Increasing the aromatic selectivity of quinoline hydrogenolysis using Pd/MOx-Al2O3

Article abstract of DOI:10.1007/s10562-014-1346-x

Catalysts consisting of Pd nanoparticles supported on highly dispersed TiO_x-Al₂O₃, TaO_x-Al₂O₃, and MoO_x-Al₂O₃ are studied for catalytic quinoline hydrogenation and selective C-N bond cleavage at 275°C and 20 bar H₂. The Pd/MO_x-Al₂O₃ materials exhibit significantly greater aromatic product selectivity and thus 10-15 % less required H₂ for a given level of denitrogenation relative to an unmodified Pd/Al₂O₃ catalyst.

Full text of DOI:10.1007/s10562-014-1346-x

Catal Lett (2014) 144:1832–1838
DOI 10.1007/s10562-014-1346-x
Increasing the Aromatic Selectivity of Quinoline Hydrogenolysis
Using Pd/MO –Al O
x
2 3
Mark Bachrach
Christian P. Canlas
Tobin J. Marks Justin M. Notestein
•
Natalia Morlanes-Sanchez
•
•
Jeffrey T. Miller
•
•
Received: 18 June 2014 / Accepted: 9 August 2014 / Published online: 11 September 2014
Ó Springer Science+Business Media New York 2014
Abstract Catalysts consisting of Pd nanoparticles sup-
ported on highly dispersed TiO –Al O , TaO –Al O , and
1 Introduction
x
2
3
x
2 3
MoO –Al O are studied for catalytic quinoline hydroge-
x 2 3
Catalyst supports play a major role in determining the
activity and selectivity of a catalyst. The support can play a
direct role by acting as an acid or base, or an indirect role
by influencing supported structures such as via a strong
metal-support interaction [1–4]. Reducible supports such as
TiO or CeO often have a direct role, while ‘irreducible’
nation and selective C–N bond cleavage at 275 °C and
0 bar H . The Pd/MO –Al O materials exhibit signifi-
2
2
x
2 3
cantly greater aromatic product selectivity and thus
0–15 % less required H for a given level of denitrogen-
1
2
ation relative to an unmodified Pd/Al O catalyst.
2
3
2
2
refractory oxides such as Al O , MgO, and SiO are often
2
3
2
Keywords C–N bond cleavage Á Hydrodenitrogenation Á
Tantalum Á Titanium Á Molybdenum Á Quinoline Á
Palladium Á Supported metal oxides
selected for their stability and inertness [5]. Al O is a
2 3
common support for metal or metal sulfide particles in
hydrotreating processes, which cleave C–X (X = N, O, S)
bonds to extrude heteroatoms from heteroorganic impuri-
ties in crude fuels [6]. The incidental acidity of Al O has
2
3
been shown to be important for C-X bond cleavage. For
example, Lobo et al. studied the hydrodeoxygenation
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-014-1346-x) contains supplementary
material, which is available to authorized users.
(HDO) of m-cresol over a Pt/Al O catalyst and implicated
2 3
the metal role as hydrogenation and the acidic support role
as subsequent extrusion of the heteroatom via dehydration
M. Bachrach Á T. J. Marks
Department of Chemistry, Northwestern University,
[
7, 8]. Doping a support with low levels of highly-dispersed
2145 Sheridan Road, Tech. G237, Evanston, IL 60208, USA
e-mail: t-marks@northwestern.edu
metal oxides is a common method to alter surface reac-
tivity, but this method has not, to our knowledge, been
studied for its effect on selective C–X bond cleavage.
Highly dispersed metal oxides and their derivatives can
have high reactivity, structural precision, and stability under a
wide range of reaction conditions [9–17]. For example, highly
N. Morlanes-Sanchez Á C. P. Canlas Á J. M. Notestein (&)
Department of Chemical and Biological Engineering,
Northwestern University, 2145 Sheridan Road, Tech. E136,
Evanston, IL 60208, USA
e-mail: j-notestein@northwestern.edu
dispersed, SiO -supported Ta hydrides have been shown to
2
Present Address:
N. Morlanes-Sanchez
King Abdullah University of Science and Technology, Thuwal,
Saudi Arabia
activate NH3 bonds (N–H bond dissociation energy =
1
08 kcal/mol) at room temperature [18, 19], and to cleave N2
bonds (bond dissociation energy = 226 kcal/mol) at 250 °C
19, 20]. Related Ti and Ta molecular complexes have been
[
Present Address:
shown to insert directly into aromatic C–N bonds [21, 22].
Overall, understanding how highly dispersed metal oxide
dopants influence C–X bond cleavage processes should be
informative for the design of new, more selective catalysts.
C. P. Canlas Á J. T. Miller
Chemical Sciences and Engineering Division, Argonne National
Laboratory, Argonne, IL 60439, USA
e-mail: millerjt@anl.gov
1
23

Enhancing Palladium-Catalyzed C–N Hydrogenolysis with MO
x
Dopants
1833
Scheme 1 Generally accepted
reaction pathway for quinoline
hydrodenitrogenation [27]
The C–N bond cleavage of quinoline (Scheme 1) with
traditional hydrodenitrogenation (HDN) catalysts such as
sulfided NiMo/Al O or NiW/Al O requires aggressive
2 Experimental
2.1 Catalyst Synthesis
2
3
2 3
conditions (340–380 °C and 80–120 bar H ) to hydroge-
2
nate the heterocyclic rings, and often saturates the carbo-
cyclic rings as part of the C–N cleavage process [23–26].
Drawn as Pathway 1 in Scheme 1, the eventual product is
Pd/MO –Al O catalysts were synthesized by grafting
x 2 3
TiO(acac) , Ta(acac)(OEt) , TaCl-calixarene dimer, or
2
4
MoO (acac) onto Al O at 1.4 wt% metal loading. Next, 1
2
2
2 3
propylcyclohexane. This leads to greater H consumption
2
or 3 wt% Pd was added by impregnation from Pd(OAc)2
than is stoichiometrically necessary for denitrogenation,
and represents a major energy inefficiency.
and the materials were calcined in air at 500 °C. Pd/Al O
2
3
catalysts were synthesized by impregnating 1 wt% Pd from
Many non-traditional materials have been studied as C–
N bond cleavage/hydrogenolysis catalysts. In contrast to
typical sulfided NiMo/Al O catalysts [28], supported and
Pd(OAc)2 onto Al O and calcining in air at 500 °C.
2
3
Complete details of the catalyst syntheses are provided in
the Supporting Information.
2
3
unsupported Mo nitrides and carbides [29–32] as well as
Nb nitrides [33], exhibit high aromatic selectivity for sul-
fur-free quinoline hydrogenolysis. On the other hand, Pd-
based catalysts are very effective in hydrogenation, but
give low selectivity to aromatics. Sulfided Pd/C or Pd/
Al O give predominantly saturated products in quinoline
2.2 Catalytic Reactions
Catalyst samples (100 mg) were loaded into a 100 mL
Hastelloy C Parr autoclave reactor with overhead stirring at
300 rpm and activated with 2 bar H for 4 h at 275 °C.
2
3
2
or indole HDN [34, 35].
After cooling to 25 °C, 50 lL (0.42 mmol) quinoline and
5 mL tetradecane were added to the reactor under Ar. The
reactor was then purged with Ar at 25 °C and charged with
Here we report the synthesis and structural as well as
catalytic characterization of a series of catalysts composed
of Pd nanoparticles supported on Al O doped with low
H to 20 bar at the reaction temperature of 275 °C. Reac-
2
3
2
levels of TiO , TaO , and MoO , and explore their activity
x
tions were carried out for time periods between 6 and 24 h.
The reactor was then cooled to 25 °C and purged with Ar
before product analysis. Products were identified by GC–
MS in reference to known standards and quantified by
GC-FID. A complete description of the product identifica-
tion parameters is provided in the Supporting Information.
x
x
for quinoline C–N bond hydrogenolysis. At low levels and
under relatively mild conditions, these oxides are not
expected to alter the support reducibility. Hydrogenation/
hydrogenolysis of quinoline and downstream intermediates
are carried out at 275 °C and 20 bar in stirred batch reac-
tors and driven to low and high hydrocarbon yields. To
provide an understanding of the intrinsic hydrogenation
and C–N bond cleavage reactivity of these materials, no
additional heteroatoms (e.g., sulfur) are added. Results are
compared to Pd/Al O and the bare oxides TiO -Al O ,
2.3 Catalyst Characterization
Materials were characterized by XRD, TGA, UV–Vis,
NMR, zeta potential, TEM, and XAS (EXAFS/XANES). A
complete description of the catalyst characterization
parameters is provided in the Supporting Information.
2
3
x
2 3
TaO –Al O , and MoO -Al O to better understand the
x
2
3
x
2 3
independent role of the supported metal oxide.
123

1
834
M. Bachrach et al.
3
Results
numbers are 7.7–9.2, relatively constant within the uncer-
tainty associated with such a fit. Overall, no major differ-
ences in Pd structure are observed when comparing Pd/
TaO –Al O and Pd/Al O .
3
.1 Catalyst Synthesis and Characterization
x
2
3
2 3
The Pd/TiO –Al O , Pd/TaO –Al O , and Pd/MoO –Al O
x
The Ta L -edge energies of 9,883.3–9,883.4 eV are
III
x
2
3
x
2
3
2
3
materials were prepared by grafting TiO(acac)2,
Ta(acac)(OEt) , TaCl-calixarene dimer, or MoO (acac)
indistinguishable from those of Ta O and are consistent
2
5
with the catalyst remaining as a Ta(V) species even after
4
2
2
onto Al O at a 1.4 wt% metal loading, adding Pd as
2
in situ H -activation or after catalytic use (Supporting
2
3
Pd(OAc) by impregnation to 1 or 3 wt% Pd, and calcining
2
Information, Figure S8A). The EXAFS regions (Support-
ing Information, Figure S8B) were fit to Ta–O average
the resulting materials (Supporting Information, Scheme
˚
bond distances and coordination numbers of 1.88–1.90 A
S1). XRD shows the support to be primarily c-Al O with
2
3
some amorphous content and some aluminum oxide hydrate
and 4.7–4.9, respectively, which are smaller than the bulk
Ta O Ta–O average bond distance and coordination
(
Supporting Information, Figure S1). The Al O support has
2
3
2 5
˚
a zeta potential of 22.3 and is in equilibrium with an aqueous
solution having a pH of 4.2 and thus has a large density of
surface protons available (Supporting Information, Table
S1). The Al O support has a zeta potential near zero when
number of 1.98 A and 6.0 [39, 40], respectively, consistent
with highly dispersed, undercoordinated Ta species. The
present EXAFS region does not change significantly with
the various catalyst treatments, leading us to conclude that
the majority of the Ta species under reaction conditions not
only remain Ta(V), but also remain undercoordinated,
highly dispersed Ta structures, rather than extended
2
3
dispersed in an aqueous solution having a pH of 9.2. Ther-
mogravimetric analysis of the Pd/TaO –Al O catalyst
x
2 3
shows that this catalyst adsorbs * 1 % water upon transfer
from the calcination oven to the reactor (Supporting Infor-
aggregates of TaO , Ta (oxy)carbides, or Ta (oxy)nitrides.
x
2
mation, Figure S2). The surface coverages of 1.07 Ti/nm ,
However, the sensitivity of the EXAFS fit is not sufficient
to rule out formation of highly dispersed, surface-coordi-
nated Ta-amido or imido structures.
2
2
.28 Ta/nm , and 0.53 Mo/nm represent less than 25 %
0
monolayer coverage, so high dispersions are expected. The
precursors were chosen to be sterically encumbered to fur-
ther enhance dispersion, and to introduce little or no residual
halide.
3.2 Catalytic Reactions
The calcined TiO –Al O , TaO –Al O , and MoO –
x
x
2
3
x
2
3
Al O supports exhibit DRUV-visible spectra blue-shifted
2
The 1 % Pd/TiO
x
–Al
, and physical mixture of 1 % Pd/Al
catalysts exhibit enhanced selectivity to pro-
at low to mod-
2 3 x 2 3
O , 1 % Pd/TaO –Al O , 3 % Pd/
3
relative to bulk TiO , Ta O , and MoO , respectively
2
TaO
TaO
x
x
–Al
–Al
2
2
O
O
3
O ?
2 3
2
5
3
(
Supporting Information, Figure S3). Such shifts are rou-
3
tinely cited as indicating highly dispersed transition metal
oxide sites [36, 37]. Due to the simpler synthetic procedure
and because both Ta precursors yield largely indistin-
guishable surfaces after calcination, the acac-derived cat-
alyst (Supporting Information, Figure S4) was used in the
majority of the experiments.
pylbenzene (PB) relative to 1 % Pd/Al
2
O
3
erate total hydrocarbon yields (Fig. 1a, b; Supporting
Information Table S3). At low total hydrocarbon yields,
these catalysts and the corresponding bare MO –Al O
x 2 3
materials exhibit similarly high aromatic selectivity (aro-
matic fraction C0.68). At high total hydrocarbon yields,
secondary hydrogenation of intermediates plausibly occurs
over the Pd domains and selectivity falls. The 1 % Pd/
The 1 % Pd/TaO –Al O catalyst was taken as a rep-
2 3
x
resentative catalyst for TEM and XAS studies (Supporting
Information, Table S2). TEM images show on average
MoO –Al O catalyst exhibits more moderate selectivity to
x 2 3
3
.2 nm particles for the H -activated 1 % Pd/Al O and
2 2 3
aromatics at low total hydrocarbon yield, however the
selectivity does not change significantly with increasing
total hydrocarbon yield (Fig. 1c). Under these conditions,
1
% Pd/TaO –Al O catalysts (Supporting Information,
x 2 3
Figures S5A-B, S6), while the used catalysts show on
average 3.5 nm particles for 1 % Pd/Al O and 4.0 nm
the Al
yield even after 12 h, and a low aromatic fraction of 0.26.
The MO –Al catalysts also give only 1–6 % total
O support alone leads to *1 % total hydrocarbon
2
3
2 3
particles for 1 % Pd/TaO –Al O (Supporting Information,
x 2 3
Figures S5C-D, S6). Similarly, all catalyst treatments
calcination, in situ H -activation, and use in reaction) for
x
O
2 3
(
hydrocarbon yields after 12 h, but a much higher aromatic
fraction of 0.68–0.82. At all total hydrocarbon yields with
2
the 1 % Pd/TaO –Al O catalysts yield Pd K-edge energies
x 2 3
(
24,349.8–24,350.0 eV) and EXAFS-derived bond dis-
the Pd/MO –Al O catalysts, quinoline is extensively
x 2 3
˚
tances (2.75–2.76 A) indistinguishable from those of Pd
foil [38], confirming that the Pd remains in the metallic
state throughout the catalytic reaction (Supporting Infor-
mation, Figure S7A-B). Fitted Pd–Pd coordination
converted to hydrogenated 1-THQ, 5-THQ, or DHQ (see
Scheme 1), indicating that ring-opening is less favorable
than the initial hydrogenation process. See full product
distributions in Supporting Information, Table S3.
1
23

Enhancing Palladium-Catalyzed C–N Hydrogenolysis with MO
x
Dopants
1835
Fig. 1 Aromatic fraction in the
hydrocarbon product versus
total hydrocarbon yield for
Al
Pd/TiO
catalysts. b Pd/TaO
catalysts, and c MoO
MoO , and Pd catalysts. The
widths of the shaded boxes
2
O
3
-supported: a TiO
, Pd/TaO , and Pd
and Pd
, Pd/
x x
, TaO ,
x
x
x
x
x
represent the average deviation
of the series from the trendline
Expressed differently, the product distributions over the
new Pd/TiO –Al O and Pd/TaO –Al O catalysts indicate
or identified downstream intermediates next were carried
out for 12 h under reaction conditions identical to those for
the quinoline C–N hydrogenolysis. Table 1 Entry 1 shows
that propylcyclohexene (PCHE) is highly reactive over Pd/
TaO –Al O but affords low aromatic selectivity (0.1 %
x
2
3
x
2 3
a 10–15 % lower required stoichiometric H consumption
2
to reach a given level of hydrocarbon yield (Supporting
Information, Figure S9) relative to Pd/Al O , and all of
2
3
x
2 3
these catalysts proceed with high yields to total hydrocar-
bons ([70 %). Likewise, the slightly greater 1-THQ
selectivities of Pd/MO -Al O relative to Pd/Al O (Sup-
propylbenzene, PB, and 99.9 % propylcyclohexane, PCH)
as expected, indicating that PCHE dehydrogenation prob-
ably does not account for a significant percentage of PB
formation from quinoline C–N bond cleavage with these
catalysts. PB itself is nearly completely converted to PCH
over Pd/TaO –Al O (Entry 3). In contrast, 2-propylaniline
x
2
3
2 3
porting Information, Figure S10) are consistent with a
greater role of the 1-THQ ? 2-PA pathway (Scheme 1
Pathway 2) in the presence of the added metal oxide.
Because the increased selectivity holds for several Pd:MOx
ratios and for physical mixtures (Fig. 1b), the two types of
active sites are proposed to communicate through the fluid
phase and/or through surface-bound intermediates [41],
x
2 3
(2-PA) affords 8 % PB and 92 % PCH at 100 % conver-
sion over Pd/TaO –Al O (Entry 2 and Supporting Infor-
x
2 3
mation, Table S3). These results argue that propylbenzene
is formed, in these reactions and for the full quinoline
system, via 2-PA denitrogenation that does not pass
through any other detectable intermediates. Selectivities
progressively drop due to further hydrogenation to
propylcyclohexane.
rather than via a new PdMO catalytic site.
x
3
.3 Reaction Pathway Analysis
The 1 % Pd/TaO –Al O and TaO –Al O catalysts were
x
Note here that 2-PA hydrogenolysis over TaO –Al O
2 3
2
3
x
2
3
x
taken as representative materials to better understand pos-
sible catalytic reaction pathways that would lead to
improved selectivity to aromatics. Reactions with plausible
leads to a low hydrocarbon yield of 1.4 % (Entry 4)
composed predominantly of PB. Also, PB hydrogenation
over TaO –Al O is non-negligible, (Entry 6) suggesting
x
2 3
123

1
836
M. Bachrach et al.
Table 1 Conversion and Product Selectivity from C–N Bond Cleavage Reactions with Downstream Intermediates and their Analogues
a
Entry
Catalyst
Substrate
R
R
R
R
R
NH2
NH2
1
2
3
4
5
6
7
Pd/TaO
Pd/TaO
Pd/TaO
x
–Al
–Al
–Al
2
O
2
O
2
O
3
3
3
PCHE (R = C
2-PA (R = C
PB (R = C
3
3
3
3
H
H
H
H
7
7
7
)
n/a
n/a
0.1 % sel.
8 % sel.
100 % conv.
0 % sel.
99.9 % sel.
92 % sel.
100 % sel.
29 % sel.
16 % sel.
100 % sel.
65 % sel.
x
x
)
100 % conv.
0 % sel.
n/a
)
n/a
95 % conv.
50 % sel.
5 % sel.
0.0 %
b
TaO
TaO
TaO
TaO
x
–Al
x
–Al
x
–Al
x
–Al
2
O
2
O
2
O
2
O
3
2-PA (R = C
7
,)
1.4 % conv.
0 % sel.
n/a
0 % sel.
24 % conv.
n/a
21 % sel.
79 % sel.
0.0 %
3
3
3
MCHA (R = CH
3
)
PB (R = C
3
H
H
7
)
)
15 % conv.
35 % sel.
PCHE (R = C
3
7
n/a
n/a
100 % conv.
Bold indicates the reactant for each entry
a
Reaction conditions: 100 mg catalyst, 50 lL substrate, 5 mL tetradecane; 12 h, 275 °C, 20 bar H
2
b
Apparent limiting conversion for the bare oxide catalysts under these conditions
Scheme 2 Proposed reaction
mechanism for the
denitrogenation of
2-propylaniline to
propylbenzene. In the
conversion of quinoline,
-propylaniline could first be
2
formed over the metal or the
oxide site
that the intrinsic selectivity for 2-PA hydrogenolysis may
be even greater than observed under these conditions.
Although alkylcyclohexylamine intermediates are not
substantially different than those on the standard Pd/Al O
2 3
catalyst and evidence minimal large-scale sintering during
use. The enhanced aromatics selectivity for the metal oxide
doped catalysts thus implicates a role of the Lewis acidic
metals in their highest oxidation states. In the following
discussion, Ta(V) is used as the representative case.
Based on the physicochemical data, the lack of evidence
for reduced sites requires that mechanisms involving oxi-
dative addition to a reduced Ta(III) resting state, such as
for NH activation [18] or N cleavage [20] discussed in
3
observed during reaction of quinoline, cleavage of the sp
C–N bond in methylcyclohexylamine is facile over TaOx–
Al O (24 % hydrocarbon yield, Entry 5), to give the
2
3
deamination product MCHE. Interestingly, PCHE under-
goes significant dehydrogenation to PB even under 20 bar
H over the TaO –Al O catalyst (Entry 7). Given these
2
x
2 3
results, the most likely direct contribution of the support is
in deamination of hydrogenated or partially hydrogenated
intermediates.
3
2
the introduction, can at most occur at a small minority of
sites. Instead, we propose that denitrogenation via partial
hydrogenation followed by NH3 elimination must be
operative on these catalysts. This type of mechanism has
been previously suggested for HDN of naphthylamine over
sulfided Co/Mo–Al O , and Ni/Mo–Al O [42], HDS of
4
Discussion
2
3
2 3
The above characterization data argue that the present Pd/
MO –Al O catalysts consist of highly dispersed Ti(IV),
dibenzothiophene and 4,6-dimethyldibenzothiophene over
Mo–Al O , Co/Mo–Al O , and Ni/Mo–Al O [43], and the
x
2
3
2
3
2
3
2 3
Ta(V), or Mo(VI) oxides on Al O . Such sites are doubt-
2
HDO of m-cresol over Pt/Al O [7, 8]. In the present case,
2 3
3
less Lewis acidic and are maintained in their highest oxi-
dation state under reaction conditions [16]. These in
0
addition contain 3–4 nm Pd particles that are not
the route to propylbenzene would be through 2-propylan-
iline hydrogenation to 1,6-dihydro-2-propylaniline at Pd
and then migration to TaO for deamination (Scheme 2).
x
1
23

Enhancing Palladium-Catalyzed C–N Hydrogenolysis with MO
x
Dopants
1837
Propylbenzene can be readily hydrogenated over Pd, which
will decrease aromatics selectivity as the reaction proceeds,
but this could, in principal, be minimized with judicious
reaction engineering. Note that 1,6-dihydro-2-propylaniline
domains and the supported noble metals to allow for
rational design of new, selective catalysts.
Acknowledgments The authors acknowledge the ACS Petroleum
Research Fund and the DOE Office of Basic Sciences Grants SC-
3
is expected to readily undergo deamination due to the sp
0
006718 (JMN) and 86ER1311 (MB, TJM) for funding. Funding for
character of the 6-carbon and the loss of ring conjugation
JTM was provided by Chemical Sciences, Geosciences and Biosci-
ences Division, U.S. Department of Energy, under contract DE-AC0-
(
C–N bond dissociation enthalpy of aniline = 102.6 kcal/
0
6CH11357. Funding for CPC was provided as part of participation in
mol, of cyclohexylamine = 87.6 kcal/mol) [19]. More-
the Institute for Atom-efficient Chemical Transformations (IACT), an
Energy Frontier Research Center funded by the U.S. Department of
Energy (DOE), Office of Science, Office of Basic Energy Sciences.
The authors also acknowledge Z. Bo, Dr. C. Downing, and Dr. C.-C.
Yang for technical assistance, and Dr. N. M. Schweitzer for helpful
discussions. Portions of this work were conducted at the MRCAT at
Sector 10 of the APS. MRCAT operations are supported by the
Department of Energy and the MRCAT member institutions. Use of
the APS, an Office of Science User Facility operated for the U.S.
Department of Energy (DOE) Office of Science by Argonne National
Laboratory, was supported by the U.S. DOE under Contract No. DE-
AC02-06CH11357. This work made use of the EPIC facility
over, Table 1 shows that TaO –Al O readily deaminates
2 3
x
MCHA. NH3 is then exchanged for new reactants to
complete the cycle. Total ring saturation over Pd is com-
petitive with the proposed pathway, and would lead
directly to propylcyclohexane.
In the absence of a distinct metal site for hydrogenation,
TaO –Al O appears, at maximum, to be capable of only
x
2 3
stoichiometric conversion of quinoline or the 2-PA inter-
mediate (ca. 1 mol converted per mole Ta, see Table 1 Entry
4
and Supporting Information, Table S3). These bare oxides
(
NUANCE Center - Northwestern University), which has received
thus appear to proceed through several mechanisms distinct
from those on Pd, albeit slowly, including a stoichiometric
denitrogenation of substituted anilines, as well as an unusual
path of propylaniline to propylcyclohexylamine to propyl-
cyclohexene to propylbenzene. These mechanisms will be
studied elsewhere. Overall, these distinct roles for the noble
metal and Lewis acid sites explain the similar, and enhanced,
support from the MRSEC program (NSF DMR-0520513) at the
Materials Research Center, Nanoscale Science and Engineering
Center (EEC-0118025/003), both programs of the NSF; the State of
Illinois; and Northwestern University. This work made use of the J.B.
Cohen X-Ray Diffraction Facility supported by the MRSEC program
of the National Science Foundation (DMR-1121262) at the Materials
Research Center of Northwestern University. This work made use of
the Keck-II facility (NUANCE Center - Northwestern University),
which has received support from the W. M. Keck Foundation,
Northwestern’s Institute for Nanotechnology’s NSF-sponsored
Nanoscale Science & Engineering Center (EEC-0118025/003), both
programs of the National Science Foundation; the State of Illinois;
and Northwestern University. NMR was performed in the North-
western University IMSERC facility supported by the NSF under
grant DMR-0521267. The CleanCat Core facility acknowledges
funding from the Department of Energy (DE-SC0001329) used for
the purchase of the GCs.
aromatic selectivities for the 1 % Pd/TaO –Al O , 3 % Pd/
x 2 3
TaO –Al O catalysts, and for the physical mixtures of Pd/
x 2 3
Al O ? TaO –Al O catalysts.
2 3
2
3
x
5
Conclusions
Here we demonstrate that Pd nanoparticles supported on
highly dispersed TiO , TaO , and MoO doped aluminas
x
x
x
can effect quinoline C–N bond cleavage with significantly
greater selectivity towards aromatic products than possible
with Pd/Al O . Reactions with downstream intermediates
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