High Performance Au-Pd Supported on 3D Hybrid Strontium-Substituted Lanthanum Manganite Perovskite Catalyst for Methane Combustion

Article abstract of DOI:10.1021/acscatal.6b01685

Bimetallic Au-Pd alloy nanoparticles (NPs) dispersed on nanohybrid three-dimensionally ordered macroporous (3DOM) La_0.6Sr_0.4MnO₃ (LSMO) perovskite catalysts were fabricated via the l-lysine-mediated colloidal crystal-templating and reduction routes. The obtained AuPd/3DOM LSMO samples possess a nanovoid-like 3DOM construction with well-dispersed Au-Pd alloy NPs (2.05-2.35 nm in size) on the internal walls of the macropores. The Au-Pd alloy presence favored catalytic activity for methane combustion. The 3DOM LSMO support exhibits three key attributes: (i) a large surface area (32.0-33.8 m²/g) which AIDS high dispersion of the noble metal NPs on the support surface; (ii) abundant Br?nsted acid sites which facilitate reactant adsorption and activation; and (iii) thermal stability. AuPd/3DOM LSMO has been synthesized with beneficial properties, including a richness of adsorbed oxygen species, increased oxidized noble metal species, low-temperature reducibility, and strong noble metal-3DOM LSMO interaction, all contributing to provide enhanced activity and a structure with high thermal and hydrothermal stability. In situ diffuse reflectance infrared Fourier transform spectroscopy studies revealed that including Au in the bimetallic system accelerated the reaction rate and altered the reaction pathway for methane oxidation by enriching the adsorbed oxygen species and decreasing the bonding strength between the reaction intermediates and the Pd atoms.

Full text of DOI:10.1021/acscatal.6b01685

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Article
High Performance Au-Pd Supported on 3D Hybrid Strontium-Substituted
Lanthanum Manganite Perovskite Catalyst for Methane Combustion
Yuan Wang, Hamidreza Arandiyan, Jason Anthony Scott, Mandana Akia,
Hongxing Dai, Jiguang Deng, Kondo-Francois Aguey-Zinsou, and Rose Amal
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.6b01685 • Publication Date (Web): 06 Sep 2016
Downloaded from http://pubs.acs.org on September 11, 2016
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High Performance Au−Pd Supported on 3D Hybrid Strontium-Substituted
Lanthanum Manganite Perovskite Catalyst for Methane Combustion
§
Yuan Wang,† Hamidreza Arandiyan,†* Jason Scott,†* Mandana Akia,‡ Hongxing Dai, * Jiguang
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§
⊥
Deng, KondoꢀFrancois AgueyꢀZinsou and Rose Amal†
Yuan Wang, Dr. Hamidreza Arandiyan, Dr. Jason Scott, Prof. Rose Amal
†
Particles and Catalysis Research Group, School of Chemical Engineering, The University of New
South Wales, Sydney, NSW 2052, Australia
Prof. KondoꢀFrancois AgueyꢀZinsou
⊥
MERLin Group, School of Chemical Engineering, The University of New South Wales, Sydney, NSW
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052, Australia
Dr. Mandana Akia
‡
Mechanical Engineering Department, University of TexasꢀRio Grande Valley, 1201 West University
Drive, Edinburg, TX 78539, USA.
Prof. Hongxing Dai, Dr. Jiguang Deng,
§
Beijing Key Laboratory for Green Catalysis and Separation, and Laboratory of Catalysis Chemistry
and Nanoscience, Beijing University of Technology, Beijing 100124, China
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ABSTRACT: Bimetallic Au–Pd alloy nanoparticles (NPs) dispersed on nanohybrid
threeꢀdimensionally ordered macroporous (3DOM) La Sr MnO (LSMO) perovskite catalysts were
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fabricated via the Lꢀlysineꢀmediated colloidal crystalꢀtemplating and reduction routes. The obtained
AuPd/3DOM LSMO samples possess a nanovoidꢀlike 3DOM construction with wellꢀdispersed Au–Pd
alloy NPs (2.05–2.35 nm in size) on the internal walls of the macropores. The AuꢀPd alloy presence
favored catalytic activity for methane combustion. The 3DOM LSMO support exhibits three key
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attributes: (i) a large surface area (32.0–33.8 m /g) which aids high dispersion of the noble metal NPs
on the support surface; (ii) abundant Brønsted acid sites which facilitate reactant adsorption and
activation; and (iii) thermal stability. The AuPd/3DOM LSMO has been synthesized with the
beneficial properties, including a richness of adsorbed oxygen species, increased oxidized noble metal
species, lowꢀtemperature reducibility, and strong noble metal–3DOM LSMO interaction, all
contributing to provide enhanced activity and a structure with high thermal and hydrothermal stability.
Inꢀsitu diffuse reflectance infrared Fourier transform spectroscopy studies revealed that including Au
in the bimetallic system accelerated the reaction rate and altered the reaction pathway for methane
oxidation by enriching the adsorbed oxygen species and decreasing the bonding strength between the
reaction intermediates and the Pd atoms.
KEYWORDS: strontiumꢀsubstituted lanthanum manganite; bimetallic goldꢀpalladium catalyst;
threeꢀdimensionally ordered macroporous perovskite; methane combustion; synergism.
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. INTRODUCTION
There is a great interest in using methane as an alternative to coal and oil, given its low carbon
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emissions. However, due to incomplete combustion, unꢀburnt methane always exists in the exhaust.
Methane removal is needed because of its strong greenhouse effect with a global warming potential 23
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2ꢀ4
times higher than that of CO2. Catalytic combustion of methane is regarded as an efficient way to
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conventional thermal combustion for energy production. The temperature of exhaust gases from
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natural gas vehicles (NGVs) is relatively low (typically varying between 300 and 500 °C), therefore
the abatement of methane emissions in the NGV exhaust requires catalysts that combine high activity
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with great resistance to thermal coarsening so as to maintain high combustion rates. Au as a catalyst
has drawn little attention due to its sluggish nature and low melting point (1063 °C). Nevertheless,
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since Hutchings et al.
first reported in 1985 that some Au catalysts were active for the
hydrochlorination of acetylene, Au catalysts have gained increasing attention due to their unique
physicochemical properties, and numerous reactions can be catalyzed by Au catalysts with high
performance. Recently, it has been shown that Pt or Pd alloyed with Au displayed high catalytic
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activities for H O synthesis, N O decomposition, toluene oxidation as well as methane combustion.
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For instance, Hutchings et al. investigated the oxidation of toluene over Au–Pd/TiO catalysts and
found that the Au performed as an electron donor for Pd and the active catalyst had a Pdꢀenriched
surface where the surfaceꢀbound oxygenꢀcentered radicals played a crucial role in toluene activation.
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Chen et al. reviewed a study on the catalytic oxidation of CH
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, and pointed out that the addition of Au
to Pd can boost the overall activity, stability, and selectivity of the supported Pd catalysts. Chen and
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coꢀworkers investigated the mechanism of the promotional effect of Pd–Au alloy catalyst for the
synthesis of vinyl acetate and found that the main role of Au in the bimetallic system was to isolate Pd
atoms which facilitated the desirable coupling of critical surface species and hindered the formation of
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unfavorable reaction byꢀproducts. Additionally, many efforts have been made to study the physical
properties of perovskiteꢀtype oxides (ABO ) which exhibit promising catalytic activity. Levasseur et al.
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synthesized a series of LaBO (B = Co, Fe, and Mn) catalysts by applying a strategy called “reactive
grinding” and found that the catalytic activity for methanol oxidation followed the order of LaMnO
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LaCoO > LaFeO . Due to its outstanding lowꢀtemperature reducibility and large number of oxygen
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vacancies, the perovskiteꢀtype oxide (e.g., LaMnO
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) exhibited better catalytic performance than TiO
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and Co O for the lowꢀtemperature oxidation of volatile organic compounds (VOCs). Considering the
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advantages of noble metals (Au and Pd) and ABO
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, a catalyst system coupling noble metals and ABO
is anticipated to deliver good catalytic activity for methane combustion.
Threeꢀdimensionally ordered macroporous (3DOM) materials have been previously employed to
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catalyze the oxidation of VOCs
due to their good transportation and diffusion properties induced
by their interconnected pore network. Using differently sized polymethyl methacrylate (PMMA)
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microspheres as a template and metal nitrates as the precursor, Arandiyan et al. synthesized
x 3
3DOMꢀstructured La1–xCe CoO (0 > x > 0.9) with a mesopore diameter of 10 nm and surface areas of
2
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6.5–35.4 m /g, where the 3D highly ordered macro/mesoporous La Ce CoO sample exhibited
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high catalytic activity (T90% = 555 °C) for CH oxidation. Earlier, Dai’s research group adopted the
PMMAꢀtemplating and polyvinyl alcohol (PVA)ꢀ or polyvinyl pyrrolidone (PVP)ꢀassisted reduction
approaches to successfully generate a range of 3DOM materialꢀsupported Au NPs, for example,
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Au/3DOM Mn
2
O
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(surface area = 34–38 m /g) , Au/3DOM La0.6Sr0.4MnO
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(surface area = 31–32
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m /g) , Au/3DOM LaCoO (surface area = 24–29 m /g) , and Au/3DOM Co O (surface area = 33–
3
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6 m /g) . Compared to the bulk materialꢀsupported Au catalysts, the 3DOMꢀstructured counterparts
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exhibited better catalytic activity for oxidizing VOCs and/or CO.
Nevertheless, one weakness of
these noble metalꢀloaded porous catalysts is their poor hydrothermal stability.
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For the first time, 3DOM La0.6Sr0.4MnO
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with 1−3 wt% Au−Pd alloy NPs dispersed on the
interconnected skeletons was prepared and the reaction mechanism of methane oxidation was studied
by inꢀsitu DRIFTS over the obtained bimetallic catalysts. The research demonstrates that
3AuPd/3DOM LSMO exhibits a low complete methane conversion temperature (350 °C) and high
thermal and hydrothermal stability. Catalyst characterization confirms the formation of bimetallic sites
and shows that the structures and chemical states remain almost unchanged during reaction at 350 °C
and in the presence of 1−5 vol% water vapor. The blending of surface chemistry (rich adsorbed oxygen,
activated noble metal species, acidic sites), structure (distinct 3DOM architecture and high surface
area), and strong electronic interaction between the Au and Pd as well as the noble metal alloy with the
3DOM support contributes to the promotion of catalytic activity and stability for methane combustion.
In addition, the nature of the key reaction intermediates, mechanism and active ensembles are
examined by inꢀsitu DRIFTS under simulated reaction conditions for methane oxidation. By
understanding the reaction mechanism of methane oxidation and the manner by which bimetallic
catalysts assist in the reaction, we can pave a new synthetic route to design hybrid bimetallic catalysts.
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2
. EXPERIMENTAL
2.1 Synthesis of 3DOM LSMO and Au–Pd supported catalysts
Wellꢀarrayed colloidal crystal template PMMA microspheres with an average diameter of ca. 218 nm
(estimated according to the SEM images (Figure S1A) and supported by particle size distribution
analysis (Zetasizer Nano Z, Figure S1B) were synthesized according to a procedure described
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elsewhere . The zAu Pd /3DOM LSMO (z = 1, 2, and 3 wt%) catalysts were prepared by a
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Lꢀlysineꢀassisted PMMA microsphere hardꢀtemplating method with La(NO
Mn(NO as the metal precursors. The Au−Pd NPs were loaded on the surface of the perovskite
4 4
support using an N ꢀbubbled reduction method, involving the reduction of HAuCl and NaPdCl
3 3 2 3 2
) ·6H O, Sr(NO ) , and
3 2
)
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solutions under an N
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atmosphere with methanol, ethylene glycol (EG), and PVA as the capping agent
(Scheme 1 and Figure S2). The typical procedures for synthesizing 1Au Pd /1DDN LSMO (Au/Pd
x
y
1 2
molar ratio (x : y) = 1 : 1, 1 : 2, and 1 : 3) and zAu Pd /3DOM LSMO catalysts (z = 1, 2, and 3 wt%)
are described in the Supporting Information.
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2.2 Catalyst characterization and activity measurements
Each of the asꢀobtained samples was characterized by X–ray diffraction (XRD) spectroscopy,
highꢀresolution scanning electron microscopy (HRSEM), energy dispersive spectroscopy (EDS),
highꢀresolution transmission electron microscopy (HRTEM), highꢀangle annular darkꢀfield scanning
transmission electron microscopy and energyꢀdispersive Xꢀray spectroscopy (HAADF–STEM–EDS),
N physisorption (Brunauer–Emmett–Teller, BET), 3D environmental atomic force microscope (3D–
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eAFM), inductively coupled plasma atomic emission spectroscopy (ICP–AES),
H
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temperatureꢀprogrammed reduction (H ꢀTPR), NH temperatureꢀprogrammed desorption (NH ꢀTPD),
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Xꢀray photoelectron spectroscopy (XPS) and inꢀsitu diffuse reflectance infrared Fourier transform
spectroscopy (inꢀsitu DRIFTS). Details on the characterization procedures can be found in Supporting
Information. Methane oxidation over the obtained catalysts was conducted according to the process
described in Supporting Information (Figure S3)
3. RESULTS AND DISCUSSION
3.1 Crystal structure and textural properties of 3DOM LSMO and Au–Pd NPs
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XRD patterns of the 3DOM LSMO support (Figure S4) confirm formation of the cubic ABO phase
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which is in good agreement with the standard La Sr MnO sample (JCPDS PDF No. 04ꢀ016ꢀ6114) .
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The calcination conditions are appropriate for generating singleꢀphase ABO3, as illustrated by the XRD
results of 3DOM LSMO with wellꢀdefined crystallinity. In the case of the supported Au, Pd, and
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bimetallic Au–Pd catalysts, loading the noble metal NPs does not alter the ABO structure. The
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average crystallite sizes (Dsupport) of the zAu
Scherrer equation, as summarized in Table 1. The average crystallite size of 3DOM LSMO is ca. 32.9
nm, which is close to those (32.0–33.8 nm) of the zAu Pd /3DOM LSMO samples. No significant
1 2
Pd /3DOM LSMO samples were estimated using the
1
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diffraction signals assignable to Au and/or Pd are observed, possibly due to the low Au and Pd
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loadings (1–3 wt%) and high dispersion of Au and Pd NPs on the 3DOM LSMO surface. The actual
loadings of Au and Pd on the 3DOM LSMOꢀsupported noble metal samples are summarized in Table 1.
It is found that the actual Au and Pd loadings are slightly lower than their nominal values, indicating
that most of the Au and Pd is deposited on the 3DOM LSMO support. The small difference between
the nominal and actual loadings indicates that the N
feasible approach for synthesizing supported Au–Pd catalysts.
Typical N adsorption–desorption isotherms and pore size distributions of the 3DOM LSMO and
zAu Pd /3DOM LSMO samples are shown in Figure S5. The N isotherm observed for each sample is
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gasꢀbubbleꢀassisted reduction strategy is a
2
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2
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classified as a type II isotherm, indicating the formation of a 3DOM structure (Figure S5(A)). The
lowꢀpressure portion of the almost linear middle section of the isotherm, which is attributed to
multilayer adsorption, suggests that the sample is macroporous. A H3ꢀtype hysteresis loop is observed
in the high relative pressure (p/p
0
) range of 0.9–1.0, which is associated with capillary condensation
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taking place in the mesopores, and confirms the presence of mesopores within the wall structure.
Figure S5(B) illustrates the BJH pore size distributions of the samples, each of which includes two
obvious peaks: one sharp peak at around 3–5 nm and one broad peak in the range of 40–100 nm. The
results indicate the coꢀexistence of macropores and textural mesopores within the skeletons of
zAu
1 2
Pd /3DOM LSMO, which is verified by the HRSEM and HRTEM analyses (see below) and pore
size distributions (2.05–2.35 nm). The BET surface areas and pore volumes of the zAu Pd /3DOM
1
2
2
3
LSMO samples are in the ranges of 32.0–33.8 m /g and 0.106–0.130 cm /g, respectively (Table 1),
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which are close to those (32.4 m /g and 0.123 cm /g) of the 3DOM LSMO support and much higher
2
3
than those (4.32 m /g and 0.017 cm /g) of the 1AuPd/1DDN LSMO sample. The 3AuPd/3DOM
2
LSMO sample possesses a large BET surface area (33.8 m /g) due to its thinner walls and nanovoid
1 2
generation. Hence, in contrast to the 1AuPd/1DDN LSMO sample, the zAu Pd /3DOM LSMO
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samples containing mesopores within a macroporous skeleton possess higher surface areas that can
provide more active sites, with the highly developed pore structure also facilitating diffusion and
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adsorption of the reactant molecules. Such unique properties are anticipated to be beneficial for
promoting the catalytic activity of the sample.
3
.2 HRSEM and HAADF–STEM
Figures 1 and 2 show the HRSEM and HRTEM images of 3DOM LSMO, single Au, Pd and bimetallic
AuꢀPd on 3DOM LSMO samples as well as the 3D–eAFM image of the PMMA template. As shown in
Figures 1a and 1b, the HRSEM and 3D–eAFM reconstruction displays a hexagonal array of
wellꢀcalibrated circular microspheres. The oneꢀdimensionally disordered nonporous 1AuPd/1DDN
LSMO sample shows an irregular morphology with a particle size range of 200–600 nm (Figure 1c).
The formation of monolithic nanohybrid ABO with a 3D hierarchical porosity in the 3DOM LSMO
3
support (Figure 1d–f) is observed, exhibiting a pore diameter of about 140 nm. The average pore
diameter of the noble metal supported 3DOM LSMO samples (Figure 1g–l) is smaller by 10–35 %,
when compared with the initial microsphere size of the PMMA template (pore size = 218 nm) as
shown in Figure S6. The shrinkage is caused by the melting of the PMMA template and the sintering
of the produced ABO . Introducing organics, including Lꢀlysine (1.00 g), methanol (3.0 mL), and EG
3
(
3.0 mL) improves the quality of the AuPd/3DOM LSMO pore structure (Figures S7 and S8). Upon
adding PVA, highꢀquality 3DOM architectures with interconnected pore channels were generated in all
of the 3DOM LSMO samples under different fabrication conditions (Figure 1f, h, j and l). From the
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HRTEM images, it is clear that a large number of noble metal NPs are highly dispersed on the surface
of the 3DOM LSMO framework with a mean NP size of 2.05–2.35 nm (Figure 2). Additionally, the
intraplanar spacing (d value) of the obtained 3DOM LSMO samples was found to be 0.260–0.262 nm,
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in good agreement with that of the (110) crystal plane of the standard La0.6Sr0.4MnO sample (0.263
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nm, JCPDS PDF No. 04–016–6114). To examine the morphology and composition of the Au–Pd NPs,
the HAADF–STEM–EDS technique was used to map the distribution of Au, Pd, and other elements in
the 1AuPd/3DOM LSMO sample, as shown in Figures 3 and S9. The EDS phase maps and line
profiles of the asꢀobtained Pd and Au NPs show a homogeneous distribution of the two elements over
the entire particle (Figure 3a–c). Furthermore, the 3D visualization of Pd and Au as well as the EDS
intensity line profiles of the 1AuPd/3DOM LSMO sample eliminates any structural variations such as
coreꢀshell and/or separate phases with the Au–Pd alloy NPs being highly dispersed on the surface of
the 3DOM LSMO skeleton structure (Figure 3d–f). An estimation of Au–Pd alloy NP sizes from the
HRTEM images (Figures S10–12) indicates that the mean NP sizes in AuPd/3DOM LSMO (2.05ꢀ2.20
nm) are uniform and slightly smaller than those for 1Au/3DOM LSMO (2.3 nm) and 1Pd/3DOM
LSMO (2.2 nm). The noble metal NPs seen in the high magnification TEM images (Figures S10b, 11b,
and 12b) imply there is a strong interfacial interaction with 3DOM LSMO as seen by the partial
incorporation of oxidized NP species into the bulk structure of the 3DOM LSMO support (i.e. a strong
2
2
metal–support interaction (SMSI) effect is present). The interaction between the Au–Pd NPs and
3DOM LSMO might be conducive to lattice oxygen mobility and making it favorable for producing
oxygen vacancies on the AuPd/3DOM LSMO surface as will be discussed in more detail in the XPS
section.
3.3 Surface elemental composition, metal oxidation state, and adsorbed oxygen
Profiles of the Mn 2p, Au 4f, and Pd 3d regions of the XPS spectra are provided in Figure 4 with key
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data extracted from the profiles given in Table S1. For each sample, there is an asymmetrical Mn 2p3/2
XPS signal that can be deconvoluted into three components at binding energy (BE) values = 641.2,
3+
4+
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6
42.4, and 643.8 eV (Figure 4A), assignable to surface Mn
,
Mn , and satellite species, respectively.
The surface Mn /Mn molar ratio of the 1AuPd/1DDN LSMO sample (1.26) is lower than that of the
DOM LSMO sample (1.42). On introducing noble metal NPs, however, the zAu Pd /3DOM LSMO
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+
3+
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1
2
3
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1
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0
3
1
2
4
+
3+
2+
0
δ+
0
surface Mn /Mn molar ratio decreases (1.15–0.89), prompting the Pd /Pd and Au /Au molar
ratios to rise (0.31–0.41 and 0.73–1.23, respectively). The 3AuPd/3DOM LSMO sample possesses the
4+
3+
2+
0
δ+
0
lowest surface Mn /Mn molar ratio (0.89) and the highest Pd /Pd (1.23) and Au /Au (0.42) molar
3+
ratios. The XPS results reveal that depositing the Au and Pd elevates the Mn content, implying there
is a strong interaction between the AuꢀPd NPs and LSMO. That is, the LSMO support partially
oxidises the Au/Pd deposits (undergoing partial reduction as a result) as described by the following
Eqns. ((1) and (2)):
Au + Mn → Auꢃꢂ + Mnꢄꢂ
ꢀ
ꢁꢂ
(1)
(2)
Pd + Mn → Pdꢃꢂ + Mnꢄꢂ
ꢀ
ꢁꢂ
The extent to which partial oxidation occurs increases with increasing Au/Pd loading (Table S1) which
has an impact on catalyst performance as is discussed later. The Pd 3d and Au 4f XPS spectra of the
zAu Pd /3DOM LSMO samples provide strong evidence to support this hypothesis.
1
2
The Au 4f spectra of the samples can be deconvoluted into four components (Figure 4B) with the
0
two peaks at BE = 83.8 and 87.5 eV representing the surface Au species and the two peaks at BE =
δ+
δ+
0
8
4.7 and 88.6 eV due to the surface Au species. It is apparent that the Au /Au molar ratio increases
δ+
0
on adding Pd (Table S1). The Au /Au molar ratios of the supported Au–Pd alloy catalysts (0.31–0.42)
are higher than that of the supported Au catalyst (0.20) and increase with the loading of Au–Pd alloy
δ+
0
NPs from 1 to 3 wt%. It has been stated by others that a higher Au /Au molar ratio is indicative of a
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better ability to activate oxygen molecules. Similar phenomena are observed in the Pd 3d XPS
2
+
0
spectra (Figure 4C), in which the Pd /Pd molar ratios of the AuPd/3DOM LSMO catalysts increase
as compared with the Pd/3DOM LSMO catalyst. The asymmetrical Pd 3d XPS spectrum of each
sample can be deconvoluted into four components: the two peaks at BE = 335.4 and 340.8 eV are
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0
assigned to the surface Pd species, while the two peaks at BE = 337.0 and 342.2 eV are attributed to
2+
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2+
0
the surface Pd species. The 1AuPd/3DOM LSMO sample exhibits a Pd /Pd molar ratio (0.73)
which is slightly higher than that of the 1Pd/3DOM LSMO sample (0.71) and considerably higher than
2
+
that of 1AuPd/1DDN LSMO (0.50), suggesting that Au addition can enhance the Pd concentration on
23ꢀ24
the surface
. The result is in good agreement with Hutchings’s finding that Au could act as an
25
2
electron promoter for Pd in bimetallic Au−Pd NPs on TiO . Additionally, it is observed that the Au 4f
and Pd 3d XPS peaks of the 1AuPd/3DOM LSMO and 2AuPd/3DOM LSMO samples shift to lower
and higher BEs (by ca. 0.3 and 0.5 eV), respectively, in relation to the 1Au/3DOM LSMO and
1
Pd/3DOM LSMO catalysts (Figure S13). Such a BE shift has been previously reported and reflects an
electronic structure modification to the surface Au and Pd atoms. That is, electron transfer from the Pd
to Au generating more oxidized Pd while simultaneously Au and Pd donate electrons to the LSMO
4+
3+
support oxidizing Au and further oxidizing Pd, an effect evidenced by the decrease in Mn /Mn
26
ratio. From Figure 4D, a broad and asymmetrical O 1s XPS spectrum for each sample can be
deconvoluted into three components at BE = 529.5, 531.2, 532.2 and 533.4 eV, ascribable to the
surface lattice oxygen (Olatt), adsorbed oxygen (Oads), hydroxyl and/or carbonate species, and adsorbed
27
−
2−
2
−
molecular water species, respectively. The electrophilic species (O , e.g., O , O or O ) can play
ads
2
28
a vital role in the deep oxidation of organics. From Table S1, the surface Oads/Olatt molar ratio follows
the order: 3AuPd/3DOM LSMO (0.94) > 2AuPd/3DOM LSMO (0.64) > 1AuPd/3DOM LSMO (0.55) >
1
Pd/3DOM LSMO (0.49) > 1AuPd/1DDN LSMO (0.44) > 1Au/3DOM LSMO (0.43) > 3DOM
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LSMO (0.34). The higher Oads/Olatt molar ratio for the AuꢀPd alloy catalysts suggests that the
bimetallic system has a strong capacity to activate oxygen, potentially boosting its performance for
29
2+
2–
CH
4
combustion. Burch et al. reported that the Pd and O species at the surface of PdO could
readily activate the almost nonꢀpolar C–H bonds by a heterolytic mechanism. Hence, the actual surface
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δ+
δ+
composition of the noble metals (Pd , Au or Pd , Au ) is crucial in determining the inherent activity
of the catalyst.
3.4 Reducibility and surface acidity
2
H ꢀTPR analysis was conducted to assess the redox properties of the asꢀobtained samples (Figure 5A).
3
+
2+
Since La and Sr are nonꢀreducible under the H ꢀTPR conditions, the peaks observed in the LSMO
2
n+
13
sample can be attributed to the reduction of Mn species. The two peaks, namely α (at ~310 °C) and
4
+
3+
3+
2+ 12, 30
β (at ~650 °C), are credited to the reduction of Mn to Mn (Eqn (3)) and Mn to Mn
(Eqn
3+
(
4)), respectively, with a shoulder at 380 °C due to the singleꢀelectron reduction of Mn located in a
3
0
coꢀordinativelyꢀunsaturated microenvironment (Eqn (5)).
1
1
III
1−x
IV
x
III
La Sr Mn Mn O + xH → La Sr Mn O + xH O
1−x
x
3
2
1−x
x
3−
x
2
2
2
2
(3)
1
1
1
La Sr MnO + H → (1− x)La O + MnO + xSrO + H O
1−x
x
3−
x
2
2
3
2
2
2
2
2
(4)
III
1−x
IV
x+
III
1−x
IV
x
La Sr Mn Mn
O3+δ
+δH → La Sr Mn Mn O +δH O
2
1−x
x
δ
2
1−x
x
3
2
(5)
When Au, Pd or Au–Pd NPs are loaded on the surface of 3DOM LSMO, the reduction peaks shift to
lower temperatures, indicating that the noble metal NPs facilitate reducibility of the sample. Improving
12ꢀ14, 20
the lowꢀtemperature reducibility is beneficial for catalytic performance.
In the case of the monometallic Au and Pd catalysts, the α peak moved significantly (to 160 °C) for the
1Pd/3DOM LSMO whereas it moved slightly (to 305 °C) for the 1Au/3DOM LSMO, suggesting that
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the PdO
x
x
species are more readily reducible than the AuO species. The reduction temperatures (200
and 162 °C) of the α peaks of the bimetallic catalysts are between those of the Au and Pd catalysts and
lower than that of the supported Pd sample when the loading was 3 wt% (125 °C), implying the Au–Pd
catalyst is in an alloyed state and strongly interacts with the 3DOM LSMO support, rather than
existing as a physical mixture of the Au and Pd catalysts.
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Variations in the surface acidity/basicity between 3DOM LSMO and 1DDN LSMO were identified
using NH ꢀTPD analysis. Two peaks are observed in the NH ꢀTPD profile for 3DOM LSMO (Figure
3
3
5B), which leads to the presumption that weak acidic sites (665 °C) and Brønsted acidic sites (860 °C),
31
exist on the surface, in good agreement with the results described by Lu and coꢀworkers. In contrast,
the 1DDN LSMO sample shows one small weak acidic site peak at a temperature of 680 °C. Brønsted
acidic sites have been reported to invoke catalytic enhancement with supported Pd and Pt NPs, helping
32
to adsorb and activate reactant molecules during the catalytic process.
.5 Catalytic performance
Figure 6 depicts the catalytic performance of the AuPd/3DOM LSMO samples for CH
3
4
combustion.
It is apparent from Figure 6A that Au or Pd alone only gives a mildly enhanced activity, whereas
alloying the Au and Pd invokes a substantial improvement in catalytic performance, illustrating a clear
synergism between the two metals. With the rise in overall bimetallic metal loading to 3 wt% the
activity also increases. The synergism between the Au−Pd alloy is further demonstrated on comparison
with a physical mixture of the neat 1Au/3DOM LSMO and 1Pd/3DOM LSMO (same overall metal
loading, Figure S14(A)). Comparing the catalytic performance of the samples on the basis of T10%
,
T
50%, and T90% (Table S1, the temperatures at which CH conversion are 10, 50, and 90 %,
4
respectively), it is apparent that the activity of the bimetallic Au–Pd catalysts increases with increasing
loading. The 1AuPd/3DOM LSMO gives T10%, T50%, and T90% values of 304, 350, and 382 °C which
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are lower than the 1AuPd/1DDN LSMO sample and considerably lower than the neat 3DOM LSMO
sample (Figure S14(B)). Figure 6A illustrates the relationship between catalytic activity and molar
2+
0
δ+
0
ratios of the surface species (i.e. Oads/Olatt, Pd /Pd , and Au /Au ). The comparison reveals that each
7
of these attributes has a clear influence on catalytic performance. Appraisal of the
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zAu Pd /3DOMLSMO catalysts on the basis of turnover frequencies (TOFs) and the reaction rate at
1
2
270 °C is provided in Table 2. The TOFAu–Pd of the samples decrease in the order of 3AuPd/3DOM
LSMO > 2AuPd/3DOM LSMO > 1AuPd/3DOM LSMO > 1Pd/3DOM LSMO >1AuPd/1DDN LSMO >
1Au/3DOM LSMO.
2 2
Figure 6B illustrates the change in TOF with the amount of H consumed during H ꢀTPR analysis
for the neat and bimetallic catalyst compositions and loadings. The change in TOF with deposit
makeꢀup (monoꢀ and bimetallic) and bimetallic loading indicates the perovskite support is having an
impact on the catalyst activity associated with the bimetallic deposits. That is, the catalytic
performance is not solely governed by the additional active sites introduced by the greater number of
Au/Pd atoms on the surface. The roughly linear relationship between the TOF and the reducibility of
the perovskite support (i.e. H consumed during the H ꢀTPR) as the bimetallic loading increases
2
2
implies an effect of the support is responsible for embellishing the activity of the Au/Pd deposits. A
potential explanation for the contribution of the support in enhancing the Au/Pd activity can be found
4
+
3+
in the XPS results (Table S1), in particular the decreasing Mn /Mn ratio (reflecting a partial
2
+
0
δ+
0
reduction in the support) and increasing Pd /Pd and Au /Au (reflecting a partial oxidation of the
deposits) with increasing bimetallic loading. The support acts to withdraw electrons from the
bimetallic deposits, which amplifies their activity beyond just the simple catalyst loading effect. The
result ties in with the findings from Figure S15B which show preꢀtreating the catalyst in oxygen is
beneficial for activity.
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4+
It is interesting also to note that earlier work indicated an increased presence of Mn on the neat
LSMO perovskite correspondingly promoted its catalytic activity for methane oxidation. Here, the
4+
effect is opposite with there being an increase in activity as the Mn presence decreases (Table S1).
The contradictory effect can be explained on the basis of the catalytic activity is being dominated by
the bimetallic deposits (and the concerted oxidising effect of the support) which supercedes any loss in
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4
+
active sites and activity by the associated reduction of Mn in the perovskite support.
To assess the impacts of the Au/Pd molar ratio and catalyst pretreatment on performance, a range of
1Au
LSMO sample being pretreated in O
S15(A) the Pdꢀrich catalysts (1Au Pd /1DDN LSMO, 1Au Pd /1DDN LSMO, and 1Pd/1DDN LSMO)
x
Pd
y
/1DDN LSMO (x/y = 1 : 1, 1 : 2, and 1 : 3) samples were synthesized with the 1Au
1 2
Pd /1DDN
2
or H at 300 °C for 2 h prior to activity assessment. In Figure
2
1
2
1
3
exhibit higher lowꢀtemperature activity (below 400 °C), as compared with the Auꢀrich catalyst. On
adding Pd, the catalytic activity significantly increases with the rise in Au/Pd molar ratio to 1:2, but
further increasing the Au/Pd molar ratio results in a decrease in activity. Hence, the best Au/Pd molar
−
1
ratio is 1:2 with the sample providing the highest TOFAuꢀPd (0.0102 s ) and the lowest apparent
activation energy (E = 72.4 kJ/mol). There remains debate in the literature on the Pd oxidation state
a
33
0
that is most active for CH
4
oxidation. For instance, Cullis et al. found that Pd showed better activity
34
35
on a γꢀAl O support for CH oxidation, whereas Burch et al. and Farrauto et al. pointed out that
2
3
4
0
the Pd species over 4 wt% PdO/Al
2
O
3
were less active or completely inactive toward CH
4
oxidation.
36
2+
After studying the active sites on Pd/Al
2
3 4
O for CH oxidation, Matamet et al. reported that Pd
species were the active sites especially at temperatures below 676 °C, but above this temperature the
reduced Pd could also catalyze the reaction. In the present study (Figure S15(B)), pretreating the
1
Au Pd / 1DDN LSMO catalyst in an O atmosphere considerably improves catalyst performance, as
1 2 2
2
compared with its untreated counterpart or subsequent pretreatment in a H atmosphere. In contrast,
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the activity is marginally better when the catalyst is pretreated in H . The result indicates that the
δ+
2+
0
0
oxidized noble metal (Au and Pd ) species appear to be more active than the metallic (Au and Pd )
species toward CH oxidation. The performance of alternative catalysts for methane oxidation from the
4
literature is summarized in Table S2. Although being influenced by variations in the individual reaction
environments, our bestꢀperforming 3AuPd/3DOM LSMO catalyst exhibits an improved activity
compared to the selected catalysts.
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0
3.6 Catalyst stability and impact of water vapor
Evidence of good catalytic stability can be seen in Figure 6C for the 3AuPd/3DOM LSMO sample
run for 50ꢀh at 350 °C and a GHSV = 50,000 mL/(g h). As moisture is a component of feedstock and
reaction products, it is important to assess its impact on catalytic performance, particularly in terms of
catalyst stability. Figure 6D illustrates the influence of water vapor (1.0, 3.0 or 5.0 vol%) on
performance of the 3AuPd/3DOM LSMO, 1Pd/3DOM LSMO, 1Au/3DOM LSMO, and LSMO
samples when it is introduced into the feed stream at 380 °C for 1 h. Over the 3DOM LSMO and
3AuPd/3DOM LSMO samples, the loss in activity arising from 3 and 5 vol% water vapor presence is
completely reversible when the water vapor is removed. Catalytic activity over the 3DOM LSMO and
3AuPd/3DOM LSMO samples is not significantly influenced by 1.0 vol% H
loss in activity in the presence of water may be due to the competitive adsorption of H O, CH , and O
2
2
O vapor. The temporary
2
4
on the 3DOM LSMO and zAu
1
Pd
2
/3DOM LSMO catalysts. At a higher temperature (550 °C, Figure
O on the samples, which is in
S16), the adsorption of oxygen may be stronger than that of H
2
37
agreement with others. In contrast to the neat support and bimetallic catalyst, introducing water to the
feed stream imposes both temporary and permanent losses to the performance of the 1Pd/3DOM
LSMO and 1Au/3DOM LSMO samples, with the degree increasing as the water content rises. Again,
the temporary loss in activity may be attributable to the competitive adsorption; however, the activity
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is not completely recoverable after introducing the water, whereby a second deactivation process may
be in effect. HRTEM images of the 1AuPd/3DOM LSMO, 1Au/3DOM LSMO, and 1Pd/3DOM
LSMO samples after exposure to water vapor (Figures S10–12) explain the irreversible deactivation of
the monometallic catalysts. The sizes of the noble metal NPs in the monometallic catalysts increase
from 2.25–2.35 to 8.43–13.48 nm upon exposure to water, whereas that of the noble metal NPs in the
bimetallic Au–Pd catalyst increase from 2.15 to 3.76 nm. It appears that the water vapor promotes
sintering of the Au and Pd NPs with the ensuing loss in dispersion, leading to a permanent loss in
activity.
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3.7 In-situ reaction mechanism
To probe the mechanism of methane oxidation over the bimetallic catalysts and understand the role of
Au in the bimetallic system, in situ DRIFTS experiments were conducted with the spectra for
1Pd/3DOM LSMO and 1AuPd/3DOM LSMO provided in Figure 7. The IR absorption bands of
Pd/3DOM LSMO (Figure 7A) can be separated into three spectral zones. The first spectral zone
–
3
displays the adsorption bands mainly corresponding to gaseous methane and CH
species, giving a
–1
sharp peak assignable to the C–H antisymmetric stretching vibration in a free molecule at 3014 cm
–1 38ꢀ39
associated with the deformation vibration of C–H bonds at 1300 cm .
The absorption band
–1
–
3
centered at C–H 1450 cm represents the asymmetric stretching in CH . The second spectral zone
–1
encompasses absorption bands at 2330 and 2360 cm ascribable to the C=O stretching mode of
40
gaseous carbon dioxide. The third spectral zone accounts for other vibrations by different species.
–1
The peaks at 1060 and 1155 cm are assigned to the oxygenꢀoxygen stretching frequency of
–
41ꢀ42
–1
chemisorbed oxygen species (O ) on LSMO.
Intense peaks at 1250 and 1415 cm belong to the
–
ω(CH ) in formaldehyde (H CO), while peaks associated with formate (HCOO ) due to strong
2
2
–1
–1
asymmetric stretching, υas (C–O), are at 1550 and 1690 cm and the absorption peak at 1840 cm
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43ꢀ45
representing the υ (C=O) stretching vibration.
Similar DRIFTS spectra are observed for the
1AuPd/3DOM LSMO sample (Figure 7B), with the exception of variations to the intermediate species
–1
from the third spectral zone. Specifically, there is no ω (CH
2
) in formate (at 1250 and 1415 cm )
–1
whereas a bidentate carbonate species appears at 1170 cm . Additionally, the oxygen species at 1130
0
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–1
cm is adsorbed on Au according to the spectra of 1Au/3DOM LSMO in Figure S17. No CO is
detected with increasing reaction temperature, indicating complete methane combustion over the
1
Pd/3DOM LSMO and 1AuPd/3DOM LSMO catalysts. It is apparent that the intensity of the CH4
–
1
absorption bands (at 3014 and 1300 cm ) decrease with the rise in reaction temperature, while the
–1
intensity of the CO
2
absorption bands (at 2330 and 2360 cm ) simultaneously increases. The
rateꢀdetermining step for the catalytic combustion of methane is often considered to be cleavage of the
46
–
3
–1
first C–H bond. According to the DRIFTS spectra, CH
species at 1300 cm emerge at 200 °C over
–
3
1AuPd/3DOM LSMO while CH species are formed over Pd/ 3DOM LSMO at 300 °C. Moreover,
–1
–1
2
nearly all the methane (at 1300 and 3014 cm ) is converted into CO (2330 and 2360 cm ) at 550 °C
for 1AuPd/3DOM LSMO, indicating an enhanced lowꢀtemperature conversion ability on adding Au, as
compared with 1Pd/3DOM LSMO.
40ꢀ41, 47ꢀ48
Based on the provided DRIFTS spectra and literature,
the methane oxidation mechanism over
the 1Pd/3DOM LSMO and 1AuPd/3DOM LSMO catalysts can be summarized as two separate
sequences of elementary steps. The mechanism proposed for the 1Pd/3DOM LSMO catalyst involves
4
+
3+
electron transfer from the PdO to LSMO, as was evidenced by XPS where the Mn /Mn ratio
–
decreased in the catalyst. The O is activated by electrons on the LSMO to form O species, with the
2
–
–
–
resulting O sites activating CꢀH bonds in CH
4
promoting dehydrogenation into CH
3
and OH . The
–
–
CH and OH subsequently bond to unsaturated sites on the PdO and undergo further Hꢀabstraction to
3
+
+
–
form H and H
2
2 2
CO. The H interacts with O to generate H O while H CO is oxidized first to form
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–
HCOO and then to generate CO
2
which completes a catalytic turnover. The mechanism coincides with
49
other mechanistic assessments for Pd catalysts reported previously which are based on kinetic and
isotopic methods combined with density functional theory (DFT) calculations.
The presence of Au in the bimetallic 1AuPd/3DOM LSMO accelerated the reaction rate and altered
several aspects of the reaction pathway (as shown in Scheme 2). According to XPS, the Au attracts
electrons from the Pd making it more electronegative. Concurrently, electrons are also transferred from
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4+
3+
Au and Pd to the LSMO as evidenced by the additional decrease in the Mn /Mn ratio for the
2
bimetallic system. Thus, O can be activated by electrons from both the Au and LSMO surface to
–
generate O species which can be verified by the oxygen species ratio from XPS (step i). When CH
4
is
–
–
–
3
dehydrogenated to form CH and OH (step ii), the additional active oxygen species promote CH
3
–
dissociation into HCOO which is subsequently oxidized to give bidentate carbonate, bonded to Pd via
two oxygens (step iv). CO is then generated (step v) to complete the turnover cycle.
2
To further appreciate the role of Au in the bimetallic system, the ease of desorption of adsorbed species
at 500 °C was examined using DRIFTS. Spectra from 0 min (which corresponds to when the reactant
gas stream is ceased (i.e. reaction end)) to 10 min under Ar purging for the 3DOM LSMO, 1Pd/3DOM
LSMO and 1AuPd/3DOM LSMO samples are shown in Figure S18. The strength by which the
adsorbed species are attached to the catalyst differs significantly depending on the presence of Pd and
AuꢀPd. Most of the species do not bond strongly to the neat 3DOM LSMO, while the bonding strength
when Pd is present increases substantially. After 10 min under the Ar flow, the intermediates remain on
50
the Pd deposits, agreeing with other reports on the strong bonding strength of Pd. However, the
presence of Au weakens the bonding strength between the Pd and the intermediate species. According
51ꢀ52
to the literature,
on adding copper or gold to an active metal like Pd, the Pd atoms are isolated and
diluted in an Au–matrix (which behaves like supported, highly–dispersed Pd catalysts), leading to an
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electronic “ligand effect”. Thus, the strength of the bond between the reactant or intermediate molecule
and the surface atoms can be modified by the electronic interaction between the surface atom and its
neighbor. From our observations, we conclude that the Au has at least two different roles in our
catalytic system: (1) to modify the electronic structure of the catalyst surface and (2) promote the
presence of adsorbed oxygen species which, in turn, impact on the reaction mechanism. Firstly, the
additional activated oxygen species on the Au and LSMO surfaces accelerates the reaction such that
0
1
2
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4
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8
9
0
1
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–
3
either the CH species are oxidized to CH O which then rapidly dissociates into HCOO– species or
2
–
–
the CH
3 2
species are oxidized directly into HCOO species (explaining the lack of CH O species
observed in the DRIFTS spectra). It has been reported that the electrophilicity of adsorbed oxygen can
–
3
53ꢀ54
–
enhance the dissociation of CH .
Under the elevated activated oxygen environment, the HCOO
2
species also tend to be oxidized to carbonates rather than associate into CO . This corresponds to
4
1
–
literature reports whereby when the O /CH > 2 adsorbed HCOO species are prone to convert to
2
4
–
carbonates. Secondly, the weaker species (e.g. CH
3
) bond strength invoked by the Au–Pd alloy may
–
improve intermediate mobility. This demonstrated by the spectra in Figure S18 where CH
3
is desorbed
–
rapidly under an Ar flow. That is, CH3 can move freely from Pd to Au and/or the LSMO surface
–
where it can more readily interact with the additional O species which accelerates the oxidation
reaction. Consequently, the weakened intermediate bonding strength invoked by the Au can also
facilitate the oxidation process.
4. CONCLUSION
2
Bimetallic AuPd/3DOM LSMO catalysts with high surface areas (32.0–33.8 m /g) for methane
oxidation were successfully fabricated. The bimetallic catalysts, possessing a unique 3DOM structure
and AuꢀPd alloy arrangement, gave excellent catalytic activity which was found to be a combined
effect of both the support and AuꢀPd NPs including (i) the high surface area, (ii) richness in adsorbed
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oxygen, (iii) oxidized noble metal species on the surface, (iv) modified electronic structure of the Au–
Pd alloy, (v) lowꢀtemperature reducibility, and (vi) strong interaction between the Au–Pd alloy and the
3DOM support. The distinctive 3DOM structure, stable NP size and electron interaction within the
bimetallic alloy allowed for optimized thermal and hydrothermal stability displayed by the
AuPd/3DOM LSMO catalysts. Inꢀsitu DRIFTS investigations showed that including Au in the AuꢀPd
bimetallic system altered the reaction pathway and accelerated the reaction rate. The benefits were
attributed to the Au weakening the bonding strength between the reaction intermediates and the Pd
atoms and intensifying the adsorbed oxygen species on the surface of the catalyst.
ASSOCIATED CONTENT
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Corresponding Authors
*
E–mail for Dr. Hamidreza Arandiyan: h.arandiyan@unsw.edu.au; Tel.: +61ꢀ2ꢀ9385ꢀ7994
*E–mail for Dr. Jason Scott: jason.scott@unsw.edu.au; Tel.: +61ꢀ2ꢀ9385ꢀ7361
E–mail for Prof. Hongxing Dai: hxdai@bjut.edu.cn; Tel.: +86ꢀ10ꢀ6739ꢀ6118
*
Notes
The authors declare no competing financial interest.
Supporting Information
Catalyst characterization procedures, synthesis and size distribution of the PMMA microspheres,
preparation of zAu
LSMO, SEM images of PMMA microspheres, HRTEM/HRSEM images of 3DOM LSMO and
AuPd/3DOM LSMO, HAADFꢀSTEM images of 1AuPd/3DOM LSMO, XPS spectra of the samples,
1 2
Pd /3DOM LSMO, catalytic activity measurement, XRD pattern of 1AuPd/3DOM
1
HRTEM/HRSEM images of 1Pd/3DOM LSMO sample after 9 h of onꢀstream 5.0 vol% water
treatment at 380 °C, effects of H and O pretreatments at 300 °C for 2 h over 1Au Pd /1DDN LSMO.
2
2
x
y
This material is available free of charge via the Internet at http://pubs.acs.org.
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ACKNOWLEDGMENTS
Y. Wang thanks the University International Postgraduate Award (UIPA) from The University of New
South Wales for financing her PhD scholarship. H. Arandiyan acknowledges financial support through
the Vice Chancellor Research Fellowship (RG142406) from The University of New South Wales. H.
Dai acknowledges the financial support from the National Science Foundation of China (21377008)
and National High Technology Research and Development Program ("863" Program) of China
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(2015AA034603).
REFERENCES
(
(
(
(
(
1) McCarty, J. G. Nature 2000, 403, 35ꢀ36.
2) Chen, J.; Shi, W.; Yang, S.; Arandiyan, H.; Li, J. J. Phys. Chem. C 2011, 115, 17400ꢀ17408.
3) Meshkani, F.; Rezaei, M.; Andache, M. J. Ind. Eng. Chem. 2014, 20, 1251ꢀ1260.
4) Chen, J.; Zhang, X.; Arandiyan, H.; Peng, Y.; Chang, H.; Li, J. Catal. Today 2013, 201, 12ꢀ18.
5) Chen, J.; Arandiyan, H.; Gao, X.; Li, J. Catal. Surv. Asia 2015, 19, 140ꢀ171.
(6) Burroughs, M. C.; Bhaway, S. M.; Tangvijitsakul, P.; Cavicchi, K. A.; Soucek, M. D.; Vogt, B. D. J.
Phys. Chem. C 2015, 119, 12138ꢀ12148.
(7) Hutchings, G. J. J. Catal. 1985, 96, 292ꢀ295.
(8) Hammer, B.; Norskov, J. K. Nature 1995, 376, 238ꢀ240.
(9) Saiman, M. I.; Brett, G. L.; Tiruvalam, R.; Forde, M. M.; Sharples, K.; Thetford, A.; Jenkins, R. L.;
Dimitratos, N.; LopezꢀSanchez, J. A.; Murphy, D. M.; Bethell, D.; Willock, D. J.; Taylor, S. H.; Knight,
D. W.; Kiely, C. J.; Hutchings, G. J. Angew. Chem. Int. Ed. 2012, 51, 5981ꢀ5985.
(
10) Chen, M.; Kumar, D.; Yi, C.ꢀW.; Goodman, D. W. Science 2005, 310, 291ꢀ293.
11) Levasseur, B.; Kaliaguine, S. Appl. Catal., A 2008, 343, 29ꢀ38.
(
(12) Arandiyan, H.; Dai, H.; Deng, J.; Liu, Y.; Bai, B.; Wang, Y.; Li, X.; Xie, S.; Li, J. J. Catal. 2013,
307, 327ꢀ339.
(13) Arandiyan, H.; Dai, H.; Deng, J.; Wang, Y.; Sun, H.; Xie, S.; Bai, B.; Liu, Y.; Ji, K.; Li, J. J. Phys.
Chem. C 2014, 118, 14913ꢀ14928.
(14) Arandiyan, H.; Dai, H.; Ji, K.; Sun, H.; Li, J. ACS Catal. 2015, 5, 1781ꢀ1793.
22
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Page 23 of 42
ACS Catalysis
1
2
3
4
5
6
7
8
9
(15) Arandiyan, H.; Scott, J.; Wang, Y.; Dai, H.; Sun, H.; Amal, R. ACS Appl. Mater. Interfaces 2016,
8, 2457ꢀ2463.
(
16) Xie, S.; Dai, H.; Deng, J.; Yang, H.; Han, W.; Arandiyan, H.; Guo, G. J. Hazard. Mater. 2014, 279,
92ꢀ401.
17) Liu, Y.; Dai, H.; Deng, J.; Li, X.; Wang, Y.; Arandiyan, H.; Xie, S.; Yang, H.; Guo, G. J. Catal.
013, 305, 146ꢀ153.
18) Li, X.; Dai, H.; Deng, J.; Liu, Y.; Xie, S.; Zhao, Z.; Wang, Y.; Guo, G.; Arandiyan, H. Chem. Eng.
J. 2013, 228, 965ꢀ975.
19) Xie, S.; Deng, J.; Zang, S.; Yang, H.; Guo, G.; Arandiyan, H.; Dai, H. J. Catal. 2015, 322, 38ꢀ48.
3
(
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2
(
(
(20) Arandiyan, H.; Dai, H.; Deng, J.; Wang, Y.; Xie, S.; Li, J. Chemical Communications 2013, 49,
10748ꢀ10750.
(
21) Yan, H.; Blanford, C. F.; Holland, B. T.; Smyrl, W. H.; Stein, A. Chem. Mater. 2000, 12,
134ꢀ1141.
22) Wei, Y.; Liu, J.; Zhao, Z.; Duan, A.; Jiang, G.; Xu, C.; Gao, J.; He, H.; Wang, X. Energy Environ.
Sci. 2011, 4, 2959ꢀ2970.
23) Tan, W.; Guo, G.; Deng, J.; Xie, S.; Yang, H.; Jiang, Y.; Dai, H. Ind. Eng. Chem. Res. 2014, 53,
8452ꢀ18461.
1
(
(
1
(24) Xie, S.; Deng, J.; Liu, Y.; Zhang, Z.; Yang, H.; Jiang, Y.; Arandiyan, H.; Dai, H.; Au, C. T. Appl.
Catal., A 2015, 507, 82ꢀ90.
(25) Kesavan, L.; Tiruvalam, R.; Rahim, M. H. A.; bin Saiman, M. I.; Enache, D. I.; Jenkins, R. L.;
Dimitratos, N.; LopezꢀSanchez, J. A.; Taylor, S. H.; Knight, D. W.; Kiely, C. J.; Hutchings, G. J.
Science 2011, 331, 195ꢀ199.
(26) Long, J.; Liu, H.; Wu, S.; Liao, S.; Li, Y. ACS Catal. 2013, 3, 647ꢀ654.
(27) Liu, Y.; Dai, H.; Deng, J.; Xie, S.; Yang, H.; Tan, W.; Han, W.; Jiang, Y.; Guo, G. J. Catal. 2014,
309, 408ꢀ418.
(28) Rousseau, S.; Loridant, S.; Delichere, P.; Boreave, A.; Deloume, J. P.; Vernoux, P. Appl. Catal., B
2009, 88, 438ꢀ447.
(29) Burch, R.; Crittle, D. J.; Hayes, M. J. Catal. Today 1999, 47, 229ꢀ234.
(30) Fierro, J. L. G.; Tascón, J. M. D.; Tejuca, L. G. J. Catal. 1984, 89, 209ꢀ216.
(31) RodríguezꢀGonzález, L.; Hermes, F.; Bertmer, M.; RodríguezꢀCastellón, E.; JiménezꢀLópez, A.;
Simon, U. Appl. Catal., A 2007, 328, 174ꢀ182.
23
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ACS Catalysis
Page 24 of 42
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(32) Fu, W.; Li, X.ꢀH.; Bao, H.ꢀL.; Wang, K.ꢀX.; Wei, X.; Cai, Y.ꢀY.; Chen, J.ꢀS. Sci. Rep. 2013, 3,
2349.
(
(
(
(
(
(
33) Cullis, C. F.; Willatt, B. M. J. Catal. 1983, 83, 267ꢀ285.
34) Burch, R.; Urbano, F. J. Appl. Catal., A 1995, 124, 121ꢀ138.
35) Farrauto, R. J.; Hobson, M. C.; Kennelly, T.; Waterman, E. M. Appl. Catal., A 1992, 81, 227ꢀ237.
36) Matam, S. K.; Aguirre, M. H.; Weidenkaff, A.; Ferri, D. J. Phys. Chem. C 2010, 114, 9439ꢀ9443.
37) Wang, C.ꢀH.; Chen, C.ꢀL.; Weng, H.ꢀS. Chemosphere 2004, 57, 1131ꢀ1138.
38) Ferrari, A. M.; Huber, S.; Knözinger, H.; Neyman, K. M.; Rösch, N. J. Phys. Chem. B 1998, 102,
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
4548ꢀ4555.
(39) Elmasides, C.; Kondarides, D. I.; Grünert, W.; Verykios, X. E. J. Phys. Chem. B 1999, 103,
5227ꢀ5239.
(40) Schmal, M.; Souza, M. M. V. M.; Alegre, V. V.; da Silva, M. A. P.; César, D. V.; Perez, C. A. C.
Catal. Today 2006, 118, 392ꢀ401.
(
(
(
(
41) Li, Z.; Xu, G.; Hoflund, G. B. Fuel Process. Technol. 2003, 84, 1ꢀ11.
42) Li, C.; Domen, K.; Maruya, K. I.; Onishi, T. J. Chem. Soc., Chem. Commun. 1988, 1541ꢀ1542.
43) Raskó, J.; Kiss, J. Catal. Lett. 111, 87ꢀ95.
44) Liao, L.ꢀF.; Wu, W.ꢀC.; Chen, C.ꢀY.; Lin, J.ꢀL. J. Phys. Chem. B 2001, 105, 7678ꢀ7685.
(45) Chuang, C.ꢀC.; Wu, W.ꢀC.; Huang, M.ꢀC.; Huang, I. C.; Lin, J.ꢀL. J. Catal. 1999, 185, 423ꢀ434.
(46) Burch, R.; Hayes, M. J. J. Mol. Catal. A: Chem. 1995, 100, 13ꢀ33.
(47) Fujimoto, K.ꢀi.; Ribeiro, F. H.; AvalosꢀBorja, M.; Iglesia, E. J. Catal. 1998, 179, 431ꢀ442.
(48) Xu, J.; Ouyang, L.; Mao, W.; Yang, X.ꢀJ.; Xu, X.ꢀC.; Su, J.ꢀJ.; Zhuang, T.ꢀZ.; Li, H.; Han, Y.ꢀF.
ACS Catal. 2012, 2, 261ꢀ269.
(
(
(
(
49) Chin, Y.ꢀH.; Buda, C.; Neurock, M.; Iglesia, E. J. Am. Chem. Soc. 2013, 135, 15425ꢀ15442.
50) Zhao, Z.ꢀJ.; Chiu, C.ꢀc.; Gong, J. Chem. Sci. 2015, 6, 4403ꢀ4425.
51) Burch, R. Acc. Chem. Res. 1982, 15, 24ꢀ31.
52) Liu, P.; Norskov, J. K. PCCP 2001, 3, 3814ꢀ3818.
(53) Silva, I. C. d.; Appel, L. G.; Braun, S. Appl. Catal., A 2006, 314, 172ꢀ178.
(54) Nasser, H.; Rédey, Á.; Yuzhakova, T.; Kovács, J. React. Kinet. Catal. Lett. 2008, 94, 165ꢀ173.
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Table 1. Macropore diameters, BET surface areas, crystallite sizes (Dsupport), pore volumes, noble
metal particle sizes, and actual AuPd loadings of the samples.
b
d
Macropore
BET surface
Pore
D
support
Mean metal
Au
Pd
Noble metal loading
a
c
d
d
Sample
diameter
area
volume
particle size
(nm)
content
(wt%)
content
(wt%)
Nominal
Measured
(wt%)
2
3
(
nm)
(m /g)
(cm /g)
(nm)
(
wt%)
3DOM LSMO
140ꢀ153
130ꢀ145
135ꢀ150
126ꢀ138
130ꢀ140
128ꢀ135
ꢀ
32.4
32.6
32.0
33.6
33.3
33.8
4.32
0.123
0.119
0.130
0.106
0.114
0.113
0.017
36
34
35
34
35
35
55
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
1
1
1
Au/3DOM LSMO
Pd/3DOM LSMO
AuPd/3DOM LSMO
2.4
2.3
2.2
2.0
2.2
2.1
0.94
ꢀ
ꢀ
1
1
1
2
3
1
0.94
0.85
0.92
1.93
2.92
0.95
0.85
0.48
0.98
1.50
0.50
0.44
0.95
1.42
0.45
2AuPd/3DOM LSMO
3
AuPd/3DOM LSMO
AuPd/1DDN LSMO
1
a
b
c
Data were estimated according to the SEM images.
Calculated based on the XRD results according to Scherrer’s equation.
Estimated by statistical analysis of more than 200 NPs in TEM images.
Determined using ICPꢀAES analysis.
d
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Table 2. The specific reaction rates, turnover frequencies (TOFs) and activation energies (E ) of the
3
DOM LSMO, AuPd/3DOM LSMO, and 1AuPd/1DDN LSMO samples.
Methane oxidation at 270°C
Specific reaction rate at 270°C
Kinetic parameter
ꢀ3 ꢀ1
ꢀ3 ꢀ1
Sample
TOFAuꢀPd (×10 s )
TOFcat (×10 s )
ꢁmol/(gcat s)
0.38
ꢁmol/(gAuꢀPd s) ꢁmol/(gLSMO s)
E
a
(kJ/mol)
92.8
3
1
1
DOM LSMO
ꢀ
0.08
0.11
ꢀ
0.38
0.78
0.94
1.00
2.29
3.63
0.90
Au/3DOM LSMO
9.45
11.2
13.5
15.3
16.0
10.2
0.77
76.8
92.8
99.2
112
117
89.5
76.1
Pd/3DOM LSMO
0.21
0.22
0.51
0.80
0.20
0.93
0.99
2.24
3.52
0.90
72.2
56.4
50.5
46.3
72.4
1AuPd/3DOM LSMO
2
AuPd/3DOM LSMO
AuPd/3DOM LSMO
3
1AuPd/1DDN LSMO
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Scheme 1. Schematic illustration of the AuPd/3DOM LSMO catalyst.
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Figure 1. HRSEM and 3DꢀeAFM images of PMMA, 3DOM LSMO, noble metal supported 3DOM
LSMO and 1DDN LSMO.
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Figure 2. HRTEM images of monometallic Au and Pd and bimetallic AuPd/3DOM LSMO catalysts.
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