Selective oxidation using supported gold bimetallic and trimetallic nanoparticles

Article abstract of DOI:10.1016/j.cattod.2014.01.033

Supported gold nanoparticles are highly effective for a range of redox reactions. In these reactions the activity is often enhanced by the addition of a second or indeed a third metallic component. A model reaction that is often investigated is the select

Full text of DOI:10.1016/j.cattod.2014.01.033

G Model
CATTOD-8880; No. of Pages5
ARTICLE IN PRESS
Catalysis Today xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Selective oxidation using supported gold bimetallic and trimetallic
nanoparticles
Graham J. Hutchings∗
Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff CF10 3AT, United Kingdom
a r t i c l e i n f o
a b s t r a c t
Article history:
Supported gold nanoparticles are highly effective for a range of redox reactions. In these reactions the
activity is often enhanced by the addition of a second or indeed a third metallic component. A model
reaction that is often investigated is the selective oxidation of benzyl alcohol using molecular oxygen as
terminal oxidant. In the presence of a solvent the complexity of this reaction can often be missed. How-
ever, in the solvent-free oxidation of benzyl alcohol to benzaldehyde using supported gold palladium
nanoparticles as catalysts, there are two pathways to the principal product, benzaldehyde. One is the
direct catalytic oxidation of benzyl alcohol to benzaldehyde by O2, while the second is the dispropor-
tionation of two molecules of benzyl alcohol to give equal amounts of benzaldehyde and toluene. The
formation of toluene is an unwanted side reaction. In this paper the research on this reaction will be
reviewed and two strategies described that can be used to switch off the formation of the non desired
toluene. The first involves the use of basic supports for the gold palladium nanoparticles, which is highly
effective in suppressing the formation of toluene and this may be related to the morphology of the gold
palladium nanoparticles and their interaction with the support. The second involves the introduction of
platinum to the gold palladium nanoparticles which also switches off toluene formation on supports that
permit toluene formation in the absence of platinum. This effect may be related to the relative stability
of platinum hydride.
Received 2 December 2013
Received in revised form 17 January 2014
Accepted 24 January 2014
Available online xxx
Keywords:
Benzyl alcohol oxidation
Supported gold palladium nanoparticles
Supported gold palladium platinum
nanoparticles
© 2014 Elsevier B.V. All rights reserved.
Introduction
significant development and this is in contrast to selective hydro-
genation with molecular hydrogen which is widely conducted at
Interest in catalysis by supported gold and gold palladium
nanoparticles continues to grow year on year in view of its great
potential in the development of environmentally benign processes.
This has led to the discoveries of gold and gold palladium based
catalysts for the direct synthesis of H2O2 from H2 and O2 [1], epox-
idation of alkenes [2,3], and oxidation of alcohols [4–7] and polyols
[8,9].
In terms of catalytic transformations oxidation is of fundamental
importance as it provides a means for functional group transfor-
mation in general organic synthetic methodologies [10]. However,
oxidations can be difficult to control as the processes typically
involve radical species and often this leads to low selectivity for
the required product. While molecular oxygen is considered to be
the most desirable terminal oxidant, many oxidations cannot be
carried out selectively with this oxidant and often relatively expen-
sive and toxic stoichiometric reagents are used leading to low atom
efficiency [11–13]. Selective oxidation catalysis therefore requires
both the laboratory and commercial scale [14]. It is known that
supported gold and palladium nanoparticles show considerable
promise as recyclable heterogeneous catalysts for oxidations using
molecular oxygen. In this paper aspects of the selective oxidation
of benzyl alcohol will be reviewed and in particular aspect of the
nature of the oxidative and non-oxidative pathways to benzalde-
hyde will be considered. This work forms part of a facet of a plenary
lecture delivered at the World Congress on Oxidation Catalysis in
2013.
Comments on the selective oxidation of benzyl alcohol
Among the alcohols, benzyl alcohol is one of the most studied
examples for the selective oxidation to aldehydes [4,15]. Benzyl
alcohol undergoes a variety of reactions depending on the reac-
tion conditions and the nature of the catalyst used. The reactions
reported so far are (a) oxidation to form benzaldehyde, benzoic acid,
and benzyl benzoate [16] (b) disproportionation to form benzalde-
hyde, toluene and water [17], (c) dehydration to form dibenzylether
[18] and (d) self-condensation (benzylation) to form anthracene
and stilbene [19]. Many reactions are active only under particular
∗
Fax: +44 2920 874 030.
E-mail address: hutch@cardiff.ac.uk
0920-5861/$ – see front matter © 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.cattod.2014.01.033
Please cite this article in press as: G.J. Hutchings, Selective oxidation using supported gold bimetallic and trimetallic nanoparticles, Catal.
Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.01.033

G Model
CATTOD-8880; No. of Pages5
ARTICLE IN PRESS
2
G.J. Hutchings / Catalysis Today xxx (2014) xxx–xxx
reaction conditions for example, condensation to form anthracene
and stilbene are found to be active at higher temperatures in the
vapour phase [19]. In the low temperature liquid phase oxidation
of benzyl alcohol, depending on the reaction conditions and cata-
lysts used, many products including benzoic acid, benzyl benzoate,
dibenzyl ether and toluene have been reported to be formed besides
the main product benzaldehyde [20]. A clear understanding of the
mechanism of the formation of all these products is necessary to
fine-tune the catalyst for the selective formation of the desired
product, benzaldehyde. It has been generally accepted that benz-
aldehyde forms by the oxidation of benzyl alcohol in the presence
of an oxidant; benzaldehyde on further oxidation then leads to the
formation of benzoic acid and the next product benzyl benzoate
is formed either by the reaction between benzoic acid and ben-
zyl alcohol or by the oxidation of a hemiacetal [20]. Toluene is the
other major product and as roughly equimolar amounts of toluene
and benzaldehyde were produced from benzyl alcohol using Au–Pd
catalyst in a helium atmosphere, it has been proposed that a dis-
proportionation of two moles of benzyl alcohol to be the origin of
toluene as shown below [17].
Fig. 1. Oxidation of benzyl alcohol using 1%(Au–Pd)/TiO2 under 1 bar O2 (relative)
pressure at 393 K; substrate to metal molar ratio: 14,000; benzyl alcohol: 18.5 mmol;
key ꢀ: benzylalcohol molar conversion; ᭹: benzaldehyde selectivity; ꢁ: toluene
selectivity; ꢂ: benzoic acid selectivity.
2 PhCH2OH → PhCHO + PhCH3 + H2O
(Scheme1)
Given an understanding of the route by which the non-desired
toluene product is formed could permit the identification of reac-
tion conditions that facilitate the “switching off” of this reaction.
conversion. The product mixture, at all times, comprises benz-
aldehyde (approx. 75%), toluene (approx. 23–24%) and a minor
amount of benzoic acid. The other possible products, namely ben-
zene, benzyl benzoate and dibenzyl ether are either observed
at a trace level of less than 0.5% or are not observed under
these experimental conditions. Benzaldehyde, the major product,
is formed by the oxidation of benzyl alcohol and toluene is formed
by the disproportionation of benzyl alcohol. Therefore, there are
two active reactions in the overall oxidation of benzyl alcohol.
As benzaldehyde is formed from the disproportionation and the
oxidation reactions, its formation cannot be used to quantify
either the oxidation or the disproportionation reactions. Toluene is
formed exclusively from disproportionation; therefore the amount
of toluene formed can be used as a measure of the extent of the
disproportionation reaction. According to Scheme 1, the number of
moles of benzyl alcohol consumed in disproportionation is twice
the number of moles of toluene formed. From this value, a dispro-
portionation turnover number (TOND) can be calculated using Eq.
(1).
Oxidation of benzyl alcohol using supported gold palladium
catalysts
Supported nanoparticles of metals can be very active for the
selective oxidation of alcohols and both monometallic gold and pal-
ladium, as well as bimetallic gold palladium alloys [4] have been
shown to be effective. There is much interest in the different ways
in which supported nanoparticles can be synthesised. In general
the following methods can be typically used:
(a) Impregnation: In this case suitable salts are impregnated with
a solution containing the metals at the required concentration.
This method is the easiest but produces a very broad range of
particle sizes, typically 5–25 nm with much larger nanoparti-
cles being observed. Hence this method does not disperse the
metals particularly well. However, this method can produce
catalysts that are very active for alcohol oxidation [4].
(b) Deposition precipitation: In this method the support is sus-
pended in a solution of the metal salts and a base is added to
precipitate the nanoparticles onto the pre-formed support. This
method can produce a reasonably narrow particle size distribu-
tion, typically 1–10 nm.
(c) Co-precipitation: In this method a solution containing the metal
salts and the support precursor is reacted with a base to precipi-
tate the metal nanoparticles or their precursors simultaneously
with the support. This method can also produce a reasonably
narrow particle size distribution, typically 1–10 nm.
2 × molTol
TOND
=
(1)
molMetal
TOND is used to represent the disproportionation reaction quan-
titatively in this paper. Benzaldehyde is formed from both the
reactions; the moles of benzaldehyde formed by disproportion-
ation is equal to the number of moles of toluene formed. By
subtraction, the moles of benzaldehyde formed by the oxidation
reaction can then be calculated and converted into an oxidation
turnover number (TONO) using Eq. (2)
(d) Sol-immobilisation: In this method metal salts are dissolved in
water. A stabilising agent is added and then a reducing agent to
form a colloidal sol. A support is then added to form the final
catalyst. This method can produce a very narrow particle size
distribution, typically 4–6 nm [21].
(molBCHO − molTol
)
TONO
=
(2)
molMetal
The TONO parameter is used for the quantitative representation
of the oxidation reaction in this paper. Using Eqs. (1) and (2), TONO
and TOND values can be calculated for the data presented in Fig. 1
and these are shown in Fig. 2. The TONTot represents the overall
reaction, calculated from the moles of benzyl alcohol consumed
and the moles of the metals contained in the catalyst. It is clear
that the disproportionation reaction is very significant using this
support.
We have found that catalysts prepared by sol-immobilisation
are very effective for the oxidation of benzyl alcohol [21,22]. A
1%(Au–Pd)/TiO2 catalyst was prepared by a sol-immobilisation
method [15,21], and this was used for solvent-free oxidation of ben-
zyl alcohol (Fig. 1). Initially, benzyl alcohol conversion increases
steeply and then reaches a near plateau at approximately 70%
Please cite this article in press as: G.J. Hutchings, Selective oxidation using supported gold bimetallic and trimetallic nanoparticles, Catal.
Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.01.033

G Model
CATTOD-8880; No. of Pages5
ARTICLE IN PRESS
G.J. Hutchings / Catalysis Today xxx (2014) xxx–xxx
3
Fig. 2. Time on line profile of the turn over numbers (TOND and TONO) corre-
sponding to the oxidation and disproportionation reactions, respectively, in the
oxidation of benzyl alcohol using 1%(Au–Pd)/TiO2 under 1 bar (relative) O2 pressure
at 393 K; substrate versus metal molar ratio: 14,000; benzyl alcohol: 18.5 mmol; key
Fig. 4. Time on line profile of the TONO calculated for the oxidation of benzyl alco-
hol using different catalysts at 393 K under 1 bar (relative) O2 substrate versus
metal molar ratio: 14,000; benzyl alcohol: 18.5 mmol; key ᭹: 1%(Au–Pd)/C ꢁ:
1%(Au–Pd)/TiO2; ꢃ: 1%(Au–Pd)/Nb2O5; ꢄ: 1%(Au–Pd)/ZnO; ꢅ: 1%(Au–Pd)/MgO.
ꢀ: TONTot; ᭹: TONO; ꢁ: TOND
.
Switching off toluene formation by using different support
materials
off the disproportionation reaction. The turnover numbers for the
oxidation and disproportionation reactions are quite revealing
(Figs. 4 and 5). TONO values for all these catalysts were found to be
more or less equivalent, with only very small deviations (Fig. 4).
This implies that the oxidation reaction is effectively independent
of the identity of the support. However, this is not the case for
the disproportionation reaction since only with MgO- or ZnO-
supported catalysts is this not observed. Analysis of the data in
Figs. 3–5 it can be concluded that the increased activity is due to the
difference in the activity for the disproportionation reaction and
not because of the oxidation reaction. This is an important result
and to determine the origin of the effect detailed STEM studies
have been conducted. While no major differences were observed
in the particle size distribution for these five catalysts (Fig. 6), and
the particle size distributions were mainly in the 3–8 nm range,
and this can be expected since the catalysts are all derived from the
same colloidal sol. However, there were clear differences observed
in the way in which the nanoparticles interact with the support
(Fig. 7) since the support controls the degree of wetting. On MgO,
ZnO and TiO2 the AuPd nanoparticles have a tendency to wet the
Au–Pd nanoparticles were supported on a variety of differ-
ent supports including Nb2O5, activated carbon, MgO and ZnO
using sol-immobilisation. Benzyl alcohol oxidation was carried
out using all these catalysts and the results are shown in Fig. 3.
Under these reaction conditions the supports themselves were
found to be inactive. The data indicates that Au–Pd supported
on activated carbon is the most active catalyst followed by the
TiO2 and Nb2O5 supported catalysts. The MgO and ZnO supported
catalysts exhibited the least activity for the reaction. However, the
catalysts are all fairly active for this reaction but the selectivity for
these five catalysts are very different. Activated carbon-, TiO2-, and
Nb2O5-supported catalysts formed toluene as a major by-product,
whereas MgO and ZnO supported catalysts did not produce any
toluene. For these latter two catalysts, benzaldehyde was the only
major product with selectivity in excess of 99%. Hence by simply
changing the catalyst support, we can either switch on or switch
Fig. 5. Time on line profile of the TOND number calculated for the oxidation of benzyl
alcohol using different catalysts at 393 K under 1 bar (relative) O2; substrate versus
metal molar ratio: 14,000; benzyl alcohol: 18.5 mmol; key ꢀ: 1%(Au–Pd)/ZnO;
ꢁ: 1%(Au–Pd)/Nb2O5; ꢂ: 1%(Au–Pd)/MgO; ꢃ: 1%(Au–Pd)/TiO2; ᭹: 1%(Au–Pd)/C. It
should be noted that no toluene is formed for the ZnO- and MgO-supported samples.
Fig. 3. Kinetic profile for the oxidation of benzyl alcohol using different supported
Au–Pd catalysts under 1 bar (relative) O2 at 393 K; substrate versus metal molar
ratio: 14,000; benzyl alcohol: 18.5 mmol; key ꢀ: 1%(Au–Pd)/C; ꢁ: 1%(Au–Pd)/ZnO;
ꢂ: 1%(Au–Pd)/TiO2; ꢃ: 1%(Au–Pd)/MgO; ᭹: 1%(Au–Pd)/Nb2O5.
Please cite this article in press as: G.J. Hutchings, Selective oxidation using supported gold bimetallic and trimetallic nanoparticles, Catal.
Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.01.033

G Model
CATTOD-8880; No. of Pages5
ARTICLE IN PRESS
4
G.J. Hutchings / Catalysis Today xxx (2014) xxx–xxx
Fig. 6. Pairs of TEM images (left) and particle size distributions (right) of the catalysts
(A): 1%(Au–Pd)/C; (B): 1%(Au–Pd)/TiO2; (C): 1%(Au–Pd)/Nb2O5; (D): 1%(Au–Pd)/ZnO
and (E): 1%(Au–Pd)MgO.
support as evidenced by particle flattening and surface faceting, as
well as the development of an extended intimate particle/support
interface. For these catalysts there is an enhanced influence of the
interfacial sites. With Nb2O5 and activated carbon as supports the
AuPd particles retain a roughly spherical shape. As noted earlier,
the activity for the disproportionation reaction follows the trend:
Activatedcarbon > Nb2O5 > TiO2 > MgO = ZnO
which is opposite for the trend observed for wetting of the support,
i.e.
Fig. 7. Pairs of HREM images (left) and STEM images (right) of the catalysts (A) and
(B): 1%(Au–Pd)/C; (C) and (D): 1%(Au–Pd)/TiO2; (E) and (F): 1%(Au–Pd)/Nb2O5; (G)
and (H): 1%(Au–Pd)/ZnO and (I) and (J): 1%(Au–Pd)MgO.
MgO = ZnO > TiO2 > Nb2O5 > activatedcarbon
Hence by controlling the nature of these interfacial sites it is
possible to switch off the non-desired formation of toluene by the
non-oxidative disproportionation pathway.
concentration in aqueous solutions, using sodium borohydride as
chemical reductant and poly vinyl alcohol (PVA) as the protective
ligand. The colloids were then immobilised onto an activated car-
bon support, followed by a washing and 120 ◦C drying process to
yield the final catalysts with 1 wt% total metal loading. For com-
parative purposes Au-only, Pd-only, Pt-only catalysts, as well as
Au–Pd, Au–Pt and Pt–Pd bimetallic catalysts were also prepared
using a similar sol-immobilisation procedure.
Switching off toluene formation using supported gold
palladium platinum trimetallic nanoparticles
Recently, we have investigated the oxidation of benzyl alco-
hol using supported trimetallic nanoparticles [23]. Supported
Au–Pd–Pt trimetallic catalysts were synthesised by the sol-
immobilisation method. This process involved the co-reduction of
three metal precursors (HAuCl4, PdCl2 and H2PtCl6) at the desired
Oxidations were carried out in a stirred autoclave reactor using
solvent free conditions (40 ml of benzyl alcohol), at 120–140 ◦C, and
pO2 = 10 bar. The catalytic results are given in Table 1 presents for
Please cite this article in press as: G.J. Hutchings, Selective oxidation using supported gold bimetallic and trimetallic nanoparticles, Catal.
Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.01.033

G Model
CATTOD-8880; No. of Pages5
ARTICLE IN PRESS
G.J. Hutchings / Catalysis Today xxx (2014) xxx–xxx
5
Fig. 8. STEM–XEDS spectrum image analysis of the 1 wt% (0.3Au–0.4Pd–0.3Pt)/C trimetallic sample. The first column shows HAADF images from representative particles
that are (a) ∼3 nm, (b) ∼5 nm, and (c) ∼10 nm in size. The scale bar represents 2 nm. The next three columns show the corresponding XEDS maps derived from the Au L
(9.64–9.84 keV), Pd L (2.75–3.05 keV) and Pt L (9.35–9.55 keV) peaks. The final column shows the corresponding RGB overlay maps where Au is red, Pd is green and Pt is blue.
(For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Table 1
of toluene formation on a support that gives high levels of toluene
formation with the gold palladium alloy catalyst. It is probable that
there may be other methodologies for controlling this non-desired
Comparison of benzyl alcohol oxidation at iso-conversion of 30% with Pd-only,
Au–Pd and various Au–Pd–Pt catalysts supported on carbon prepared by the sol-
immobilisation method.
pathway and this study shows the importance of catalyst design in
securing highly effective selective oxidation catalysts.
Selectivity (%)
Catalyst
Toluene Benzaldehyde Benzoic
acid
Benzyl
benzoate
References
1%(0.65Au/0.35Pd)/C
1%(0.5Au/0.5Pd)/C
1%(0.3Au/0.4Pd/0.3Pt)/C
1%(0.4Au/0.4Pd/0.2Pt)/C
1%(0.45Au/0.45Pd/0.1Pt)/C 0.4
1%Pd/C 5.6
8.1
6.9
0.8
0.6
80.5
81.5
85.7
83.3
86.7
78.7
2.6
3.6
6.5
6.8
5.9
5.8
8.8
8.0
7.0
9.3
7.0
9.9
[1] J.K. Edwards, B. Solsona, E. Ntainjua, N.A.F. Carley, A.A. Herzing, C.J. Kiely, G.J.
Hutchings, Science 323 (2009) 1037.
[2] M.D. Hughes, Y.J. Xu, P. Jenkins, P. McMorn, P. Landon, D.I. Enache, A.F. Carley,
G.A. Attard, G.J. Hutchings, F. King, E.H. Stitt, P. Johnston, K. Griffin, C.J. Kiely,
Nature 437 (2005) 1132.
[3] J. Huang, T. Akita, J. Faye, T. Fujitani, T. Takei, M. Haruta, Angew. Chem. Int. Ed.
48 (2009) 7862.
[4] D.I. Enache, J.K. Edwards, P. Landon, B. Solsona-Espriu, A.F. Carley, A.A. Herzing,
M. Watanabe, C.J. Kiely, D.W. Knight, G.J. Hutchings, Science 311 (2006)
362.
[5] C. Bianchi, F. Porta, L. Prati, M. Rossi, Top. Catal. 13 (2000) 231.
[6] P. Haider, B. Kimmerle, F. Krumeich, W. Kleist, J. Grunwaldt, A. Baiker, Catal.
Lett. 125 (2008) 169.
[7] A. Abad, P. Concepcion, A. Corma, H. García, Angew. Chem. Int. Ed. 44 (2005)
4066.
[8] L. Prati, M. Rossi, J. Catal. 176 (1998) 552.
[9] M. Sankar, N. Dimitratos, D.W. Knight, A.F. Carley, R. Tiruvalam, C.J. Kiely, D.
Thomas, G.J. Hutchings, ChemSusChem 2 (2009) 1145.
[10] I. Hermans, E.S. Spier, U. Neuenschwander, N. Turra, A. Baiker, Top. Catal. 52
(2009) 1162.
[11] R.A. Sheldon, I.W.C.E. Arends, G.J.T. Brink, A. Dijksman, Acc. Chem. Res. 35 (2002)
774–781;
R.A. Sheldon, Chem. Tech. 21 (1991) 566.
[12] R.A. Sheldon, J.K. Kochi, Metal-Catalysed Oxidations of Organic Compounds,
Academic Press, New York, NY, 1981.
isoconversion of benzyl alcohol of 30%. As noted in the previous
section the oxidation of benzyl alcohol with O2 under solvent-
free conditions proceeds efficiently with very high catalytic activity
using carbon-supported Au–Pd nanoparticles and the main product
is benzaldehyde with the major by-product being toluene. Addition
of Pt to the AuPd supported nanoparticles switches off the forma-
tion of toluene. These results clearly demonstrate that only a small
amount of Pt is needed for the effective termination of toluene for-
mation. We consider the effect is due to the relative stability of
platinum hydride in comparison with palladium hydride and it is
this enhanced stability that leads to the reduction in toluene for-
mation. Detailed characterisation of these trimetallic nanoparticles
by aberration corrected scanning transmission electron microscopy
showed that they comprised homogeneous trimetallic nanoalloys
(Fig. 8).
[13] J.E. Backvall, Modern Oxidation Methods, Wiley-VCH, Weinheim, 2004.
[14] A. Stanislaus, B.H. Cooper, Catal. Rev. Sci. Eng. 36 (1994) 75.
[15] M. Sankar, E. Nowicka, R. Tiruvalam, Q. He, S.H. Taylor, C.J. Kiely, D. Bethell,
D.W. Knight, G.J. Hutchings, Chem. Eur. J. 17 (2011) 6524.
[16] M. Jayamani, C.N. Pillai, J. Catal. 82 (1983) 485.
Concluding comments
[17] R. Valarivan, C.N. Pillai, C.S. Swamy, React. Kinet. Catal. Lett. 59 (1996) 343.
[18] G. Li, D.I. Enache, J. Edwards, A.F. Carley, D.W. Knight, G.J. Hutchings, Catal. Lett.
110 (2006) 7.
It is clear that the oxidation of benzyl alcohol involves two
competing processes. The first is the selective oxidation pathway
leading to the formation of benzaldehyde as the primary product.
The second competing pathway involves a disproportion of ben-
zyl alcohol forming both toluene and benzaldehyde. The formation
of toluene can effectively be eliminated by careful design of the
catalysts. Two methods have been demonstrated; one approach
involves the nature of the support and basic oxides decrease the for-
mation of toluene substantially. However, the addition of platinum
to the gold palladium alloy catalysts also leads to a switching off
[19] D.M. Meier, A. Urakawa, A. Baiker, J. Phys. Chem. C 113 (2009) 21849.
[20] S.G. Kovtun, T. Kameneva, S. Hladyi, M. Starchevsky, Y. Pazdersky, I. Stolarov,
M. Vargaftik, I. Moiseev, Adv. Synth. Catal. 344 (2002) 957.
[21] N. Dimitratos, J.A. Lopez-Sanchez, D. Morgan, A.F. Carley, R. Tiruvalam, C.J. Kiely,
D. Bethell, G.J. Hutchings, Phys. Chem. Chem. Phys. 11 (2009) 5142.
[22] S. Meenakshisundaram, E. Nowicka, P.J. Miedziak, G.L. Brett, R.L. Jenkins, N.
Dimitratos, S.H. Taylor, D.W. Knight, D. Bethell, G.J. Hutchings, Faraday Discuss.
145 (2010) 341.
[23] Q. He, P.J. Miedziak, L. Kesavan, N. Dimitratos, M. Sankar, J.A. Lopez-Sanchez,
M.M. Forde, J.K. Edwards, D.W. Knight, S.H. Taylor, C.J. Kiely, G.J. Hutchings,
Faraday Discuss. 162 (2013) 365.
Please cite this article in press as: G.J. Hutchings, Selective oxidation using supported gold bimetallic and trimetallic nanoparticles, Catal.
Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.01.033