.85 nm for CeO 2 , Ce 0.95 Ni 0.05 O 2−δ , and Ce 0.9 Ni 0.05 Sr 0.05 O 2−δ , respectively. Apparently, with the doping of Ni and the co-doping of Ni and Sr, the material became further nanocrystalline in nature. , The pristine CeO 2 crystallized in a phase-pure cubic fluorite structure with the space group Fm 3̅ m (JCPDS 34-0394). ,, Upon Ni doping, Ce 1– x Ni x O 2−δ did not show any additional diffraction peaks corresponding to Ni or NiO phases. Even with co-doping of Sr, there was complete retention of the pure fluorite phase in Ce 1– x – y Ni x Sr y O 2−δ without any SrO x impurity, as can be seen from the XRD patterns in Figures a and S2a.…”

“…22,23 The pristine CeO 2 crystallized in a phase-pure cubic fluorite structure with the space group Fm3̅ m (JCPDS 34-0394). 15,16,24 Upon Ni doping, Ce S2b). The XRD pattern of 5% NiO/5%SrO/Al 2 O 3 is also plotted in Figure S2b, where the NiO peaks are prominently present.…”

“…Moreover, if the reducible support shows oxophilicity and is prone to the adsorption of oxygenated species, such as −OOH, at a lower potential, then it may further promote the oxidation of CO to CO 2 . Among the range of low-cost oxides, CeO 2 is of particular interest as a result of its high surface area, significant surface defects, and high oxygen storage capacity (redox Ce 4+ /Ce 3+ sites). − In this context, a sizable number of reports showing excellent promotional and anti-poisoning activities of CeO 2 for MOR are available in the literature. , However, most of the reports only focus on the surface dispersion of active metal on CeO 2 and their limited interactions. Furthermore, the unanswered fundamental questions are as follows: (i) does the reducible support of CeO 2 facilitate the Ni 2+ → Ni 3+ oxidation?…”

Beneficial Synergistic Intermetallic Effect in ZnCo2O4 for Enhancing the Limonene Oxidation Catalysis

“…The peaks at 529.4, 531.0, and 532.2 eV can be ascribed to lattice oxygen (O1), oxygen vacancy sites (O2), and water species adsorbed on the catalyst surface, respectively. 42,43 The corresponding areas of the curve fitted peaks are commonly used to estimate the surface elemental contents of the metal oxides. The ZnCo 2 O 4 possesses a higher Co 2+ /Co 3+ ratio of 0.55 than the Co 3 O 4 Oxidation Results and Structure−Performance Study.…”

Low-Temperature Total Oxidation of Propane Using Silver-Decorated MnO2 Nanorods

“…Transition metal oxides such as MnOx, CoOx, and CeOx with well-defined and rationally designed nanostructures have become immensely attractive in research for the complete oxidation of VOCs due to their cost effectiveness and thermal stability. The origin of catalytic activity of these metal oxides toward catalytic oxidation processes is generally described by the classic Mars–van–Krevelen (MvK) mechanism. , That is, the reactants adsorbed on the metal oxides will be oxidized by the lattice oxidation, after which oxygen vacancy (OV) will be created on the surface and these vacant sites will capture fresh oxygen species, resulting in a catalytic cycle. Thus, the formation and regeneration of OVs play a critical role in the redox processes, and the catalytic activity could be significantly enhanced by increasing the OVs.…”