A Pd/CeO2 “H2 Pump” for the Direct Amination of Alcohols

Article abstract of DOI:10.1002/cctc.201600855

A Pd/CeO₂ catalyst with a prominent reversible H₂ storage capacity revealed a high activity and selectivity in the direct amination of benzyl alcohol with aniline and ammonia via the borrowing hydrogen mechanism.

Full text of DOI:10.1002/cctc.201600855

Accepted Article
Title: A Pd/CeO2 "H2 pump" for the direct amination of alcohols
Authors: Marc Pera-Titus, Zhen Yan, Ajay Tomer, Gaetan Perrussel,
Mohamad Ousmane, Benjamin Katryniok, Franck Dumeignil,
Anne Ponchel, and Armin Liebens
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10.1002/cctc.201600855
ChemCatChem
COMMUNICATION
A Pd/CeO2 “H2 pump” for the direct amination of alcohols
Zhen Yan,[a] Ajay Tomer,[a,b] Gaetan Perrussel,[a,b] Mohamad Ousmane,[a] Benjamin Katryniok,[b] Franck
Dumeignil,[b] Anne Ponchel,[b] Armin Liebens[a] and Marc Pera-Titus[a]*
Abstract: A Pd/CeO2 catalyst with a prominent reversible H2 storage
capacity revealed a high activity and selectivity in the direct amina-
tion of benzyl alcohol with aniline and ammonia via the borrowing
hydrogen mechanism.
has been reported so far for C-N coupling reactions for amine
synthesis.11 However, ceria was reported to rapidly produce aro-
matic imines by direct condensation of aromatic alcohols and
aniline under air at room temperature.12 Furthermore, ceria-pro-
moted Au nanoparticles (2.5wt.%Au/CeO2) afforded the coupling
of two multistep catalytic cycles for the one-pot synthesis of
propargylamines from N-benzylamine and benzyl alcohol.13
The most versatile catalysts reported so far for the direct
synthesis of amines from alcohols via the borrowing H2 mecha-
nism rely on Ni, Cu and NiCu NPs supported over alkaline or
amphoteric oxides (e.g., γ,θ-Al2O3).11a,b,14 In contrast, very few
examples have been reported on supported Pd formulations for
the direct amination of alcohols (i.e. Pd/MgO, Pd/Fe2O3, Pd/K-
OMS-2).15 Herein we disclose for the first time a highly active
and selective Pd/CeO2 catalyst for the amination of benzyl
alcohol with aniline and ammonia. We also report a correlation
between the ability of supported Pd catalysts to reversibly store
H2 via spillover over the support and their performance for
amination.
Ceria and ceria-containing materials are best known for their
extensive use in car converters, but also find relevant applica-
tions as catalysts or metal promoters/stabilizers for dehydration,
alkylation, ketonization, steam reforming, water-gas shift, total/
partial oxidation and hydrogenation/dehydrogenation reactions.1
The catalytic properties of ceria emerge primarily from the labile
Ce(III)/Ce(IV) redox couple, affording a high lattice oxygen
mobility and H2 activation at temperatures below 600 oC via a
mechanism encompassing surface hydroxylation (i.e. formation
of Ce(III)-OH groups).2 These intrinsic features are conditioned
by the presence of dopants, impurities and structural defects in
the fluorite framework,3 as well as by the size, shape and crystal
orientation of the ceria particles.2a,4
Recently, ceria has been reported as a promoter of metal
nanoparticles (NPs) for catalyzing C-C coupling reactions under
a borrowing H2 pathway.5 This tandem mechanism, which has
been well established with organometallic homogeneous cata-
lysts,6 comprises three sequential steps: (1) dehydrogenation of
an alcohol to an intermediate carbonyl compound, (2) aldol con-
Briefly, a series of metal-supported catalysts (8 wt.% for Ni,
Co, Cu and 2 wt.% for Pd, Pt) was prepared by incipient wet-
ness impregnation using a nitrate precursor over high-surface
cerias pretreated at variable temperatures (i.e. CeO2-X-HS_Y, X
= Zr, La-Zr, Y = 500-900 oC, SI). The specific surface area of the
cerias ranged from 30 to 210 m2/g (Table 1), whereas the mean
particle size evolved from 6.6 to 9.0 nm as inferred from HR-
TEM and XRD (Figure S1, S2). FT-IR experiments revealed the
absence of surface carbonates over ceria after calcination at a
densation of two carbonyl molecules to
a α,β-insaturated
carbonyl compound, and (3) hydrogenation of C=C (and/or C=O)
bonds using the borrowed H2 to generate the final product.
Using this catalytic cycle, Shimizu and co-workers reported the
α-alkylation of methyl ketones with aliphatic secondary alcohols
over 0.2mol%Pt/CeO2 in the absence of additives affording
moderate-to-high yields (65-99%) compared to benchmark cata-
o
temperature higher than 700 C (Figure S3). After impregnation,
the samples were dried at 120 °C overnight, calcined at 400 °C
o
for 2 h under air and reduced when necessary at 200 C under
o
lysts after reaction at 130 C for 48 h.7 Likewise, Pt/CeO2 exhi-
H2 flow. These mild reduction conditions were selected to
discourage the genesis of oxygen vacancies (i.e. irreversible H2
desorption),16 as well as strong-metal support interactions
encompassing Pd decoration by Ce(III).17 For comparison, a
series of Pd catalysts were also prepared over low-surface ceria
(CeO2-LS, 2 m2/g, 50 nm particle size) and over standard
supports (i.e. SiO2, γ-Al2O3, TiO2, MgO, carbon). In all cases, Pd
showed a high dispersion (range 50-76%) as can be inferred by
H2-TPD from -50 to 40 oC. No large Pd particles were visualized
in neither the XRD patterns (absence of a peak at 2θ = 33.5o
being indicative of PdO) nor the TEM micrographs.
bited high yields (90-99%) in the C3 alkylation of oxindole with
o
substituted benzyl, linear and heteroaryl alcohols at 170 C for
24 h under additive-free conditions.8 The same team reported
the self-coupling of a series of aliphatic alcohols to β-alkylated
o
ketones over 3wt.%Ni/CeO2 with a yield up to 87% at 144 C.9
Finally, Dumesic and co-workers studied the self-aldol conden-
sation/hydrogenation reaction of 2-hexanone in the presence of
1- and 2-butanol (10 mol%) over 0.25wt.%Pd/CeZrOx.10 The
cross-aldol condensation product (7-methyl-5-undecanone) was
generated with 26% and 11% selec-tivity at 350 oC for 1- and 2-
butanol, respectively, via H2 transfer from the alcohol to the α,β-
insaturated carbonyl intermediates.
The catalytic performance of the different metal-supported
high-surface cerias was assessed on the model reaction
o
between benzyl alcohol and aniline at 160 C for 3 h under N2
Unlike C-C coupling reactions, no promoting effect of ceria
atmosphere (Figure 1A, Table S1). Before the reaction, all the
catalysts except Pd/CeO2-HS_500 were pre-reduced under a H2
flow at variable temperatures (see H2-TPR profiles in Figure S4).
Among the catalysts, Pd/CeO2-HS_500 exhibited the highest
conversion (82%) and N-benzylaniline (BZA) yield (79%) with a
remarkably higher BZA productivity compared to 8wt.%Ni/ CeO2-
HS_500 and the benchmark 8wt.%Ni/Al2O3. For comparison,
2wt.%Ni/Al2O3 was almost inactive due to the generation of
stable nickel aluminates. Besides BZA and the intermediate N-
benzylideneaniline (BZIA), trace amounts of toluene and benz-
aldehyde (BAH) were observed after reaction for all catalysts.
[a]
[b]
Dr. Z. Yan, Mr. A. Tomer, Mr. G. Perrussel, Dr. M. Ousmane, Dr. A.
Liebens and Dr. M. Pera-Titus
Eco-Efficient Products and Processes Laboratory (E2P2L), UMI
3464 CNRS-Solvay,
Shanghai, 201108 (China)
E-mail: marc.pera-titus-ext@solvay.com
Mr. A. Tomer, Dr. G. Perrussel, Dr. B. Katryniok, Prof. F. Dumeignil
and Prof. A. Ponchel
Univ. Lille, CNRS, Centrale Lille, ENSCL, Univ. Artois, UMR 8181 -
UCCS - Unité de Catalyse et Chimie du Solide,
Lille, F-59000 (France)
This article is protected by copyright. All rights reserved.

10.1002/cctc.201600855
ChemCatChem
COMMUNICATION
Table 1. Reducibility and reversible H2 storage capacity of supported Pd catalysts (2 wt.%Pd) (see Table S6 for additional results)
Reducibility (H2-TPR)
Reversible H2 desorption (H2-TPD)b
SBET
φPd
Ref. Support
H2 uptake
(µmol/g)
351
Desorbed H2
(µmol/g)
147 (104)
291 (126)
503 (140)
6 (5)
Main peak
Reducibility Main peak
H2 release
(%)
42 (30)
57 (25)
35 (10)
3 (2)
(m2/g)
(%)a
(oC)
21
32
92
(%)
13
18
(oC)
83
104
87
(1)
(2)
(3)
(4)
(5)
(6)
(7)
CeO2-HS_900
31
87
207
2
156
200
230
52 (2.5)
44 (3.1)
76 (1.6)
51 (2.6)
36 (3.9)
61 (2.0)
39 (3.6)
CeO2-HS_700
CeO2-HS_500
CeO2-LS_500
Al2O3_500
SiO2_500
MgO_500
511
1436
243
52 / 53c
22
11
-
-
-
27
1.3
7.0
73
138
190
477
402
24
193
81 (8)
70 (30)
43 (49)
59 (6)
35 (18)
9 (10)
a Pd dispersion measured by H2-TPD from -50 to 40 oC after reduction at 200 oC for 2 h. In parentheses, particle size (in nm) measured assuming cubooctahedral
particle shape (see SI). The dispersion measured for Pd/CeO2-HS_500 corresponds to the second H2-TPD cycle after H2 chemisorption at -50 oC
Reversible H2 uptake measured by H2-TPD in the temperature range from 40 to 400 oC under Ar flow after reduction at 200 oC for 2 h. In parentheses, values
b
measured by H2-TPD after H2 chemisorption at -50 oC
c Measured by XPS after reduction at 130 oC (O1s core level)
In parallel, we measured the BZA yield for a broad series of
Pd-supported catalysts as a function of the mean particle size of
Pd NPs (Figure 1B, Table S1, S2). Among the different supports,
(BZIA)
CeO2-HS_500
Aniline conversion
(BZA)
(BZDA)
Pd/CeO2-HS catalysts showed the highest BZA yields at compa-
rable Pd particle sizes. Noteworthy, Pd impregnated over stan-
dard supports and CeO2-LS displayed an almost constant BZA
yield with the Pd particle size regardless of the support. If we
assume a cubooctahedral shape for Pd NPs,18 this observation
can be interpreted by a major contribution of square and trian-
gular Pd sites on the catalysis with an almost constant atomic
density in the 2-7 nm size range (Figure S5). This idea can be
reinforced by representing the BZA productivity (PBZA) with
respect to square and triangular Pd sites (Figure 1C), showing
also an almost constant trend with the Pd particle size.
Opposing this behavior, no constant trend with the particle size
was found for Pd/CeO2-HS catalysts. This observation points out
a remarkable promoting effect of high-surface cerias on the
catalytic properties for amination. This effect depends to an
important extent on the calcination temperature of the ceria, as
well as on the ceria composition.
Al2O3_500
(A)
100
80
60
40
20
0
(24)
(131)
BZA yield
BZIA yield
(13)
(2.7)
(0.5)
(8.1)
(2.4)
Ni
Ni
Pd
(2 wt.%) (2 wt.%) (8 wt.%) (8 wt.%) (8 wt.%)
Pt
Cu
Co
Ni
(8 wt.%) (2 wt.%)
100
80
60
40
20
0
Pd/CeO2-HS_700
Pd/CeO2-HS_500
(B)
The remarkable performance of Pd/CeO2-HS catalysts for
amination prompted us to study in detail their catalytic mecha-
nisms. To this aim, we surveyed the catalytic properties of Pd/
CeO2-HS_500 in the reaction of benzyl alcohol with aniline. The
BZA selectivity reached a value of 98% at almost full aniline
conversion after 3 h when increasing the temperature from 160
oC to 180 oC (Table S3, Figure S6) and decreased slightly in the
range 100-140 oC (Table S3). The BZA selectivity was also
unaffected by the Pd loading in the range 0.5-5 wt.% (Table S4).
A kinetic study on this sample at 160 °C revealed an almost
constant BZA selectivity during the reaction and an apparent first
order with respect to aniline (Figure 1D,E). No Pd leaching was
observed after the reaction, confirming the catalyst integrity.
However, a decline of the aniline conversion at nearly constant
BZA selectivity was observed after a consecutive catalytic test,
which can be attributed to coke formation according to the TGA /
DTG profiles (see Figure S7 and also ref.19).
Other supports
1
2
3
4
5
6
7
8
Pd particle size (nm)
100
80
60
40
20
0
(E)
0,4
(D)
0.4
BZA selectivity
0,2
0.2
0,0
0.0
r2 = 0.9993
Aniline conversion
-0,2
-0.2
-0,4
-0.4
-0,6
-0.6
Pd/CeO2-HS_500
Pd/CeO2-HS_500
-0,8
-0.8
0
1
2
3
4
0
1
2
3
4
Reaction time (h)
Reaction time (h)
Figure 1. (A) Aniline conversion, N-benzylaniline (BZA) yield and N-benzyl-
ideneaniline (BZIA) and BZA productivity (PBZA, values on top) per total num-
ber of metal sites for Ni, Co, Cu, Pt and Pd-supported catalysts over CeO2-
HS_500 pre-reduced under H2 flow for 2 h at 120 oC (Pd), 150 oC (Pt), 250 oC
(Cu) and 450 oC (Co, Ni), as well as for 8wt.%Ni/Al2O3 and 2wt.%Ni/Al2O3 pre-
reduced at 580 oC (see Figure S4 for H2-TPR profiles); (B) and (C) Evolution
of the BZA yield and productivity with respect to square and triangular sites as
a function of the Pd particle size (measured from H2-TPD, Table 1) for Pd
supported over HS cerias (squares) and standard (circles) supports (i.e. SiO2 ,
Al2O3, TiO2, MgO, carbon, CeO2-LS) without pre-reduction; (D) and (E) time-
evolution of aniline conversion and BZA selectivity for Pd/CeO2-HS_500 and
log-plot of aniline conversion. Reaction conditions: 2 mmol aniline, 6 mmol
benzyl alcohol, 60 mg catalyst, 160 oC, 600 rpm, N2 atmosphere.
Subsequently, the different catalysts were tested in the reac-
o
tion between benzyl alcohol and excess ammonia at 160 C for
24 h under N2 atmosphere (Table S5). Pd/CeO2-HS_500 displa-
yed the highest selectivity to mono-, di- and tribenzylamine (ca.
70%) with preference to the secondary amine at full benzyl alco-
hol conversion (Pamines = 691). In contrast, in addition to a mode-
rate selectivity to amines (44%), Pd/CeO2-LS_500 exhibited a
lower benzyl alcohol conversion at ca. 75% (Pamines = 227).
The initial pale-yellow Pd/CeO2 catalysts turned into grey
after the reaction with either aniline or ammonia, reflecting a par-
tial ceria reduction by benzyl alcohol (Figure S8). This observa-
tion is compatible with the H2-TPR profiles (Figure 2A, Figure
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10.1002/cctc.201600855
ChemCatChem
COMMUNICATION
S9A). These consisted of a main reduction peak below the reac-
tion temperature (160 oC) that can be ascribed to Pd and surface
ceria reduction, and two broader peaks at ca. 240 °C and 780 °C
that are reminiscent of surface and bulk reduction of the parent
ceria. The main reduction peak was strongly affected by the cal-
cination temperature and the ceria composition, evolving from
92.5 °C for Pd/CeO2-HS_500 to 21.4 oC for Pd/CeO2-HS_900
and Pd/CeO2-LS_500. In contrast, Pd/SiO2_500 and Pd/Al2O3_
500 displayed a small peak at ~5 °C with a shoulder at ~25 °C
and a desorption band at 50-60 °C (Figure S9B). The reducibility
of Pd/CeO2-HS_500 was confirmed by XPS after in situ reduc-
Fast, even without catalyst
NH2
Ph
Ph
Ph
Ph
N
O
Fast with H2
H2O
Slow formation of
Ph
Pd
Ph
BAH without aniline
N
H
Ph
OH
Ce(III)
Ce(IV)
o
o
tion at 130 C and 350 C under H2 flow. Irrespective of the re-
duction temperature, the Ce3d core level exhibited neat bands
centered at a binding energy (BE) of 916.8 eV (Ce3d3/2) and
898.5 eV (Ce3d5/2), respectively, after deconvolution that can be
attributed to Ce(III) (Figure S10). Moreover, the O1s core level
showed a characteristic band at 531.4 eV that can be attributed
to hydroxyl groups (Figure 2B, Figure S11A).
To further assess the influence of the support reducibility on
the catalytic properties, we conducted the reaction of benzyl
alcohol with aniline Pd/CeO2-HS_500 after pre-reduction with H2
at 200 oC for 2 h (Table S1). While no remarkable variation of
the BZA selectivity was observed, the aniline conversion was
enhanced from 82% to 95% after pre-reduction. We also explo-
red the catalytic properties of an on-purpose poisoned Pd/CeO2-
HS catalyst impregnated using a chlorinated Pd precursor (i.e.
Pd(Cl)/CeO2-HS_500), shifting the main reduction peak to 147.7
oC due to the generation of stable cerium oxychlorides (Figure
2A).20 Interestingly, this catalyst exhibited a much lower amine
selectivity and conversion compared to Pd/CeO2-HS_500 in the
reaction of benzyl alcohol with aniline and ammonia (Table S1,
S5). Overall, these results indicate that ceria reducibility below
100 oC was mandatory to ensure activation.
Figure 3. Hydrogen transfer pathway over Pd/CeO2-HS for the amination of
benzyl alcohol with aniline (and ammonia). For the sake of clarity, only a
CeO2(111) plane is represented.
To gain insight into the rate-limiting step of the amination
reaction between benzyl alcohol and aniline, we carried out
additional catalytic tests over pre-reduced Pd/CeO2-HS_500 and
the parent CeO2-HS_500 at 160 oC and 180 oC for 3 h. Figure 3
summarizes the results obtained. Both catalysts were inactive
towards BZIA hydrogenation in the absence of H2. However,
BZA was rapidly generated over Pd/CeO2-HS_500 in the tem-
perature range 120-160 oC upon exposure to a H2 flow. We also
explored the generation of BZIA from the condensation of BAH
with aniline over CeO2-HS_500 and Pd/CeO2-HS_500. In both
o
cases, BZIA was rapidly produced at 160 C and could be even
generated at room temperature over CeO2-HS_500 under air in
agreement an earlier report from Tomishige and co-workers.12
Overall, this body of results point out that benzyl alcohol
dehydrogenation was most likely the rate-limiting step of the
amination reaction. Noteworthy, our results oppose the obser-
vation reported on Pd/MgO (870 m2/g), where BZIA hydrogen-
ation was found to be rate-limiting.15a However, in this analysis,
no kinetic data for benzyl alcohol dehydrogenation was
measured in the presence of the aniline, which could impact the
catalytic activity of Pd (i.e. potential assistance effect).
A
Surface ceria
Surface ceria + Pd
We further investigated the reversible H2 storage capacity of
the different Pd/CeO2 catalysts. To this aim, we measured first
the H2-TPD profiles from -50 to 400 oC after reduction with H2 at
200 oC for 2 h (Figure 4A-D, Figure S12). The catalysts pre-
sented two main desorption bands: (1) a band at low tempe-
T = 160 oC
(reaction)
APd/CeO2-HS_500
BPd/CeO2-HS_700
o
C
Pd/CeO2-HS_900
rature (<40 C) that can be attributed to H2 desorption from Pd,
and (2) a broader band in the temperature range 40-400 oC with
variable intensity that is indicative of H2 back spillover from ceria
to Pd. Interestingly, H2 spillover over Pd/CeO2-HS catalysts was
strongly conditioned by the calcination temperature before Pd
impregnation (i.e. decrease in the intensity of the second band)
and almost vanished for CeO2-LS_500. The latter pattern was
similar to that observed on non-ceria supports (Figure S13). Also
noteworthy, the low-temperature band for Pd/CeO2-HS_500
showing the highest H2 spillover capacity displayed two separate
peaks that can be attributed to different Pd species. Further XPS
experiments on this sample after in situ reduction under a H2
flow at 130 and 350 oC followed by evacuation revealed Pd3d
peaks at a BE of 341.1/342.6 (Pd3d3/2) and 335.7/337.5 eV
(Pd3d5/2) (Figure 2C, Figure S11B). The peaks at lower BEs can
be ascribed to Pd(0), whereas the peaks at higher BEs can be
D
Pd(Cl)/CeO2-HS_500
E
Pd/CeO2-LS_500
0
100
200
T (oC)
300
400
(B) O1s
(C) Pd3d
Pd3d5/2
Pd3d3/2
Lattice O - 47%
Hydroxyl - 53%
Pd(0) - 62%
Pd(II) - 38%
538 536 534 532 530 528 526
350
345
340
335
330
BE (eV)
BE (eV)
+
δ
attributed to highly dispersed Pd -O-Ce(III) species lying most
Figure 2. (A) H2-TPR profiles in the temperature range from -50 to 400 oC for
the different Pd/CeO2 catalysts prepared in this study (undoped); (B) and (C)
O1s and Pd3d XP spectra of Pd/CeO2-HS_500 after in situ reduction at 130 oC
for 2 h under H2 flow. Additional TPR profiles and XP spectra can be found in
Figure S9 and Figure S10, S11, respectively.
likely at the Pd-CeO2 interface.2e,21 No evidence of PdHx species
(BE Pd3d5/2 = 336.1 eV) was observed after deconvolution.22
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10.1002/cctc.201600855
ChemCatChem
COMMUNICATION
corresponding to Pd/CeO2HS catalysts (Figure 4E, Figure S14).
In contrast, the BZIA yield showed a maximum at Hrev/Pd ≈ 1.0
and declined drastically for Hrev/Pd > 4.0. When transposing BZA
yields into productivities defined with respect to surface Pd sites
in square and triangular positions (Figure 4F), one can clearly
devise a linear trend with the reversible H2 storage capacity.
This observation suggests that such positions are the most
active for amination irrespective of the size of Pd NPs (Figure
1A), these being localized most likely near the Pd/CeO2 interface.
We further explored the influence of the reversible H2
storage capacity on the properties of Pd supported catalysts for
benzyl alcohol amination with ammonia (Figure S15). Overall,
the yield to amines showed an increasing trend until Hrev/Pd ≈
1.5 followed by an almost constant value in the Hrev/Pd range
1.5-5.0 and a sudden increase at Hrev/Pd > 5.0 corresponding to
Pd/CeO2-HS_500. In the case of benzonitrile, this exhibited a
monotonous decreasing trend with the H2 storage with the
lowest yields corresponding to Pd/CeO2-HS_500.
(B)
(A) Pd/CeO2-HS_500 (3)
Pd/CeO2-HS_700 (2)
1st
1st
2nd
2nd
(C) Pd/CeO2-HS_900 (1)
(D)
Pd/CeO2-LS (4)
1st
1st
2nd
2nd
0
100
200
T (oC)
300
400 0
100
200
T (oC)
300
400
100
80
60
40
20
0
(E)
BZA yield
BZIA yield
(2)
Finally, we investigated the catalytic properties of Pd/CeO2-
(3)
o
HS catalysts in the amination of n-octanol with aniline at 180 C
1000
800
600
400
200
0
(F)
for 24 h after pre-reduction at 200 oC for 2 h under H2 flow
(Figure S16). The results point out a much higher catalytic acti-
vity of Pd/CeO2-HS_500 towards N-octylaniline compared to Pd/
CeO2-LS_500 and other standard catalysts (i.e. Pd/SiO2_500
and Pd/C_500), for which almost no catalytic activity was
observed.
(3)
(2)
(1)
(5)
(5)
(7)
(1)
(4)
(6)
(6)
(4)
(7)
0
1
2
3
4
5
6
7
8
In summary, a Pd/CeO2 catalyst based on high-surface
Hrev/Pd molar ratio (-)
o
CeO2 pre-treated at 500 C revealed an abnormally high activity
and selectivity in the amination of benzyl alcohol with aniline and
ammonia. Unlike standard Pd supported catalysts, a promoted
H2 transfer on high-surface Pd/CeO2 via (back)spillover between
Pd and ceria can be regarded as a main driver for amination
under the hydrogen borrowing mechanism. The results presen-
ted in this study open an avenue for the fine design of H2 pumps
based on ceria for industrially relevant amination reactions.
0
1
2
3
4
5
6
7
8
Hrev/Pd (mol/mol)
Figure 4. (A-D) Consecutive H2-TPD profiles characterizing H2 desorption
from Pd (-50 oC to 40 oC) and H2 back spillover from the support (from 40 to
400 oC) for Pd/CeO2 catalysts calcined at different temperatures; (E) BZA and
BZIA yield as a function of the reversible H2 storage capacity measured by H2-
TPD (1st and 2nd cycles) in the temperature range 40-400 oC; and (F) BZA
productivity as a function of Hrev/Pd ratio. Experimental conditions and sample
indexation as in Table 1.
Acknowledgements
The combination of the H2-TPR and H2-TPD profiles allowed
the measurement of the reducibility and reversible H2 storage
capacity of the different catalysts (Table 1, Table S6). When
necessary, a consecutive H2-TPD profile was measured by coo-
ling the samples from 400 to -50 oC under Ar followed by pulsed
The authors would like to express their gratitude to Solvay,
CNRS and the French Agency of Research (ANR) for funding
through SHAPes program (grant No ANR-13-CDII-0004). The
Chevreul Institute (FR 2638), Ministère de l’Enseignement
Supérieur et de la Recherche, Région Nord – Pas de Calais and
the FEDER program are also acknowledged for supporting and
funding partially this work. The authors are grateful to Dr. Barry
Southward from Solvay Special Chem for fruitful discussions on
rare-earth catalysis.
o
H2 chemisorption at -50 C. This profile allowed a reliable mea-
surement of both the Pd dispersion and the resilient H2 still
adsorbed on the support after the first H2-TPD test (see SI for
calculation details). Overall, Pd/CeO2-HS_500, Pd/CeO2-HS_
700 and Pd/CeO2-Pr-HS_500 displayed the highest reducibility
and H2 release, reflecting a promoted H2 transfer between Pd
and ceria. For comparison, Pd/CeO2-Zr-HS_500 and Pd/CeO2-
Zr-La-HS_500 showed a similar reducibility to that of Pd/CeO2-
HS_500 (52%). Conversely, the amount of desorbed H2 decrea-
sed significantly from 35-57% for the former samples to 19% for
Pd/CeO2-Zr-HS_500, most likely due to a higher oxygen mobility
in the latter case, favoring an irreversible H2 desorption pathway.
Finally, in the case of Pd/CeO2-LS_500, the reducibility was as
low as 11% with 50% H2 release of the total amount adsorbed.
With these results in hand, we assessed the influence of H2
spillover over the different Pd supported catalysts on their per-
formance for benzyl alcohol amination with aniline. Noticeably,
the representation of the BZA yield against the reversible H2
storage capacity of the catalysts exhibited a linear trend until
Hrev/Pd ≈ 4.0 and a plateau at larger H2 storage capacities
Keywords: Direct amination • borrowing H2 • ceria • palladium •
H2 spillover
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Entry for the Table of Contents
A Pd/CeO2 catalyst with a prominent
Zhen Yan, Ajay Tomer, Gaetan
reversible
H2
storage
capacity
Perrussel,
Mohamad
Ousmane,
revealed a high activity and selectivity
in the direct amination of benzyl
alcohol with aniline and ammonia via
the borrowing hydrogen mechanism.
Benjamin Katryniok, Franck Dumeignil,
Anne Ponchel, Armin Liebens and Marc
Pera-Titus
Page No. – Page No.
A
high-surface Pd/CeO2 catalyst
showed high activity and selectivity
in the amination reaction of benzyl
alcohol with aniline and ammonia.
This article is protected by copyright. All rights reserved.