Applied Catalysis A: General 486 (2014) 49–54
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
In situ studies of structural changes in DME synthesis catalyst with
synchrotron powder diffraction
Kazi Bayzid Kabir , Helen E. Maynard-Caselyb,1, Sankar Bhattacharyaa,∗
a
a
Department of Chemical Engineering, Monash University, Clayton, Victoria -3800, Australia
Australian Synchrotron, 800 Blackburn Road, Clayton, Victoria -3168, Australia
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 June 2014
Received in revised form 14 August 2014
Accepted 22 August 2014
Available online 29 August 2014
Structural changes in a bi-functional dimethyl ether synthesis catalyst (CuO-ZnO-Al O -MgO + ␥-Al O ,
2
3
2
3
BFC), a methanol synthesis catalyst (CuO-ZnO-Al2O3-MgO, MSC) and a methanol dehydration cata-
lyst (␥-Al2O3, MDC), were studied using X-ray synchrotron powder diffraction. The catalysts were
first reduced in 10% H2/He and then treated in a gas containing CO, H2 and CO2. Measurements were
◦
◦
taken at temperatures between 50 C and 500 C. These measurements were complemented by ex-situ
techniques—thermogravimetry (TG) and scanning electron microscopy (SEM)/energy-dispersive X-ray
spectroscopy (EDS). The X-ray diffraction (XRD) results showed that the copper oxide phase, present in
methanol synthesis and bi-functional catalysts, reduced to form Cu0 after reduction. No further chemical
changes were observed for these catalysts. ␥-Al2O3 was resistant to structural and chemical changes.
The copper crystallite sizes of the methanol and bi-functional catalysts were found to increase with
temperature. The extent of deactivation was higher for CuO-ZnO-Al2O3-MgO + ␥-Al2O3 compared to
CuO-ZnO-Al2O3-MgO.
Keywords:
Dimethyl ether
Bi-functional catalyst
Synchrotron radiation
X-ray diffraction
Structural changes
©
2014 Elsevier B.V. All rights reserved.
1
. Introduction
catalyst [10]. A combination of these two catalysts, usually called
a bi-functional catalyst [11], is a relatively new concept and merits
extensive investigation for optimal integration of the two conven-
tional steps.
Single-step conversion of syngas to dimethyl ether (DME) has
received significant attention in the synthetic fuel research area
since 1991 [1]. Conventional two-step synthesis involves produc-
tion of methanol from syngas, purification of methanol and then
dehydration of methanol in a separate reactor to produce DME.
The single-step process eliminates the intermediate step, by incor-
porating both the reactions in the same reactor. This process also
has higher yield than the conventional process, since it removes
the thermodynamic limitation of CO-hydrogenation [2] by in situ
dehydration of methanol to DME. A hydrogenation catalyst (usu-
ally copper based [2]) and a dehydration catalyst (usually ␥-Al O
The properties of the catalyst under reaction conditions can be
different from ambient conditions. Therefore, ex situ characteri-
sation of catalysts does not always provide useful data on how
the catalyst would perform in realistic reaction conditions. The
1
10
high-flux of synchrotron based radiation sources (10 to 10 times
brighter than conventional laboratory X-ray sources [12]) enables
the study of solid catalysts in situ within high-pressure and high-
temperature environment [13].
Advantageous features of synchrotron radiation (SR), such as
beam stability and continuous tunability, have resulted in immense
progress in the application of SR based techniques for catalyst char-
acterisation over the past 20 years [12]. Combination of different
techniques also enables acquisition of complementary data from
the same set of experiments. Conversion of aurichalchite precur-
sor to copper catalyst (for reverse water gas shift) was studied by
recording diffraction and absorption sequentially with a very short
time delay [14]. Time-resolved XRD was combined with Raman
and mass spectroscopy to investigate the behaviour of SAPO-34
under methanol-to-olefin (MTO) condition [15]. XRD identified the
chemical and structural changes in the catalyst. The nature of coke
formed during the MTO condition was observed in the Raman
2
3
[
3]) placed in a single reactor are responsible for one-step con-
version of syngas to DME. Copper-based catalysts have various
industrial applications (i.e. methanol synthesis, water-gas shift,
methanol reforming) and hence extensively studied over the years
[
∗ Corresponding author.
Current address: Bragg Institute, Australian Nuclear Science and Technology
1
Organisation, Kirrawee DC, NSW-2232, Australia.
0
926-860X/© 2014 Elsevier B.V. All rights reserved.