DOI: 10.1002/cssc.201801709
Full Papers
Interfacial CoOx Layers on TiO2 as an Efficient Catalyst for
Solvent-Free Aerobic Oxidation of Hydrocarbons
Hai Wang,[a] Liang Wang,*[a] Jian Zhang,[b] Chengtao Wang,[b] Ziyu Liu,[e] Xinhua Gao,[f]
Xiangju Meng,[b] Seung Jo Yoo,[g] Jin-Gyu Kim,[g] Wei Zhang,*[c, d] and Feng-Shou Xiao*[a, b]
Construction of efficient interfaces to improve the performance
of supported metal catalysts is a challenging but effective
technique. A newly synthesized catalyst with layered cobalt
oxide on the surface of titania (layer-CoOx/TiO2) is highly selec-
tive towards the aerobic oxidation of CÀH bonds in a series of
hydrocarbons under sustainable conditions. The layer-CoOx/
TiO2 easily outperforms the state-of-the-art noble metal cata-
lysts and homogeneous cobalt salts used in industry. In-depth
structural and functional characterization reveal that the
layer-CoOx/TiO2 readily reacts with O2 for the adsorption and
activation of CÀH bonds. The layered structure of CoOx can
maximize the interfacial effect of CoOx/TiO2 leading to a good
performance for the oxidation of CÀH bonds.
Introduction
Metal nanostructures supported on the surface of metal oxides
have emerged as efficient heterogeneous catalysts for sustain-
able production of chemicals and fuels.[1–19] The interface
between the metal oxide and the active sites is crucial for the
adsorption/activation of reactants/intermediates, and the im-
proved performance can be applied to catalyze various indus-
trial reactions such as CO2 reduction,[1,2] water–gas shift,[3,4] CO
oxidation,[7–10] methane reforming,[11–13] and Fischer–Tropsch
synthesis.[17–19] In-depth knowledge about the nature of an in-
terface could provide a conceptual link between its structure
and performance, thereby facilitating the development of
better heterogeneous catalysts. To date, studies regarding het-
erogeneous–catalyst interfaces have been mostly focused on
nanostructured noble-metal particles on metal oxide/hydroxide
supports. Examples of such systems include Pt/FeOx,[8,20]
Pt/Fe(OH)x,[21] Pd/CeO2,[22] Au/CeO2,[23] and Au/TiO2,[10,24,25] as
[a] H. Wang, L. Wang, F.-S. Xiao
Key Lab of Biomass Chemical Engineering of Ministry of Education
College of Chemical and Biological Engineering, Zhejiang University, Hang-
zhou 310027 (P.R. China)
well as some industrial non-noble-metal catalysts such as Cu/
[26,27]
ZnO/Al2O3
and Ni/CeO2.[11] Comparatively, little is known
about how the interfacial effect can be employed to boost the
activity/selectivity of non-noble-metal catalysts. Simple loading
of metal-oxide nanoparticles on the supports generally
produces limited interfaces, whereas rational construction of
interfaces on non-noble-metal catalysts is challenging.
[b] J. Zhang, C. Wang, X. Meng, F.-S. Xiao
Key Lab of Applied Chemistry of Zhejiang Province, Department of Chemis-
try
Zhejiang University, Hangzhou 310028 (P.R. China)
Aerobic oxidation of sp3-hybridized carbon–hydrogen bonds
is regarded as an important industrial process for producing
alcohols, aldehydes, ketones, and epoxides from petroleum hy-
drocarbons.[28–39] Normally, these reactions are performed at
high temperatures to activate the stable sp3-hybridized CÀH
bonds. This process is unsustainable because of high energy
consumption and poor selectivity due to over oxidation (to
form CO2). Industrial liquid-phase oxidation of cyclohexane is
an example of the low-temperature CÀH bond oxidation pro-
cess. The procedure involves using Co or Mn salts as homoge-
[c] W. Zhang
Key Laboratory of Mobile Materials MOE, Electron Microscopy Center and
School of Materials Science & Engineering, Jilin University
Changchun 130012 (P.R. China)
[d] W. Zhang
CIC Energigune, Albert Einstein 48, 01510 MiÇano
and IKERBASQUE, Basque Foundation for Science
Bilbao 48013 (Spain)
[e] Z. Liu
Key Laboratory of Low-Carbon Conversion Science & Engineering
Shanghai Advanced Research Institute, Chinese Academy of Sciences
Shanghai 201210 (P.R. China)
neous catalysts at around 1608C to obtain cyclohexanol and
[40]
cyclohexanone (denoted as KA oil),
which are required for
[f] X. Gao
production of Nylon-66 and Nylon-6.[41] However, in this tech-
nique the cyclohexane conversion is artificially restricted below
5% to minimize over oxidation, which is unfavorable for KA oil
production.[42,43] To date, many catalysts have been developed
to achieve high conversion and selectivity simultaneously.
However, for developing a successful catalyst, several challeng-
es and drawbacks still need to be overcome, such as use of
State Key Laboratory of High-efficiency Utilization of Coal and Green Chem-
ical Engineering, Ningxia University, Yinchuan 750021 (P.R. China)
[g] S. J. Yoo, J.-G. Kim
Electron Microscopy Research Center
Korea Basic Science Institute, Daejeon 34133 (South Korea)
Supporting Information and the ORCID identification number(s) for the
author(s) of this article can be found under:
ChemSusChem 2018, 11, 1 – 11
1
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