Abstract
In the present study, the catalytic activity of palladium oxide (PdOx) supported on ceria nanorods (CeO2-NR) for aerobic selective oxidation of benzyl alcohol (BnOH) to benzaldehyde (PhCHO) was evaluated. The CeO2-NR was synthesized hydrothermally and the Pd(NO3)2 was deposited by a wet impregnation method, followed by calcination to acquire PdOx/CeO2-NR. The catalysts were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), transmission electron microscopy (TEM), Brunauer–Emmet–Teller (BET) surface area analysis, and X-ray photoelectron spectroscopy (XPS). In addition, the TPR-reduced PdOx/CeO2-NR (PdOx/CeO2-NR-Red) was studied by XRD, BET, and XPS. Characterizations showed the formation of CeO2-NR with (111) exposed plane and relatively high BET surface area. PdOx (x > 1) was detected to be the major oxide species on the PdOx/CeO2-NR. The activities of the catalysts in BnOH oxidation were evaluated using air, as an environmentally friendly oxidant, and various solvents. Effects of temperature, solvent nature and palladium oxidation state were investigated. The PdOx/CeO2-NR showed remarkable activity when protic solvents were utilized. The best result was achieved using PdOx/CeO2-NR and boiling ethanol as solvent, leading to 93% BnOH conversion and 96% selectivity toward PhCHO. A mechanistic hypothesis for BnOH oxidation with PdOx/CeO2-NR in ethanol is presented.
Highlights
The catalytic activity of supported noble metals showed dependence on the properties of metal particles [1,2,3] but may depend on the type and characteristics of the chosen support [4].Higher surface area of the nano-structure supports might help with better dispersion of the metal, and if a strong affinity between support and particles occurs, low metal leaching can be achieved
The catalytic activity single atoms supported on different ceria morphologies, namely nanocube, nanorod, and truncated of reduced palladium single atoms supported on different ceria morphologies, namely nanocube, octahedron, in benzyl alcohol (BnOH) oxidation using molecular oxygen as oxidant was investigated by Xin et al [43]
2, respectively), proving oxidation when either toluene or ethanol were utilized as solvent (Table 3, experiments 1 and 2, that the ceria support similar was to the observation by Xin et al, for the aerobic respectively), provingwas thatnot theactive, ceria support not active, similar to the observation by XinBnOH
Summary
The catalytic activity of supported noble metals showed dependence on the properties of metal particles [1,2,3] but may depend on the type and characteristics of the chosen support [4]. The catalytic activity single atoms supported on different ceria morphologies, namely nanocube, nanorod, and truncated of reduced palladium single atoms supported on different ceria morphologies, namely nanocube, octahedron, in BnOH oxidation using molecular oxygen as oxidant was investigated by Xin et al [43]. 26.6% BnOH conversion and 100% PhCHO selectivity This result was slightly higher than that as support (~24% BnOH conversion), even though both CeO2 morphologies exposed the (111) plane, achieved using truncated octahedral CeO2 as support (~24% BnOH conversion), even though both which has a synergy with palladium for catalyzing selective BnOH oxidation [43]. Palladium/ceria catalysts in BnOH oxidation were focused on reduced palladium For this purpose, Pd) and studied its catalytic activity and its PhCHO selectivity in aerobic BnOH oxidation.
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