Full text of DOI:10.1007/BF03214836

In its bulk form, gold has been regarded to be chemically inert
towards chemisorption of reactive molecules such as oxygen
and hydrogen. Consequently, pure gold was considered to be
an uninteresting metal from the point of view of catalysis. The
most noticeable exception to this was its use as a ‘diluent’ for
an active metal: the addition of the inert gold to an active
metal such as platinum affects to a significant extent the
selectivity of the catalyst (1). However, recently, gold catalysts
have attracted a dramatic growth of interest, since gold was
reported to be extremely active in the oxidation of carbon
monoxide if deposited as nanoparticles on partly reducible
oxides. It is in particular the pioneering work of Haruta et al,
which has stimulated research in this area (2). Early work
performed with gold catalysts has been reviewed by Bond (3)
and by Hutchings (4). For recent reviews on gold catalysis see
references 2 and 5 - 7.
Catalysis by Gold
Nanoparticles
Ruud Grisel, Kees-Jan Weststrate, Andrea
Gluhoi and Bernard E Nieuwenhuys*
Leiden Institute of Chemistry, Leiden University
PO Box 9502, 2300 RA Leiden The Netherlands
E-mail: b.nieuwe@chem.leidenuniv.nl
Received: 4 March 2002
Gold catalysts have superior activity in CO and other
oxidations at low temperatures. Both a small ( 5nm)
~
particle size and the presence of a partly reducible
oxide (ceria or a transition metal oxide) have a
beneficial effect on the catalyst performance. The
present paper reviews our recent studies focused on
understanding the specific role of the Au particle size
and that of the oxide (MO). Our personal viewpoint on
gold catalysis is outlined. The effects of Au particle size
and of the oxidic additive are distinguished by using
several alumina-supported gold catalysts having
different gold particle sizes and various oxidic
additives. The most active catalyst in CO oxidation is
A large range of chemical reactions are now known to be
catalysed by gold catalysts including total and selective
oxidation, and reduction of nitrogen oxides. Based on the
growth of the number of papers and patents dealing with
gold-based catalysts for a range of potential applications in
pollution control, chemical processes and development of
fuel cells, it can be concluded that there may be a bright
future for gold-based catalysis.
In the present paper we discuss some of our research on
catalysis by gold (8 - 14), and in particular, the following
topics will be discussed:
the multicomponent catalyst Au/MgO/MnO
MgO being a stabilizer for the Au particle size and
MnO being the cocatalyst. This catalyst also exhibits
good performance in selective oxidation of CO in a
hydrogen atmosphere, a reaction relevant for the
development of polymer electrolyte fuel cell
technology.
x
/Al
2
O
3
with
a) the effect of the gold particle size and the role of the
oxidic additive;
x
b) the selective oxidation of CO in the presence of hydrogen,
a reaction relevant to hydrogen fuel cell applications.
Experimental
All the catalysts discussed in this paper are supported on
γ-alumina, the gold loading is 5.0 wt%. The gold catalysts
were prepared by homogeneous deposition precipitation
using urea as precipitating agent. The advantage of the use
of alumina as support is the high stability of the catalysts up
to relatively high temperatures (10, 11). The following
techniques were used for characterization of the catalysts: X-
ray diffraction, high resolution transmission electron
microscopy with facilities for chemical analysis by EDX,
1
97
atomic absorption spectroscopy and Au-Mössbauer effect
spectroscopy. For details of catalyst preparation and
characterization, the experimental set-up and the activity
measurements, see references 10 - 14. The flow rate used
-1
-1
was 40 ml min , GHSV 2500h . The gold and metal oxide
MO) phases are well dispersed on the alumina support and
(
the HRTEM/EDX results point to close contact between the
gold and MO phases.
Gold Bulletin 2002 • 35/2
39

Results and Discussion
Synergistic and Particle Size Effects
In order to distinguish the effects of gold particle size and
the presence of MO, a comparative study was performed on
the behaviour of several gold-based catalysts in CO oxidation:
1
New regulations in the United States, Japan and Europe will
make it mandatory that automotive emissions decrease
substantially from current levels. Consequently, there is a
strong incentive to develop improved catalysts with better
oxidation activity at low temperatures, since most of the
hydrocarbons and CO are emitted immediately following the
cold start of engines (15).
2CO + O
2
→ 2CO
2
(2)
Some of the results are shown in Figure 2. All the catalysts
examined had ␥-Al as the support. The pure MO /Al
O
2 3
x
2
O
3
catalysts are not very active in low-temperature CO oxidation.
No significant CO conversion was found below 150°C, a
temperature at which full conversion is reached over a
A possible option may be the application of gold catalysts,
making use of their superior activity in oxidation of CO and
hydrocarbons at low temperatures. This is clearly illustrated in
Figure 1 which indicates the conversion of propene over
Au/Al
figure). The CO oxidation activity of the alumina-supported
metal oxides decreases in the order: CoO > FeO > MnO
NiO >CrO >> MgO and ZnO. Addition of MOx to Au/Al
2
O
3
catalyst with 4nm Au particles (not shown in the
x
x
x
>
x
x
O
2 3
three types of alumina supported catalysts, viz CeO
Au/Al and the multicomponent catalyst consisting of both
Au and CeO
x
/Al
2
O
3
,
greatly influences the CO conversion in the low temperature
region. Since none of the selected MOx was found to be
active at these low temperatures, the activity enhancement
must be due to either changes in the gold phase or to
O
2 3
x
, Au/CeO
x
/Al
2
O
3
(16):
2C
H
3 6
+ 9O
2
→ 6CO
2
+ 6H
2
O
(1)
synergistic effects between gold and the MO
x
. To illustrate
the large beneficial effect of MO
x
addition, the temperatures
For all of the gold catalysts the average particle size is 3.0 nm.
Clearly, the multicomponent catalyst is much more active at
low temperatures than the monocomponent ones. It should
1.00
be noted that the ␥-Al
2
O support itself is not active under the
3
conditions used in the experiments shown in the Figure 1. The
presence of such a synergistic effect has been reported before
for highly dispersed gold catalysts supported on reducible and
0
0
0
0
.75
.50
.25
.00
catalytically active supports such as FeO
x
, CoO
x
, TiO
x
and MnO
x
for a number of reactions (2 - 14). Hence, the interesting
observation is that gold-based catalysts are more active if:
a) the gold particle is nanosized, ie of the order of ca
5
nm, and
b) the gold particles are combined with an oxidic catalyst
MO ).
0
100
Reactor temperature (°C)
MgO/Al Au/CrO
Au/MnO MnO /Al
FeO /Al Au/CoO
Au/NiO NiO /Al
ZnO /Al
200
300
400
(
x
Au/MgO/Al
CrO /Al
Au/FeO
CoO /Al
Au/ZnO
2
O
3
2
O
3
x 2 3
/Al O
1
.2
1
x
2
O
3
x
/Al
2
O
3
x
2 3
O
x
/Al
2
O
3
x
2
O
3
x 2 3
/Al O
x
2
O
3
x
/Al
2
O
3
x
2 3
O
0
0
0
0
.8
.6
.4
.2
0
x
/Al
2
O
3
x
2 3
O
Figure 2
CO oxidation over gold-based catalysts:
Au/MgO/Al and MgO/Al
2
O
3
2 3
O
Au/CrO /Al O and CrO /Al O
x
2
3
x
2
3
Au/MnO
x
/Al
2
O
3
and MnO
x
/Al
2
O
3
Au/FeO
Au/CoO
Au/NiO /Al
Au/ZnO /Al
The CO conversion over Au/MgO/Al
x
/Al
2
O
3
and FeO
and CoO
and NiO
and ZnO
x
/Al
2
O
3
0
100
CeO
200
Reactor temperature (°C)
/Al Au/Al Au/CeO
300
400
500
/Al
x
/Al
2
O
3
x
/Al
O
2 3
x
2
O
3
x
/Al
2
O
3
Al
2
O
3
x
2
O
3
2
O
3
x
2
O
3
x
2
O
3
x 2 3
/Al O
2 3 x 2 3
O and Au/MnO /Al O is 100% in
Figure 1
the whole temperature range studied
Gold loading = 5%
Synergistic effect - oxidation of propene over γ-Al
2 3 x 2 3
O , CeO /Al O ,
Au/Al and Au/CeO /Al (16)
2
O
3
x
2
O
3
Atomic ratio Au: M (= Mg, Cr, Mn, Fe, Co, Ni and Zn) = 1 : 1
40
Gold Bulletin 2002 • 35/2

3
2
1
00
00
00
0
CO
→ COads
→ 2Oads
(3)
(4)
(5)
O
O
2
ads + COads → CO
2
Cr
The mechanism of the CO oxidation reaction on gold
catalysts is not fully understood. In the opinion of the
Co
Zn
present authors the mechanism on Au/Al
to that on the platinum group metal (PGM) catalysts. If this
is so, the difficult step is the dissociative adsorption of O on
2
O
3
may be similar
Fe
Ni
Mg
2
Mn
gold, step 4. Gold is not very active in the O-O bond scission.
However, O adatoms are stable on gold at room
temperature. The beneficial effect of the addition of a
0
2
4
6
8
10
12
Average Au particle diameter (nm)
transition metal oxide may be that the MO
needed for the reaction. The reaction may occur at the Au-
MO interface with CO adsorbed on Au reacting with O on
MnO . The O-vacancies on MO will then react with O and
x
supplies the O
Figure 3
Temperature needed for 95% CO conversion versus the average gold
particle size of Au/Al calcined at 300°C (g), Au/Al calcined at
00°C ( e), Au/Al calcined at 900°C (c) and Au/MO / Al (a)
catalysts. The three Au/Al catalysts have been calcined at 300, 400
and 600°C in order to change the average Au particle size
x
2
O
3
2 3
O
x
x
2
6
2
O
3
x
2 3
O
the catalytic cycle is completed. An alternative explanation
is that O atoms spill over to the gold surface and then react
with adsorbed CO according to step 5.
2 3
O
Large synergistic effects have been reported earlier for
combinations of Pt or Pd with reactive metal oxides (15, 20,
21). An example is shown in Table 1 for CO oxidation over Pt
needed for 95% CO conversion (T 95%) are plotted versus
the average gold particle size as determined from XRD line
broadening. Figure 3 summarizes the results obtained for
catalysts. Pt/CoO
x
/SiO
2
and Pt/CoO
x
/Al
2
O belong to the most
3
seven multicomponent Au/MO
monocomponent Au/Al catalysts with an average gold
particle size between 4 and 11nm. The gold particle size of
the three Au/Al catalysts was varied by heating a standard
Au/Al catalyst in an oxygen atmosphere at 300, 400 and
x
/Al
2
O
3
and three
active Pt catalysts investigated in our laboratories. Even at
room temperature CO is oxidized. The high activity of
O
2 3
Pt/CoO
x
/SiO in CO oxidation is related to the absence of CO
2
O
2 3
inhibition effects at low temperatures (22). At temperatures
up to about 200°C Pt surfaces are almost inactive for CO
oxidation because the whole Pt surface is covered with CO.
Oxygen cannot adsorb and dissociate on a CO-covered Pt
surface. At higher temperatures this CO-inhibition disappears
because some of the CO desorbs, resulting in oxygen
adsorption and reaction. On the multicomponent Pt catalysts
CO inhibition does not occur, the transition metal oxide
O
2 3
6
00°C. In this way the average particle size increases from
.6nm via 9 to 11nm.
3
The results clearly demonstrate that small gold particles
(< 5nm) are required for high activity. This observation is in
line with literature data (2, 5 - 7, 17 - 19). The addition of MO
x
has a large beneficial effect on the activity at low
temperatures. This effect is larger than can be expected from
the presence of stable small Au particles alone. For example,
Table 1 Temperature (°C) Needed for 50% O
2
or CO* Conversion at
Several CO/O
2
Ratios after a Reductive or an Oxidative Treatment
the Au/MnO
.2 ± 1.4 nm has a T 95% that is 100 degrees lower than that
found for Au/Al with an average particle size of 3.6 ± 1.4
nm. In fact, the CO conversion over Au/MnO /Al is higher
at ambient temperature than the CO conversion over the
Au/Al catalyst at 150°C. Most probably, the role of MO is
x
/Al
2
O
3
catalyst with an average particle size of
Ratio
Pretreatment 1:1
CO:O
2
4
O
2 3
Catalyst
2:1
3:1
x
O
2 3
Pt/CoO
Pt/MnO
Pt/SiO
x
/SiO
2
Reduction
Oxidation
15
101
26
103
29
103
O
2 3
x
x
/SiO
2
Reduction
Oxidation
94
150
114
173
125
162
twofold. Firstly, the oxide (in particular, MgO) may stabilize
the small size of the gold particles throughout preparation
and activity measurements (promoter effect). Secondly, the
oxide may actively take part in one of the steps involved in
the catalytic cycle (ie it acts as a co-catalyst).
2
Reduction
Oxidation
175
187
212
210
204
210
CO conversion starts between 300 and 350°C over CoO
x 2
/SiO and
MnO /SiO catalysts. However, 50% conversion was not reached over
x
2
The dominant mechanism of CO-oxidation at low
temperatures over the platinum group metals (PGMs) is that
of a Langmuir-Hinshelwood type between adsorbed CO and
adsorbed O (15):
these catalysts at 400°C, the maximum temperature used in these
series of experiments
* Conversion of O for reducing and stoichiometric gas mixtures, and
2
conversion of CO for oxidizing gas mixtures.
Gold Bulletin 2002 • 35/2
41

supplies the O needed for the reaction. It is likely that the
reaction takes place at the Pt-MO interface (22).
oxidized in preference to hydrogen in the temperature range
of 100-200°C over Al supported Ru, Rh, and Pt catalysts
x
2
O
3
Some of the gold-based catalysts are clearly superior to
the Pt-based catalysts. For example, full conversion of CO is
(24 - 27). The interesting observation is that CO oxidation is
enhanced by the presence of hydrogen. Possible
mechanisms include the effect of hydrogen on the heat of
reached over Au/MnO
whereas a temperature of 100°C is needed for complete
conversion over Pt/CoO /SiO . In the opinion of the present
x
/Al
2
3
O below room temperature,
adsorption of CO and interaction of the hydroxylated Al
2
O
3
x
2
support with CO adsorbed on Pt (25). For Pt catalysts an
optimum in activity and selectivity was found at 200-250°C
(24, 25). At lower temperatures (desired temperature
authors the superior activity of the Au-based catalysts is
related to the low Au-O and Au-CO bond strengths.
The gold catalysts could be used as a start-up automotive
catalyst because of the short warm-up period required to heat
the catalyst to the temperature at which it becomes effective.
Alternatively, new generations of automotive three-way
catalysts based on gold might be feasible, since Au-based
catalysts are also able to reduce nitrogen oxides (8, 9, 23).
70°C) CO oxidation was rather slow due to CO inhibition of
~
oxygen adsorption. At a higher temperature the selectivity
decreased because CO desorption enables hydrogen
adsorption and oxidation.
We have studied SCO of CO over various multicomponent
Au-Pt-, Rh-, Pd- and Ru-based catalysts. Some of the results
obtained over gold-based catalysts are summarized in the
present paper. For more details see references 13 and 14.
Gold catalysts are promising candidates for SCO for two
reasons:
2
Selective Oxidation of CO in the
Presence of Hydrogen
1
) They exhibit an extraordinarily high activity in CO oxidation
in the low temperature range relevant for fuel cell
applications.
The hydrogen-air PEM (Polymer Electrolyte Membrane) fuel
cell is potentially an attractive and clean energy source for
vehicle propulsion and auxiliary power units. However, it is
not practical to store hydrogen in large quantities aboard a
vehicle. Hydrogen storage and distribution can be avoided by
producing hydrogen locally (on-board) from gasoline,
methanol or natural gas via steam-reforming, or partial
oxidation combined with water-gas shift reaction processes.
A major problem is the presence of a few per cent of CO in
the hydrogen product stream. It decreases the efficiency of
the fuel cell by CO-poisoning of the Pt-based electrode at the
operating temperature of the fuel cell, typically 60-100°C.
The most promising approach to reduce the CO
concentration to acceptable levels is by selective catalytic
oxidation (SCO) of CO, ie reaction (2). Hence, an efficient
catalyst must be highly active in CO oxidation at
temperatures compatible with the operation of the PEM fuel
2) The catalysts have another unique property: the rate of
CO oxidation exceeds that of hydrogen oxidation in the
relevant temperature range (13, 14, 28).
Results obtained for four alumina-supported Au-based
catalysts will be discussed here: Au, Au/MnO
very small gold particles and the multicomponent
Au/MgO/MnO catalyst. All these catalysts are able to oxidize
x
, Au/MgO with
x
CO at room temperature with the multicomponent catalyst
being the most active: 100% conversion at 20°C. Hydrogen
is also oxidized over these catalysts. However, as shown in
Table 2, significantly higher temperatures are needed for
hydrogen oxidation compared to CO oxidation. When
hydrogen is present in the feed, the behaviour of the
catalysts towards CO oxidation changes. Figure 4 shows the
conversion of CO, hydrogen and oxygen for a mixture
cell and very selective to CO
2
formation. The selectivity is
H
2
: CO : O = 4 : 2 : 1. This composition was chosen because
2
defined as the ratio of oxygen used for CO oxidation over the
total oxygen concentration which includes the oxygen loss
it contains just enough oxygen to oxidize all the CO,
if hydrogen does not participate in any oxidation reaction.
Up to 50°C relatively high CO conversions are obtained as
was the case for measurements without hydrogen in the
feed. However, at higher temperatures hydrogen oxidation
starts at the expense of CO oxidation. Over the most active
due to H O formation:
2
2H
2
+ O
2
2
→ 2H O
(6)
For a number of reasons these catalyst requirements - high
activity in CO oxidation at 60-100°C and almost no hydrogen
oxidation - are hard to meet:
catalysts, Au/MgO and Au/MgO/MnO
all the oxygen is
x
consumed, even at 20°C. Depending on the composition of
the catalyst, hydrogen conversion exceeds that of CO at
temperatures between 150 and 250°C. At temperatures
higher than 300°C CO oxidation increases again.
a) reaction (6) is faster than reaction (2) on most of the
noble metal catalysts;
b) in the relevant temperature range CO oxidation is very
slow on Pt and Pd due to CO inhibition (15).
The presence of CO distinctly suppresses the oxidation of
hydrogen at low temperatures over all four of the catalysts.
For example, over Au/MgO the hydrogen conversion at 20°C
Results reported in the literature show that CO can be
42
Gold Bulletin 2002 • 35/2

Table 2 CO and Hydrogen Oxidation over Alumina Supported Gold Catalysts. Gold Loading 5wt%
Catalyst
Average Au
CO oxidation
H
2
oxidation
Particle Size (nm)
α CO
T 50% (°C)
α H T 25% (°C)
2
Au
3.6 ± 1.4
9.2 ± 2.7
2.2 ± 1.0
2.7 ± 1.0
0.22
0.49
0.59
1.00
57
0.16
0.19
0.41
0.19
63
102
< 20
57
Au/MnO
x
35
Au/MgO
< 20
Au/MgO/MnO
x
< 20
2 2 2
Conversion α at 20°C and temperature needed for a conversion of 25% hydrogen and 50% (CO). Ratio CO/O = 1 and H /O = 4.
-1
-1
2 2
Reactant flow 40 ml/min , GHSV = 2500 h with a mixture of H , CO and O in helium (96 vol%)
in the absence of CO in the feed is 0.45 (see Table 2) and in
the presence of CO it is zero. The CO selectivity of Au/MgO
and Au/MgO/MnO is higher than 90% in the temperature
However at temperatures higher than 100°C the CO
2
2
selectivity of Au/MgO decreases rapidly with increasing
temperature. This decrease of selectivity is much slower
x
range of interest for fuel cell applications (up to 100°C).
using the multicomponent Au/MgO/MnO
x
catalyst.
c)
a)
1
.00
1
0
0
0
0
.00
.75
.50
.25
.00
O
2
O
H
2
0.75
0.50
0.25
0.00
CO
CO
2
H
2
0
50 100 150 200 250 300 350 400
5
0
100 150 200 250 300 350 400
0
Temperature (°C)
Temperature (°C)
O
2
CO
H
2
O
2
CO
H
2
b)
d)
1
0
0
0
0
.00
.75
.50
.25
.00
1.00
0.75
0.50
0.25
0.00
O
2
O2
CO
CO
H
2
H2
0
50 100 150 200 250 300 350 400
0
50 100 150 200 250 300 350 400
Temperature (°C)
Temperature (°C)
O
2
CO
H
2
O
2
CO
H
2
Figure 4
2 2 2 3 2 3 2 3 2 3
Conversion of CO (a), H (g) and O (c) versus temperature over (a) Au/Al O , (b) Au/MnOx/Al O , (c) Au/MgO/Al O and (d) Au/MgO/MnOx/Al O .
Au loading 5wt%Au: M (M = Mg and Mn). Atomic ratio = 1 : 5. The Au : Mg : Mn atomic ratio was 1 : 5 : 5 in the case of Au/MgO/MnO
from (13))
x
/Al
2
O
3
. (Adapted
Gold Bulletin 2002 • 35/2
43

1
0
0
0
0
.00
.75
.50
.25
.00
1.00
0.75
0.50
0.25
0.00
A]
B]
b)
a)
b)
c)
a)
c)
0
50
100 150 200 250 300
0
50
100 150 200 250 300
Temperature (°C)
Temperature (°C)
Figure 5
CO conversion in hydrogen rich feed: over: A] Au/MgO/Al
0 vol% H and CO + O (1.2 vol%) in helium ( 29 vol%) Au loading 5 wt%; Au : Mg atomic ratio 1 : 5; Au : Mg : Mn atomic ratio 1 : 5 : 5; a) λ = 4,
b) λ = 2 and c) λ = 1
2 3 x 2 3
O B] Au/MgO/MnO /Al O
7
2
2
~
Table 3 CO Conversion at 70°C for Three Values of λ (see text) in 70
CO
2
selectivity (24 - 27). The addition of MnO
x
to Au/Mg/Al O
2 3
vol% Hydrogen.
improves the CO conversion and CO
2
selectivity over the
whole temperature range studied for all values of λ used.
Based on the results discussed, the following model is
proposed for the oxidation of CO in a hydrogen atmosphere.
In our opinion gold nanoparticles have an intrinsic activity in
CO oxidation and in hydrogen oxidation according to the
same mechanism that has been established for PGMs (15).
Catalyst
λ = 4
0.77
0.99
λ = 2
0.81
0.95
λ = 1
0.45
0.72
Au/MgO/Al
2
O
3
Au/MgO/MnO
x
/Al
O
2 3
Feed composition: H
2 2
(70 vol%) and CO+O (1.2 vol%) in helium
(
29 vol%)
For CO oxidation the relevant steps are 3, 4 and 5 and for H
oxidation (6) steps 8, 9 and 10:
2
The high CO oxidation activity of Au/MgO is mainly due to the
presence of small gold particles. Its performance in CO oxidation
can be enhanced by the addition of MnO . Another beneficial
effect of MnO addition is that the high activity of Au/MgO in
hydrogen oxidation is lowered by the presence of MnO
x
H
2
→ 2Hads
→ 2Oads
(8)
x
O
2
(9)
x
.
2Hads + Oads → H
2
O (via OHads
)
(10)
All the results discussed up to now have been obtained in
a diluted hydrogen atmosphere. Figure 5 and Table 3 show
results obtained under more realistic conditions for the two
In this view gold nanoparticles have the ability to dissociate
(step 9) and H (step 8). Some recent results obtained in
O
2
2
most promising catalysts viz Au/MgO/Al
2
O
3
and
. These experiments were performed in
70 vol%) and O + CO (1.2 vol%) in helium
: CO molar ratios (␭ = 1,
and 4). The parameter ␭ is defined as the concentration of
our laboratory support this proposal. It was found that the
rate of the hydrogen-deuterium exchange reaction (11) is
Au/MgO/MnO
x
2
/Al O
3
a mixture of H
2
(
2
much faster over Au/Al
oxidation, than over Al
2
O
3
catalysts, active in H
2
and CO
~
(
29 vol%) using three different O
2
2
O
3
(29):
~
2
→
O
2
in the feed divided by the concentration of O
2
needed to
H
2
+ D
2
←
2HD
(11)
oxidize completely all the CO in the feed:
The significant differences between Au and the PGM catalysts
are the lower heat of CO adsorption and the lower binding
energies of H and O on Au combined with the slower rate of
dissociative adsorption of oxygen and hydrogen on gold.
The mechanism proposed includes adsorption of CO on
the small, mainly metallic, gold particles. At low
temperatures hydrogen adsorption is blocked by CO (T <
100°C). At higher temperatures the CO coverage becomes
small, allowing more hydrogen to dissociate and react with
O
2
, initial
␭
=
(7)
2
CO, initial
The results clearly show that a large excess of hydrogen
results in a lower CO conversion. Under these conditions more
oxygen is needed to increase the CO conversion (higher ␭) at
the expense of the CO
reported for Pt/Al , Ru/Al
hydrogen partial pressure leads to a significant lowering of the
2
selectivity. Similar effects have been
2
O
3
O
2 3
and Rh/Al : an increase in
O
2 3
oxygen resulting in a decrease in the selectivity towards CO
. An
2
44
Gold Bulletin 2002 • 35/2

increase in λ, ie upon lowering the CO partial pressure, may
induce a similar effect. At low temperatures most of the O may
Research and Development of Isotopic and Molecular
Technologies at the Cluj Napoca, Romania for three years.
Her main research interest is in the influence of support and
additives on the catalytic activity and selectivity of gold-
based catalysts in oxidation and reduction reactions.
originate from the lattice of MnO
reaction most likely occurs at the Au-MnO
multicomponent Au/MgO/MnO /Al catalyst has the best
x
. At these temperatures the
x
interface. The
x
O
2 3
performance in SCO of CO. The presence of MgO enables the
formation of small, highly dispersed, and thermally stable gold
particles on γ-Al
oxidation. The CO oxidation activity is improved by adding
MnO . In addition, the hydrogen oxidation on these
multicomponent catalysts is suppressed, leading to an overall
increase of CO selectivity in the temperature range relevant for
2
O
3
which are highly active in CO and H
2
References
x
1
V. Ponec and G.C. Bond, in ‘Catalysis by Metals and Alloys’, eds. B.
Delmon and J. T. Yates, Stud.Surf,Sci.& Catal., Elsevier Sci./Amsterdam,
1995, 95
2
fuel cell applications ( 70°C).
~
2
3
M. Haruta, Catal. Today, 1997, 36, 153
G.C. Bond, Catal. Today, 2002, 72, 5; G.C. Bond, Gold Bull., 2001, 34,
117
Acknowledgement
4
5
6
7
8
G.J. Hutchings, Gold Bull., 1996, 29, 123
The authors acknowledge financial support from the
Netherlands Organization for Scientific Research (NWO). The
work was also supported by INTAS (project nr 99-01882). The
work has been performed under the auspices of NIOK
D.T. Thompson, Gold Bull., 1998, 31, 111
G.C. Bond and D.T. Thompson, Catal. Rev. - Sci. Eng., 1999, 41, 319
M. Haruta and M. Date, Appl. Catal. A, 2001, 222, 427
M.A.P. Dekkers, M.J. Lippits and B.E. Nieuwenhuys, Catal. Lett., 1998,
56, 195
(Netherlands Institute for Catalysis Research). NIOK report nr
UL UL02-2-01.
9
M.A.P. Dekkers, M.J. Lippits and B.E. Nieuwenhuys, Catal. Today, 1999,
54, 381
10
R.J.H. Grisel, P.J. Kooyman and B.E. Nieuwenhuys, J. Catal., 2000, 191,
430
About the Authors
11
R.J.H. Grisel and B.E. Nieuwenhuys, Catal. Today, 2001, 64, 69
Ben Nieuwenhuys is the principal investigator and supervisor
of the research group at Leiden Institute of Chemistry, Leiden
University in The Netherlands, where the investigations
described here were undertaken. He has more than 170
publications on various surface chemistry topics and
heterogeneous catalysis. The research progamme of the
group focuses on the understanding of heterogeneous
catalysis on the atomic level; and, in particular, the relationship
between activity, selectivity of the catalyst and the
structure/composition of sites present on the surface. These
goals are achieved by correlating results of experiments on
model systems using the surface science approach with those
obtained on high surface area (‘real’) catalysts.
12 R.J.H. Grisel, J.J. Slyconish and B.E. Nieuwenhuys, Topics in Catal., 2001,
16/17, 425
13 R.J.H. Grisel and B.E. Nieuwenhuys, J. Catal., 2001, 199, 48
14 R.J.H. Grisel, C.J. Weststrate, A. Goossens, M.W.J. Crajé, A.M. van der
Kraan, and B.E. Nieuwenhuys, Catal. Today, 2002, 72, 123
15 B.E. Nieuwenhuys. Adv. Catal., 1999, 44, 49
16 A. Gluhoi and B.E. Nieuwenhuys, to be published
17 S.K. Tanielyan and R.L. Augustine, Appl. Catal., 1992, A85, 73
18 M. Valden, S. Pak, X. Lai and D.W. Goodman, Catal. Lett., 1998, 56, 7
19 S. Tsubota, T. Nakamura, K. Tanaka and M. Haruta, Catal. Lett., 1998,
56, 131
20 Y.J. Mergler, A. van Aalst, J. van Delft and B.E. Nieuwenhuys, Appl. Catal.,
1996, B10, 245
Ruud Grisel was a PhD student at the Leiden University
before he moved to ASM (Advanced Semiconductor Materials)
in 2001. He will defend his PhD thesis entitled ‘Supported Gold
Catalysts for Environmental Applications’ in June 2002.
Kees-Jan Weststrate investigated the activity of gold and
other noble metal catalysts in the selective oxidation of CO in
21 G.C. Bond, M.J. Fuller and L.R. Mulloy, Proc.6th Int. Congr. Catal., 1976,
A26
22 Y.J. Mergler, J. Hoebink and B.E. Nieuwenhuys, J. Catal., 1997, 167, 305
23 A. Ueda and M. Haruta, Gold Bull., 1999, 32, 3
24 M. Watanabe, H. Uchida, H. Igarashi and M. Suzuki, Chem. Lett., 1995,
21
the presence of H
2
for his MSc thesis. From April 2002 he has
25 M.J. Kahlich, H.A. Gasteiger and R.J. Behm, J. Catal., 1997, 171, 93
26 S.H. Oh and R.M. Sinkevitch, J. Catal., 1993, 142, 254
27 M.L. Brown, A.W. Green, G. Cohn and H.C. Anderssen, Ind. Eng. Chem.
Res., 1960, 52, 841
been working on his PhD. His research involves the study of
carbon species on noble metal surfaces during different
reactions, such as partial oxidation of methane to syn-gas.
Andrea Gluhoi joined the Heterogeneous Catalysis and
Surface Science Group in 2000 as a PhD student. Before
28 R.H. Torres Sanchez, A. Ueda, K. Tanaka and M. Haruta, J. Catal., 1997,
168, 125
2000 she worked as a researcher at the National Institute for
29 H.S. Vreeburg, J.W. Bakker and B.E. Nieuwenhuys, unpublished results.
Gold Bulletin 2002 • 35/2
45