Tuning of oxygen species and active Pd2+ species of supported catalysts via morphology and Mn doping in oxidative carbonylation of phenol

• Published in: Molecular catalysis 2018-10, Vol.457 (C), p.1-7
• Main Authors: Yang, Xiaojun, Hu, Yue, Bai, Hang, Feng, Maoqi, Yan, Zhiguo, Cao, Shuo, Yang, Bin
• Format: Article
• Language: English
• Subjects: Ceria; Dopants; Morphology; Oxidative carbonylation; Oxygen species
• ISSN: 2468-8231; 2468-8231
• DOI: 10.1016/j.mcat.2018.07.004

[Display omitted] •Mn doping is more efficient at controlling active oxygen species and increasing active Pd2+ species than morphology tuning.•The highest reaction rate was obtained for the Pd/Mn3Ce1O-cube catalyst due to the increased activity of the Pd2+species. A series of nanocubes and nanorods of CeO2 and MnxCeyO (x,y = 1 or 3) oxides were prepared by the hydrothermal method. Samples as prepared were characterized by Transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy, in order to gain a fundamental understanding of the effects of the morphology and Mn dopant on the oxygen species and active Pd2+ species in the oxidative carbonylation of phenol using Pd catalysts supported on as-prepared oxides. Although the oxygen species on supports with different morphologies varied, the catalytic performance in the oxidative carbonylation reaction did not show the significant change. Comparatively speaking, the doping of Mn is a more efficient method to control active oxygen species. It is deduced that Pd and Mn are “dopants” for pure CeO2, both of which improve the formation of oxygen vacancies that help to mitigate the reduction of active Pd species due to the strong interaction between the Pd2+ and the MnxCeyO support. Furthermore, we propose that Oβ (hydroxyl oxygen, chemisorbed oxygen or the oxygen vacancy) species acted as intermediates to lower the reduction of active palladium species by the strong interaction between the noble metal and supports, while the lattice oxygen Oα were involved in the redox cycle of Pd0/Pd2+ in the oxidative carbonylation of phenol to diphenyl carbonate. All results suggest that Mn dopants play a more important role in the activity than morphology does.