Partially reduced iridium oxide clusters dispersed on titania as efficient catalysts for facile synthesis of dimethylformamide from CO2, H 2 and dimethylamine

Article abstract of DOI:10.1039/c4cc02973a

A novel bifunctional catalyst based on partially reduced iridium oxide supported on TiO₂ was found to be exceedingly efficient for the organic-solvent-free synthesis of dimethylformamide from CO₂, H ₂ and dimethylamine. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4cc02973a

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Partially reduced iridium oxide clusters dispersed
on titania as efficient catalysts for facile synthesis
of dimethylformamide from CO , H and
Cite this: Chem. Commun., 2014,
0, 9138
5
2
2
Received 22nd April 2014,
Accepted 23rd June 2014
dimethylamine†
Qing-Yuan Bi, Jian-Dong Lin, Yong-Mei Liu, Song-Hai Xie, He-Yong He and
Yong Cao*
DOI: 10.1039/c4cc02973a
www.rsc.org/chemcomm
A novel bifunctional catalyst based on partially reduced iridium catalyst for the high yield (ca. 97%) synthesis of DMF employing high
1
0
oxide supported on TiO
the organic-solvent-free synthesis of dimethylformamide from besides the inherent limitations associated with the handling pro-
CO , H and dimethylamine. blems, this system requires the use of ridiculously expensive dimethyl-
2
was found to be exceedingly efficient for pressure CO –H mixtures (total pressure up to 12 MPa). However,
2 2
2
2
10
ammonium dimethylcarbamate (DIMCARB) as the amine source.
source Thus, the development of an efficient catalytic process for practical
for the synthesis of fuels or value-added chemicals is a topic of current DMF synthesis based on CO reduction (eqn (1)) using a cost-effective
clearly calls for amine source under mild conditions is highly desirable.
2 1
The use of CO as a renewable and environmentally friendly C
2
1
interest. The high thermodynamic stability of CO
2
highly efficient activation which must be coupled with a strong
thermodynamic driving force to ensure irreversible fixation. One
NH(CH
From a synthetic point of view, it appears that a multifunctional
as well as H would be a
3
)
2
+ CO
2
+ H
2
- HCON(CH
3
)
2
+ H
2
O
(1)
2
promising approach to overcoming the low reactivity of CO is its
2
activation by catalytic hydrogenation to form formic acid or its catalyst with excellent capacity to activate CO
2
2
3
derivatives. This transformation offers direct access to chemical better candidate for this particular transformation. Ir-containing
products based on waste material from the energetic use of fossil catalysts have been extensively employed in the past years for
2
fuels, opens a possible route to convert CO into CO, and is discussed the reduction of nitric oxide, decomposition of hydrazine hydrate
11
as a potential option for the development of new chemical processes or ammonia and synthesis of quinolines. Moreover, it is also
4
that utilize renewable resources. The industrial implementation of established that Ir complexes including Ir(II) and Ir(III) are very active
1
2
such advanced CO -utilization concepts faces a number of ecological, for a number of carboxylation or hydrogenation of CO2. Given the
2
5
economic and technical challenges. On the most fundamental level, high efficiency of specifically designed Ir complexes for both CO2
it is essential to develop a new, innovative and highly effective catalytic and H
method which can allow facile reductive activation of CO under using Ir-based heterogeneous catalysts for improved DMF synthesis
favorable conditions to yield a range of key chemical compounds.
Dimethylformamide (DMF) is an important primary product, an efficient titania supported Ir catalyst for straightforward synthesis
and has the high performance as a solvent, being particularly of DMF from CO , H and aqueous NHMe under mild, practical and
2
activation, we were motivated to explore the possibility of
2
1,2,5
2 2
via CO hydrogenation in the presence of NHMe . Herein, we report
2
2
2
used in manufacture of polyurethane leatherette and polyacrylo- organic-solvent-free conditions. The key to the successful application
6
nitrile fiber. Currently, this compound is produced in industry of the catalyst was the favorable creation of partially reduced iridium
from carbonylation of dimethylamine (NHMe ) employing toxic oxide (Ir/IrO ) clusters enabling facile reductive activation of CO2
2
x
7
CO as the C
presence of various amine substrates has been broadly investigated, catalytic system for the production of DMF, but also add another
the direct formation of DMF using CO as a C source in a highly important example of heterogeneous Ir-catalyzed reactions.
facile and quantitative manner remains presently elusive. A very
recent report describes the use of a Cu–ZnO nanocomposite as the in the presence of commercially available aqueous NHMe
1 2 2
feedstock. Although the hydrogenation of CO in the under an H atmosphere. These findings not only provide a new
2
1
8,9
We began our study by examining the direct hydrogenation of CO
(40 wt%)
2
2
at 140 1C, as this is expected to represent the easiest scheme for DMF
Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and
Innovative Materials, Fudan University, Shanghai 200433, P. R. China.
E-mail: yongcao@fudan.edu.cn; Fax: +86-21 65643774
production from CO . First of all, we have studied several potential
2
noble-metal-based catalysts prepared by a conventional impregna-
tion technique in the presence of 60 bar H
use, all catalysts were pretreated in an H
2
/CO
2
(see ESI†). Prior to
†
Electronic supplementary information (ESI) available: Chemicals and materials,
atmosphere to ensure
catalyst characterization, catalyst preparation and activity tests. See DOI: 10.1039/
c4cc02973a
2
all metal species were reduced to their metallic state (see ESI†).
9138 | Chem. Commun., 2014, 50, 9138--9140
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Table 1 Activity of various catalysts for DMF synthesis from CO
2
, H
2
and
a
aqueous NHMe
2
DMF productivity
b
À1 À1
Entry Catalyst
Time (h) Yield (%) (mmol gMetal
h )
1
2
3
4
5
6
7
8
9
1
1
1
1
Pd/P25-IM
Ru/P25-IM
Rh/P25-IM
10
10
10
10
10
10
10
10
9.9
9.2
3.4
8.7
6.3
16.8
13.1
12.4
10.4
12.2
7.1
150
139
51
132
95
255
198
187
157
184
108
Pd/ZrO
Ru/ZrO
Ir/P25-IM
Ir/ZrO -IM
Ir/Al -IM
Ir/ZnO-IM
Ir/CeO -IM
2
-IM
2
-IM
2
2
O
3
10
10
10
0
1
2
3
2
Ir/MgO-IM
Cu/ZnO-CP
Ir/HSA-TiO
c
14
5.1
25.6
0.6
388
2
-IM 10
a
All noble-metal-based catalysts were prepared by the impregnation
method and the metal loading was 0.5 wt%. Reaction conditions:
2
00 mg catalyst, 15.1 mmol NHMe , PCO2 = PH2 = 30 bar at 25 1C, 140 1C,
2
b
c
1,4-dioxane as the internal standard. Based on the NHMe
2
feed. Prepared
via conventional the co-precipitation method.
Fig. 1 TEM images of (a) Ir/HSA-TiO
2 2
and (b) Ir/HSA-TiO -A, and (c) XPS
While palladium, ruthenium, and rhodium displayed very poor
performances for DMF synthesis with the yield lower than 10%
data and (d) CO -TPD profiles of both catalysts.
2
(Table 1, entries 1–5), only catalysts based on Ir can deliver
notable activity with appreciable DMF yields (entries 6–11). Note
that the previously reported co-precipitation-derived Cu/ZnO
catalyst was nearly inactive under the present reaction conditions,
probably due to its inherent weak water-tolerance (entry 12). Of the
catalytic active species enabling facile activation of both CO2
and H . While TEM measurements have confirmed that the DP
2
method can result in the formation of smaller Ir domains
(Fig. 1a) with higher metal dispersion than its impregnation-
Ir catalysts tested, the use of TiO , especially high surface area TiO
2
2
derived analogue (Fig. S3, ESI†), XPS analysis reveals the presence of
2
(HSA-TiO , Fig. S1, ESI†), as a support can afford much higher
both metallic and oxidized Ir species on the surface of the used Ir/
activity with a moderate DMF yield of ca. 26% (entry 13). This
2
HSA-TiO -A sample (Fig. S5, ESI†). Moreover, it was confirmed in two
À1 À1
corresponds to a DMF productivity of ca. 388 mmol gIr
h .
separate experiments that whereas the air-pretreated Ir/HSA-TiO2
sample showed a prominent increase in its activity, a drastic activity
decrease was identified for the H -pretreated Ir/HSA-TiO -A sample
Already, this result represents the best catalyst productivity ever
reported for DMF synthesis via CO hydrogenation in the presence
2
2
2
8,10
2
of NHMe .
(
Table 2, entries 5 and 6). To better understand the superior
performance of Ir/HSA-TiO -A, both catalysts were characterized with
CO -temperature-programmed desorption (CO -TPD). The fact that
Ir/HSA-TiO
Ir/HSA-TiO
Bearing in mind that the particle size has proven to be
especially influential for supported Ir catalysts, we envisioned
that dispersed Ir nanoclusters (NCs) with improved metal
dispersion could be more effective for the direct synthesis of
2
2
2
2
-A exhibited much higher CO
(Fig. 1d) indicates that the CO
2
adsorption capacity than
molecule can be activated
2
2
DMF from CO
new heterogeneous Ir catalyst sample composed of ultra-small Ir
NCs finely dispersed on HSA-TiO (denoted as Ir/HSA-TiO ) was
prepared by a deposition–precipitation (DP) method (Fig. 1a, for Table 2 DMF synthesis from CO
2 2
and aqueous NHMe . To explore this possibility, a
much more readily on the surface of the oxidized Ir species.
2
2
2
2 2
, H and aqueous NHMe over different
a
2
DP-derived TiO supported Ir catalysts
details see ESI†). To our delight, this catalyst gave much higher
À1 À1
activity: 43.4% yield and 657 mmol gIr
h
productivity (Table 2,
-A sample Entry Catalyst
DMF productivity
b
À1 À1
entry 1). Of yet further interest is that the Ir/HSA-TiO
prepared under otherwise identical conditions without H
ment can deliver a much higher efficiency toward DMF synthesis
entry 2). More relevant is that an even higher yield of ca. 93.5%
can be obtained over Ir/HSA-TiO -A and extended reaction time
2
Time (h) Yield (%) (mmol gIr
h )
2
pretreat-
1
2
3
4
5
6
Ir/HSA-TiO
Ir/HSA-TiO -A
2
10
10
16
10
43.4
60.6
93.5
31.6
36.7
62.6
657
918
882
955
555
946
2
Ir/HSA-TiO
Ir/HSA-TiO
Ir/HSA-TiO
2
2
2
-A
-A
(
c
2
d
e
-A-H 10
under 60 bar and 140 1C (entry 3). Particularly noteworthy is
2
Ir/HSA-TiO -H-A 10
that this iridium catalyst gave an exceptional productivity up to
a
Ir loading was 0.5 wt%. Reaction conditions: 200 mg catalyst, 15.1 mmol
= PH2 = 30 bar at 25 1C, 140 1C, 1,4-dioxane as the internal
À1 À1
9
55 mmol gIr
h
(entry 4). This is the best value reported so far
NHMe , P
standard. Based on the NHMe
A-H denotes the sample obtained by a further treatment of the Ir/HSA-
TiO
2
CO
2
8,10
b
c
d
for DMF synthesis from CO
The outstanding efficiency for DMF synthesis over Ir/HSA-
TiO -A under the conditions mentioned above clearly reflects
the fast surface kinetics as a result of the creation of favorable material in air at 400 1C for 2 h.
2
, H
2
and NHMe
2
.
2 2
feed. 100 mg catalyst. Ir/HSA-TiO -
e
2 2 2
-A catalyst in 5 vol% H /Ar at 400 1C for 2 h. Ir/HSA-TiO -H-A
2
denotes the sample obtained by further calcination of the Ir/HSA-TiO
2
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contribute to the design of more efficient catalytic systems and
may provide a new strategy for the development of green organic
transformations using CO as the renewable resource.
2
This work was supported by the National Natural Science
Foundation of China (21073042, 21273044), the Research Fund
for the Doctoral Program of Higher Education (2012007000011)
and Science & Technology Commission of Shanghai Munici-
pality (08DZ2270500).
Notes and references
1
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facilitate the desired DMF synthesis.
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Ir and IrO species over Ir/HSA-TiO -A was proposed (Scheme S1,
2
ESI†). Further investigation into the effect of reaction parameters on
the performance of the Ir/HSA-TiO -A catalyst revealed that a
2
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reaction, thus poisoning the Ir-based catalyst and decreasing the
DMF productivity (Fig. S6, ESI†). The increase of total pressure is in
favor of reaction proceeding (Fig. S7, ESI†), and the reaction at an
equivalent molar ratio of CO to H is most suitable (Fig. S8, ESI†).
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2
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2
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3
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(
1
0.1 ppm), revealing that no leaching occurred during the reaction.
9
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2
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2
for the used Ir catalyst (Fig. S9, ESI†). The recovered Ir/HSA-TiO -A
1
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product yield and specific productivity after the 5th reuse (Fig. 2).
In conclusion, we have demonstrated that partially reduced
1
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2
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1
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,
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9
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using other amine substrates showed that the present Ir-catalyzed
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Table S1, ESI†). The catalytic system present here, in which the
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in a cooperative manner, may
383–388.
9
140 | Chem. Commun., 2014, 50, 9138--9140
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