Effect of support redox character on catalytic performance in the gas phase hydrogenation of benzaldehyde and nitrobenzene over supported gold

Article abstract of DOI:10.1016/j.cattod.2016.06.030

A range of oxides (γ-Al₂O₃, TiO₂, ZrO₂, CeO₂, α-Fe₂O₃ and Fe₃O₄) with different redox properties were used to support nano-scale (mean = 2–8 nm) Au and employed in the gas phase hydrogenation of benzaldehyde and nitrobenzene. The catalysts were subjected to TPR, H₂/O₂ titration, H₂ TPD, XRD, TEM/STEM and XPS analysis. The supported Au phase promoted partial reduction of the reducible supports through the action of spillover hydrogen (based on TPD), which generated surface oxygen vacancies (demonstrated by O₂ titration) that inhibit Au particle sintering during catalyst activation. Electron transfer to generate charged Au species (determined by XPS) correlates with support ionisation potential. Higher nitrobenzene hydrogenation (to aniline) TOFs were recorded relative to benzaldehyde where rate increased with decreasing Au size (from 8 to 4 nm) with measurably lower TOF over Au <3 nm. Strong binding of [sbnd]CH[dbnd]O and [sbnd]NO₂ functions to oxygen vacancies resulted in lower hydrogenation rates. Higher temperatures (>413 K) promoted benzaldehyde hydrogenolysis to toluene and benzene. The formation of Au^δ? on non-reducible Al₂O₃ favoured selective reduction of [sbnd]CH[dbnd]O with full selectivity to benzyl alcohol at 413 K.

Full text of DOI:10.1016/j.cattod.2016.06.030

G Model
CATTOD-10275; No. of Pages10
ARTICLE IN PRESS
Catalysis Today xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Effect of support redox character on catalytic performance in the gas
phase hydrogenation of benzaldehyde and nitrobenzene over
supported gold
Maoshuai Li, Xiaodong Wang, Fernando Cárdenas-Lizana∗, Mark A. Keane
Chemical Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, Scotland, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
A range of oxides (␥-Al2O3, TiO2, ZrO2, CeO2, ␣-Fe2O3 and Fe3O4) with different redox properties
were used to support nano-scale (mean = 2–8 nm) Au and employed in the gas phase hydrogenation
of benzaldehyde and nitrobenzene. The catalysts were subjected to TPR, H2/O2 titration, H2 TPD, XRD,
TEM/STEM and XPS analysis. The supported Au phase promoted partial reduction of the reducible sup-
ports through the action of spillover hydrogen (based on TPD), which generated surface oxygen vacancies
(demonstrated by O2 titration) that inhibit Au particle sintering during catalyst activation. Electron trans-
fer to generate charged Au species (determined by XPS) correlates with support ionisation potential.
Higher nitrobenzene hydrogenation (to aniline) TOFs were recorded relative to benzaldehyde where rate
increased with decreasing Au size (from 8 to 4 nm) with measurably lower TOF over Au <3 nm. Strong
binding of CH O and NO2 functions to oxygen vacancies resulted in lower hydrogenation rates. Higher
temperatures (>413 K) promoted benzaldehyde hydrogenolysis to toluene and benzene. The formation
of Au␦− on non-reducible Al2O3 favoured selective reduction of CH O with full selectivity to benzyl
Received 30 December 2015
Received in revised form 2 June 2016
Accepted 10 June 2016
Available online xxx
Keywords:
Selective hydrogenation
Benzaldehyde
Nitrobenzene
Reducible supports
Oxygen vacancies
Au particle size effect
alcohol at 413 K.
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
port. Smaller Au particles are formed on reducible oxides (e.g. TiO2
and CeO2) relative to non-reducible ZrO2 and SiO2 [11,12]. Higher
The selective hydrogenation of benzaldehyde to benzyl alco-
hol and nitrobenzene to aniline are important in the production of
herbicides, dyes, pigments and fine chemicals [1,2]. Conventional
batch synthesis delivers low product yields, is energy inefficient
and generates significant waste where exclusive reduction of the
carbonyl and nitro group is challenging [3]. Continuous gas phase
reaction presents a number of advantages including ease of prod-
uct/catalyst separation and reduced downtime [4]. Supported Au at
the nano-scale (<10 nm) exhibits unique selectivity in the hydro-
genation of multi-functional reactants although activity is lower
compared with conventional transition metals (Pt, Ru, Pd and Ni)
[5] due to the limited capacity of Au to chemisorb/dissociate H2 [6].
Studies to date on the catalytic hydrogenation of carbonyl (acrolein,
benzalacetone, cinnamaldehyde and crotonaldehyde) [7,8] and
nitro (chloronitrobenzene, nitrostyrene and nitrobenzaldehyde)
[9,10] compounds have shown a dependence on the electronic and
geometric properties of the Au phase that are influenced by the sup-
turnover frequencies (TOF) with decreasing Au size (2–9 nm) has
been reported in the hydrogenation of crotonaldehyde [11,13]
and nitrobenzene [14] for Au supported on TiO2, Al2O3 and SiO2.
Okumura et al. [11] observed higher alcohol selectivity (from cro-
tonaldehyde) over Au/TiO2 than Au/Al2O3 and Au/SiO2. Milone
and co-workers [15] proposed that reducible iron oxides promote
the formation of electron-rich Au through metal-support electron
transfer that favours CH O reduction. Rojas et al. [16] concluded
that negatively charged Au (on SiO2) binds the electrophilic car-
bon in CH O facilitating hydrogenation of cinnamaldehyde and
benzalacetone.
In nitro group reduction, the high selectivity exhibited by
Au/TiO2 has been attributed to metal-support synergy that pro-
motes NO2 activation [17]. Shimizu et al. [18] considered the role
of Al2O3 acidity/basicity in tandem with coordinatively unsatu-
rated Au to dissociate H2 to H+/H− at the metal/support interface
and selectively reduce NO2 in the presence of other reac-
tive functionalities. In the hydrogenation of p-chloronitrobenzene
unwanted hydrodechlorination was reported for Au/Ce0.62Zr0.38O2
and ascribed to C Cl scission at oxygen vacancy sites [19]. Selective
hydrogenation has been well established for Au catalysts but the
∗
Corresponding author.
E-mail address: f.cardenaslizana@hw.ac.uk (F. Cárdenas-Lizana).
http://dx.doi.org/10.1016/j.cattod.2016.06.030
0920-5861/© 2016 Elsevier B.V. All rights reserved.
Please cite this article in press as: M. Li, et al., Effect of support redox character on catalytic performance in the gas phase hydrogenation
of benzaldehyde and nitrobenzene over supported gold, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.06.030

G Model
CATTOD-10275; No. of Pages10
ARTICLE IN PRESS
2
M. Li et al. / Catalysis Today xxx (2016) xxx–xxx
contribution of the support in modifying Au structure, reactant acti-
vation and overall surface reaction mechanism is far from resolved.
In this study we compare the catalytic action of Au nanoparticles on
oxides (␥-Al2O3, ZrO2, TiO2, CeO2, ␣-Fe2O3 and Fe3O4) with distinct
redox character in the hydrogenation of CH O (benzaldehyde)
and NO2 (nitrobenzene) and correlate performance with cata-
lyst structure. We propose surface reaction mechanisms to account
for the role of support reducibility in governing CH O and NO2
activation and product selectivity.
method. Pore volume was measured using the Micromeritics Gem-
ini VII 2390p system. Prior to analysis, samples were outgassed
at 423 K for 1 h in N2. Total pore volume was obtained at a rel-
ative N2 pressure (P/P0) = 0.95. X-ray diffractograms (XRD) were
recorded on a Bruker/Siemens D500 incident X-ray diffractometer
using Cu K␣ radiation. Samples were scanned at 0.02◦ step−1 over
the range 20◦ ≤ 2␪ ≤ 80◦ and the diffractograms identified against
the JCPDS-ICDD reference standards, i.e. Au (04-0784), ␥-Al2O3
(10-0425), anatase-TiO2 (A-TiO2, 21–1272), rutile-TiO2 (R-TiO2,
21–1276), monoclinic-ZrO2 (M-ZrO2, 37–1784), tetragonal-ZrO2
(T-ZrO2, 50–1089), CeO2 (43–1002), ␣-Fe2O3 (hematite, 33-0664)
and Fe3O4 (magnetite, 19-0629). X-ray photoelectron spectro-
scopic (XPS) analysis was performed on a VG ESCA spectrometer
equipped with monochromatised Al K␣ radiation (1486 eV). The
sample was adhered to conducting carbon tape, mounted in the
sample holder and subjected to ultra-high vacuum conditions
(<10−8 Torr). Full range surveys (Au 4f5/2 and 4f7/2 spectra) were
collected where the binding energies (BE) were calibrated with
respect to the C 1s peak (284.5 eV). The Au 4f spectra were fitted
with abstraction of the Shirley background using the Gaussian-
Lorentzian function in XPSPEAK 41. Gold particle morphology (size
and shape) was examined by transmission (TEM, JEOL JEM 2011)
and scanning transmission (STEM, JEOL 2200FS field emission
gun-equipped unit) electron microscopy, employing Gatan Digi-
tal Micrograph 1.82 for data acquisition/manipulation. Samples for
analysis were dispersed in acetone and deposited on a holey car-
bon/Cu grid (300 Mesh). The surface area weighted mean Au size
2. Experimental
2.1. Catalyst preparation and activation
The supports employed in this study were obtained from
commercial sources (␥-Al2O3 (Puralox, Condea Vista), TiO2 (P25,
Degussa) and CeO2 (Grace Davison)) or synthesised (␣-Fe2O3,
Fe3O4 and ZrO2) as described elsewhere [12,20]. Supported Au
catalysts were prepared by deposition-precipitation using urea
(Riedel-de Haën, 99%) as basification agent. An aqueous solution of
urea (100-fold excess) and HAuCl4 (3–7 × 10−3 M, 400 cm3, Sigma
Aldrich, 99%) was added to the support (10–30 g). The suspension
was stirred and heated (2 K min−1) to 353 K where the pH progres-
sively increased (to 6.5–8.0) as a result of urea decomposition:
NH2 CO NH2 + 3H2OT=353K
→
2NH+4 + 2OH− + CO2
(1)
The solid obtained was separated by filtration, washed with dis-
tilled water until Cl free (from AgNO3 test) and dried (2 K min−1
(d) was based on a count of at least 300 particles according to
)
ꢀ
in 45 cm3 min−1 He at 373 K for 5 h. The catalyst precursors were
sieved (ATM fine test sieves) to mean particle diameter = 75 ␮m and
activated at 2 K min−1 to 423–673 K in 60 cm3 min−1 H2. The cata-
lysts were cooled to ambient temperature and passivated in 1% v/v
O2/He for off-line characterisation.
nidi3
i
d =
(2)
ꢀ
nidi2
i
where ni is the number of particles of diameter di.
2.2. Catalyst characterisation
2.3. Catalytic procedure
Gold content was measured by atomic absorption spectroscopy
(Shimadzu AA-6650 spectrometer with an air-acetylene flame)
from the diluted extract in aqua regia (25% v/v HNO3/HCl). The
pH associated with the point of zero charge (pHpzc) of the support
was determined using the potentiometric mass titration technique
described in detail elsewhere [21]. Temperature programmed
reduction (TPR), H2 chemisorption/temperature programmed des-
orption (TPD), O2 chemisorption and specific surface area (SSA)
measurements were conducted on the CHEM-BET 3000 (Quan-
tachrome) unit equipped with a thermal conductivity detector
(TCD) for continuous monitoring of gas composition and the
TPR WinTM software for data acquisition/manipulation. Samples
were loaded into a U-shaped Pyrex quartz cell (3.76 mm i.d.)
and heated in 17 cm3 min−1 (Brooks mass flow controlled) 5% v/v
H2/N2 at 2 K min−1 to 423–673 K for supported Au catalysts and
to 1073–1273 K for the supports where the effluent gas passed
through a liquid N2 trap. The activated samples were swept with
65 cm3 min−1 N2 for 1.5 h, cooled to reaction temperature (413 K)
and subjected to a H2 (BOC, >99.98%) pulse (10 ␮l) titration pro-
cedure. Samples were cooled to ambient temperature, thoroughly
flushed in N2 (65 cm3 min−1) to remove weakly bound H2 and sub-
jected to TPD (at 50 K min−1) to 873–1173 K with a final isothermal
hold until the signal returned to baseline. Oxygen (BOC, 99.9%)
pulse (50 ␮l) titration at 413 K post-TPR was employed to deter-
mine the extent of support reduction where any contribution from
Au to total O2 adsorption is negligible [22]. SSA (reproducible to
8%) was recorded in 30% v/v N2/He with undiluted N2 (BOC,
99.9%) as internal standard. At least three cycles of N2 adsorption-
desorption were employed using the standard single point BET
Catalyst testing was carried out at atmospheric pressure, in
situ after activation, in a continuous flow fixed bed tubular reac-
tor (i.d. = 15 mm) at 413–573 K under conditions of negligible
heat/mass transport limitations. A layer of borosilicate glass beads
served as preheating zone, ensuring the organic reactant was
vaporised and reached reaction temperature before contacting
the catalyst (10–40 mg). Isothermal conditions ( 1 K) were main-
tained by diluting the catalyst bed with ground glass (75 ␮m).
Reaction temperature was continuously monitored by a thermo-
couple inserted in a thermowell within the catalyst bed. Reactants
(benzaldehyde (Fluka, ≥98%), nitrobenzene (Riedel-de Haën, ≥99%)
or benzyl alcohol (Riedel-de Haën, ≥99%)) were delivered as an
ethanolic (Sigma Aldrich, ≥99%) solution to the reactor via a
glass/teflon air-tight syringe and teflon line using a micropro-
cessor controlled infusion pump (Model 100 kd Scientific) at a
fixed calibrated flow rate. Reactions were conducted in a co-
current flow of reactant with H2 (BOC, >99.98%, 60 cm3 min−1
)
at GHSV = 2 × 104 h−1. The molar Au to inlet organic molar feed
rate (n/F) spanned the range 1.2 × 10−3–3.7 × 10−3 h. In blank tests,
passage of each reactant in a stream of H2 through the empty
reactor or over the support did not result in any detectable con-
version. The reactor effluent was collected in a liquid nitrogen
trap for subsequent analysis using a Perkin-Elmer Auto System XL
gas chromatograph equipped with a programmed split/splitless
injector and a flame ionisation detector (FID), employing a DB-
1 (50 m × 0.33 mm i.d., 0.20 ␮m film thickness) capillary column
(J&W Scientific). Data acquisition and manipulation were per-
formed using the TurboChrom Workstation Version 6.3.2 (for
Please cite this article in press as: M. Li, et al., Effect of support redox character on catalytic performance in the gas phase hydrogenation
of benzaldehyde and nitrobenzene over supported gold, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.06.030

G Model
CATTOD-10275; No. of Pages10
ARTICLE IN PRESS
M. Li et al. / Catalysis Today xxx (2016) xxx–xxx
3
Fig. 1. Temperature programmed reduction (TPR) profiles for (I) supported Au (solid lines) and (II) the corresponding supports (dotted lines): (A) ␥-Al2O3, (B) TiO2, (C) ZrO2,
(D) CeO2, (E) ␣-Fe2O3, (F) Fe3O4.
Fig. 2. Hydrogen temperature programmed desorption (TPD) profiles: (A) Au/␥-Al2O3, (B) Au/TiO2, (C) Au/ZrO2, (D) Au/CeO2, (E) Au/␣-Fe2O3, (F) Au/Fe3O4.
Windows) chromatography data system. Reactant conversion (X)
is defined by
where subscripts “in” and “out” refer to inlet and outlet gas
streams. Catalytic activity is also quantified in terms of initial con-
version obtained from time on-stream measurements and turnover
frequency (TOF, rate per active site) calculated using Au dispersion
(D) obtained from STEM analysis [23] according to:
reactant − reactant
[
]
[
]
out
in
X % =
( )
× 100
(3)
(4)
reactant
[
]
in
R
TOF(h−1) =
(5)
and selectivity (S) to product (j) is given by
D
product
[
]
j, out
where
R
represents
reactant
consumption
rate
Sj % =
( )
× 100
in
(molreactant molmetal−1 h−1). Repeated reactions with different
reactant − reactant
[
]
[
]
out
Please cite this article in press as: M. Li, et al., Effect of support redox character on catalytic performance in the gas phase hydrogenation
of benzaldehyde and nitrobenzene over supported gold, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.06.030

G Model
CATTOD-10275; No. of Pages10
ARTICLE IN PRESS
4
M. Li et al. / Catalysis Today xxx (2016) xxx–xxx
samples from the same batch of catalyst delivered raw data
reproducibility and mass balances within 5%.
3. Results and discussion
3.1. Catalyst characterisation
3.1.1. Structural characteristics and temperature programmed
reduction (TPR)
Catalyst physico-chemical characteristics are presented in
Table 1. SSA range from 11 m2 g−1 (Au/Fe3O4) to 166 m2 g−1
(Au/␥-Al2O3) with a corresponding increase in pore volume (0.02-
0.36 cm3 g−1). Values obtained for each catalyst are in good
agreement with those reported in the literature [24–27]. The TPR
profiles of the supported Au catalyst precursors and corresponding
supports are presented in Fig. 1. TPR of Au/␥-Al2O3 (AI) and Au/ZrO2
(CI) generated positive signals with associated temperature max-
ima (Tmax) at 451 and 476 K, respectively where H2 consumption
matched the requirement for Au3+ reduction to Au0 (Table 1). The
profiles generated for the ␥-Al2O3 (AII) and ZrO2 (CII) supports
were featureless with no evidence of H2 uptake or release, as noted
elsewhere [25]. Activation of Au/TiO2 (BI) and Au/CeO2 (DI) pre-
sented H2 consumption peaks at lower temperatures (Tmax = 364
and 420 K) suggesting weaker metal-support interactions. This is
consistent with the work of Delannoy et al. [28] who examined the
effect of support redox character on Au reducibility and reported
more facile reduction on TiO2 and CeO2 relative to Al2O3. Hydro-
gen consumed during TPR of Au/TiO2 exceeded that required for
Au3+ → Au0 (Table 1) and can be attributed to a combined Au reduc-
tion with Ti4+ conversion to Ti3+ at the metal/support interface [29].
The bare TiO2 support did not exhibit a detectable TPR response
(BII). In contrast, thermal treatment of CeO2 generated two broad
signals at 742 K and 1148 K (DII) that can be ascribed to surface
(523–848 K [30]) and bulk (>1073 K [30]) reduction. Hydrogen con-
sumed during the activation of Au/CeO2 exceeded Au precursor
reduction (Table 1) but was significantly lower than the amount
needed for full reduction of the CeO2 carrier (3300 ␮mol g−1). This
suggests partial support reduction where the incorporation of Au
on CeO2 lowered the requisite temperature [31]. TPR of Au/␣-Fe2O3
(EI) resulted in excess H2 consumption at Tmax = 389 K whereas TPR
of ␣-Fe2O3 (EII) generated a signal at 709 K with a broader con-
sumption at T >800 K suggesting a two-stage reduction of hematite,
i.e. ␣-Fe2O3 → Fe3O4 → FeO. The TPR response for Au/Fe3O4 (FI)
also reveals a down shift in Tmax relative to the support (FII). The
excess H2 consumed (Table 1) fell below that for conversion of
Fe3O4 to FeO (4250 ␮mol g−1) again indicative of partial support
reduction. Our results demonstrate a more facile reduction of ceria
and iron oxide supports due to the presence of Au. Jacobs et al. [32]
have established partial CeO2 reduction by spillover hydrogen fol-
lowing dissociative adsorption on supported Au. Furthermore, Scirè
and co-workers [33] proposed that Au can weaken the Fe-O bond
in iron oxide substrates resulting in greater lattice oxygen mobility
and enhanced reducibility.
3.1.2. Hydrogen temperature programmed desorption (TPD) and
O2 chemisorption
Application of TPD to measure surface hydrogen release can
allow differentiation between chemisorbed and spillover species
which both serve as reactive hydrogen in hydrogenation [34]. The
TPD profiles generated for all the catalysts are shown in Fig. 2.
The literature suggests a lower temperature requirement for H2
desorption from metal sites (<473 K) compared with release of
spillover from the support (>503 K) [35]. A predominant H2 des-
orption at Tmax ≥ 575 K was observed in this work suggesting that
the main contribution is due to spillover. Hydrogen spillover is
Please cite this article in press as: M. Li, et al., Effect of support redox character on catalytic performance in the gas phase hydrogenation
of benzaldehyde and nitrobenzene over supported gold, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.06.030

G Model
CATTOD-10275; No. of Pages10
ARTICLE IN PRESS
M. Li et al. / Catalysis Today xxx (2016) xxx–xxx
5
Fig. 3. XRD patterns for activated/passivated (A) Au/␥-Al2O3, (B) Au/TiO2, (C) Au/ZrO2, (D) Au/CeO2, (E) Au/␣-Fe2O3 and (F) Au/Fe3O4; reference JCPDS-ICDD patterns (see
card No. in Section 2.2) are included for Au, ␥-Al2O3, anatase TiO2 (A-TiO2), rutile TiO2 (R-TiO2), monoclinic ZrO2 (M-ZrO2), tetragonal ZrO2 (T-ZrO2), CeO2, ␣-Fe2O3 (hematite)
and Fe3O4 (magnetite).
Fig. 4. Representative TEM/STEM images of (A) Au/␥-Al2O3, (B) Au/TiO2, (C) Au/ZrO2, (D) Au/CeO2, (E) Au/␣-Fe2O3 and (F) Au/Fe3O4 with associated Au size distribution
histograms.
influenced by the concentration of initiating and acceptor sites, cat-
alyst activation and metal nanoparticle size (i.e. degree of contact
between participating phases and metal-support interaction(s))
[35]. As a general observation, H2 release from Au supported on
non-reducible (Al2O3, ZrO2) supports (28–51 mmol gAu−1) was sig-
nificantly greater than that recorded for Au on reducible carriers
Please cite this article in press as: M. Li, et al., Effect of support redox character on catalytic performance in the gas phase hydrogenation
of benzaldehyde and nitrobenzene over supported gold, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.06.030

G Model
CATTOD-10275; No. of Pages10
ARTICLE IN PRESS
6
M. Li et al. / Catalysis Today xxx (2016) xxx–xxx
Fig. 5. XPS spectra over the Au 4f region for (A) Au/␥-Al2O3, (B) Au/TiO2, (C) Au/ZrO2, (D) Au/CeO2, (E) Au/␣-Fe2O3 and (F) Au/Fe3O4; experimental data are given by ᭿ where
lines represent data fitting with peak deconvolution.
(≤9 mmol gAu−1). There is compelling evidence in the literature
pre-treatment [25]. The XRD patterns of Au on CeO2, ␣-Fe2O3 and
Fe3O4 (Fig. 3(D–F)) match those of the supports and we can discount
bulk support reduction, i.e. CeO2 → Ce2O3, Fe2O3 → Fe3O4 and/or
Fe3O4 → FeO.
for hydrogen spillover onto Al2O3 [34,35] and ZrO2 [36,37] from
supported metals (Pd, Ni, Cu and Ru). The greater H2 desorption
from Au/␥-Al2O3 relative to Au/ZrO2 can be attributed (at least in
part) to the higher SSA of Al2O3 which can accommodate more
spillover. Consumption of spillover hydrogen in the partial reduc-
tion of (reducible) titania, ceria and iron oxide can account for the
observed lower levels of H2 TPD [34]. We employed O2 chemisorp-
tion post-TPR as a measure of support reduction [22]. Gold on CeO2,
␣-Fe2O3 and Fe3O4 exhibited greater O2 uptake (Table 1) than that
measured for Au/TiO2, Au/␥-Al2O3 and Au/ZrO2. The difference in
Gold particle morphology was evaluated by TEM/STEM and
the representative images in Fig. 4 reveal quasi-spherical parti-
cles at the nano-scale. Surface area weighted mean Au size was
obtained from the size distribution histograms and are recorded in
Table 1. Gold on ␥-Al2O3 (A) exhibited metal particles in the 1–8 nm
range with a mean of 4.3 nm. Appreciably larger Au particles
(2–12 nm, mean = 7.0 nm) are observed on ZrO2 (C), consistent with
the report of Mohr et al. [45] for Au/ZrO2 preparation by deposition-
precipitation. Reducible CeO2 (D) and ␣-Fe2O3 (E) supports show
narrower Au size distribution (1–5 nm) and smaller mean values
(2.0-2.6 nm) than Au/TiO2 ((B), 1–9 nm, mean = 4.5 nm). Support
oxygen vacancies stabilise transition metal nanoparticles and
inhibit sintering [46], which may result in the formation of smaller
Au particles on ␣-Fe2O3 and CeO2 that bear a greater number
of vacancies than Au/TiO2 (Table 1). It should be noted that a
wider Au size range and mean (=7.6 nm) characterised Au/Fe3O4.
Support charge density, reflected in the pH point of zero charge
(pHpzc), determines precursor-support interaction in synthesis by
deposition-precipitation and can govern ultimate Au size post-TPR.
Where solution pH < pHpzc, the support bears a positive charge
favouring interaction with anionic Au species. Conversely, where
solution pH > pHpzc the Au precursor and support experience
repulsive effects due to the negative surface charge resulting in
weaker Au-support interaction leading to Au−agglomeration dur-
ing activation [47]. Solution pH controls AuCl4 hydrolysis rate via
O2 adsorption can be correlated with support redox character [38],
where the former group of oxides are characterised by higher redox
potentials (Eredox) (Table 1). Increasing O2 chemisorption coincided
with greater excess H2 consumption during TPR due to support
reduction with the formation of oxygen vacancies. Oxygen defi-
cient sites can be generated by loss of lattice oxygen from reducible
metal oxides during thermal treatment in H2 or CO [39]. Boccuzzi
et al. [40,41] demonstrated by FTIR spectroscopy the formation of
oxygen vacancies following reduction in H2 of Fe2O3, TiO2 and CeO2
to 523 K. Moreover, formation of Ce3+ defects/surface vacancies in
Au/CeO2-Fe2O3 has been linked to the action of spillover hydrogen
[42].
3.1.3. X-ray diffraction (XRD) and electron microscopy analysis
Structural analysis by XRD generated the diffractograms pre-
sented in Fig. 3. There was no clearly discernible peak for Au (at
2␪ = 38.1◦) which may be due to masking by stronger signals due to
the support or the formation of Au particles at the nano-scale and
below detection limit ( < 5 nm) [43]. The XRD pattern of Au/␥-Al2O3
is characterised by peaks at 2␪ = 37.6◦, 39.5◦, 45.9◦ and 67.0◦ due to
cubic ␥-Al2O3. XRD analysis of Au/TiO2 revealed a mixture of tetrag-
onal anatase (2␪ = 25.3◦, 37.8◦, 48.1◦ and 62.8◦) and tetragonal rutile
(2␪ = 27.4◦, 36.1◦, 41.2◦, 54.3◦, 56.6◦, 69.0◦ and 69.8◦) phases with
an anatase:rutile ratio (5:1) that matches the reported Degussa P25
composition [44]. Au/ZrO2 showed mixed monoclinic (2␪ = 28.2◦,
31.5◦, 34.2◦, 34.4◦, 35.3◦, 40.8◦, 49.3◦, 50.2◦, 50.6◦ and 55.6◦) and
tetragonal (2␪ = 30.3◦, 35.3◦, 50.4◦, 50.7◦, 59.6◦ and 60.2◦) phases
with monoclinic/tetragonal ∼2. Zirconia phase composition is sen-
sitive to synthesis route and calcination temperature with ratios
in the range 1.2-3.2 reported for comparable ZrO2 preparation and
substitution of Cl− by OH− where Au(OH)4 predominates at the
−
final pH (6.5–8.0, see experimental Section 2.1) [48]. Support pHpzc
are given in Table 1 where the lower value for Fe3O4 (5.8) does
not favour interaction with (anionic) Au precursor species and can
account for larger Au size.
3.1.4. X-ray photoelectron spectroscopy (XPS) analysis
XPS measurements were conducted to probe support effects
in modifying Au electronic character. XPS profiles over the Au
4f binding energy (BE) region are given in Fig. 5. The Au 4f7/2
BE for Au/␥-Al2O3 (83.3 eV) and Au/TiO2 (83.5 eV) are close to
values reported in the literature (Au/Al2O3 (83.1 eV) [49] and
Please cite this article in press as: M. Li, et al., Effect of support redox character on catalytic performance in the gas phase hydrogenation
of benzaldehyde and nitrobenzene over supported gold, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.06.030

G Model
CATTOD-10275; No. of Pages10
ARTICLE IN PRESS
M. Li et al. / Catalysis Today xxx (2016) xxx–xxx
7
Au/TiO2 (83.3 eV) [50]) and fall below the reference metallic Au
(83.7–84.0 eV) [51], indicative of electron donation from the sup-
port [52]. Gold on CeO2 (Table 1) exhibits an Au 4f7/2 BE consistent
with that published for Au/CeO2 (84.5 eV) [53] but lower than Au+
(85.8–86.0 eV) [51]. A partial positive charge (Au␦+) has been pro-
posed for Au/CeO2 resulting from electron transfer from Au [54].
The data presented in Fig. 6 show a dependence of Au 4f7/2 BE on
support redox potential where electron transfer from Au is facili-
tated by carriers with higher potential. Gold electronic structure is
also dependent on Au cluster size where any shift in BE is more pro-
nounced with decreasing coordination number [55]. The formation
of smaller particles on Au/CeO2 can also contribute to an upshift of
BE.
3.2. Catalyst activity/selectivity
Fig. 6. Dependence of Au 4f7/2 binding energy (BE) on the standard redox potential
(Eredox) of the oxide supports: (A) ꢀ Au/␥-Al2O3; (B) ꢁ Au/TiO2; (C) ꢂ Au/ZrO2; (D)
ꢃ Au/CeO2; (E) ꢄ Au/␣-Fe2O3; (F) ᭿ Au/Fe3O4.
Benzyl alcohol was the sole product detected in the hydrogena-
tion of benzaldehyde at 413 K. In contrast, gas phase (383–413 K)
benzaldehyde conversion over (SiO2, Al2O3, TiO2, CeO2 and ZrO2)
supported Cu and Ni resulted in CH O hydrogenolysis (to toluene)
and/or C C scission (to benzene) [56,57]. The relationship between
benzaldehyde turnover frequency (TOF at 413 K) and Au particle
size (d) is shown in Fig. 7(I). An increase in TOF is evident with
decreasing Au particle size over the 8–4 nm range which can be
linked to greater H2 uptake under reaction conditions (Table 1).
The highest specific rate was recorded for Au/␥-Al2O3 with no
detectable activity for catalysts bearing the smallest Au sizes (Au/␣-
Fe2O3 and Au/CeO2). It has been established that Au exhibits
metal to insulator transition for particles ≤3 nm [58] and decreas-
ing hydrogenation activity for smaller Au particles (5 → 1 nm) has
been ascribed to a critical loss of metallic character [59]. Although
there is insufficient published data to arrive at any reliable trends
regarding Au size effects in CH O hydrogenation, we can note
the reported decrease in acrolein TOF over Au/ZrO2 for Au par-
ticles >4 nm [45] and increase with increasing Au size (1–5 nm)
over Au/ZrO2 and Au/TiO2 [59]. In contrast to the benzaldehyde
reaction, each catalyst was active in nitrobenzene hydrogenation
(Fig. 7(II)) with a TOF maximum for Au/␥-Al2O3. The greater reactiv-
ity of the nitro-reactant agrees with results (for Pt/Al2O3) reported
by Arai et al. [60] where a six-fold higher rate was recorded for
nitrobenzene relative to benzaldehyde hydrogenation. This was
linked to reaction thermodynamics where nitrobenzene to aniline
(ꢀG413K = −436 1 kJ mol−1) is more favourable than benzalde-
hyde hydrogenation to benzyl alcohol (ꢀG413K = −24 2 kJ mol−1).
With respect to support reducibility, TOF was higher at lower
redox potential as shown in Fig. 8. Au/ZrO2 deviates somewhat
from the general trend, which we tentatively attribute to the occur-
rence of larger Au particles (Fig. 4(C)) that show low activity in
hydrogenation. Lower TOF at higher redox potential suggests that
Table 2
Effect of reaction temperature on turnover frequency (TOF) and product selectivity
(Sj) for the conversion of benzaldehyde over Au/␥-Al2O3, Au/Fe3O4 and Au/CeO2.
Catalyst
T (K)
TOF (h−1
)
Sbenzene (%)
Stoluene
Sbenzylalcohol
(%)
(%)
413
473
573
82
126
258
0
0
71
0
70
21
100
30
8
Au/␥-Al2O3
a
413
473
573
–
10
21
–
90
79
–
0
0
Au/Fe3O4
192
378
a
413
473
573
–
0
20
–
100
80
–
0
0
Au/CeO2
8
49
a
No detectable activity.
or NO2 activation for reaction. It is known that these vacan-
cies can strongly bind adsorbed oxygenated species [61]. Gold on
non-reducible ␥-Al2O3 with the formation of Au␦− (from XPS anal-
ysis) delivered the highest TOF. This agrees with published studies
[16,62] which have shown that CH O activation and alcohol for-
mation is facilitated on negatively charged Au via interaction with
the electrophilic carbon. Given the negligible benzaldehyde hydro-
genation activity over catalysts with smaller (<4 nm) and larger
(>7 nm) Au particles at 413 K, we evaluated the effect of reac-
tion temperature on rate and selectivity for Au/CeO2 and Au/Fe3O4
which can be compared with Au/␥-Al2O3 in Table 2. In each case
an increase in TOF was observed at higher temperature. A switch
was observed from exclusive CH O hydrogenation (to benzyl
alcohol) at 413 K to hydrogenolysis (to toluene) at 473 K with a
oxygen vacancies on reducible supports do not favour CH
O
Fig. 7. (I) Benzaldehyde (T = 413 K, n/F = 1.2 × 10−3 h) and (II) nitrobenzene (T = 413 K, n/F = 3.7 × 10−3 h) turnover frequency (TOF) as a function of Au particle size (d): (A) ꢀ
Au/␥-Al2O3; (B) ꢁ Au/TiO2; (C) ꢂ Au/ZrO2; (D) ꢃ Au/CeO2; (E) ꢄ Au/␣-Fe2O3; (F) ᭿ Au/Fe3O4.
Please cite this article in press as: M. Li, et al., Effect of support redox character on catalytic performance in the gas phase hydrogenation
of benzaldehyde and nitrobenzene over supported gold, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.06.030

G Model
CATTOD-10275; No. of Pages10
ARTICLE IN PRESS
8
M. Li et al. / Catalysis Today xxx (2016) xxx–xxx
Fig. 8. Dependence of turnover frequency (TOF) on the standard redox potential of the oxide supports (Eredox from [38]) in (I) benzaldehyde and (II) nitrobenzene hydro-
genation: (A) ꢀ Au/␥-Al2O3; (B) ꢁ Au/TiO2; (C) ꢂ Au/ZrO2; (D) ꢃ Au/CeO2; (E) ꢄ Au/␣-Fe2O3; (F) ᭿ Au/Fe3O4.
Table 3
base [70]. FTIR analysis has demonstrated that surface Lewis acid
sites on Al2O3 promote CH O activation in the hydrogenation
of nitrobenzaldehyde [71]. Activation and scission of CH2–OH
Benzyl alcohol turnover frequency (TOF) and product selectivity (Sj) for reaction
over Au/Fe3O4 and Au/CeO2: T = 573 K.
Catalyst
TOF (h−1
)
S benzene (%)
S toluene (%)
S benzaldehyde (%)
(steps B and C, Fig. 10), CH O (step D) and the aryl-carbonyl bond
(steps E and F) is promoted at elevated temperature (473–573 K)
with the formation of toluene and benzene. In the conversion of
nitrobenzene (Fig. 9(II)) nitro group interaction with oxygen vacan-
cies (steps A and B) has been proposed [72]. Attachment to surface
vacancies can also stabilise the nitro group with lower resultant
reaction rates but the greater reactivity of the NO2 function (rela-
tive to CH O) resulted in measurable activity for each catalyst at
413 K. Interaction of NO2 with an oxygen vacancy and N O bond
dissociation generates nitrosobenzene (step C) with subsequent
reduction to a phenylhydroxylamine intermediate (step D) and ani-
line formation and release (step E) [68]. Dissociative interaction of
H2O with oxygen vacancies serves to re-oxidise the support.
Au/Fe3O4
Au/CeO2
364
17
0
8
95
17
5
75
predominant aryl-carbonyl hydrogenolytic scission (to benzene)
at 573 K over Au/␥-Al2O3. A higher temperature (to 498 K) has
been shown to promote benzaldehyde conversion to toluene and
benzene over Cu/Al2O3 [56] and Ni/SiO2 [63]. Benzaldehyde hydro-
genation to benzyl alcohol was not observed over Au/Fe3O4 and
Au/CeO2 at any reaction temperature (Table 2). Increased temper-
ature generated toluene as principal product with higher selectivity
to benzene at 573 K (Table 2). Gold on redox supports exhibited a
dominant hydrogenolytic character. Reaction of benzyl alcohol as
feedstock (at 573 K) over Au/Fe3O4 generated toluene as principal
product and benzaldehyde (with no detectable benzene) at a sim-
ilar TOF to that recorded for the benzaldehyde reaction (Table 3).
This points to production of toluene from benzaldehyde via consec-
utive conversion of benzyl alcohol whereas benzene is generated
from aldehyde hydrogenolysis. Benzaldehyde was the principal
product in reaction over Au/CeO2, which can be attributed to oxida-
tive dehydrogenation [64]. This step involves the catalytic action of
surface or lattice oxygens associated with the support and the high
aldehyde selectivity exhibited by Au/CeO2 (Table 3) must be due
to greater oxygen mobility relative to Fe3O4 as inferred from O2
chemisorption (Table 1).
Surface oxygen vacancies have been proposed as active sites in
a range of applications from automobile exhaust treatment [65],
water-gas shift [66] to steam reforming of oxygenates [67]. There
is ample evidence that these vacancies can participate in a Mars
and van Krevelen (MvK) mechanism with catalyst surface reduc-
tion (oxygen depletion) and re-oxidation (oxygen generation) [68].
We propose the involvement of oxygen vacancies in MvK cat-
alytic hydrogenation, as illustrated in Fig. 9. The vacancies, created
through H2 chemisorbed on Au that spills onto the support (step
A, Fig. 9(I)) with H2O release, act as strong anchoring sites for the
carbonyl group (steps B and C) [69], inhibiting reactivity. The sta-
bilised carbonyl function can be activated at elevated temperature
(473 K) with benzyl alcohol formation and subsequent hydrogenol-
ysis (step D) or direct hydrogen scission of the CH O bond (step
E) to toluene. Higher temperature facilitates hydrogen cleavage to
give benzene (step F). In contrast, adsorption on non-reducible sur-
faces (e.g. Al2O3) via the carbonyl function (step A, Fig. 10) results in
hydrogenation to the alcohol at low reaction temperature (413 K).
DFT calculations have shown that a perpendicular adsorption mode
is the most stable configuration with CH O bonded to the metal
oxide surface via the oxygen lone electron pair that acts as a Lewis
4. Conclusions
We have demonstrated that oxide support reducibility and Au
size (mean = 2–8 nm) governs the catalytic performance of Au in
the reduction of CH O (benzaldehyde) and -NO2 (nitrobenzene).
TPR coupled with oxygen chemisorption has established partial
support (TiO2, CeO2, ␣-Fe2O3 and Fe3O4) reduction due to the
action of spillover hydrogen generated by H2 dissociation on Au.
XPS analysis provided evidence of electron transfer between Au
and the oxide carriers. Increasing reaction rates were observed
with decreasing Au size (from 8 to 4 nm) with measurably lower
rates over Au <3 nm. Gold on reducible supports (CeO2, ␣-Fe2O3
and Fe3O4 where Eredox > 0) exhibited lower benzaldehyde and
nitrobenzene TOF relative to Au/␥-Al2O3, Au/TiO2 and Au/ZrO2
(Eredox < 0), which we attribute to inhibition due to the action of
surface oxygen vacancies. There was no measurable benzaldehyde
hydrogenation activity over Au/CeO2, Au/␣-Fe2O3 and Au/Fe3O4 at
413 K. Reaction at higher temperatures generated toluene as prin-
cipal product with secondary benzene formation and no detectable
alcohol production. In contrast, reaction over Au/␥-Al2O3 resulted
in exclusive benzyl alcohol formation at 413 K with a progressive
shift to hydrogenolysis (to toluene and benzene) at higher temper-
atures.
Acknowledgements
The authors are grateful to Dr. N. Perret for her involvement in
this work. EPSRC support for free access to the TEM facility at the
University of St. Andrews and financial support to Dr. M. Li and Dr.
X. Wang through the Overseas Research Students Award Scheme
(ORSAS) are also acknowledged.
Please cite this article in press as: M. Li, et al., Effect of support redox character on catalytic performance in the gas phase hydrogenation
of benzaldehyde and nitrobenzene over supported gold, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.06.030

G Model
CATTOD-10275; No. of Pages10
ARTICLE IN PRESS
M. Li et al. / Catalysis Today xxx (2016) xxx–xxx
9
Fig. 9. Proposed reaction mechanism for (I) benzaldehyde and (II) nitrobenzene hydrogenation over Au on reducible supports; M = Ce or Fe.
Fig. 10. Proposed reaction mechanism for benzaldehyde hydrogenation over Au/␥-Al2O3 (M = Al) at different reaction temperatures.
Please cite this article in press as: M. Li, et al., Effect of support redox character on catalytic performance in the gas phase hydrogenation
of benzaldehyde and nitrobenzene over supported gold, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.06.030

G Model
CATTOD-10275; No. of Pages10
ARTICLE IN PRESS
10
M. Li et al. / Catalysis Today xxx (2016) xxx–xxx
References
[37] H. Ishikawa, J.N. Kondo, K. Domen, J. Phys. Chem. B 103 (1999) 3229–3234.
[38] D. Haffad, U. Kameswari, M.M. Bettahar, A. Chambellan, J.C. Lavalley, J. Catal.
172 (1997) 85–92.
[39] M.V. Ganduglia-Pirovano, A. Hofmann, J. Sauer, Surf. Sci. Rep. 62 (2007)
219–270.
[40] F. Boccuzzi, A. Chiorino, M. Manzoli, D. Andreeva, T. Tabakova, J. Catal. 188
(1999) 176–185.
[41] T. Tabakova, F. Boccuzzi, M. Manzoli, D. Andreeva, Appl. Catal. A: Gen. 252
(2003) 385–397.
[42] T. Tabakova, G. Avgouropoulos, J. Papavasiliou, M. Manzoli, F. Boccuzzi, K.
Tenchev, F. Vindigni, T. Ioannides, Appl. Catal. B: Environ. 101 (2011) 256–265.
[43] G.C. Bond, C. Louis, D.T. Thompson, Catalysis by Gold, Imperial College Press,
London, 2006.
[44] G.L. Haller, D.E. Resasco, Adv. Catal. 36 (1989) 173–235.
[45] C. Mohr, H. Hofmeister, P. Claus, J. Catal. 213 (2003) 86–94.
[46] L.F. Liotta, G. Pantaleo, F. Puleo, A.M. Venezia, Catal. Today 187 (2012) 10–19.
[47] N. Perret, X. Wang, L. Delannoy, C. Potvin, C. Louis, M.A. Keane, J. Catal. 286
(2012) 172–183.
[48] F. Moreau, G.C. Bond, A.O. Taylor, J. Catal. 231 (2005) 105–114.
[49] S. Arrii, F. Morfin, A.J. Renouprez, J.L. Rousset, J. Am. Chem. Soc. 126 (2004)
1199–1205.
[50] S. Schimpf, M. Lucas, C. Mohr, U. Rodemerck, A. Brückner, J. Radnick, H.
Hofmeister, P. Claus, Catal. Today 72 (2002) 63–78.
[51] A.M. Visco, F. Neri, G. Neri, A. Donato, C. Milone, S. Galvagno, Phys. Chem.
Chem. Phys. 1 (1999) 2869–2873.
[52] Y.-F. Han, Z. Zhong, K. Ramesh, F. Chen, L. Chen, T. White, Q. Tay, S.N. Yaakub,
Z. Wang, J. Phys. Chem. C 111 (2007) 8410–8413.
[53] W. Deng, A.I. Frenkel, R. Si, M. Flytzani-Stephanopoulos, J. Phys. Chem. C 112
(2008) 12834–12840.
[54] A.N. Pestryakov, V.V. Lunin, A.N. Kharlanov, D.I. Kochubey, N. Bogdanchikova,
A. Yu Stakheev, J. Mol. Struct. 642 (2002) 129–136.
[55] S. Peters, S. Peredkov, M. Neeb, W. Eberhardt, M. Al-Hada, Surf. Sci. 608 (2013)
129–134.
[56] A. Saadi, Z. Rassoul, M.M. Bettahar, J. Mol. Catal. A: Chem. 164 (2000) 205–216.
[57] A. Saadi, R. Merabti, Z. Rassoul, M.M. Bettahar, J. Mol. Catal. A: Chem. 253
(2006) 79–85.
[58] M. Chen, D.W. Goodman, Acc. Chem. Res. 39 (2006) 739–746.
[59] P. Claus, A. Brückner, C. Mohr, H. Hofmeister, J. Am. Chem. Soc. 122 (2000)
11430–11439.
[60] M. Arai, A. Obata, Y. Nishiyama, React. Kinet. Catal. Lett. 61 (1997) 275–280.
[61] C.T. Campbell, C.H.F. Peden, Science 309 (2005) 713–714.
[62] C. Milone, C. Crisafulli, R. Ingoglia, L. Schipilliti, S. Galvagno, Catal. Today 122
(2007) 341–351.
[63] M.A. Keane, J. Mol. Catal. A: Chem. 118 (1997) 261–269.
[64] M.A. Vannice, D. Poondi, J. Catal. 169 (1997) 166–175.
[65] H. He, H.X. Dai, L.H. Ng, K.W. Wong, C.T. Au, J. Catal. 206 (2002) 1–13.
[66] J.A. Rodriguez, S. Ma, P. Liu, J. Hrbek, J. Evans, M. Pérez, Science 318 (2007)
1757–1760.
[1] M. Turáková, T. Salmi, K. Eränen, J. Wärnå, D.Y. Murzin, M. Králik, Appl. Catal.
A: Gen. 499 (2015) 66–76.
[2] J. Scognamiglio, L. Jones, D. Vitale, C.S. Letizia, A.M. Api, Food Chem. Toxicol.
50 (Suppl. 2) (2012) S140–S160.
[3] V. van Brunt, J.S. Kanel, in: S. Kulprathipanja (Ed.), Reactive Separation
Processes, Taylor & Francis, London, 2002, pp. 51–92.
[4] R.J. Giraud, P.A. Williams, A. Sehgal, E. Ponnusamy, A.K. Phillips, J.B. Manley,
ACS Sust. Chem. Eng. 2 (2014) 2237–2242.
[5] T. Mitsudome, K. Kaneda, Green Chem. 15 (2013) 2636–2654.
[6] E. Bus, J.T. Miller, J.A. van Bokhoven, J. Phys. Chem. B 109 (2005) 14581–14587.
[7] L. McEwan, M. Julius, S. Roberts, J.C.Q. Fletcher, Gold Bull. 43 (2010) 298–306.
[8] M. Pan, A.J. Brush, Z.D. Pozun, H.C. Ham, W.-Y. Yu, G. Henkelman, G.S. Hwang,
C.B. Mullins, Chem. Soc. Rev. 42 (2013) 5002–5013.
[9] A. Corma, P. Serna, H. García, J. Am. Chem. Soc. 129 (2007) 6358–6359.
[10] A. Taketoshi, M. Haruta, Chem. Lett. 43 (2014) 380–387.
[11] M. Okumura, T. Akita, M. Haruta, Catal. Today 74 (2002) 265–269.
[12] X. Wang, N. Perret, M.A. Keane, Appl. Catal. A: Gen. 467 (2013) 575–584.
[13] R. Zanella, C. Louis, S. Giorgio, R. Touroude, J. Catal. 223 (2004) 328–339.
[14] U. Hartfelder, C. Kartusch, M. Makosch, M. Rovezzi, J. Sa, J.A. van Bokhoven,
Catal. Sci. Technol. 3 (2013) 454–461.
[15] C. Milone, R. Ingoglia, L. Schipilliti, C. Crisafulli, G. Neri, S. Galvagno, J. Catal.
236 (2005) 80–90.
[16] H. Rojas, G. Díaz, J.J. Martínez, C. Castan˜eda, A. Gómez-Cortés, J.
Arenas-Alatorre, J. Mol. Catal. A: Chem. 363–364 (2012) 122–128.
[17] M. Boronat, P. Concepción, A. Corma, S. González, F. Illas, P. Serna, J. Am.
Chem. Soc. 129 (2007) 16230–16237.
[18] K. Shimizu, Y. Miyamoto, T. Kawasaki, T. Tanji, Y. Tai, A. Satsuma, J. Phys.
Chem. C 113 (2009) 17803–17810.
[19] X. Wang, N. Perret, J.J. Delgado, G. Blanco, X. Chen, C.M. Olmos, S. Bernal, M.A.
Keane, J. Phys. Chem. C 117 (2013) 994–1005.
[20] F. Cárdenas-Lizana, S. Gómez-Quero, L. Kiwi-Minsker, M.A. Keane, Int. J.
Nanotech. 9 (2012) 92–112.
[21] N. Perret, F. Cárdenas-Lizana, D. Lamey, V. Laporte, L. Kiwi-Minsker, M.A.
Keane, Top. Catal. 55 (2012) 955–968.
[22] G.C. Bond, Molecules 17 (2012) 1716–1743.
[23] M. Li, X. Wang, N. Perret, M.A. Keane, Catal. Commun. 46 (2014) 187–191.
[24] J. Lenz, B.C. Campo, M. Alvarez, M.A. Volpe, J. Catal. 267 (2009) 50–56.
[25] X. Zhang, H. Shi, B.-Q. Xu, J. Catal. 279 (2011) 75–87.
[26] G. Jacobs, T.K. Das, Y. Zhang, J. Li, G. Racoillet, B.H. Davis, Appl. Catal. A: Gen.
233 (2002) 263–281.
[27] B. Campo, C. Petit, M.A. Volpe, J. Catal. 254 (2008) 71–78.
[28] L. Delannoy, N. Weiher, N. Tsapatsaris, A.M. Beesley, L. Nchari, S.L.M.
Schroeder, C. Louis, Top. Catal. 44 (2007) 263–273.
[29] M. Ousmane, L.F. Liotta, D. di Carlo, G. Pantaleo, A.M. Venezia, G. Deganello, L.
Retailleau, A. Boreave, A. Giroir-Fendler, Appl. Catal. B: Environ. 101 (2011)
629–637.
[30] F. Arena, P. Famulari, G. Trunfio, G. Bonura, F. Frusteri, L. Spadaro, Appl. Catal.
B: Environ. 66 (2006) 81–91.
[31] D. Andreeva, V. Idakiev, T. Tabakova, L. Ilievaa, P. Falaras, A. Bourlinos, A.
Travlos, Catal. Today 72 (2002) 51–57.
[32] G. Jacobs, S. Ricote, P.M. Patterson, U.M. Graham, A. Dozier, S. Khalid, E.
Rhodus, B.H. Davis, Appl. Catal. A: Gen. 292 (2005) 229–243.
[33] S. Scirè, C. Crisafulli, S. Minicò, G.G. Condorelli, A. Di Mauro, J. Mol. Catal. A:
Chem. 284 (2008) 24–32.
[34] R. Prins, Chem. Rev. 112 (2012) 2714–2738.
[35] C. Amorim, M.A. Keane, J. Hazard. Mater. 211–212 (2012) 208–217.
[36] K.-D. Jung, A.T. Bell, J. Catal. 193 (2000) 207–223.
[67] T.-J. Huang, H.-J. Lin, T.-C. Yu, Catal. Lett. 105 (2005) 239–247.
[68] C. Doornkamp, V. Ponec, J. Mol. Catal. A: Chem. 162 (2000) 19–32.
[69] A. Sepúlveda-Escribano, F. Coloma, F. Rodrıı´guez-Reinoso, J. Catal. 178 (1998)
649–657.
[70] S. Sitthisa, T. Sooknoi, Y. Ma, P.B. Balbuena, D.E. Resasco, J. Catal. 277 (2011)
1–13.
[71] N. Perret, X. Wang, T. Onfroy, C. Calers, M.A. Keane, J. Catal. 309 (2014)
333–342.
[72] A. Maltha, S.C. van Wermeskerken, T.L.F. Favre, P. Angevaare, E.J.
Grootendorst, C.A. Koutstaal, A.P. Zuur, V. Ponec, Catal. Today 10 (1991)
387–391.
Please cite this article in press as: M. Li, et al., Effect of support redox character on catalytic performance in the gas phase hydrogenation
of benzaldehyde and nitrobenzene over supported gold, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.06.030