Mild temperature palladium-catalyzed ammoxidation of ethanol to acetonitrile

Article abstract of DOI:10.1016/j.apcata.2015.09.030

The ammoxidation of ethanol is investigated as a renewable process for the production of acetonitrile from a bio-feedstock. Palladium catalysts are shown to be active and very selective (>99%) to this reaction at moderate to low temperatures (150-240 °C), with acetonitrile yields considered a function of Pd morphology. Further investigations reveal that the stability of these catalysts is influenced by an unselective product, and that any deactivation observed is reversible. Interpretation of this deactivation allows operating conditions to be defined for the stable, high yielding production of acetonitrile from ethanol.

Full text of DOI:10.1016/j.apcata.2015.09.030

Applied Catalysis A: General 506 (2015) 261–267
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Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Mild temperature palladium-catalyzed ammoxidation of ethanol to
acetonitrile
Conor Hamilla, Hafedh Drissb, Alex Gogueta, Robbie Burcha, Lachezar Petrovb,
Muhammad Daousb,∗, David Rooneya,∗∗
a School of Chemistry and Chemical Engineering, Queen’s University Belfast, Belfast BT8 5AG, UK
b Chemical and Materials Engineering Department, King Abdulaziz University, Jeddah, P.O. Box 80035 Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history:
The ammoxidation of ethanol is investigated as a renewable process for the production of acetonitrile
from a bio-feedstock. Palladium catalysts are shown to be active and very selective (>99%) to this reac-
tion at moderate to low temperatures (150–240 ◦C), with acetonitrile yields considered a function of Pd
morphology. Further investigations reveal that the stability of these catalysts is influenced by an unselec-
tive product, and that any deactivation observed is reversible. Interpretation of this deactivation allows
operating conditions to be defined for the stable, high yielding production of acetonitrile from ethanol.
© 2015 Published by Elsevier B.V.
Received 21 August 2015
Received in revised form
18 September 2015
Accepted 21 September 2015
Available online 25 September 2015
Keywords:
Palladium
Bio-based chemicals
Renewable solvents
Product security
Sustainable chemistry
1. Introduction
propylene availability and acrylonitrile demand. Recently, Asahi
Kasei announced the closure of a 150,000-ton/year acrylonitrile
The development of sustainable industry requires a funda-
mental change in societal dependence on petroleum resources.
The production of chemicals from ‘carbon neutral’ biomass offers
improved supply securities and could significantly reduce indus-
try’s environmental impact [1]. Currently 95% of all organic
chemicals are produced from fossil resources [2]. U.S. legislation
is targeting a 25% replacement with biomass derived chemicals by
2025 [3], thus reinforcing the need for the development of sus-
tainable processes to aid the realization of a bio-based chemical
industry.
Acetonitrile is an important fine chemical which is widely used
as a solvent in the agrochemical, pharmaceutical and petrochem-
ical sectors. The pharmaceutical industry in particular accounts
for over 70% of the total global demand [4]. Presently, acetoni-
trile is a co-product in the manufacture of acrylonitrile (SOHIO
Process), whereby 40–60 kg of acetonitrile are produced for every
tonne of acrylonitrile [5]. Consequently, output is heavily reliant on
plant [6], citing increased propylene prices associated with shale
gas production [7] and reduced acrylonitrile demands due to the
slowdown in the Chinese economy. These markets trends are omi-
nous for future acetonitrile reserves, and could prompt a situation
similar to the observed crisis of 2008–2009 [8]. It is therefore imper-
ative to develop a more secure supply of acetonitrile.
The ammoxidation of bio-ethanol affords a possible sustain-
able route for the production of acetonitrile. Bio-ethanol has the
potential to become a renewable platform chemical due to its
existing high volume production and the continued advancements
in feedstock selection [9]. Ethanol ammoxidation was previously
reported [10,11], however relatively high temperatures (>350 ◦C)
were needed and the modest activity required high catalyst load-
ing. More recently, Oishi et al. [12] have reported the ammoxidation
of aromatic alcohols to nitriles. However, they note in their work,
an inability to activate aliphatic alcohols. Nitrile synthesis from
such alcohols has been reported previously [13]; however, the
array of reagents required could be difficult and expensive to scale-
up. The ammoxidation of ethane [8,14] and ethylene [15] have
also been explored as alternative acetonitrile production routes.
However, these suffer from high temperature demands and low
product selectivity, (maximum yields of 26% reported at tempera-
tures greater than 450 ◦C), and ultimately do not offer a solution to
∗
Corresponding author. Fax: +966 26952257.
Corresponding author. Fax: +44 2890974687.
E-mail addresses: mdaous@kau.edu.sa (M. Daous), d.rooney@qub.ac.uk
∗∗
(D. Rooney).
http://dx.doi.org/10.1016/j.apcata.2015.09.030
0926-860X/© 2015 Published by Elsevier B.V.

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C. Hamill et al. / Applied Catalysis A: General 506 (2015) 261–267
the overarching issue of product security, as they remain heavily
dependent on petrochemical resources.
detector (FID) and fitted with a 30 m Restek Stabilwax column. A
Hiden HPR 20 mass spectrometer was operated in parallel to the GC
to monitor the evolution of additional products. All GC data were
recorded on a temperature ramp down. Each temperature interval
was held for 40 min and an average analysis was recorded.
The production of acetonitrile from ethanol has also been
explored via a reductive amination route [16–18], however, these
again requires high temperatures (≈340 ◦C) and display poor cat-
alyst activity. The oxidative dehydrogenation of ‘bio’ ethylamine
was proposed as a possible production route, reporting a selectiv-
ity of 80% under continuous conditions [19]. The economics of this
proposed pathway are, however, doubtful, since mono-ethylamine
is a more expensive chemical than acetonitrile [20]. The amina-
tion of glycerol to acetonitrile has also been examined [21], but the
selectivity was less than 50%.
The application of noble metals for ammoxidation is limited
[22,23], with the most widely applied ammoxidation catalysts
comprising of supported oxides of vanadium and molybdenum
[24]. However, the use of these sites for ethanol ammoxidation
[10,25] have had limited success requiring high temperatures
(>400 ◦C) to display modest yields (60–80%). In the ammoxida-
tion reaction partial oxidation species, in particular carbonyls, are
widely acknowledged as crucial intermediates in facilitating nitro-
gen insertion [24,26]. In the present work supported palladium
catalysts have been selected to investigate the ammoxidation of
ethanol given the metal’s ability to selectively oxidize alcohols to
the corresponding aldehyde at low temperatures [27–29]. Herein
we report on the moderate to low temperature production of ace-
tonitrile via the ammoxidation of a renewable resource; ethanol,
using highly selective palladium based catalysts under conditions
yielding stable operation.
2.3. Catalyst characterization
The XPS measurements were carried out in an ultra-high
vacuum multi-technique surface analysis system (SPECS GmbH,
Germany) operating at a base pressure of 10−10 m bar. A standard
dual anode X-ray source SPECS XR-50 with Al-K␣, 1486.6 eV was
used to irradiate the sample surface with 13.5 kV, 100 W X-ray
power and a take-off-angle for electrons at 90◦ relative to sample
surface plane. The high energy resolution or narrow scan spectra
were recorded at room temperature with a 180◦ hemispherical
energy analyzer model PHOIBOS-150 and a set of nine channel
electron multipliers MCD-9. The analyzer was operated in Fixed
Analyzer Transmission (FAT) and medium area lens modes at pass
energy of 20 eV, step size of 0.1 eV and dwell time of 2.0 s. As is
the standard practice in XPS studies, the adventitious hydrocarbon
C1s line (285 eV) corresponding to CC bond has been used as the
binding energy reference for charge correction.
The TEM analysis of the Pd catalysts was performed using a
Tecnai G2 F20 Super Twin at 200 kV with a LaB6 emitter. The
microscope was fully equipped for analytical work with an energy-
dispersive X-ray (EDX) detector with a S-UTW window and a
high angle annular dark-field (HAADF) detector for STEM imag-
ing. Unless stated otherwise, the scanning transmission electron
microscopy (STEM) imaging and all analytical work were per-
formed with a probe size of 1 nm resulting in a beam current of
about 0.5 nA. TEM images and selected area diffraction (SAD) pat-
terns were collected on an Eagle 2K HR 200 kV CCD camera. The
HAADF-STEM EDX and CCD line traces were collected fully auto-
matically using the Tecnai G2 User Interface and processed with
the Tecnai Imaging and Analysis (TIA) software Version 1.9.162.
The DRIFT spectra were recorded using a Bruker Equinox 55
spectrometer using an average of 128 scans and a resolution of
4 cm−1. The DRIFTS setup consisted of an in-situ high temper-
ature diffuse reflectance IR cell (Spectra-Tech) fitted with ZnSe
windows which was modified in house to behave as a plug flow
reactor, the details of which have been previously reported [32,33].
The samples were pre-reduced for 1 h at 100 ◦C in a pure H2
stream (40 ml min−1). The cell was then cooled to 35 ◦C. A back-
2. Experimental
2.1. Catalyst preparation
The supported Pd catalysts were typically prepared using a col-
loidal technique called sol immobilization [30,31]. In a standard
preparation, an aqueous solution of PdCl2 (Sigma–Aldrich) was pre-
pared. Polyvinyl alcohol (PVA) solution (1 wt%) was added to obtain
a resulting ratio of PVA/Pd (wt/wt) = 1.2. A freshly prepared solution
of NaBH4 (0.1 M, NaBH4/Pd (mol/mol) = 5) was then added. After
30 min of sol generation, the colloid was immobilized by the sup-
port under vigorous stirring conditions. Note TiO2-P25 (Degussa)
SiO2 (BDH) and ZrO2 (Alfa-Aesar) supports were acidified to a pH of
1 using sulfuric acid prior to immobilization, ␥-Al2O3 (Grace) was
untreated. After 2 h the slurry was filtered, the solid washed thor-
oughly with distilled water and dried at 120 ◦C overnight. The same
method was employed when preparing catalysts with different
metal loadings. Pd/TiO2 was also synthesized via wet impregnation.
A predetermined volume of PdCl2 solution was added to a specific
quantity of TiO2-P25. The mixture was stirred at 50 ◦C until a paste
like material was generated. This was then dried at 120 ◦C for 4 h
and calcined at 500 ◦C for an additional 4 h. For details concern-
ing characterization of these catalysts please see the supporting
information.
ground spectra was collected after purging with Ar (40 ml min−1
)
for 30 min. A 1%CO/Ar stream (40 ml min−1) was subsequently
passed through the cell for 30 min, with the resulting spectra
recorded every minute. The gas flow was then switched back
to Ar (40 ml min−1). The cell was evacuated for a further 30 min
with spectra recorded every minute. During this step any weakly
adsorbed CO species are removed, and only the features corre-
sponding to strongly adsorbed CO molecules remain.
3. Results and discussion
2.2. Catalyst testing
Fig.1a reports the ethanol ammoxidation activity obtained with
the 0.3–10 wt% Pd/TiO2 (30–1000Pd) catalysts. Complete conver-
sion of the alcohol was achieved from circa 215 ◦C for the highest
Pd loaded catalysts. It was observed that increasing the nominal
loading of palladium from 0.3 wt% to 2 wt% (30–200Pd) has a min-
imal impact on this conversion. Further increases to 5 wt% (500Pd)
and 10 wt% (1000Pd) yielded significant improvements in the rate
of ethanol conversion. Note however, that there was no differ-
ence in the conversion profiles of the 500Pd and 1000Pd catalysts.
Fig. 1b reports the acetonitrile selectivity of these materials as a
Catalyst testing was performed in an isothermal fixed bed reac-
tor (I.D 6 mm) placed in a ceramic tubular furnace controlled by
a Eurotherm2604 PID controller. Typically a 50 s cm3 min−1 gas
stream comprising of 525 ppm ethanol, 4200 ppm NH3, 6825 ppm
O2, 1% Kr, balanced with Ar (unless otherwise stated), flowed
through a 138 mg catalytic packed bed (particle size: 212–425 ␮m).
The ethanol was fed via a calibrated temperature controlled satu-
rator. The concentrations of ethanol and acetonitrile were analyzed
using a PerkinElmer Clarus 500 GC, equipped with a flame ionized

C. Hamill et al. / Applied Catalysis A: General 506 (2015) 261–267
263
Table 1
100
90
80
70
60
50
40
30
20
10
0
a)
XPS and H2 chemisorption analysis of various palladium loaded catalysts supported
on TiO2.
Sample
Pd0 (%)
Pd2+ (%)
D (%)
dp (nm)
1000Pd
500Pd
200Pd
100Pd
50Pd
–
–
38.3
32.0
43.5
33.8
–
–
61.7
68.0
56.5
66.2
14.7
18.3
20.4
22.6
26.1
28.9
7.63
6.13
5.50
4.97
4.30
3.88
30Pd
100
150
200
250
300
100
90
80
70
60
50
40
30
20
10
0
Temperature (oC)
a)
100
90
80
70
60
50
40
30
20
10
0
b)
100
150
200
250
300
Temperature (oC)
100
150
200
250
300
100
90
80
70
60
50
40
30
20
10
0
b)
Temperature (oC)
Fig. 1. The effect of palladium loading on ethanol conversion (a) and acetonitrile
selectivity (b) as a function of temperature. 1000Pd (×), 500Pd (᭿), 200Pd (᭹),
100(ꢀ), 50Pd (ꢁ) and 30Pd (+), all supported on TiO2.
100
150
200
250
300
Temperature (oC)
Fig. 2. The effect of support type on ethanol conversion (a) and acetonitrile selec-
tivity (b) as a function of temperature. For 1 wt% Pd (nominal) supported on ␥-Al2O3
(ꢁ), ZrO2 (᭿), TiO2 (᭹), and SiO2 (ꢀ).
Scheme 1. Proposed reaction pathway for the ammoxidation of ethanol over
Pd/TiO2 catalysts.
dium oxide fraction [35,36]. However, XPS analysis of the palladium
catalysts (30–200Pd), revealed that metal loading had a negligible
impact on their initial oxidation state (see Table 1) indicating that
product distribution is most likely independent of the initial oxi-
dation state of the palladium. To further probe this hypothesis, the
least selective catalyst; 30Pd was pre-reduced at 100 ◦C under H2
for 1 h before its activity was assessed. This pre-treatment had no
observable impact on performance.
It has been widely reported that the interactions between a
metal and its support can govern the effectiveness of a catalyst
[37]. To explore the influence of the supporting material on the
catalytic performance, palladium was deposited (nominal 1 wt%)
onto various oxide supports; TiO2, ZrO2, ␥-Al2O3 and SiO2. The
ensuing conversion of ethanol is reported in Fig. 2 a. It can be
observed that ammoxidation activity follows the trend; TiO2 > ␥-
Al2O3 > ZrO2 > SiO2. The selectivity of these catalysts as a function
of temperature is reported in Fig. 2b. Note the characteristic selec-
tivity profile described previously was observed for all catalysts. It
can be seen that ZrO2 was the most selective support, displaying
an acetonitrile selectivity of approximately 94% at 170 ◦C. Note also
that the results demonstrate that Pd/TiO2 was the most productive
catalyst as, on average, it gave the highest yield of acetonitrile.
The diverse acid/base properties of the supports were investi-
gated to elucidate the observed variations in acetonitrile selectivity.
Acid sites are considered to be important for the insertion of nitro-
gen into partially oxidized intermediates during the ammoxidation
function of temperature. Below about 190 ◦C, acetonitrile selectiv-
ity increased with temperature for all catalysts; this is attributable
to the suppression of ethyl acetate production. This is consistent
with the results of Gaspar et al. [34] who reported ethyl acetate
production over Pd catalysts via a condensation reaction between
ethanol and acetaldehyde (see Scheme 1). At higher temperatures
a sharp decline in acetonitrile production was observed due to the
dominance of competing combustion reactions, evidenced by CO2
production. Note that the presence of HCN or acetamide was not
observed in the gas phase. Fig. 1b reveals that varying the palladium
content had a significant influence on the product distribution. In
the low temperature region, acetonitrile selectivity increased with
palladium loading, with the lower loaded catalysts forming more
ethyl acetate. The catalysts with lower Pd concentration conversely
displayed improved acetonitrile selectivity at higher temperatures
(>240 ◦C), due to a reduced affinity for combustion reactions evi-
denced by a decline in CO2 production (see Fig. S.1). From Table 1 it
can be observed that the least dispersed catalyst (1000Pd) was the
most selective to acetonitrile, and the least selective (30Pd) was the
most disperse.
The possible dependence on initial oxidation state of the
catalysts was postulated to elucidate the observed relationship
between selectivity and metal concentration in Fig. 1. Lee et al. [27]
report that a decreased metal loading yields an increase in the palla-

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C. Hamill et al. / Applied Catalysis A: General 506 (2015) 261–267
Table 2
100
ICP, BET and H2 chemisorption analyses of palladium loaded on the various oxide
supports.
90
80
70
60
50
40
30
20
10
0
Sample
ICP (%)
BET (m2/g)
D (%)
dp (nm)
1%Pd/ZrO2
1%Pd/TiO2
1%Pd/␥-Al2O3
1%Pd/SiO2
0.50
0.68
0.61
0.50
19.0
54.9
195.6
295.3
18.1
22.6
28.9
34.3
6.19
4.97
3.88
3.47
1980
200Pd
100Pd
50Pd
0
20
40
60
1925
Bridged / Linear CO
30Pd
Support
0.05
Fig. 4. Acetonitrile selectivity at 167 ◦C as a function of the proportion bridged
bonded to linear adsorbed CO determine via DRIFTS. 30Pd/TiO2( ), 50Pd/TiO2(
), 100Pd/TiO2( ), 200Pd/TiO2( ), 500Pd/TiO2( ), 1000Pd/TiO2(᭹), 100Pd/Al2O3
(
), 100Pd/ZrO2 ( ) 100Pd/SiO2 ( ).(For interpretation of the references to colour
in this figure legend, the reader is referred to the web version of this article.)
2078
100
a)
90
80
70
60
50
40
30
20
10
0
2100
2000
1900
1800
1700
Wavenumber (cm-1)
Fig. 3. DRIFTS spectra of adsorbed CO on various palladium loaded catalysts sup-
ported on TiO2 (500Pd & 1000Pd not shown).
100
150
200
250
300
Temperature (oC)
reaction [24,38]. Gaspar et al. [39] also cite the importance of
acid/base properties in the production of the ethyl acetate. To
evaluate the relationship between catalyst acidity and acetonitrile
selectivity NH3-TPDs were conducted to quantify the acid sites.
The results of Fig. S.2 indicate that the acid/base characteristics of
the support do not play a dominant role in the production of ace-
tonitrile. The least selective catalyst Pd/SiO2, was less acidic than
Pd/TiO2 and more acidic than Pd/ZrO2, both of which displayed
superior selectivities. The metal dispersion of these catalysts was
also assessed to probe the possible relationship between nitrile
selectivity and morphology. From Table 2 it can be observed that the
palladium dispersion increased with support surface area. The least
dispersed catalyst, Pd/ZrO2, was the most selective, and conversely
the most disperse catalyst, Pd/SiO2, was the least selective. These
results were correlated with those found for the titania-supported
catalysts with different Pd loadings (see Fig. S.3), The result dis-
play that acetonitrile selectivity increases with decreasing metal
dispersion, which suggests that the product distribution may be a
function of Pd morphology.
100
90
80
70
60
50
40
30
20
10
0
b)
100
150
200
250
300
Temperature (oC)
Fig. 5. The effect of preparation method on ethanol conversion (a) and acetonitrile
selectivity (b) as a function of temperature. 100Pd via sol immobilisation (᭿) and
100Pd via impregnation (ꢀ), both supported on TiO2.
the ratio of bridged to linear (B/L) species increased with palladium
loading. This infers that the average size of the palladium crystal-
lites are also increasing, which complements the chemisorption
data reported in Table 1. The B/L ratio of the other oxide supported
palladium catalysts were also evaluated and compared with the
Pd/TiO2 samples. It should be noted that the band positions for CO
adsorption onto palladium were independent of supporting mate-
rial [41]. The acetonitrile selectivity of all the Pd catalysts at 167 ◦C
is plotted as function of their B/L ratio in Fig. 4. From this it would
appear that the selectivity increases with an increase in the B/L
ratio; the exact reason for this remains unknown. However, these
results do suggest that the terraced palladium planes are more
selective for nitrile production.
To further evaluate the relationship between dispersion and
selectivity, a CO adsorption Diffuse Reflectance Infrared Fourier
Transform Spectroscopy study was conducted. In general two types
of adsorbed CO are identifiable on palladium. Fig. 3 displays the
IR spectra of CO adsorbed onto various loaded Pd/TiO2 catalysts
(0.3–2 wt%). Two bands appeared in the region of 1800–2100 cm−1
;
that close to 2078 cm−1 was ascribed to mono-coordinated, lin-
early bonded CO. The broad band appearing under 2000 cm−1 was
assigned to multi-coordinated bridged–bonded CO [40]. Linearly,
bonded CO species are typically associated with adsorption onto
low coordinated (corner and edges) Pd atoms, whereas bridged
species are synonymous with CO adsorption on facetted planes.
Smaller particles expose a larger fraction of the former type of sites
than larger crystallites [40]. From Fig. 3 it can be observed that
increasing the palladium loading led to an increase in the inten-
sity of bands assigned to linear and bridge adsorbed CO. However,
The possible structure sensitivity of ethanol ammoxidation was
further examined by investigating the catalyst preparation method.
The sol immobilization (S.I.) method, used thus far, affords control
over the morphology and size distribution of supported nanopar-
ticles [42]. 1 wt% Pd/TiO2 was prepared via the wet impregnation

C. Hamill et al. / Applied Catalysis A: General 506 (2015) 261–267
265
Fig. 6. HRTEM images of (a, b) fresh 100Pd catalyst, (c) selected area diffraction (SAD) of a particle within the 100Pd sample and (d–f) the impregnated sample100Pd-IMP.
Both supported on TiO2-P25.
(100Pd IMP) method and its performance was compared to the S.I.
sample (100Pd). Fig. 5 reveals that the 100Pd catalyst is significantly
more active than its impregnated counterpart, with considerable
differences observed in product distribution. The impregnated
sample yields considerable quantities of acetaldehyde, ethylene,
diethyl ether, ethyl acetate and COx. The findings of Grunwaldt et al.
[43] and Lee et al. [27] suggest that this contrasting performance
could be due to the electronic properties of the supported Pd. How-
ever, XPS analysis (see Table S.1) of the samples reveals that this
result was not due to variations in the initial oxidation states of
palladium.
Note that large PdO particles were also observed via XRD (Fig.
S.5). Conversely, the S.I. method yielded more uniformly dispersed
Pd nanoparticles in the range of 3–5 nm, which agrees with the
chemisorption analysis in Table S.1. These results support the
hypothesis that acetonitrile production over palladium is structure
sensitive. They suggest that selectivity can be optimized by success-
fully tuning the morphology and size of the supported particles.
Long term activity tests revealed that these Pd catalysts were
susceptible to deactivation. To further evaluate the nature of this
deactivation, a Pd/TiO2 catalyst (200Pd) was deactivated at 150 ◦C,
treated at 300 ◦C under feed conditions and subsequently retested.
Following this treatment, the original catalytic activity was fully
recovered, (Fig. 7) and the catalyst proceeded to deactivate at a
similar rate. This regeneration indicated that the small restruc-
TEM investigations (see Fig. 6) revealed that the impregnated
catalyst possessed a broad particle size distribution; ranging from
small nanoparticles (<5 nm) to large cluster ensembles (>100 nm).

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C. Hamill et al. / Applied Catalysis A: General 506 (2015) 261–267
50
45
40
35
30
25
20
15
10
5
0.0035
100
90
80
70
60
50
40
30
20
10
0
300oC
150oC
150oC
0.003
0.0025
0.002
0.0015
0.001
0.0005
0
ZrO2
TiO2
Al2O3
SiO2
0
Fig. 9. The relationship between catalyst deactivation and selectivity at 180 ◦C, for
0
200
400
600
800
1000
1200
the various supported palladium catalysts.
Time on Stream (min)
Fig. 7. Deactivation profile of the 200Pd catalyst (GHSV: 7126 cm−3 g−1 h−1) at
100
90
80
70
60
50
40
30
20
10
0
150 ◦C including regeneration under feed conditions.
0.005
0.0045
0.004
0.0035
0.003
0.0025
0.002
0.0015
0.001
0.0005
0
100
90
80
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
Time on Stream (h)
500Pd
200Pd
30Pd
Fig. 10. Acetonitrile yield over the 100Pd catalyst at 230 ◦C.
Fig. 8. The relationship between catalyst deactivation and selectivity at 150 ◦C, for
500Pd, 200Pd* and 30Pd* catalysts. *Note GHSV = 7126 ml g−1 h−1
.
100
90
80
70
60
50
40
30
20
10
0
turing/sintering observed in Fig. S.6 is not the major source of
deactivation for Pd/TiO2 catalysts. The result suggests that the
activity loss may be due to the strong adsorption of a reaction
product or the deposition of carbon on the catalyst surface. A
temperature programmed desorption study (see Fig. S.7) excluded
acetonitrile self-poisoning as a deactivation mechanism. To evalu-
ate carbon deposition as a deactivation mechanism, a temperature
programmed oxidation (TPO) was conducted with a deactivated
catalyst (100Pd). The resulting profile is displayed in Fig. S.8. and
showed the release of CO2 from about 225 ◦C. It is possible that the
carbon dioxide observed via temperature programmed oxidation
could be due to adsorbed ethyl acetate and/or a similar or asso-
ciated product. The performance of the 500Pd, 200Pd and 30Pd
catalysts was examined at 150 ◦C to investigate the influence of
product distribution on catalyst stability. Fig. 8 reports the deactiva-
tion rate constant and acetonitrile selectivity of each material. It can
be observed that the most stable catalyst, 500Pd, is also the most
selective to acetonitrile, and the least selective, 30Pd, is conversely
the least stable. Similar analysis was conducted on the various oxide
supported palladium catalysts at 180 ◦C (see Fig. 9) and a compara-
ble relationship between selectivity and stability was noted. These
results re-enforce the suggestion that the production/interaction
of an unselective species is involved in the deactivation of the cat-
alyst. Recalling that ethyl acetate is the major by-product in the
reaction would imply that it has an important role in the deacti-
vation mechanism. The stability of the catalysts was reassessed at
230 ◦C, where no ethyl acetate production was observed. Fig. 10
reports a typical result obtained with the 100Pd sample and stable
activity was observed, with a yield to acetonitrile of approximately
93%.
100
150
200
250
300
Temperature (oC)
100
90
80
70
60
50
40
30
20
10
0
100
150
200
250
300
Temperature (oC)
Fig. 11. The effect of ethanol concentration on its conversion (a) and selectivity to
acetonitrile (b) as a function of temperature over the 200Pd catalyst. 525 ppm (᭿),
1050 ppm (ꢁ) and 1575 ppm (ꢀ). Note in all tests the concentrations of ammonia and
oxygen remain constant. Ratio of NH3:EtOH; 8, 4 and 2.7 and O2:EtOH; 13:6.5:4.3
respectively.
0
the exothermic nature of the reaction (ꢀHr = −371 kJ mol−1) and
Finally, the performance of the catalyst was tested at increas-
ing initial concentrations of ethanol to assess its behavior when
the conditions are moved toward more realistic ones. Note that
further increases in the reactant concentration were constraint by
the reactor design employed. The results obtained (Fig. 11) first,
demonstrate that nitrile yield is independent of the ethanol par-
tial pressure, and second, the NH3:EtOH ratio can be significantly
reduced (down to 2.7 in this case as NH3 partial pressure remained

C. Hamill et al. / Applied Catalysis A: General 506 (2015) 261–267
267
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The moderate to low temperature production of acetonitrile
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Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.apcata.2015.09.
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