(NH4)AgMoS4: Synthesis, structure and catalytic activity

Article abstract of DOI:10.1002/zaac.201200309

The synthesis, characterization and crystal structure of (NH ₄)AgMoS₄ is presented. (NH₄)AgMoS₄ was prepared by the stoichiometric reaction of AgNO₃ with (NH ₄)₂MoS₄.

Full text of DOI:10.1002/zaac.201200309

Job/Unit: Z12309
/KAP1
Date: 10-09-12 10:34:41
Pages: 5
ARTICLE
DOI: 10.1002/zaac.201200309
(
NH )AgMoS : Synthesis, Structure and Catalytic Activity
4
4
[a]
[a]
[a]
Maryam Shafaei-Fallah, Christos D. Malliakas, and Mercouri G. Kanatzidis*
Keywords: Heterogeneous catalysis; Syngas conversion; Alcohol synthesis; Thiomolybdates
Abstract. The synthesis, characterization and crystal structure of ion at 1350–1400 cm–1 and for the [MoS
NH )AgMoS is presented. (NH )AgMoS was prepared by the stoi- observed. Crystals of (NH )AgMoS were investigated using a syn-
chiometric reaction of AgNO with (NH MoS . The black micro- chroton source. (NH )AgMoS is isostructural to (NH )CuMoS and
crystalline (NH )AgMoS is thermally unstable and contaminated by crystallizes in the tetragonal space group I4 (Z = 2, a = 7.8740(3), c
a phase that analyzes for Ag MoS . In the TGA continuous weight = 5.7733(4) Å). (NH )AgMoS can be used as a catalyst in the syngas
loss was observed corresponding to the loss of ammonia gas subse-
quent loss of sulfur and H S to give Ag S and MoS . In the infrared
spectrum of (NH )AgMoS , characteristic bands for the ammonium
]2– group at 460 cm–1 are
4
(
4
4
4
4
4
4
3
4
)
2
4
4
4
4
4
¯
4
4
2
4
4
4
conversion to higher alcohols with showing good activity and ethanol
selectivity.
2
2
2
4
4
Introduction
search we present a case study of the metal thiomolybdate
(
NH )AgMoS , its synthesis, structural analysis and prelimi-
4 4
Thiomolybdates have been studied extensively with a focus
nary results of catalytic activity in HAS.
[1–4]
[5,6]
on bioinorganic chemistry,
heterogeneous catalysis,
and
coordination chemistry.[ Their importance as lubricants is
probably the most widely known property of molybdenum
sulfides that is a direct consequence of the low-dimensional
7]
Results and Discussion
structures usually found within this class of compounds.[
8,9]
For the catalytic screening of late transition metal thiomo-
lybdates in HAS, (NH )AgMoS (1) was prepared from the
Over the last three decades significant progress has been made
4
4
in synthetic and structural thiometalate chemistry.[ Particu-
larly, tetrathiomolybdates and tetrathiotungstates are good pre-
cursors in the synthesis of transition metal sulfides.[ The fact
that both molybdenum and sulfur can exist in various oxidation
10]
stoichiometric reaction between AgNO and (NH ) MoS4
3 4 2
19]
(
Scheme 1).[
11]
states, led to a variety of molecular thiomolybdate spe-
cies.[
1,4,7,12]
Scheme 1. Synthesis of 1.
Only a few polymeric structures have been solved
by single crystal structure analysis containing coinage metal
cations, forming extended structured with the thiometallate
The presence of silver, molybdenum and sulfur in 1 was
confirmed by EDS (Supporting Information). The infrared
spectrum of 1 showed characteristic bands for the ammonium
anions.[10,13–17]
The growing number of compounds available
allows a systematic screening of thiometallates as hydrodesul-
furization and hydrodenitrogenation catalysts as well as in
higher alcohol synthesis (HAS) from syngas. The latter is a
crucial process to meet the increasing demand of ethanol as
additive to conventional gasoline, as chemical feedstock and
as hydrogen carrier. The historic and current developments of
this ongoing search for an efficient catalytic process for the
conversion of syngas to ethanol have recently been published
–1
2–
–1
ion at 1350–1400 cm and for the [MoS4] group at 460 cm
19]
(
Figure 1).[ In the TGA continuous weight loss was ob-
served possibly corresponding to the loss of ammonia gas until
70 °C and subsequent loss of sulfur and H S to give Ag S
1
2
2
and MoS until 400 °C (Figure 1). The instability of (NH )
2
4
AgMoS in heating is attributed to the release of NH and the
4
3
transfer of a proton to a sulfide ion. The elimination of H S is
2
in a comprehensive review.[
18]
also accompanied by internal redox chemistry that converts the
Here, as a contribution to this
6+
4+
Mo to Mo that leads to the formation MoS2.
The structural characterization of (NH )AgMoS (1) was
initially carried out by powder diffraction (Figure 1).
4
4
*
Prof. Dr. M. G. Kanatzidis
Fax: +1-847-491-5937
E-mail: m-kanatzidis@northwestern.edu
The diffraction patterns showed 1 to be isostructural to
[
a] Department of Chemistry
Northwestern University
[19]
(
NH )CuMoS .
The characterization of 1 by single crystal
4
4
2
145 Sheridan Road
X-ray diffraction was very challenging because of the intrinsic
tendency to crystallize rapidly as microcrystals as soon as the
solutions of the reagents are combined. Very tiny black single
crystals were structurally characterized using synchrotron radi-
Evanston, IL 60208, USA
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201200309 or from the au-
thor.
Z. Anorg. Allg. Chem. 0000, ᭿,(᭿), 0–0
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1

Job/Unit: Z12309
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Date: 10-09-12 10:34:41
Pages: 5
M. Shafaei-Fallah, C. D. Malliakas, M. G. Kanatzidis
ARTICLE
HAS) were determined (Table 1). It is noteworthy that the
overall catalyst performance is similar to other previously in-
[
18]
vestigated transition metal thiomolybdate catalysts.
Also
desirable conversions Ͼ 10% with good ethanol and propanol
[
21]
selectivities were obtained at temperatures below 350 °C.
Table 1. Conversion of Syngas on (NH
4
)AgMoS
-free Selectivity /%
–C MeOH EtOH n-PrOH
4
catalyst.
T /°C
Conv. /%
CO
2
4
CH
C
2
6
HC
3.3
4.7
8.0
13
300
320
340
360
4.8
9.2
16
17
28
31
38
53
42
30
15
21
23
22
21
3.8
4.8
6.2
9.1
25
The MoS (DOW Chemical) catalyst, however, remains the
2
benchmark in the direct conversion of syngas to higher
alcohols with higher CO conversion (29.2 at 295 °C) and
higher ethanol selectivity 40.7%.[
22]
(NH )AgMoS4 (1) in
4
Figure 1. a) Simulated and experimental powder X-ray diffraction
comparison shows ethanol selectivity of ca. 20% in the inves-
pattern of 1. b) Thermogravimetric analysis of 1 (heating rate 10
K·min–1 under nitrogen flow 30 mL·min ). c) Infrared spectrum of 1 tigated temperature range of 300–360 °C with a maximum CO
–1
–1
showing the characteristic N–H band at 1390 cm and the Mo–S band
conversion of 25% at 360 °C.
–1
at 460 cm . d) Solid-state UV/Vis optical absorption spectra of 1 (con-
In summary, the synthesis, characterization and investigation
of the new compound (NH )AgMoS (1) are reported along
verted from reflectance) showing a band gap of ca. 0.7–1 eV.
4
4
with preliminary results on the catalytic performance in higher
alcohol synthesis. The data indicates that decomposition of
crystalline chalcogenido molybdates into metal sulfides and
ation (Advanced Photon Source, Argonne National Labora-
tory). Compound 1 crystallizes in the tetragonal space group
¯
I4. The compound is isostructural to the previously reported
MoS at elevated temperatures could produce a family of im-
2
[15, 19, 20]
salts (NH )MWS (M = Cu, Ag) and (NH )CuMoS .
4
4
4
4
proved MoS -based catalysts for higher alcohol synthesis. Fur-
2
The main structural features of 1 are the 1D arrangement of
ther investigations into the influence of the transition metal on
selectivity and CO conversion are in progress.
–
4 n
[
AgMoS ] units consisting of tetrahedrally coordinated silver
and molybdenum atoms (Figure 2). A detailed structural dis-
cussion has been published for (NH )MWS (M = Cu, Ag) and
4
4
[15,19,20]
(
NH )CuMoS .
The material absorbs light over a wide Experimental Section
4
4
range of the spectrum include the entire visible spectrum, Fig-
ure 1(d). This strong absorption is not found in the single
(
NH
cedure. The preparation of (NH
gen-filled glovebox. (NH MoS
in H O (40 mL) to give a dark red solution. Upon addition of a solution
of AgNO (1.36 g, 8.00 mmol) in H O (25 mL), a black precipitate
4
)
2
MoS
4
(1) was synthesized according to a published pro-
)AgMoS was performed in a nitro-
(2.08 g, 8.00 mmol) was dissolved
[
11]
2
–
4
4
[
MoS4] ion and is attributed to intense charge transfer transi-
tions from sulfur based orbitals to silver and molybdenum
based orbitals.
4
)
2
4
2
3
2
Having characterized 1, the catalytic properties of 1 in the formed immediately suspended in a dark red solution. The mixture
syngas conversion to higher alcohols (higher alcohol synthesis, was stirred for 1 h. The product was filtered and washed, first with
Figure 2. Structure of (NH
4 4
)AgMoS (1) in the solid state. Unit cell diagram in [010] (left) and [001] (right) direction. Selected bond lengths /
i i ii iv i iv
Å and angles /°: Mo–S 2.2047(8), Ag–S 2.5158(8), Ag–Mo 2.8867(2), S–Mo–S 106.91(2), S –Mo–S 114.73(4), S –Ag–S 117.09(2), S –Ag–
v
iii
S 95.12(4), Mo–S–Ag 75.08(3). Symmetry labels i –y+1/2, x+1/2, –z+1/2; ii y–1/2, –x+1/2, –z+1/2; iii x, y, z–1; iv –x, –y+1, z+1; v x, y, z+1.
2
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4 4
(NH )AgMoS : Synthesis, Structure and Catalytic Activity
water (40 mL), subsequently with EtOH (15 mL) and with diethyl
ether (10 mL). The microcrystalline compound was dried under re-
0.5 mm particle sizes. These particles (1.5 g) were diluted with an
equal volume of 0.2–0.5 mm quartz chips and loaded in 3 mm internal
diameter stainless steel tubing heated within an aluminum block heater.
duced pressure overnight. Yield: 1.95 g (70%) (NH
presence of silver, molybdenum, and sulfur was confirmed by se-
miquantitative energy dispersive X-ray analysis (EDS) with a Hitachi 47.5, 47.5 and 5 v/v% respectively was provided from compressed gas
4 4
)AgMoS . The
2 2
A feed mixture consisting of CO, H and N gases at a fixed ratio of
S-3400 scanning electron microscope (SEM) equipped with a PGT
energy dispersive X-ray analyzer. Found: S 67.4, Mo14.4, Ag 18.2 at.-%.
cylinders (Airgas, UHP grade) with flows controlled by Brooks digital
mass flow controllers at a total flowrate of 300 sccm. An activated
Single-crystalline needles of (NH
amounts of amorphous Ag MoS
taminant: Found: S 59.6, Mo10.4, Ag 30.0 at.-%. Powder X-ray dif-
4
)AgMoS
and possibly Ag
4
are contaminated by tiny carbon trap was used in the line to trap any undesired iron carbonyl
2
4
2
S. EDX of the con-
species, which may originate from the CO cylinder. The reaction prod-
ucts were analyzed using a Siemens MAXUM gas chromatograph with
fraction (PXRD) analyses were performed using an INEL CPS120 a Reoplex precolumn to separate oxygenates and hydrocarbons con-
powder diffractometer (flat geometry) with graphite monochromatized nected in series with a Porapak QS column and a Molsieve 5 Å column
Cu-K radiation. Infra-red spectra of solid samples were obtained with to separate the fixed gases.
α
a Thermo Nicolet 6700 FT-IR spectrometer. Spectra were obtained on
fine powders in diffused reflectance mode under nitrogen atmosphere
–
1
and averaging 256 interferograms with resolution of 2 cm . The TGA
measurements were performed on a Shimadzu TGA-50 thermogravi-
X-ray Crystallographic Study
–
1
Data for 1 was collected with a Bruker Smart Apex II diffractometer
using synchrotron radiation (Advanced Photon Source, Argonne
National Laboratory; λ = 0.4428 Å). The structure was solved by direct
2
metric analyzer in aluminum boats under N flow (30 mL·min ). UV/
vis diffuse reflectance spectra were recorded at room temperature with
a Shimadzu model UV-3101PC double-beam, double monochromator
2
[
23]
methods and refined by full-matrix least-squares on F (all data) using
spectrophotometer as described elsewhere.
Details of the single
[
24]
the SHELXTL program package.
BASF = 0.50481). Hydrogen atoms were refined with a fixed bond
length of 0.96 Å using the DFIX instruction, non-hydrogen atoms were
Table 2. Details of the X-Ray Data Collection and Refinement for assigned anisotropic thermal parameters. A summary of crystal data
1 was refined as a racemic twin
crystal structure refinement of (NH
listed in Table 2 and Table 3.
4 4
)AgMoS and coordinates are
(
(NH
4
)AgMoS
4
(1).
and refinement parameters is given in Table 2. Atomic coordinates are
listed in Table 3.
1
formula
formula weight
T /K
crystal system
space group
a /Å
NH
350.09
100(3)
4
AgMoS
4
Supporting Information (see footnote on the first page of this article):
Details of the EDX analysis of compound 1 and the amorphous by-
product.
Tetragonal
¯
I4
7.8740(3)
5.7733(4)
357.94(3)
2
3.248
8.433
328
Acknowledgment
c /Å 3
V /Å
Financial support from the National Science Foundation is gratefully
acknowledged. We thank DOW Chemical who provided testing facili-
ties for catalytic screening. We thank Dr. David Barton for help with
the catalytic screening.
Z
–
3
ρ /g·cm
μ /mm–1
F(000)
reflections collected
unique data
5408
1258
R
int
0.0380
20
0.0284
0.0707
References
parameters
a)
R
1
b[)IϾ2σ(I)]
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= {Σ[w(|F 2 |2)2]/Σ[w(|F
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4
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)AgMoS (1).
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y
z
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[
[
[
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© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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Date: 10-09-12 10:34:41
Pages: 5
M. Shafaei-Fallah, C. D. Malliakas, M. G. Kanatzidis
ARTICLE
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Received: July 02, 2012
Published Online: ᭿
4
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© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 0000, 0–0

Job/Unit: Z12309
/KAP1
Date: 10-09-12 10:34:41
Pages: 5
4 4
(NH )AgMoS : Synthesis, Structure and Catalytic Activity
M. Shafaei-Fallah, C. D. Malliakas,
M. G. Kanatzidis* ............................................................. 1–5
(
NH )AgMoS : Synthesis, Structure and Catalytic Activity
4 4
Z. Anorg. Allg. Chem. 0000, 0–0
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
5