A. Wang et al.
Catalysis Communications 153 (2021) 106302
adsorption sites and favorable mass transfer related to the ordered
macroporous structure of OM-Co3O4 support.
support, thereby forming the close interface between them. This is well
consistent with the powder XRD results. Meanwhile, one can discern the
lattice fringes of the (101) and (511) crystal facets of Ru0 and Co3O4
phases with facet spacing of 0.206 and 0.155 nm, respectively. In this
case, both the ordered macroporous framework of OM-Co3O4 and the
high dispersion of Ru NPs may favor full exposure of the adsorption and
reaction active sites. In contrast, in addition to a few aggregates of
particles, larger Ru particles with the size of ~15–20 nm are found to be
distributed over the surface of the commercial Co3O4- supported Ru
sample (Fig. S3, ESI). The above results illustrate that OM-Co3O4 support
shows a promotional effect on the improvement of the dispersion of Ru
and the formation of smaller Ru NPs.
2. Experimental
2.1. Catalysts synthesis
Polymethyl methacrylate (PMMA) template beads were prepared by
emulsion polymerization [17]. OM-Co3O4 support was fabricated by a
sacrificial hard template method, and the resulting OM-Co3O4 supported
Ru sample having a Ru loading of about 1.1 wt% was synthesized by the
liquid-phase reduction process using sodium borohydride as reductant
(see details in the Electronic Supporting Information, ESI). Other 3D
ordered macroporous NiO and Al2O3 (denoted as OM-NiO or OM-Al2O3)
and resulting supported Ru catalyst samples were synthesized according
to identical procedures to those for OM-Co3O4 and Ru/OM-Co3O4
samples.
The structural defects can be easily generated through calcination or
reduction treatments during the synthesis of supported catalysts, and
further promote their catalytic performance of catalysts [18,19].
Therefore, XPS characterization was performed to identify surface
electronic states of metal and oxygen species on Ru-based samples
(Fig. 2). In the XPS of Ru 3d5/2 region for the Ru/OM-Co3O4 and Ru/
Co3O4 samples, a peak with a binding energy at ~280.3 eV is observed,
minoring the presence of metallic Ru0 species (Fig. S4, ESI). In the
deconvoluted Co 2p region, Co 2p3/2 and Co 2p1/2 core levels appear at
777–785 and 792.5–801 eV, respectively, indicative of the presence of
Co2+ and Co3+ species [20]. Notably, the surface fraction of Co2+ in the
total Co species on the Ru/OM-Co3O4 (0.51) is larger than that on Ru/
Co3O4 (0.42), reflecting the formation of more defective Co2+ sites.
Meanwhile, XPS of the O 1 s region depicts the existence of three kinds of
oxygen species at ~529.6, 531.3 and 532.8 eV, respectively, which
correspond to lattice oxygen (OI), oxygen species adsorbed on defects (e.
g., oxygen vacancies) or hydroxyl species (OII), and surface carbonate
ions (OIII) [21]. Noticeably, the surface OII/(OI + OII + OIII) fraction on
the Ru/OM-Co3O4 (0.48) is higher than that on the Ru/Co3O4 (0.41),
likely suggestive of the generation of more oxygen vacancies.
2.2. Sample characterizations
Samples were characterized by X-ray diffraction (XRD), scanning
electron microscopy (SEM), transmission electron microscopy (TEM), X-
ray photoelectron spectroscopy (XPS), H2 temperature programmed
desorption (H2-TPD), H2 temperature programmed reduction (H2-TPR),
and Raman spectroscopy (see details in the Electronic Supporting In-
formation, ESI).
2.3. Catalytic HDO tests
Details of catalytic HDO tests are included in the Electronic Sup-
porting Information (ESI).
Raman spectra provide insight into the defective crystal structures.
As illustrated in Fig. S5 (ESI), compared with those for Ru/Co3O4, five
characteristic Raman peaks (F12g, E2g, F22g, F32g, and A1g) of Co3O4 phase
for the Ru/OM-Co3O4 solid all shift to low frequencies at the 532-nm
laser wavelength, despite the reduced peak intensities. These results
demonstrate the presence of lattice distortion/strain of Co3O4 spinel
phase, and thus the formation of more Co2+-Ov-Co2+ like structural
defects (Ov: oxygen vacancies) in the vicinity of Co2+ species on the Ru/
OM-Co3O4 [22,23], mainly thanks to the multiple calcination processes
conducted during the synthesis of OM-Co3O4.
3. Results and discussion
3.1. Sample characterization
As presented in Fig. S1 (ESI), XRD patterns for Ru/OM-Co3O4 sample
exhibit several diffraction peaks, which match well those of the cubic
Co3O4 spinel phase (JCPDS 42–1467). No diffractions corresponding to
metallic Ru0 phase were observed, mainly owing to the small size (< 4
nm) of Ru0 particles and the low Ru loading used (~ 1.1 wt%) deter-
mined by ICP-AES analysis. The results reflect the good dispersion of Ru
species on the surface of OM-Co3O4 support. As shown in Fig. S2 (ESI),
Ru/OM-Co3O4 displays a 3D honeycomb-like ordered macroporous
structure, in which hollow spheres are interconnected together through
walls. TEM images of Ru/OM-Co3O4 (Fig. 1) depict that the large
quantities of small Ru NPs with an average diameter of ~2.53 nm are
uniformly attached on the surface of a nearly uniform OM-Co3O4
3.2. Catalytic HDO performance of supported Ru catalysts
Fig. 3 shows the variation of anisole conversion and product distri-
bution with reaction time after HDO reaction at 250 ◦C and 0.5 MPa over
the Ru/OM-Co3O4 catalyst. The main deoxygenated products are
Fig. 1. TEM (a) and high-resolution TEM (b) images of Ru/OM-Co3O4 catalyst sample. Insets in (a) and (b) show the macroporous network structure and the lattice
fringes of Ru0 and Co3O4 phases, respectively.
2