Increasing the Aromatic Selectivity of Quinoline
Hydrogenolysis using Pd/MOx-Al2O3
Mark Bachrach,a Natalia Morlanes-Sanchez,b Christian P. Canlas,b Jeffrey T. Miller,c* Tobin J.
Marks,a* and Justin M. Notesteinb*
a
Northwestern University, Department of Chemistry, 2145 Sheridan Road, Tech. G237,
Evanston, IL 60208, USA.
b
Northwestern University, Department of Chemical and Biological Engineering, 2145 Sheridan
Road, Tech. E136, Evanston, IL 60208, USA.
c
Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, IL
60439, USA.
Corresponding Authors
*Justin M. Notestein, Email: j-notestein@northwestern.edu
*Tobin J. Marks, Email: t-marks@northwestern.edu
*Jeffrey T. Miller, Email: millerjt@anl.gov
S1
Experimental
Catalysts were prepared using standard Schlenk line or glovebox techniques. TaCl5 (Aldrich),
Ta(acac)(OEt)4 (Alfa-Aesar), and p-tert-butylcalix[4]arene (Aldrich) were vacuum sublimed prior
to use. Pd(OAc)2 (Strem), TiO(acac)2 (Alfa-Aesar), and MoO2(acac)2 (Alfa-Aesar) were used as
received. Tetradecane (Aldrich), toluene (Aldrich), quinoline (Alfa-Aesar), n-propylbenzene
(Aldrich), n-propylcyclohexane (Aldrich), and 2-propylaniline (Aldrich) were dried over CaH2 and
distilled prior to use. N-propylcyclohexene was synthesized according to the literature procedure.1
1 wt. % Pd / (1.4 wt. % Ta) TaOx-Al2O3 catalyst synthesis: The reagents TaCl5 (139 mg,
0.39 mmol) and p-tert-butylcalix[4]arene (251 mg, 0.39 mmol) were refluxed in 50 mL toluene on
a Schlenk line under N2 for 48 h to form the TaCl-calixarene dimer and then added to 5.0 g Al2O3
(Selecto Al2O3-A, BET surface area = 165m2/g, partially dehydroxylated at 120°C) in the
glovebox.2-4 Alternatively, a solution of 178 mg (0.39 mmol) Ta(acac)(OEt)4 in 50 mL toluene
was added to 5.0 g Al2O3 in the glovebox. The TaOx-Al2O3 suspension was stirred for 24 h at RT
in the glovebox, filtered, washed with 100 mL toluene, and dried under vacuum. Pd was then added
by impregnation of 105 mg (0.47 mmol) Pd(OAc)2 in 4 mL toluene, to the TaOx-Al2O3 inside the
glovebox. The Pd/TaOx-Al2O3 catalyst was left overnight to dry in the glovebox at room
temperature and then calcined at 500°C in air for 6 h prior to use.
1 wt. % Pd / (1.4 wt. % Ti) TiOx-Al2O3 and 1 wt. % Pd / (1.4 wt. % Mo) MoOx-Al2O3
catalyst syntheses: A solution of 383 mg (1.46 mmol) TiO(acac)2 or 238 mg (0.73 mmol)
MoO2(acac)2 in 50 mL toluene was added to 5.0 g Al2O3 in the glovebox. The suspension was
stirred for 24 h at RT in the glovebox, filtered, washed with 100 mL toluene, and dried under
vacuum. Pd was then added by impregnation of 105 mg (0.47 mmol) Pd(OAc)2 in 4 mL toluene
to the TiOx-Al2O3 or MoOx-Al2O3 inside the glovebox. The resulting Pd/TiOx-Al2O3 or
S2
Pd/MoOx-Al2O3 catalyst was allowed to dry overnight in the glovebox at room temperature and
then calcined at 500°C in air for 6 h prior to use.
1 wt. % Pd/Al2O3 catalyst synthesis: Pd was added to 5.0 g Al2O3 (Selecto Al2O3-A, BET
surface area = 165m2/g, partially dehydroxylated at 120°C) in the glovebox by impregnation of
105 mg (0.47 mmol) Pd(OAc)2 in 4 mL toluene. The Pd/Al2O3 catalyst was left overnight to dry
in the glovebox at room temperature and then calcined at 500°C in air for 6 h prior to use.
Product Characterization
GC analysis was performed on an Agilent 7890 GC with a 5975 Triple Axis MS detector,
and Agilent Chemstation software. Methods were developed for either a HP-5 MS or a VF-Wax
MS column to assay quinoline (Q), 1-tetrahydroquinoline (1-THQ), 5-tetrahydroquinoline (5THQ), decahydroquinoline (DHQ), 2-n-propylaniline (2-PA), n-propylcyclohexane (PCH), npropylcyclohexene (PCHE), n-propylbenzene (PB), ethylcyclohexane (ECH), ethylbenzene
(EB), methylcyclohexane (MCH), toluene (TOL), cyclohexane, and benzene. Calibration curves
were developed for compounds detected in significant quantities: Q, 1-THQ, 5-THQ, DHQ, PB,
PCH, ECH, EB, MCH, and TOL. Yields reported here were found to vary with reaction time (624 h). The aromatic fractions include any significant cracking products and are defined as:
(PB+EB+TOL)/(PB+EB+TOL+PCH+ECH+MCH). Significant cracking to the ethyl- and
methyl-branched compounds (up to 38% of the hydrocarbon products) was observed but no
significant cracking to benzene and cyclohexane was observed. Cracking/unification of ~1% of
the solvent was also detected, primarily to dodecane and hexadecane.
General Catalyst Characterization
13
C CPMAS NMR spectroscopy was performed at a spinning rate of 5 KHz on a 400 MHz
Varian VNMRS NMR spectrometer. Powder x-ray diffraction data were collected on a Rigaku
S3
DMAX PXRD instrument operating with Cu Kα (λ = 1.54059 Å) radiation. Data were recorded
with a 1° divergent slit, 1° scattering slit, and a 0.6mm receiving slit with a Ni filter at a dwell time
of 7s and 0.1° step size. Diffuse reflectance UV-Vis spectra were obtained on a Shimadzu UV3600 spectrometer equipped with a Harrick Praying Mantis accessory. Spectra were collected
under ambient conditions and polytetrafluoroethylene (PTFE) was used as a blank for calculating
Kubelka-Munk pseudoabsorbances. Zeta potential measurements of the Al2O3 support were
obtained on a Malvern Instruments Zetasizer Nano ZS at 25°C. Samples were prepared by
dispersing 25 mg Al2O3 in 35 mL of H2O (Barnstead Nanopure) and pH treating the dispersion
with nitric acid or aqueous NaOH to obtain the desired dispersion pH. Samples were vortexed
overnight at room temperature and pH measurements were obtained prior to zeta potential
determination. Transmission electron microscopy of the Pd nanoparticles was performed on a
JEOL JEM 2100F TEM. The diameter of the Pd nanoparticles was measured using the ImageJ
software and the average of 60-140 nanoparticles was taken. TGA measurements were conducted
in a TA Instruments Q500 TGA under a helium atmosphere.
X-ray Absorption Spectroscopy (XAS)
In situ XAS was performed at the bending magnet beamline of the Materials Research
Collaborative Access Team (MRCAT, Sector 10-BM-B) at the Argonne National Lab Advanced
Photon Source. The catalyst was pressed into a 4 mm wafer and loaded into a stainless steel sample
holder capable of supporting six samples. The sample holder was inserted into a quartz tube (1 in.
O.D., 10 in length) capped with Ultra-Torr Fittings and sealed with Kapton windows. The reactor
was equipped with shut off valves as well as an internal thermocouple placed adjacent to the
samples to control the clamshell furnace temperature.5
S4
The H2-activated samples were heated to 275°C under He and treated with 3.5% H2/He for 1
h at 275°C in the quartz tube reactor. The reactor was then purged with He and cooled to 25°C.
The reactor was sealed off and then placed in the beam. ‘Used’ samples following a typical reaction
were prepared by removing the catalyst from the autoclave under air, washing the catalyst with
hexanes, and vacuum filtering to remove the hexanes as well as residual tetradecane and reaction
products, to yield dry powders which could be pelletized.
Ionization chambers were optimized to the midpoints of the Ta and Pd spectra to yield
maximum current with linear response (~1010 photons s-1). For the Ta LIII edge, 100% N2 (10%
absorption) was used in the incident X-ray detector and a mixture of 50% Ar in N2 (70%
absorption) was used in the transmission X-ray detector. For the Pd K edge, 60% Ar in N2 (10%
absorption) was used in the incident X-ray detector and 100 % Ar (15% absorption) was used in
the transmission X-ray detector. A third detector in series simultaneously collected a Ta or Pd foil
reference spectra, respectively, with each measurement for calibration of the absorption edge. A
cryogenically cooled Si(111) double crystal monochromator was used and detuned to 50% in order
to minimize the presence of harmonics. Data were recorded at 25°C in transmission mode with an
X-ray beam size of 0.5 × 1.5 mm.
XANES energies were determined with the Athena software package by locating the
inflection point in the edge, i.e., the maximum in the first derivative spectra or the zero point in
the second derivative spectra. EXAFS data were analyzed using WinXAS97 software. The
coordination parameters were obtained by a least-squares fit in R-space with a k2 weighting to the
Fourier transform. Experimental phase-shift and backscattering amplitudes were obtained for PdPd and Ta-O from Pd foil and Ta2O5 references, respectively.
S5
Scheme S1. Synthesis of highly dispersed Pd/TaOx-Al2O3 materials.
3000
*
2500
Counts
2000
*
!
1500
##
*
1000
500
0
10
30
50
70
90
2θ
Figure S1. PXRD of Al2O3 support. The reflections at 37°, 46°, and 67° (*) are indicative of γAl2O3.6 The broad shoulder from 21-30° (!) shows the presence of an amorphous component to
the support. The peak at 39° and 42° (#) are indicative of aluminum oxide hydrate.7
S6
Table S1. Zeta Potential of the Al2O3 Support
pH
4.2a
4.3b
6.8b
7.5b
9.2b
9.6b
11.1b
11.9b
Native Al2O3 support dispersed in H2O
Al2O3 dispersed in H2O and pH adjusted with HNO3/NaOH
Wt. %
b
100.0%
0.2
99.5%
0.15
99.0%
0.1
98.5%
0.05
98.0%
0
25
75
125
175
Temperature (°C)
225
Figure S2. TGA of the 1% Pd/TaOx-Al2O3 catalyst.
S7
Deriv. Wt. %
a
Zeta Potential
+22.3
+28.1
+30.6
+34.0
-0.0677
-5.45
-28.5
-26.8
Figure S3. DRUV-Vis spectra of calcined MOx-Al2O3 catalysts and bulk oxides.
Figure S4. CP-MAS 13C NMR of Ta(acac)(OEt)4 grafted onto Al2O3.
S8
Table S2. EXAFS Fitting Parameters
Catalyst
Edge Edge
Energy
(eV)
N
R(Å)
Δσ2
E0
Particle
Size
(nm)
1%Pd/Al2O3 (H2)
Pd
24349.8
8.1
2.75
0.0005
-0.51
3.1
1%Pd/Al2O3 (Used- H2)
Pd
24349.8
8.6
2.76
0.0005
-0.57
3.6
1%Pd/TaOx-Al2O3 (H2)
Pd
24350.0
7.7
2.75
0.0005
-0.85
2.8
1%Pd/TaOx-Al2O3 (Used- H2)
Pd
24349.8
9.2
2.75
0.0005
-0.35
4.3
Pd Foil Reference (Air)
Pd
24350.0
12.0
2.75
1%Pd/TaOx-Al2O3 (Calcined- Air)
Ta
9883.4
4.9
1.90
0.004
-2.11
1%Pd/TaOx-Al2O3 (H2)
Ta
9883.4
4.7
1.88
0.004
-2.28
1%Pd/TaOx-Al2O3 (Used- Air)
Ta
9883.4
4.9
1.89
0.004
-2.15
1%Pd/TaOx-Al2O3 (Used- H2)
Ta
9883.4
4.8
1.88
0.004
-2.38
Ta2O5 Reference (Air)
Ta
9883.3
6.0
1.98
Figure S5. TEM images of (A) H2-activated 1%Pd/Al2O3, (B) H2-activated 1%Pd/TaOx-Al2O3,
(C) Used 1%Pd/Al2O3, (D) Used 1%Pd/TaOx-Al2O3.
S9
60%
% of Nanoparticles
50%
H2-activated Pd/Al2O3
Used (H2) Pd/Al2O3
H2-activated Pd/TaOx-Al2O3 Used (H2) Pd/TaOx-Al2O3
40%
30%
20%
10%
0%
0-2
2-3
3-4
Particle Size (nm)
4-5
5-7
Figure S6. TEM Particle size distribution for Pd/Al2O3 and Pd/TaOx-Al2O3 catalysts.
Figure S7. Pd K edge A) XANES and B) EXAFS for H2-activated and used Pd/Al2O3 and
Pd/TaOx-Al2O3 compared to a Pd foil reference material.
S10
Figure S8. A) XANES and B) EXAFS of the Ta LIII edge of the calcined, H2-activated, and used
Pd/TaOx-Al2O3 catalysts compared to a Ta2O5 reference material.
S11
Table S3. HDN Product Selectivities
Catalyst
Reaction
Time
(hrs)
Q
Al2O3
TiOx-Al2O3
TiOx-Al2O3
TaOx-Al2O3a
TaOx-Al2O3a
MoOx-Al2O3
MoOx-Al2O3
1%Pd/Al2O3b,c
1%Pd/Al2O3
1%Pd/Al2O3
1%Pd/Al2O3
1%Pd/Al2O3
1%Pd/Al2O3
1%Pd/Al2O3
1%Pd/TiOx-Al2O3
1%Pd/TiOx-Al2O3
1%Pd/TiOx-Al2O3
1%Pd/TiOx-Al2O3
1%Pd/TiOx-Al2O3
1%Pd/TiOx-Al2O3
1%Pd/TiOx-Al2O3
1%Pd/TaOx-Al2O3a,b
1%Pd/TaOx-Al2O3a
1%Pd/TaOx-Al2O3a
1%Pd/TaOx-Al2O3d
1%Pd/TaOx-Al2O3a
3%Pd/TaOx-Al2O3a,b
3%Pd/TaOx-Al2O3a
3%Pd/TaOx-Al2O3a
3%Pd/TaOx-Al2O3d
3%Pd/TaOx-Al2O3d
1%Pd/Al2O3+TaOx-Al2O3a
1%Pd/Al2O3+TaOx-Al2O3d
1%Pd/Al2O3+TaOx-Al2O3a
1%Pd/Al2O3+TaOx-Al2O3d
1%Pd/MoOx-Al2O3
1%Pd/MoOx-Al2O3
1%Pd/MoOx-Al2O3
1%Pd/MoOx-Al2O3
1%Pd/MoOx-Al2O3
1%Pd/MoOx-Al2O3
1%Pd/MoOx-Al2O3
1%Pd/MoOx-Al2O3
12
12
12
12
12
12
12
12
6
9
14
12
12
9
6
12
12
12
18
12
24
12
9
15
12
12
12
12
6
12
12
6
8
12
12
12
24
12
12
24
12
12
24
20%
85%
68%
24%
22%
56%
65%
2%
0%
0%
0%
0%
0%
0%
2%
1%
1%
4%
1%
1%
3%
0%
0%
0%
1%
0%
0%
0%
0%
1%
0%
0%
0%
0%
0%
1%
1%
1%
1%
0%
1%
1%
0%
1THQ 5THQ+ Sat’d Arom. Conv. Aromatic
DHQ HC
HC to HC Fraction
of HC
75%
13%
23%
68%
68%
40%
22%
22%
9%
10%
7%
3%
0%
1%
39%
30%
9%
25%
9%
5%
3%
16%
12%
12%
5%
4%
12%
2%
2%
2%
1%
11%
5%
6%
3%
19%
15%
11%
30%
33%
19%
25%
12%
a
5%
0%
4%
5%
6%
1%
5%
68%
68%
65%
52%
52%
13%
12%
43%
41%
33%
46%
34%
33%
7%
75%
62%
51%
41%
24%
53%
34%
26%
9%
6%
64%
34%
38%
18%
66%
55%
58%
26%
18%
28%
3%
15%
1%
<1%
1%
1%
1%
<1%
1%
3%
11%
12%
21%
35%
84%
68%
4%
4%
9%
29%
37%
48%
68%
2%
9%
13%
32%
43%
11%
46%
41%
67%
80%
11%
27%
41%
53%
7%
18%
19%
24%
21%
21%
31%
45%
<1%
1%
4%
2%
3%
2%
5%
3%
12%
13%
20%
9%
3%
19%
11%
23%
23%
15%
20%
12%
17%
7%
17%
24%
22%
29%
24%
18%
31%
20%
14%
14%
29%
20%
25%
6%
11%
10%
21%
20%
25%
33%
25%
Derived fromTa(acac)(OEt)4
Reactor was purged with Ar at 275°C before the quinoline and tetradecane were loaded
c
10mg catalyst was used
d
Derived from Ta- p-tert-butylcalix[4]arene
b
S12
1%
1%
5%
3%
4%
3%
6%
7%
23%
25%
41%
45%
87%
87%
15%
27%
37%
44%
57%
61%
85%
8%
27%
37%
54%
72%
35%
64%
72%
88%
93%
25%
56%
61%
78%
13%
28%
29%
35%
42%
46%
65%
71%
0.26
0.74
0.76
0.68
0.73
0.82
0.82
0.51
0.54
0.53
0.48
0.21
0.04
0.22
0.71
0.85
0.76
0.35
0.36
0.20
0.20
0.80
0.66
0.64
0.41
0.40
0.69
0.28
0.43
0.23
0.15
0.55
0.52
0.32
0.33
0.49
0.38
0.34
0.59
0.49
0.54
0.52
0.36
Figure S9. H2 consumption vs. HC conversion for Al2O3 supported A) Pd/TiOx, Pd/TaOx, and
Pd catalysts and B) Pd/TaOx and Pd catalysts.
Figure S10. 1-THQ fraction of the N-intermediates for Al2O3 supported A) Pd/TiOx, Pd/TaOx,
and Pd catalysts and B) Pd/TaOx and Pd catalysts. Height of the shaded boxes represent the average
deviation of the series from the trendline and are drawn to scale with the Y-axis.
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