Catalysis with chemically modified mesoporous silicas: Stability of the mesostructure under Suzuki-Miyaura reaction conditions

Article abstract of DOI:10.1016/j.jcat.2009.04.020

The use of functionalized mesoporous silicas such as SBA-15 and MCM-41 as supports for Pd catalysis has become increasingly common, notably in important reactions such as the Suzuki-Miyaura reaction. However the analysis of the structural consequences of

Full text of DOI:10.1016/j.jcat.2009.04.020

Journal of Catalysis 265 (2009) 148–154
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Catalysis with chemically modified mesoporous silicas: Stability
of the mesostructure under Suzuki–Miyaura reaction conditions
Ben W. Glasspoole, Jonathan D. Webb, Cathleen M. Crudden *
Department of Chemistry, Queen’s University, 90 Bader Lane, Kingston, Ontario, Canada K7L 3N6
a r t i c l e i n f o
a b s t r a c t
Article history:
The use of functionalized mesoporous silicas such as SBA-15 and MCM-41 as supports for Pd catalysis has
become increasingly common, notably in important reactions such as the Suzuki–Miyaura reaction. How-
ever the analysis of the structural consequences of exposure to these harsh reaction conditions is not
nearly as common. We report herein a study of the effect of the Suzuki–Miyaura reaction conditions
on the mesoporous material, and on the catalytic activity of the resulting material. Although it has been
determined that aqueous base is highly detrimental to the structure of the material, the boric acid pro-
duced during the actual coupling reaction has a significant protective effect on the material. This protec-
tive effect can be mimicked by the addition of exogenous boric acid to the reaction medium. The use of
aluminum-doped material provides an additional protective effect that is not dependent on the presence
of boric acid. Finally, we demonstrate conclusively that access to the pores is essential for catalysis, since
loss of mesoporosity is coincident with loss of catalytic activity.
Received 19 December 2008
Revised 22 April 2009
Accepted 24 April 2009
Available online 29 May 2009
Keywords:
Palladium
Cross-coupling
SBA-15
MCM-41
Stability
Ó 2009 Elsevier Inc. All rights reserved.
1
. Introduction
Despite the remarkable importance of metal-catalyzed transfor-
needs to be assessed. Although the thermal and hydrothermal sta-
bility of mesoporous materials has been exhaustively studied [13–
17], their stability to other more forcing reaction conditions such
as those employed herein, has received little or no attention.
Thus we report herein the effect of the Suzuki–Miyaura reaction
conditions on supported heterogeneous catalysts derived from a
variety of materials, and the effect of material collapse on the
resulting catalytic activity. MCM-41, calcined SBA-15, Al-stabilized
SBA-15, and various other materials have been subjected to typical
Suzuki–Miyaura reaction conditions, and the resulting effects on
the materials properties and catalytic activities are described. We
demonstrate the protective effects of elements such as aluminum
and boron on the order of the material under these harsh reaction
conditions. We also demonstrate conclusively that access to the
interior pores of the material is essential for catalytic activity.
mations in the synthesis of fine chemicals, pharmaceuticals, and
commodity chemicals, contamination of the organic products with
metals remains a serious challenge [1]. The Suzuki–Miyaura reac-
tion (Scheme 1) [2,3] stands out among the currently available
coupling reactions for the synthesis of pharmaceutical compounds
as the most commonly employed reaction in the pharmaceutical
industry for the formation of carbon–carbon bonds [4]. However,
considering the strict guidelines placed on Pd levels in products
destined for human consumption [1], there is a great need for
methods to prevent Pd incorporation into the organic products of
this important reaction. These methods can be broadly divided into
scavenging and preventative approaches, the latter being domi-
nated by the use of leach-resistant heterogeneous catalysts.
Our group and others [5–9] have shown that it is possible to use
mercaptopropyl trialkoxysilane-modified materials both as scav-
engers for soluble Pd and as recoverable catalysts that leach low
amounts of Pd into solution. The support most commonly em-
ployed for the thiol-ligated Pd is SBA-15 [10–12], a mesoporous sil-
ica material with high porosity and, compared to other
mesoporous materials, relatively good stability. However, for ex-
tended use of these materials in the Suzuki–Miyaura reaction, their
stability to the reaction conditions, particularly hot aqueous base,
2
. Materials and methods
2.1. Chemicals
Pluronic P123 (EO20PO70EO20), tetraethyl orthosilicate (TEOS),
sodium aluminate (NaAlO ), sodium chloride, decane, dimethoxy-
2
benzene (DMB) potassium carbonate, and pinacol were obtained
from Aldrich and were used without further purification. Bromo-
acetophenone (BrPhAc, Aldrich) was recrystallized from ethanol.
2
Phenyl boronic acid and Pd(OAc) were obtained from Frontier
Chemical and Pressure Chemical, respectively. Mercaptopropyl tri-
methoxysilane (MPTMS) was obtained from Fluka, and was used as
*
Corresponding author.
E-mail address: cruddenc@chem.queensu.ca (C.M. Crudden).
0
021-9517/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved.
doi:10.1016/j.jcat.2009.04.020

B.W. Glasspoole et al. / Journal of Catalysis 265 (2009) 148–154
149
analysis at 77 K using a Micromeritics ASAP2010 instrument. Sam-
ple degassing was performed at room temperature for all catalysts
to prevent thermal decomposition of the attached organics and Pd
catalysts. TEM images and Powder X-Ray Diffraction patterns were
obtained on a JEOL 2011 Scanning TEM and Philips XRD System,
respectively.
X
B(OR)2
SBA-15-SH Pd (1%)
eq. K CO , DMF/H O
+
1
2
3
2
Scheme 1. The Suzuki–Miyaura cross-coupling reaction.
received. Solvents were of Certified A.C.S. grade and used as re-
ceived, though DMF (Aldrich) was deoxygenated with bubbling
Ar (g) prior to use.
3
. Results and discussion
3.1. Effect of Suzuki–Miyaura reaction conditions on silica structure
2.2. Synthesis of mesoporous silica materials
The use of thiol-functionalized mesoporous silicas as supports
for Pd catalysts has provided leach-resistant, recyclable catalysts
that are capable of affecting a variety of coupling reactions with
minimal leaching. However, preliminary studies of material stabil-
ity under typical Suzuki–Miyaura conditions indicated that mate-
rial degradation occurred more quickly than under simple
hydrothermal conditions [7–9]. Unlike other cross-coupling reac-
tions such as the Sonogashira et al. [18] or Stille [19] reactions,
the Suzuki–Miyaura reaction [2,3] (Eq. (1)) requires aqueous base
to activate the boronate ester component [20]. Considering the
known sensitivity of silica-based materials to an aqueous base
SBA-15 was synthesized as previously reported [11,22]. Typi-
cally, 4 g of P123 was dissolved in acidic water (pH ꢀ2) before
the addition of the silica source (9 mL TEOS). Condensation of the
silica network about the polymer template proceeded for 20 h at
3
5 °C before being treated hydrothermally at 80 °C for 48 h in a
sealed vessel. Surfactant was removed from the as-made material
by either calcination (1 °C/min ramp, 550 °C for 6 h) or extraction
with ethanol. SBA-15-NaCl-type materials were synthesized in
similar fashion, with 5 g of NaCl being added to the acidic solution
before the addition of the silica source. Aluminum was incorpo-
rated into both SBA-15- and SBA-15-NaCl-type materials by adding
[
21], we targeted this component as a likely source of material
degradation.
0
2
.153 g NaAlO to the aqueous solution after 6 h of silica condensa-
tion, as reported by Li et al. [39]. Adjusting the pH to 5 proved to be
crucial in obtaining stable materials, and was monitored using a
digital pH meter. Hydrothermal treatment was continued for
2
4 h after pH adjustment.
MCM-41 was synthesized following known procedures [22]. A
modified MCM-41 material was prepared by adding decane as a
pore-swelling agent, and hydrothermally treating the as-made
material in the mother liquor for 48 h at 80 °C to encourage thick-
ening of the walls.
ð1Þ
In order to test the stability of various materials to the reaction
conditions without sacrificing large quantities of the organic sub-
strates, a set of conditions was developed to emulate the Suzuki–
Miyaura reaction. These conditions consisted of stirring the insol-
2.3. Organic functionalization of silica surface and catalyst formation
uble silica at 80 °C in 20:1 DMF:H
the presence of the slightly soluble K
2
O under inert atmosphere in
CO in the absence of reac-
2
3
Thiol groups were tethered to the silica surface by dispersing
tion substrates. When tested under these pseudo-reaction condi-
tions, both MCM-41 [22] and SBA-15-type materials lost their
mesoporosity in under 4 h, illustrating the dichotomy between
the hydrothermal conditions typically used to assess material sta-
bility and Suzuki–Miyaura cross-coupling reaction conditions [23].
For the subsequent stability studies, we employed SBA-15 pre-
pared in the presence of NaCl (so-called SBA-15-NaCl), which
the material in toluene that contained an excess of MPTMS and
refluxing the mixture for 16 h. Sulfur content of the functionalized
materials was determined by elemental analysis. Typical sulfur
loadings were between 0.5 and 1.0 mmol S/g material, though
higher loadings could be achieved by pre-hydrolyzing the silica
2
surface prior to thiol addition. Sufficient Pd(OAc) (Pressure Chem-
ical) to afford a 2:1 S:Pd catalyst was then added as a solution in
THF. After treatment with the thiolated material, the solution be-
came colourless, consistent with the previously reported absorp-
tion of >99.99% of Pd from solution [7–9].
1
1
200
000
2.4. Heterogeneous Suzuki–Miyaura catalysis
c
8
6
00
00
In a typical reaction, 0.5 mmol of aryl bromide (bromoacetophe-
none) was reacted with a slight excess of phenyl boronic acid pina-
colate ester (PhBpin, column) at 80 °C in 20:1 DMF:H O in the
presence of K CO and the Pd catalyst. Reaction progress was mon-
b
2
2
3
itored via examination of aliquots obtained from the reaction mix-
ture by GC (FID), using dimethoxybenzene as an internal standard
and a calibration curve to quantify the FID response. The heteroge-
neous catalyst was recovered by filtration of the reaction mixture
and washing the collected solids with copious amounts of EtOAc
400
200
0
a
and H
2
O.
0
.0 0.2 0.4 0.6 0.8 1.0
Relative Pressure (P/Po)
2.5. Material characterization
Fig. 1. Effect of base on the structure of an ordered mesoporous silicate. (a) SBA-15-
The degree of order and porosity of the synthesized materials
and recycled catalysts was ascertained through nitrogen sorption
2
NaCl (b) SBA-15-NaCl heated in 20:1 DMF: H O, 8 h (c) SBA-15-NaCl heated with
base.

1
50
B.W. Glasspoole et al. / Journal of Catalysis 265 (2009) 148–154
provides a more sensitive material that would permit us to rapidly
screen different reaction conditions [24]. The results obtained in
this study were then applied to SBA-15 prepared in the absence
of NaCl.
c
The drastic effect of aqueous base is clearly demonstrated in
Fig. 1. After 8 h of treatment with DMF/water at 80 °C (typical reac-
tion temperature), there was no loss of order (compare Fig. 1a and
b). However, upon addition of base, the pore structure of SBA-15-
NaCl underwent complete collapse (Fig. 1c).
Although it is clear that the hot aqueous base is the main cause
of material degradation, we were surprised to find that all the
materials tested showed significantly higher stability under actual
reaction conditions than under pseudo-conditions using the same
amount of base. Consistent with this, the use of the filtrate from a
completed Suzuki–Miyaura reaction as a solvent instead of freshly
b
a
1.0
1.5
2.0
2.5
3.0
2
prepared 20:1 DMF:H O provided the same protective effect. These
2θ (degrees)
facts prompted us to systematically investigate the effect of reac-
tion side products on material stability. A material exposed to
KBr in the presence of base showed a similar rapid degradation
Fig. 3. XRD patterns of ordered mesoporous silicate and effect of boric acid on
stability. (a) Pristine SBA-15-NaCl; (b) SBA-15-NaCl heated with base and 2 eq.
B(OH) . (c) SBA-15-NaCl heated with base alone.
3
(
compare Fig. 2a and c). However, the addition of the other major
side product, boric acid, resulted in virtually complete retention of
porosity (Fig. 2b) and long-range order confirmed by pXRD (Fig. 3).
The effect of boric acid was also found to be concentration
dependent, with the best results being observed with >1 equiva-
lent [25]. The consequence of this under actual reaction conditions
is that reactions that quickly attain high conversion of the organic
substrates (producing boric acid as a side product) will result in
greater material stability compared to those that react more slowly
[40]. Additionally, since structural Al is tetra-coordinated, it im-
parts an anionic character to the aluminosilicate wall, protecting
the surface from attack by hydroxide [42,43], which is the starting
point for degradation by hydrolysis of Si–O–Si bonds [44]. Even ex-
tra-framework, octahedral Al is proposed to have a protective ef-
fect, by reacting with surface silanols, protecting them and also
reactive siloxane bridges, from attack by base [43]. Shen and Kawi
demonstrated this conclusively by coating the surface of pre-
[
26]. Although adding boric acid at the beginning of every run was
an effective strategy to stabilize the material, we decided to exam-
ine the direct incorporation of a similar group 13 element, alumi-
num, directly into the material. Although boron-containing
mesoporous materials have been described in the literature [27–
formed all-silica MCM-41 with Al
2 3
O , which resulted in a material
that still retained high surface area after one week in boiling water
[40].
Aluminum-doped SBA-15 [33,45] was prepared following the
method of Li et al. [39] in the hope that it would also show resis-
tance to aqueous base. Li et al. showed that the stability of the
material prepared by incorporating Al during materials synthesis
depended strongly on both the temperature and the pH of the
mother liquor during hydrothermal treatment, with the sturdiest
materials being prepared at pH 5 and temperatures in excess of
100 °C [39]. Using these conditions, we prepared aluminum-doped
ordered materials, which will be designated Al-SBA-15. The pres-
3
2], the hydrothermal stability of aluminum-containing materials
has received significantly greater attention due to the interest in
preparing mesoporous materials with high-acidity for cracking
applications [33–38]. Al-doped mesoporous materials have been
reported to have remarkable stability under hydrothermal condi-
tions (300 h in boiling water and 6 h of steaming at 600 °C) [39],
however, stability to aqueous base has not been examined.
Several rationales have been proposed for the stabilizing effect
of aluminum [40]. When incorporated into the walls of mesopor-
ous materials, the so-called ‘‘structural Al” decreases the overall or-
der of the material [41], making it thermodynamically more stable
2
7
ence of a large signal at 52 ppm in the Al NMR of all doped mate-
rials indicates that aluminum is primarily in tetrahedral
arrangement, bound to four silicon centers through siloxane bonds
14,46]. However, the broadness of this signal makes it difficult to
a
[
rule out the presence of small amounts of extra-framework octahe-
dral aluminum. During exposure to reaction conditions, the tetra-
hedral form of aluminum becomes more prevalent, indicating
that the extra-framework Al is being either removed from the
material, or incorporated during the reorganization of the silicate
wall structure. As will be shown in the following section, these
materials have greater stability under the reaction conditions than
SBA-15 itself, consistent with the greater hydrothermal stability
reported for Al-doped mesoporous materials [34,40,46–48].
1
1
1
1
600
400
200
000
d
c
8
6
4
2
00
00
00
00
0
b
3.2. Catalysis on mesoporous silicate supports
a
Having gained an understanding of the factors affecting the sta-
bility of the material, we examined derivatized versions of these
materials as catalysts for the Suzuki–Miyaura reaction under ac-
tual reaction conditions. In order to retain Pd on the various sup-
ports, the surface was first treated with mercaptopropyl
trimethoxysilane (MPTMS) to provide a ligand for Pd [49]. This
type of thiolated material has been shown by our group and others
to be a superb scavenger for Pd, reducing 500 ppm solutions to a
few ppb [8,50]. After the absorption of Pd, the resulting materials
0
.0 0.2 0.4 0.6 0.8 1.0
Relative Pressure (P/P )
o
Fig. 2. Effect of major side products of the Suzuki–Miyaura reaction on material
stability. (a) Pristine SBA-15-NaCl; (b) SBA-15-NaCl heated with base and 2 eq. of
B(OH)
base.
3
(c) SBA-15-NaCl heated with base and KBr; (d) SBA-15-NaCl heated with

B.W. Glasspoole et al. / Journal of Catalysis 265 (2009) 148–154
151
function as effective, leach-resistant catalysts depending on the
800
700
600
500
S:Pd ratio. In order to minimize leaching and maximize activity,
the S:Pd ratio should be ca. 2:1. At lower ratios, Pd leaching be-
comes more significant, and at higher ratios, the catalyst is inactive
c
[
7].
b
a
3.2.1. MCM-41 Pd catalysts
With wall thicknesses of only ꢀ10 Å, and short lifetimes dem-
4
3
2
1
00
00
00
00
onstrated in the pseudo-studies, thiol-functionalized MCM-41 Pd
catalysts (henceforth MCM-41-SHꢁPd) were not expected to be
highly reusable catalysts. Near quantitative conversions for the
first two cycles (Fig. 4) indicated that catalysis is not limited by
the smaller pore size of MCM-41 materials, though a sudden loss
of activity is observed during the third run (see Fig. 4).
Examination of the material’s structural integrity over time
(
Fig. 5) indicated that the MCM-41-SH Pd catalyst underwent al-
0.0
0.2
0.4
0.6
0.8
1.0
most complete degradation after less than 5 h of use in the Suzu-
ki–Miyaura reaction. Thus in the case of MCM-41, the stabilizing
effect of boric acid produced during the reaction is unable to over-
come the fragility of the thin, ca. 10 Å, walls. The most interesting
fact gleaned from this study was that in all cases, the loss of activity
occurred concurrently with the loss of pore structure. Our group has
previously shown that active catalysts can be made with amor-
phous silica [7], therefore, the long-range order is not necessary
for catalysis, but porosity is necessary. Thus it appears that loss
of order in a support which was mesoporous to begin with results
in a complete loss of catalytic activity. This likely occurs by the
trapping of active Pd species in the collapsed pore structure. The
same effect was observed using meta-stable NaCl-doped SBA-15-
based catalysts as shown in Fig. 6. Loss of catalytic activity was
concomitant with loss of order.
Relative Pressure (P/Po)
Fig. 5. N
2
isotherms of MCM-41-SHꢁPd catalyst and subsequent uses in Suzuki
coupling reactions. (a) Pristine catalyst; (b) first use and (c) third use.
1
00
8
0
60
4
0
0
0
2
Various methods have been described to improve the hydro-
thermal stability of MCM-41, including hydrothermal restructur-
ing [51]. the addition of inorganic salts during the synthesis
0
50
100
150
200
250
Time (min.)
Second Use
First Use
Third Use
[
4
52,53], and doping alumina into the material [14,33,34,39–
1,43,45–48]. Thus the effect of hydrothermally treating MCM-41
after silica condensation (H
1200
600
0
x
MCM-41-SHꢁPd, 0.77 mmol S/g mate-
rial) was examined. Although the catalyst showed a similar activity
in the Suzuki–Miyaura coupling, hydrothermal treatment did not
afford an increase in stability over the course of multiple uses.
Materials with higher thiol content were also prepared (MCM-
4
1-xSHꢁPd, 1.50 mmol S/g material) in the hope that the increased
organic functionality would protect the surface by rendering it
more hydrophobic [54]. Again, only slight improvements of the
material stability were observed. Considering these facts, we fo-
cused our attention on the thicker-walled SBA-15-type materials.
0
0.2
0.4
0.6
0.8
1
Relative Pressure (P/P )
o
SBA-15-NaCl-SH Pd
First Use
Third Use
1
00
Fig. 6. N
coupling reactions.
2
isotherms of SBA- NaCl-15-SHꢁPd catalyst and subsequent uses in Suzuki
First Use
Second Use
Third Use
80
60
40
20
0
3.2.2. SBA-15 Pd catalysts
When coupled with the stabilizing effect of boric acid, the sub-
stantially thicker walls of SBA-15 were better able to withstand the
harsh reaction conditions than MCM-41 based materials. This
translated to a higher reusability of SBA-15-derived Pd catalysts
with SBA-15-SHꢁPd, (0.62 mmol S/g material), which remained or-
dered and catalytically active for a considerably longer time. As
shown in Fig. 7, the catalyst retains virtually all of its order after
three runs, corresponding to a total of 24 h, although a slight drop
in catalytic activity is observed in the last run.
0
20
40
60
80
100
120
As Al-SBA-15 is reported to have improved hydrothermal stabil-
ity compared to regular SBA-15 [33,34], we were optimistic that it
would serve as a rugged support for Pd catalysis. Indeed, the
Time (min.)
Fig. 4. MCM-41-SHꢁPd Suzuki cross-coupling recycle study.

1
52
B.W. Glasspoole et al. / Journal of Catalysis 265 (2009) 148–154
1
00
1200
e
d
c
b
a
80
60
40
20
0
1000
8
6
00
00
First Use
Second Use
Third Use
400
2
00
0
100
200
300
400
500
Time (min.)
0
.0
0.2
0.4
0.6
0.8
1.0
1
1
200
000
Relative Pressure (P/Po)
d
Fig. 9. N2 isotherms for four consecutive uses of Al-SBA-15-SHꢁPd in the Suzuki
Reaction. (a) Pristine Catalyst. (b)–(e) First to fourth use of catalyst.
8
6
4
2
00
00
00
00
c
b
a
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/Po )
Fig. 7. Suzuki–Miyaura conversion (top) and N
2
isotherms (bottom) for SBA-15-
SHꢁPd catalyst. (a) Pristine SBA-15. After first (b), second (c) and third (d) uses.
Al-SBA-15-SHꢁPd (1.79 mmol S/g material) catalyst also remained
well ordered over 20 h of Suzuki reaction time and, unlike the
SBA-15-SHꢁPd catalysts, retained full catalytic activity throughout
the course of the entire recycle sequence (Figs. 8 and 9). Examina-
tion of the material by TEM (Fig. 10) showed that the Al-SBA-15-
SHꢁPd catalyst is still highly ordered after 20 h of use. The observa-
tion of Pd nanoparticles by TEM, seen as dark spots in the pores of
the material and occasionally on the exterior, is consistent with our
previous studies of SBA-15-SHꢁPd [7]. XRD analysis of a second ser-
Fig. 10. TEM images of pristine Al-SBA-15-SHꢁPd (top) and Al-SBA-15-SHꢁPd after
four recycles totalling 20 h under Suzuki–Miyaura conditions (bottom).
ies of recycles confirms that the long-range order of the material is
maintained after three catalyst uses, although the intensity of the
1
00
1
00 signal is decreased compared with pristine material, Fig. 11.
8
6
4
2
0
0
0
0
0
3
.3. Assessment of leaching
With information about support stability and reusability in
hand, the next important factor to be determined was leaching of
Pd. In our previous work we showed that pure silica-based materi-
als functionalized by MPTMS were able to affect the Suzuki–Miya-
ura coupling shown in Eq. (2) with extremely low levels of
leaching. As ppm is a concentration-dependent measurement, we
prefer to report the Pd leaching as a percentage of initially added
Pd. We should note, however, that in all cases the solutions at
the end of the reaction were less than 0.5 ppm, and were often in
the low ppb range.
First Use
Second Use
Third Use
Fourth Use
0
50
100
150
Time (min.)
200
250
300
Thus it was necessary to determine whether or not the incorpo-
ration of aluminum into the material had any deleterious effect on
Fig. 8. Conversions for series of Suzuki reactions catalyzed by Al-SBA-15-SHꢁPd.

B.W. Glasspoole et al. / Journal of Catalysis 265 (2009) 148–154
153
rious reordering of otherwise stable mesoporous silicate materials.
This degradation is mitigated by the formation of boric acid as a
reaction side product. A strengthening effect could be achieved
by doping aluminum into the material, producing a material with
dramatically increased stability to the reaction conditions. Thiol
functionalization and Pd loading of the stable aluminosilicate
material yielded a highly active and reusable catalyst, one that re-
tained its mesoporosity and long-range order over the course of
multiple recycles. By performing catalytic runs and material anal-
ysis in concert, we were able to show that catalytic activity is lost
when the material structure degrades. Finally, the examination of
Pd leaching at the completion of the reaction indicated that the
Al-incorporated material was at least as good as, if not better than
the regular SBA-15-based thiolated catalysts that were prepared
previously by our group.
b
a
1
.0 1.5 2.0 2.5 3.0 3.5
Acknowledgments
2
θ (degrees)
Fig. 11. (a) XRD pattern of pristine Al-SBA-15.Pd and (b) after three uses totalling
5 h under Suzuki–Miyaura conditions.
The Natural Sciences and Engineering Research Council are
acknowledged for their support of this work in terms of research
and infrastructure grants to CMC and a Canada Scholarship to
JDW. The Canada Foundation of Innovation is acknowledged for
infrastructure support and Queen’s University is acknowledged
for Queen’s Graduate Awards to BWG and JDW. DRE is thanked
for useful discussions.
1
Table 1
Pd leaching from thiolated mesoporous materials with and without Al.
Appendix A. Supplementary material
27Al, 29
Si MAS NMR spectra and concentration dependence of
boric acid effect on silicate stability. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.jcat.2009.04.020.
ð2Þ
Entry
Support material
S:Pd ratio
Yield (%)
Pd leaching (%)
1
2
3
4
5
Al-SBA-15-SH
SBA-15-SH
2:1
2:1
2:1
1.75:1
1:1
99
98–99
98
99
86
0.02
0.12
0.06
0.16
0.3
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Al-SBA-15-SH
SiO -SH
2
-SH
[
[
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