Au/Mo2N as a new catalyst formulation for the hydrogenation of p-chloronitrobenzene in both liquid and gas phases

Article abstract of DOI:10.1016/j.catcom.2012.01.027

The batch liquid phase hydrogenation of p-chloronitrobenzene over Mo ₂N resulted in the sole formation of p-chloroaniline. Incorporation of Au nanoparticles (mean size = 8 nm) enhanced hydrogen uptake with a four-fold increase in rate, retention of ultraselectivity with stability over repeated reaction cycles. Reaction exclusivity to p-chloroaniline extended to continuous gas phase operation where Au/Mo₂N outperformed Au/Al ₂O₃ as a benchmark. Under the same conditions, Pd/Mo ₂N was non-selective, generating nitrobenzene and aniline via combined hydrodechlorination and hydrogenation. These results demonstrate the viability of Au/Mo₂N as a new catalyst formulation in selective substituted nitroarene hydrogenation.

Full text of DOI:10.1016/j.catcom.2012.01.027

Catalysis Communications 21 (2012) 46–51
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Au/Mo2N as a new catalyst formulation for the hydrogenation of
p-chloronitrobenzene in both liquid and gas phases
a
b
c
Fernando Cárdenas-Lizana a, , Daniel Lamey , Noémie Perret , Santiago Gómez-Quero ,
⁎
Lioubov Kiwi-Minsker a, Mark A. Keane b,⁎⁎
a
Group of Catalytic Reaction Engineering, Ecole Polytechnique Fédérale de Lausanne (GGRC-ISIC-EPFL), Lausanne CH-1015, Switzerland
Chemical Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, Scotland, United Kingdom
Van't Hoff Institute for Molecular Sciences, University of Amsterdam, Amsterdam 1090 GS, The Netherlands
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
The batch liquid phase hydrogenation of p-chloronitrobenzene over Mo2N resulted in the sole formation of p-
chloroaniline. Incorporation of Au nanoparticles (mean size=8 nm) enhanced hydrogen uptake with a four-
fold increase in rate, retention of ultraselectivity with stability over repeated reaction cycles. Reaction exclu-
sivity to p-chloroaniline extended to continuous gas phase operation where Au/Mo2N outperformed Au/
Al2O3 as a benchmark. Under the same conditions, Pd/Mo2N was non-selective, generating nitrobenzene
and aniline via combined hydrodechlorination and hydrogenation. These results demonstrate the viability
of Au/Mo2N as a new catalyst formulation in selective substituted nitroarene hydrogenation.
© 2012 Elsevier B.V. All rights reserved.
Received 19 December 2011
Received in revised form 23 January 2012
Accepted 25 January 2012
Available online 3 February 2012
Keywords:
Selective hydrogenation
p-Chloronitrobenzene
p-Chloroaniline
Au/Mo2N
Batch liquid phase
Continuous gas phase
1. Introduction
corporations (the ACS GCI Pharmaceutical Roundtable) has highlighted
the switch from batch to continuous processing as crucial for the sus-
Catalysis has a crucial role to play in sustainable chemical manufac-
ture where chemoselectivity, the ability to react one functional group
while preserving other (often more reactive) functionalities, is a
major challenge [1]. Indeed, the appreciable waste resulting from the
conversion of nitroarenes, the focus of this study, led Sheldon [2] to in-
troduce the concept of the E(nvironmental) Factor (kg waste/kg prod-
uct), which highlighted the severe environmental impact associated
with the production of substituted amines as high value chemical com-
modities [3]. Taking the hydrogenation of chloronitrobenzenes as an ex-
ample, nitroso- and hydroxylamine-intermediates can undergo side
reactions to generate toxic (dichloroazoxybenzene, dichloroazoben-
zene and dichlorohydrazobenzene) by-products [3]. Moreover, C\Cl
bond scission results in the formation of nitrobenzene (NB) and aniline
(AN) as principal products [4]. A critical advancement in cleaner amine
synthesis in batch operation using oxide supported Au catalysts has
resulted from the work of Corma et al. [5], who demonstrated a prefer-
ential activation of \NO2 with H2 dissociation at low coordination Au
sites by in situ IR spectroscopy and theoretical calculations. A recent
brainstorming exercise involving the American Chemical Society
(ACS), Green Chemistry Institute (GCI) and global pharmaceutical
tainable manufacture of fine chemicals [6]. Adopting this imperative,
we have established in previous work [4,7,8] \NO2 hydrogenation che-
moselectivity over Au in gas phase continuous operation. Studies to
date have shown low hydrogenation activity for Au that can be ascribed
to a restricted activation/dissociation of H2 [9], which is dependent on
Au particle size [10]. Given that hydrogen activation can be a limiting
factor, we have explored the use of a support for Au that can chemisorb
H2 (increasing surface concentration) as a possible route to higher hy-
drogenation rates.
Mo nitrides exhibit a significant hydrogen uptake capacity, which
has been attributed to a contraction of the d-band and modification of
electron density as a result of the interstitial incorporation of N in the
Mo metal lattice [11]. The use of Mo nitrides in hydrogen mediated
reactions has been considered to some extent with evidence of cata-
lytic activity for gas phase NO reduction [12] and the hydrogenation
of CO [13] and ethyne [14]. As Mo2N can chemisorb hydrogen and
Au is selective for nitro-group reduction, we propose in this study
the combination of Au with Mo nitride as a new catalyst formulation
directed at elevating hydrogenation rate while maintaining chemo-
selectivity. Taking p-chloronitrobenzene (p-CNB) as a test reactant,
we have examined the catalytic action of Mo2N and Au/Mo2N in
both batch liquid and continuous gas phase operation. We have also
compared the catalytic action of Au/Mo2N with Au/Al2O3 (as bench-
mark [8]) to probe a possible support effect, i.e. Mo2N vs. Al2O3.
⁎
Corresponding author. Tel.: +41 21 693 3186.
E-mail addresses: fernando.cardenaslizana@epfl.ch (F. Cárdenas-Lizana),
M.A.Keane@hw.ac.uk (M.A. Keane).
1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2012.01.027

F. Cárdenas-Lizana et al. / Catalysis Communications 21 (2012) 46–51
47
Moreover, as Pd has shown enhanced activity in \NO2 reduction [15],
we have also examined the catalytic performance of Pd/Mo2N.
was assessed over three reaction cycles. In the first cycle, the catalyst
was activated ex-situ in
quartz tube (60 cm3 min−1 H2;
a
GHSV=200 h−1) at 673 K, cooled to room temperature and transferred
to the reactor in a flow of N2. Hydrogen consumption during reaction
was monitored on-line with a press flow gas controller (BPC-6002,
Büchi, Switzerland). In a series of blank tests, reactions carried out in
the absence of catalyst did not result in any measurable conversion. A
non-invasive liquid sampling system via a syringe with in-line filters
allowed a controlled removal of aliquots (≤0.5 cm3) from the reactor.
After reaction, the catalyst was filtered, reactivated as above and sub-
jected to a second and a third reaction cycle.
2. Experimental section
2.1. Catalyst preparation and characterisation
Mo2N was prepared by heating MoO3 (99.9995% w/w, Alfa Aesar) in
15 cm3 min−1 (GHSV=1500 h−1) 15% v/v N2/H2 at 5 K min−1 to 933 K
(18 h). Reduction/nitridation was quenched in Ar (65 cm3 min−1), the
sample cooled to room temperature and passivated (in 1% v/v O2/He)
for off-line analysis. Nitride passivation post-synthesis served to provide
a superficial oxide film and was required to avoid sample autothermal
oxidation upon contact with air [16]. A suspension of HAuCl4 (300 cm3,
3×10−4 M, Aldrich), aqueous urea (100 cm3, 0.86 M) and Mo2N was
mixed (at 300 rpm) and heated (1 K min−1) to 353 K (2.5 h). The solid
was filtered and washed with distilled water until the wash water was
Cl-free (based on the AgNO3 test), dried in He (45 cm3 min−1) at
383 K for 3 h, sieved into a batch of 75 μm average particle diameter
Gas phase p-CNB hydrogenation was carried out (PH =1 bar;
2
T=493K) in a fixed bed vertical glass reactor (i.d.=15 mm), operat-
ed under conditions of negligible heat/mass transport limitations. A
layer of borosilicate glass beads served as preheating zone, ensuring
that the organic reactant was vaporised and reached reaction temper-
ature before contacting the catalyst. Isothermal conditions ( 1 K)
were maintained by diluting the catalyst bed with ground glass
(75 μm); the ground glass was mixed thoroughly with catalyst before
insertion in the reactor. The reaction temperature was continuously
monitored using a thermocouple inserted in a thermowell within
the catalyst bed. p-CNB (Sigma-Aldrich, ≥99%) in ethanol (Sigma Al-
drich, ≥99.8%) was delivered at a fixed calibrated flow rate via a
glass/Teflon air-tight syringe and Teflon line using a microprocessor
controlled infusion pump (Model 100 kd Scientific). A co-current
flow of p-CNB and ultra pure H2 (b1% v/v organic in H2) was main-
tained at GHSV=330 min−1 with a catalyst mass to inlet p-CNB
molar rate (W/F) in the range 8×103–8×104 g mol−1 min. Product
composition was determined using a Perkin-Elmer Auto System XL
chromatograph equipped with a programmed split/splitless injector
and a flame ionization detector, employing a DB-1 capillary column.
Repeated reactions with the same batch of catalyst delivered conver-
sion/selectivity values that were reproducibility to within 7%.
and stored at 277 K under He in the dark. Pd/Mo2N (2.5×10−4
M
Pd(NO3)2, Aldrich) was synthesised following the same protocol. For
comparison purposes, Au supported on Al2O3 (Puralox, Condea Vista
Co.) was prepared by standard impregnation with HAuCl4 as described
previously [17], dried and stored as above.
Temperature programmed reduction (TPR) and H2 chemisorption
(at 290 K) measurements were conducted using the commercial
CHEM-BET 3000 (Quantachrome) unit. Samples were activated in
17 cm3 min−1 5% v/v H2/N2 at 2 K min−1 to 493–673 1 K (1 h),
swept with 65 cm3 min−1 N2 (1.5 h) and cooled to room tempera-
ture. After TPR, the reduced samples were swept with
a
65 cm3 min−1 flow of N2 for 1.5 h, cooled to room temperature and
subjected to H2 chemisorption using a pulse (10 μl) titration proce-
dure. BET area was recorded in a 30% v/v N2/He flow and pore volume
determined at a relative N2 pressure of 0.95 using a Micromeritics
Flowsorb II 2300 unit. Powder X-ray diffractograms were recorded
on a Bruker/Siemens D500 incident X-ray diffractometer (Cu Kα radi-
ation) and identified against JCPDS-ICDD standards (Mo2N (25-
1368); Au (04-0784)). Analysis by scanning electron microscopy
(SEM) was conducted on a Philips FEI XL30-SFEG operated at an ac-
celerating voltage of 10–20 kV. The samples for analysis were sub-
jected to a hydrocarbon decontamination treatment using a plasma-
cleaner (EVACTRON). Analysis of nitrogen content was performed
using an Exeter CE-440 Elemental Analyser after sample combustion
at ca. 1873 K. The Au and Pd content (supported on β-Mo2N or
Al2O3 and in solution during reaction) was determined by atomic ab-
sorption spectrometry (Shimadzu AA-6650 spectrometer) using an
air–acetylene flame. High resolution transmission electron microsco-
py (HRTEM) employed a JEOL JEM 2011 unit operated at an accelerat-
ing voltage of 200 kV using Gatan DigitalMicrograph 3.4 for data
treatment. The specimens were prepared by dispersion in acetone
and deposited on a holey carbon/Cu grid (300 mesh). The mean
metal (Au or Pd) particle size is given as surface area-weighted
mean (d) [7] where over 200 individual metal particles were counted
for each catalyst.
3. Results and discussion
3.1. Catalyst characterization
The formation of Mo2N was confirmed by XRD (see Fig. 1(AI))
where signals over the range 2θ=38°–81° can be assigned to the
eight principal planes of β-nitride (JCPDS-ICDD 25–1368). The repre-
sentative TEM image in Fig. 1(AII) coupled with diffraction analysis
(IIa) establishes a spacing of 0.24 nm between the planes in the atom-
ic lattice that is characteristic of the β-Mo2N (112) plane. Moreover,
nitrogen content (5.4% wt.), BET surface area (7 m2 g−1) and pore
volume (0.02 cm3 g−1) are close to those quoted in the literature
for molybdenum nitride [19]. The SEM micrograph of the as-
prepared sample is presented in Fig. 1(A)III and shows an agglomer-
ation of crystallitesb5 μm (see IIIa). As the starting MoO3 is charac-
terised by a platelet morphology [20], the reduction/nitridation
process (MoO3 → MoO2 → Mo → Mo2N) resulted in a non-
topotactic transformation where the precursor orthorhombic crystal
structure was not maintained [21]. Temperature programmed reduc-
tion (TPR) of Mo2N (Fig. 2, profile I) generated a single peak at
Tmax =637 K that can be associated with hydrogen consumption for
the removal of the passivation overlayer [22]. It has been proposed
[23] that passivation of Mo2N results in the formation of one or two
chemisorbed oxygen monolayers. The incorporation of Au (0.25% w/
w, see Table 1) with Mo2N induced a shift in the main hydrogen con-
sumption peak (by 34 K) to a lower temperature, demonstrating a
more facile removal of the passivating oxygen due to the presence
of Au (Fig. 2, profile II). Although we could not find any directly com-
parable TPR analysis in the open literature, our results are in line with
the work of Wang et al. [24] who recorded a decrease in the reduction
temperature (up to 150 K) of the passivation layer due to the inclu-
sion of Ni. Chemisorption measurements have revealed a measurable
2.2. Catalysis procedures
Liquid phase reactions (PH =11 bar;T=423K) were carried out in
a commercial batch stirred st2ainless steel reactor (100 cm3 autoclave,
Büchi AG, Uster, Switzerland). Operation under negligible mass transfer
resistance was established using the Madon and Boudart approach [18].
A stainless steel 6-blade disc turbine impeller equipped with a self-
gassing hollow shaft provided effective agitation at a stirring speed of
1800 rpm. A recirculator (HAAKE B-N3) was used to stabilize the reac-
tion temperature at T=423 1 K. The initial catalyst/p-CNB ratio
spanned the range 320–1078 g mol−1. Hydrogenation performance

48
F. Cárdenas-Lizana et al. / Catalysis Communications 21 (2012) 46–51
A
B
I
I
20
30
40
50
60
70
80
90
2 (degrees)
θ
5 nm
5nm
II
II
IIb
IIIa
0.24nm
IIa
2 μm
IIa
III
d = 8 nm
20
10
0
III
10 μm
Particle size range (nm)
Fig. 1. (A) Mo2N: XRD pattern (I, including peak assignments based on JCPDS-ICDD 25-1368), representative TEM image (II) with diffractogram pattern (IIa) and SEM micrograph (III) with
higher magnification image (IIIa) illustrating crystal morphology. (B) Au/Mo2N: representative medium (I) and high (II) resolution TEM images and metal particle size distribution (III). Note:
diffractogram pattern of isolated Au particle (IIa) and intensity profile revealing distance between planes of the atomic lattice in the 12 nm segment marked on the nitride support (IIb).
increase in hydrogen uptake due to the inclusion of Au (Table 1), a re-
sult that suggests the presence of well dispersed Au nanoparticles
(b10 nm) where dissociative adsorption can occur at low coordina-
tion sites, notably at steps, edges and corners [10]. The TEM image
provided in Fig. 1(B)I serves to illustrate the nature of Au dispersion
and morphology. The diffractogram pattern for an isolated Au parti-
cle (Fig. 1(B)IIa) confirms the presence of metallic Au with associated
d-spacings=0.20/0.23 nm consistent with the (200) and (111)
planes of Au0 (JCPDS-ICDD 04–0784). The intensity profile across
the support shown in Fig. 1(B)IIb delivered an average d-
spacing=0.24 nm, consistent with β-Mo2N. The Au particles exhibit
diameters≤10 nm, i.e. the proposed critical Au size range for catalyt-
ic activity in hydrogen mediated reactions [25].
As the aim of this work is to explore the possibility of an enhanced
selective hydrogenation rate over Mo nitride supported Au, we have
taken Au/Al2O3 as a benchmark catalysts that has exhibited ultra-
selectivity in \NO2 group reduction [4]. We have established previ-
ously [17] that the reference Au/Al2O3 shows the same mean Au par-
ticle size (8 nm) as Au/Mo2N. Given that nitroarene hydrogenation
rate over supported Au is sensitive to dispersion [7], an explicit com-
parison of performance in terms of a support effect necessitates
equivalence in terms of Au size. The synthesised Au/Mo2N demon-
a
pseudo-spherical morphology and
a
size distribution in the
strated an appreciably higher (by a factor of 8) level of hydrogen
−1
2–14 nm range, as illustrated in the histogram given in Fig. 1(B)III,
with a mean particle size of (d =) 8 nm (Table 1). It should be
noted that there is an appreciable component of Au particles with
chemisorption relative to Au/Al2O3 (mmol mol , see Table 1),
Au
which must be due to a contribution from both Au and Mo2N compo-
nents. As both samples exhibit the same mean Au size, differences in

F. Cárdenas-Lizana et al. / Catalysis Communications 21 (2012) 46–51
49
700
500
300
significant Au leaching from TiO2 and Al2O3 for reactions in liquid
phase [31].
673 K
3.2.2. Continuous gas phase operation
Following on from the recommendations of the ACS GCI Pharma-
ceutical Roundtable [6], the potential of the Au/Mo2N catalyst formu-
lation was further tested in gas phase continuous operation. It must
be stressed from the very outset that nitroarene hydrogenations to
date have focused on batch liquid phase processing and this study
represents the first instance where the feasibility of both operational
modes is demonstrated. 100% selectivity to p-CAN extended to gas
phase operation with increased p-CAN production over Au/Mo2N rel-
ative to Mo2N as a function of time on-stream (see Fig. 4(AI)). The im-
proved catalytic performance resulting from the combination of Au
with Mo2N is further demonstrated in the pseudo-first order kinetic
plots presented in Fig. 4(AII). This response then holds in both liquid
and gas phase reactions and can be linked to the increased hydrogen
uptake on Au/Mo2N (Table 1). Variations in hydrogen surface concen-
tration are known to influence the catalytic response where a con-
comitant increase in activity and surface hydrogen for molybdenum
nitrides has also been reported elsewhere [32]. Zhang et al. [33],
studying the hydrogenation of cyclohexene and the hydrodesulphur-
isation of thiophene over Mo2N, associated the higher activity with
the incorporation of Zr to an increase in weakly bound hydrogen.
A major finding in this work is the appreciably greater activity
exhibited by Au/Mo2N relative to Au/Al2O3 (at a common mean Au
particle size), which is demonstrated in Fig. 4(B). We take this as a
demonstration of a surface cooperative effect involving Au and
Mo2N that results in a concomitant enhanced hydrogen uptake
(Table 1) and catalytic efficiency. This effect can be tentatively attrib-
uted to electronic interactions at the Au/support interface. Blaser et al.
[3] concluded that reaction at the gold-support interface can contrib-
ute to overall hydrogenation rate acceleration. Shimizu et al. [34]
studied the effect of the carrier for supported Ag catalysts in nitroar-
ene reduction and reported a synergy between Ag and Al2O3 that gov-
erned the rate-limiting H2 dissociation to generate a H+/H− pair at
the metal/support interface. The hydrogenation rate can also be influ-
enced by differences in p-CNB/surface interaction (\NO2 activation)
where the Au–Mo2N interface may play a critical role. Corma and
co-workers [35] have differentiated between \NO2 group adsorption
on the support and Au-support interface in terms of reactant activa-
tion, notably for Au/TiO2. We have indirectly probed this effect by ex-
amining the catalytic action of Pd/Mo2N where a higher p-CNB
hydrogenation rate (Fig. 4(B)) relative to Au/Mo2N was recorded.
These results are consistent with published literature where in-
creased hydrogen uptake/activity over supported Pd (relative to Au)
has been reported [4]. In marked contrast to Au/Mo2N and Au/
Al2O3, at a common p-CNB conversion Pd/Mo2N promoted the forma-
tion of NB and AN as products of hydrodechlorination and hydrogena-
tion (Fig. 4(B)). Interaction with Pd/Mo2N serves to activate the C\Cl
bond, which is then susceptible to hydrogenolytic cleavage. This cat-
alytic response is consistent with the literature where hydrodechlor-
ination has been shown to predominate in the hydrotreatment of
chloronitrobenzenes over Pd/Al2O3 [4]. Use of Pd/Mo2N in practical
(industrial) application would require the incorporation of down-
stream separation units in order to extract the target p-CAN. This is
circumvented in the case of Au/Mo2N, which delivered the best per-
formance in this study. Process efficiency can be further improved
by operating multiple passes through the catalyst bed where the
ultra-selectivity imposed by Au/Mo2N can deliver complete conver-
sion of the inlet p-CNB to p-CAN.
(II)
(I)
0
100
t (min)
200
Fig. 2. TPR profiles for (I) Mo2N and (II) Au/Mo2N.
uptake can be attributed to the Au/support interface where electronic
interactions have been proposed to impact on hydrogen chemisorp-
tion capacity [26]. Since the catalytic action of Pd in \NO2 reduction
is well established [27], we have also considered reaction over Pd/
Mo2N in order to evaluate the effect of incorporating a different
metal with Mo2N. Pd/Mo2N presented a uniform distribution of Pd
nanoparticles (size range=1–7 nm, mean=2 nm) and exhibited in-
creased H2 chemisorption (see Table 1) compared with the supported
Au systems, as has been noted elsewhere [4].
3.2. Catalysis results
3.2.1. Batch liquid phase operation
We achieved 100% selectivity to the target p-chloroaniline (p-
CAN) for reaction over Mo2N in batch liquid phase operation at
100% conversion of p-CNB. There was no detectable hydrogenolytic
activity to produce chlorobenzene, NB, AN or benzene. This is an im-
portant finding in the light of previous studies where C\Cl scission
accompanied high CNB conversion in liquid phase reaction. Indeed,
dechlorination in the hydrogenation of chloroarenes has been a fea-
ture of reactions over supported Pt, Rh, Ru, Ni and Cu [28,29] cata-
lysts. Reaction kinetics exhibited pseudo-first order behaviour
(correlation coefficient, r2 >0.98; see Fig. 3(AI)) and catalytic activity
can be quantified in terms of the initial rate of p-CNB consumption
(157 μmol g−1 min−1). Incorporation of Au with Mo2N served to in-
crease hydrogenation rate (by a factor of 4) with p-CAN again as the
sole product (Fig. 3(A)II). Furthermore, 100% selectivity to p-CAN
was retained at extended reaction times (up to 27 h, not shown). Cat-
alyst stability was considered and the feasibility of reuse can be
assessed from the entries in Fig. 3(B). The reaction rate generated
using Au/Mo2N after three consecutive runs was equivalent to that
obtained in the first reaction cycle (632 vs. 639 μmol g−1 min−1
)
and reaction exclusivity to p-CAN was maintained in each cycle.
Moreover, there was no evidence of Au leaching during reaction.
This is an important consideration that has been emphasised by
Arens and Sheldon [30]: supported metal catalysts must be resistant
to metal leaching into solution under operation conditions in order
to have a real synthetic utility. While this feature has not been exam-
ined in any great detail for supported Au systems, there is evidence of
Table 1
Hydrogen chemisorption, metal (Au or Pd) loading and particle size range and mean
value (d).
Catalyst
Mo2N Au/Mo2N Au/Al2O3 Pd/Mo2N
The results presented in this study provide the first evidence of
the combined catalytic action of Au and Mo2N that serves to elevate
surface hydrogen, resulting in an increased hydrogenation rate of p-
CNB to the target p-CAN in both liquid and gas phase operations. Fu-
ture work will focus on structural modification of molybdenum
Metal loading (%w/w)
–
0.25
0.42
32
2–14
8
1
0.21
4
1–20
8
0.32
0.51
–
H2 chemisorption (μmol g−1
)
0.29
–
−1
(mmol mol
Metal size range (nm)
d (nm)
)
Au
–
1–7
2
–

50
F. Cárdenas-Lizana et al. / Catalysis Communications 21 (2012) 46–51
(AI)
(AII)
6
1.5
1.0
0.5
0.0
4
2
0
0
50
100
150
0
50
100
150
t (min)
t (min)
(BI)
(BII)
(BIII)
6
4
2
0
6
4
2
0
6
4
2
Reaction Cycle 1
Reaction Cycle 3
Reaction Cycle 2
0
0
200
400
0
200
400
0
200
400
t (min)
t (min)
t (min)
Fig. 3. Catalytic response in batch liquid phase operation: (A) temporal variation of p-CNB (solid symbols) and p-CAN (open symbols) concentration (per g of catalyst, Ci/W) for
reaction over (I) Mo2N (▲,△) and (II) Au/Mo2N (■,□); (B) temporal variation of p-CNB (■) and p-CAN (□) concentration (per g of catalyst, Ci/W) for reaction over Au/Mo2N in
three consecutive reactions (I–III); reaction conditions: PH =11 bar, T=423 K.
2
nitride (e.g. crystallographic phase and/or surface area) and control
over Au particle size to increase activity while retaining selectivity.
Catalytic applications will consider hydrogenation of polyfunctional
nitroarenes where chemoselectivity is extremely challenging.
0.4
0.2
0.0
(AII)
4. Conclusions
Au/Mo2N as a new catalyst formulation promotes the (batch) liq-
uid and (continuous) gas phase hydrogenation of p-CNB with 100%
selectivity to p-CAN where the yield was maintained in repeated re-
action cycles. Incorporation of Au with Mo2N served to increase H2
uptake with a four-fold higher hydrogenation rate relative to Mo2N.
Moreover, Au/Mo2N outperformed a benchmark Au/Al2O3 catalyst
that exhibited an equivalent mean Au particle size. Under the same
reaction conditions, Pd/Mo2N was non-selective and promoted a
combined hydrodechlorination/hydrogenation to give NB and AN.
We demonstrate here, for the first time, the viability of Au/Mo2N in
the selective reduction of nitroarenes with versatility in gas and liq-
uid phase operations.
(AI)
0
200
400
600
800
10-2 × W/ F (g mol-1 min)
100
80
60
40
20
0
1.2
0.8
0.4
0.0
(B)
Acknowledgements
The authors acknowledge financial support from the Swiss Na-
tional Science Foundation (Grant 200020-132522/1) and EPSRC
(Grant 0231 110525). EPSRC support for free access to the TEM/SEM
facility at the University of St Andrews is also acknowledged.
Au/Mo N
Au /Al O
Pd/Mo N
2
2
2
3
Fig. 4. Catalytic response in continuous gas phase operation: (AI) time on-stream p-
CAN production over Mo2N (▲) and Au/Mo2N (■); (AII) fractional initial conversion
of p-CNB (X0) as a function of W/F over Mo2N (▲) and Au/Mo2N (■) where the lines
represent fit to pseudo-first order kinetics; (B) specific activity with selectivity to p-
CAN (open bars), AN (hatched bars) and NB (solid bars) under conditions of equal frac-
tional p-CNB conversion (X0 ~0.2) over Au/Mo2N, Au/Al2O3 and Pd/Mo2N; reaction
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2

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