Investigation of the Inhibiting Role of Hydrogen in the Steam Reforming of Methanol

Article abstract of DOI:10.1002/cctc.201900738

Steam reforming of methanol (SRM) was investigated over palladium zinc oxide catalyst modified with chromium, copper supported on alumina modified manganese oxide and commercial copper catalyst supported on zinc oxide modified with alumina. These catalysts showed high activity and selectivity towards hydrogen and carbon dioxide at low reaction temperatures. Temperature-programmed desorption, diffuse reflectance infrared Fourier-transform spectroscopy and catalytic performance studies, indicated that the presence of hydrogen in the gas stream influenced the course of SRM reaction. Such effects were related to hydrogen concentration over the catalysts, the reaction temperature and also the type of catalyst. Semi-kinetic catalytic studies evidenced that an increase in hydrogen concentration in gas stream led to the decrease of methanol conversion at low-reaction temperatures and decrease of selectivity to CO₂ at high reaction temperatures. It was pointed out that strong interactions of hydrogen with the surface of catalysts may retard transformation of surface species into the SRM products.

Full text of DOI:10.1002/cctc.201900738

Accepted Article
Title: Investigation of inhibiting role of hydrogen in the steam reforming
of methanol
Authors: Wojciech Gac, Witold Zawadzki, Magdalena Greluk, Grzegorz
Słowik, Andrzej Machocki, Joan Papavasiliou, and George
Avgouropoulos
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemCatChem 10.1002/cctc.201900738
Link to VoR: http://dx.doi.org/10.1002/cctc.201900738
A Journal of
www.chemcatchem.org

10.1002/cctc.201900738
ChemCatChem
FULL PAPER
Investigation of inhibiting role of hydrogen in the steam
reforming of methanol
Wojciech Gac*[a], Witold Zawadzki[a], Magdalena Greluk[a], Grzegorz Słowik[a], Andrzej Machocki[a],
Joan Papavasiliou[b,c], George Avgouropoulos*[c]
In Memoriam of Professor Andrzej Machocki
discussion. Methanol, in contrast to hydrogen, is a liquid fuel,
which can be easily stored, delivered to the end users and
converted to hydrogen e.g. via the steam reforming of methanol
(SRM) at relatively low temperatures (lower than 250 oC) and
ambient pressure:
Abstract: Steam reforming of methanol (SRM) was investigated over
palladium zinc oxide catalyst modified with chromium, copper
supported on alumina modified manganese oxide and commercial
copper supported on zinc oxide modified with alumina. These
catalysts showed high activity and selectivity towards hydrogen and
carbon dioxide at low reaction temperatures. Temperature-
programmed desorption, diffuse reflectance infrared Fourier-
transform spectroscopy and catalytic performance studies, indicated
that the presence of hydrogen in the gas stream influenced the course
of SRM reaction. Such effects were related to hydrogen concentration
over the catalysts, the reaction temperature and also the type of
catalyst. Semi-kinetic catalytic studies evidenced that an increase in
hydrogen concentration in gas stream led to the decrease of methanol
conversion at low-reaction temperatures and decrease of selectivity
to CO2 at high reaction temperatures. It was pointed out that strong
interactions of hydrogen with the surface of catalysts may retard
transformation of surface species into the SRM products.
CH3OH + H2O ⇆ CO2 +3H2 ΔHo298K = 49.4 kJ mol-1
(1)
Product stream may contain up to 75% of H2 and small quantities
of CO (ca. 0.5-2%) which allows integration of the small and
portable SRM units and proton exchange polymer electrolyte fuel
cells (PEMFCs) for electricity production.
Removal of reaction products in a reversible processes is a
common strategy to shift the equilibrium of the reaction to the
product side. This approach can be also used to reduce the
concentration of that component which acts as an inhibitor of the
reaction rate. Fundamentals of SRM equilibrium are very well
established and several studies have been published,[1-3] all
arriving at more or less similar findings. Recently, Kunkes and
Behrens[4] reviewed methanol chemistry, including SRM process.
Commercially available copper-based catalysts (i.e. Cu/ZnO and
Cu/ZnO/Al2O3) have been widely studied for hydrogen production
from methanol.[5-29] Relevant experimental studies have been also
performed for noble metal catalysts, mainly palladium and
platinum supported on zinc, indium and gallium oxides.[30-45]
Unlike methanol synthesis, which is also carried out on similar
catalysts and temperatures, SRM process is not limited by
thermodynamic constraints at low temperatures. Thermodynamic
restrictions play a lesser role in SRM, as the inverse of methanol
synthesis, steam reforming and decomposition reactions can be
considered irreversible at atmospheric pressure. However small
amounts of carbon monoxide could be produced due to the
methanol decomposition (MD) and reverse water-gas shift
reaction (RWGS), accordingly to the equations (2) and (3), and
such processes become especially significant at high
temperatures (above 400 oC):[46]
Introduction
Development of novel catalysts and process engineering for
efficient utilization of fossil fuels and renewable energy sources
belongs to the most important contemporary challenges. One of
the most attractive energy carriers is methanol. It is produced now
in large quantities from synthesis gas, which is obtained by the
conversion of fossil fuels in such processes as the steam
reforming or partial oxidation of hydrocarbons. New possible ways
of methanol production by conversion of biomass, utilization of
carbon dioxide and hydrogen produced by the application of
renewable wind or solar energy are the topics of actual wide
CH3OH ⇆ CO +2H2
CO2 + H2 ⇆ CO +H2O
ΔHo298K = 90.2 kJ mol-1
ΔHo298K = 41.2 kJ mol-1
(2)
(3)
Sorption enhanced processes, utilizing CO2 adsorbents and H2
membrane reactors have been proposed as possible methods to
increase methanol conversion and improve selectivity.[47-51]
Recently, we have demonstrated that this objective can be also
achieved via in-situ electrochemical pumping of H2 in an internal
reforming methanol fuel cell, where at atmospheric pressure and
[a]
Dr. hab. W. Gac, Prof. UMCS, Dr. W. Zawadzki, Dr. M. Greluk, Dr.
G. Słowik, Prof. Dr. hab. A. Machocki
Department of Chemical Technology,
Faculty of Chemistry
University of Maria Curie-Skłodowska
3 M. Curie-Skłodowska Sq.
20-031 Lublin (Poland)
E-mail: wojciech.gac@umcs.lublin.pl
Dr. J. Papavasiliou
Foundation for Research and Technology-Hellas (FORTH)
Institute of Chemical Engineering Sciences (ICE-HT)
P.O. Box 1414 GR-26504 Patras (Greece)
E-mail: jpapav@iceht.forth.gr
o
low temperatures in the range of 200 - 210 C, the equilibrium
methanol conversion is close to 100%.[22,27,31,52-54] In addition to
that, inhibition of the reaction rate by the produced carbon
monoxide is minimized since its concentration is well below the
WGS equilibrium and follows secondary pathways, however all
[b]
[c]
Dr. G. Avgouropoulos
Department of Materials Science
University of Patras
GR-26504 Rio Patras (Greece)
E-mail: geoavg@upatras.gr
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/cctc.201900738
ChemCatChem
FULL PAPER
the kinetic reports on SRM process do not contain a relative
parameter in the proposed equations.
critical active sites. Activation of the catalysts takes place either
ex-situ, where exposure in air after this treatment should be done
very carefully in order to avoid pyrophoricity phenomena (this
applies in copper catalysts) or in-situ under the reaction mixture.
Especially for the copper catalysts reduction takes place at low
temperature ca. 200-250oC, and if non-concentrated hydrogen
mixtures are employed sintering is avoided. Up to our knowledge
deactivation of the catalysts due to exposure in hydrogen is not
taking place, and this inhibition effect is fully reversible. To the
best of our knowledge the identification and comparison of such
effects for commercial copper catalysts supported on aluminum
modified zinc oxide, and copper catalysts supported on
manganese modified by small amounts of aluminum, as well as
highly active palladium on zinc oxide catalyst modified by
chromium, of high potential applicability has not been performed
and widely discussed.
On the other hand, a SRM reaction rate can be inhibited by
hydrogen, and this effect has been reported by many research
groups working on methanol reforming process.[5-16] The negative
order dependence on hydrogen partial pressure has been
included in various kinetic equations. This effect could be
especially important in a long packed bed, tubular or long
microchannel reactors, where the stream of high hydrogen
concentration flows through the large part of the catalytic bed. In
a practical process, for example a monolithic reactor, a gradient
in the concentration of hydrogen is expected, where hydrogen
content will be enriched towards the exit of the reactor. We have
recently presented the double reformer arrangement, where a
methanol reformer is introduced inside the anode sides of a fuel
cell stack. The second layer of the reformer is fed with hydrogen
rich mixture produced from the first layer, however due to the high
concentration of hydrogen in this reformate, high inhibition takes
place and methanol conversion is not significantly improved.[55]
Diverse power-law and Langmuir–Hinshelwood rate expressions
have been proposed in the literature and were reviewed and
discussed by Lee et al.[10] The model proposed by Jiang et al. was
based on the consideration of elementary surface reactions,
which involved reaction of methanol with water to carbon
monoxide and hydrogen and subsequent WGS reaction for the
production of hydrogen and carbon dioxide.[5] This model
underlined significant role of both methanol and hydrogen
adsorption on the rate of SRM reaction. This mechanistic model
has been extended further by Peppley et al., who discussed a
series of surface reactions occurred on two types of active sites,
responsible for methanol decomposition and water-gas shift
reaction.[6,7] Taking into account predictions of the models, one
can state, that the nature of surface sites and hydrogen
concentration may affect the rate of SRM reaction. The inhibiting
role of H2 on the kinetics of the steam reforming reaction can be
attributed to the effect of H2 content in the stream on the
equilibrium-kinetics individual surface reactions, such as
dehydrogenation of methoxy species, further successive
transformation to formate or methyl formate intermediates, as well
as formation of OHad groups originating from the dissociative
adsorption of water. However, most of kinetic studies on SRM
were based on the application of copper catalysts.
Results and Discussion
Properties of the catalysts
Commercial catalyst (denoted CuZnAlOx) contains ca. 36 wt. %
of Cu, while the content of active metal in the CuMnAlOx catalyst
is smaller (ca. 25 wt. %) (Table 1). Palladium catalyst contains 4.6
wt. % of Pd and ca. 17 wt.% Cr.[56] The catalysts show different
reducibility. The temperature-programmed reduction curves of
catalysts are presented in Figure 1. Reduction of commercial
CuZnAlOx catalyst starts at around 120 oC. The main peak is
slightly asymmetric towards the lower temperatures. The
maximum of the TPR peak is located at ca. 245 oC. Small
amounts of oxide phases are reduced in the range of 300 - 600
oC. The observed peaks are mainly connected with reduction of
copper oxide, according to the reaction equation CuO + H2 → Cu0
+ H2O. High temperature peaks can be mainly attributed to the
reduction of ZnO support.
Table 1. Properties of catalysts; contents of active metals, specific surface
area (SBET), active surface area of catalysts (Sa), and mean crystallite size
of active metals (dCh).
Catalyst
Content (wt. %)
SBET
Sa
dCh
Pd
Cu
The aim of this work was the investigation of hydrogen inhibition
effects in the SRM process over different types of catalysts
employing semi kinetic measurements, accompanied with
temperature-programmed desorption techniques and in-situ
diffuse reflectance infrared Fourier-transform spectroscopy.
Highly active and selective catalysts were selected from two
groups of SRM catalysts containing different active metallic sites,
formed either by copper or palladium-zinc alloy. The preparation
methods, the composition of the catalysts within each group,
including the contents of the active phase, the type of modifiers
and activation conditions were designed earlier in advance to
obtain optimal catalytic performance. Copper-manganese and
palladium-zinc oxide catalysts are active in this reaction under
reduced form, where metallic copper and the PdZn alloy are the
PdZnCrOx
CuMnAlOx
CuZnAlOx
4.60±0.14
-
89.0
19.1
83.2
6.0
3.9
-
-
24.9±0.9
35.9±1.3
5.0
34.0
16.0
14.7
The reduction profile of CuMnAlOx catalyst is more complex. Two
well resolved and partially overlapped reduction peaks, located
between 150 - 300 and 300 - 500 oC with maximum at ca. 340 oC
can be distinguished. The position of the low-temperature peak
can be attributed to the reduction of copper species in the
CuMnAlOx catalyst. High temperature peaks can be ascribed to
the reduction of lattice spinel, mainly via successive
transformation of manganese ions to the lower oxidation state
This article is protected by copyright. All rights reserved.

10.1002/cctc.201900738
ChemCatChem
FULL PAPER
o
Mn4+→ Mn3+→Mn2+.[57,58] This catalyst cannot be fully activated as
CuZnAlOx catalyst at 220 oC to obtain high activity and selectivity
towards hydrogen production in the SRM reaction. Therefore, a
higher reduction temperature equal to 280 C was used prior to
the SRM studies.
optimum activation temperature was selected to be 350 C. The
o
active surface area of PdZnCrOx catalyst reduced at 350 C is
equal to 6 m2 g-1. The average metallic crystallite size calculated
from the chemisorption studies (dCh) is equal to 3.9 nm. Formation
of PdZn alloy was identified by the microscopic studies. HRTEM
images of PdZnCrOx catalyst after reduction at 350 oC with
identification of PdZn alloys are presented in Figure 2a.
o
a)
Figure 1. Temperature-programmed reduction curves of catalysts.
The TPR curve of PdZnCrOx catalyst shows low-temperature
peak located between -50 and 120 oC, attributed to the
consumption of hydrogen during reduction of palladium oxide
species: PdO + H2 → Pd0 + H2O.[59-61] Minor shoulder at ca. 60 oC
indicates palladium hydride decomposition. Wide small high-
temperature reduction peak can be ascribed to the partial
reduction of support. The reduction of chromium modified zinc
oxides at high-temperatures can be attributed to the partial
reduction of chromium species (Cr6+ → Cr3+) and zinc oxide (Zn2+
→ Zn0), which facilitate formation of finely dispersed PdZn alloy
crystallites.[56]
b)
c)
The active surface area and Cu crystallite size after different
activation conditions is presented in the Supplementary Material.
CuZnAlOx catalyst shows the highest active surface area among
investigated catalysts. This effect results from the high copper
loading and also the presence of small Cu crystallites. The mean
size of copper crystallites in the CuZnAlOx catalyst after reduction
at 220 oC is equal to 16 nm. Copper-manganese catalyst shows
lower reducibility hence the activation was performed at higher
temperature than CuZnAlOx catalyst (i.e. 280 oC). The active
surface area and larger mean Cu crystallite size is observed for
this catalyst. In spite of high reducibility of palladium oxide phases
in PdZnCrOx catalyst, the reduction was performed at higher
temperature to create PdZn alloy phases. The surface atoms of
such phases form active centers in SRM process.[30] High-
temperature TPR peaks indicate that PdZn alloys can be formed
in the PdZnCrOx catalyst above 300 oC. It is worth to note that an
application of high reduction temperatures, i.e. 500 or 600 oC may
lead to fast alloy formation and simultaneously to the strong
sintering of metallic nanoparticles and sublimation of ZnO. An
Figure 2. TEM and STEM images of PdZnCrOx catalyst; phase identification
and distribution based on interplanar distance (a), PdZn crystallite size
distribution from TEM studies (b) and STEM images with identification of
elements (c)
This article is protected by copyright. All rights reserved.

10.1002/cctc.201900738
ChemCatChem
FULL PAPER
Highly dispersed PdZn nanoparticles with different exposed
planes are visible. The catalyst contains PdZn crystallites of the
size ranging from ca. 1 to 8 nm (Fig. 2b). Mean size of PdZn
crystallites determined from the microscopic studies (dTEM) is
equal to 3.8 nm, which well correspond to size of crystallites
calculated from the results of hydrogen chemisorption. The
support is a multi-phase material and consists of a mixture of
monometallic oxides of ZnO and Cr2O3 with different size and
exposed planes, while other complex oxide systems, such as
ZnCr2O4, ZnCr2O5 are also present. Such species may retard
different strength. Small, middle-temperature maxima are located
at ca. 160 and 200 oC. Two large high-temperature peaks can be
o
o
found at 375 C and 460 C, respectively. The area under TPD
curve recorded for PdZnCrOx catalyst is smaller than for
commercial CuZnAlOx catalyst, but higher than for CuMnAlOx
catalyst. The corresponding maxima on the TPD curves of the
CuMnAlOx catalyst are at higher temperatures compared to the
CuZnAlOx catalyst. More evident shift is observed for PdZnCrOx
catalyst. Such effects indicate the increase of the strength of the
sites. The observed changes of the surface properties of catalysts
sintering of PdZn crystallites during activation and SRM operation, imply different stability of intermediate surface species formed
and on the other hand can be responsible for suitable activation
and transformation of surface intermediates in the SRM process.
STEM and element map images reveal high dispersion of metallic
nanoparticles located on the homogeneously distributed zinc and
chromium oxides (Figure 2c).
during elementary surface SRM reactions. The increase of the
strength of the sites may enhance abstraction of hydrogen from
the surface intermediates. Stronger adsorption sites can be
regarded as more active in the initial stages of dehydrogenation
elementary surface reactions. However, higher strength of such
sites may hinder surface diffusion of hydrogen atoms and
subsequent desorption of H2 molecules. Hydrogen is one of the
main reaction products in the steam reforming of methanol, hence
the increase of the contribution of the strong sites on the surface
of catalysts may additionally influence the course of reaction,
especially when hydrogen concentration in the fed stream is
increased. Adsorption sites on the surface of palladium catalysts
are stronger than in copper catalysts, and thus the inhibition effect
associated with hindering the transformation of surface groups
can more pronounced.
Figure
3 presents temperature-programmed desorption of
hydrogen from the activated catalysts. Three partially overlapped
desorption peaks can be found on the TPD profiles of copper-
based catalysts. Their presence can be connected with formation
of different active sites on copper crystallites.
Catalytic properties
All three catalysts show high activity and selectivity in SRM
reaction. Methanol conversion with respect to the reaction
temperature is presented in Figure 4. The catalysts were activated
under hydrogen streams at different temperatures, with respect of
different reducibility and active phase formation, as discussed
above. The copper-based catalysts required activation at much
lower temperatures than palladium-based catalyst, desirably
closer to the working temperature of the steam reforming of
methanol, and more especially closer to the working temperature
of an internal reforming methanol fuel cell, i.e. 200-220 oC.
[22,27,31,52,53] Methanol conversion in the SRM reaction in the range
of 180-340 oC over commercial CuZnAlOx catalyst is higher than
in the presence of CuMnAlOx. This behavior can be attributed to
the higher active surface area of commercial catalyst, i.e. larger
number of active sites. The activity of commercial and palladium-
based catalysts is quite similar at low temperatures (in the range
Figure 3. Temperature-programed desorption of hydrogen from the catalysts.
Strong peaks, with maxima located at ca. 35, 130 and 252 oC are
observed for CuZnAlOx catalyst. In the case of CuMnAlOx
catalyst, these peaks are centered at ca. 35, 181 and 311 oC. The
intensity of corresponding peaks is lower than for commercial
CuZnAlOx catalyst, which is in general agreement with the
changes of active surface area, determined by the N2O
decomposition (Table 1). Different contribution of suitable TPD
peaks for these two types of copper catalysts can be observed,
which indicates different nature and number of suitable active
copper sites in catalysts. The adsorption step was performed at
higher temperature for Pd-based catalyst (100 oC), hence low-
temperature hydrogen desorption peaks are not observed for this
sample. The irregular course of TPD profile for PdZnCrOx catalyst
may indicate the presence of several types of adsorption sites of
o
of 180 – 200 C). However, the conversion of methanol sharply
increases for the former catalyst at temperatures higher than 200
oC. In turn, the activity of palladium catalyst in the range of 210-
260 oC is comparable to the activity of CuMnAlOx catalyst.
o
Complete conversion of methanol is observed above 340 C for
all three catalysts. Copper-based catalysts show excellent
selectivity towards CO2 at low temperatures, keeping CO
selectivity below 1% up to the reaction temperature of 260 oC
(Figure 4b). Nevertheless, CO production becomes competitive
with further increase of the reaction temperature, resulting in
gradual increase of the corresponding selectivity for copper-
based catalysts. It is interesting that the selectivity towards CO
This article is protected by copyright. All rights reserved.

10.1002/cctc.201900738
ChemCatChem
FULL PAPER
production under such conditions is not strongly related to the
number of active sites and their strength.
increase of the partial pressure of hydrogen, and thus may
influence the transformation of reaction intermediates and change
the reaction selectivity. To study the inhibition effects resulted
from the presence of produced hydrogen in the stream and
intensification of suitable surface processes, the reaction mixture
was enriched with hydrogen. Several tests were carried out for all
catalysts using reaction mixtures containing additional amounts of
a)
b)
hydrogen. Figure
5 shows methanol conversion and CO
selectivity determined at selected temperatures under different
initial hydrogen concentration in the feed stream. The total flow
rate of the inlet mixture was kept constant, partially replacing
nitrogen with hydrogen. Total hydrogen content in the gas stream
was calculated as the sum of the amount of hydrogen introduced
to the reactor inlet and the amount of hydrogen produced in the
catalytic reaction.
Temperature / o
C
Temperature / o
C
c)
a)
b)
Temperature / o
C
Hydrogen concentration / %
Hydrogen concentration / %
Figure 4. Methanol conversion (a), selectivity to carbon monoxide (b) and water
conversion (c) in the steam reforming of methanol in the presence of copper
and palladium-based catalysts.
c)
d)
In turn, PdZnCrOx catalyst presents slightly higher CO selectivity
o
(at the level of 1–2%) in the range of 180-300 C, as compared
with copper-based catalysts. Similar trend of CO selectivity
changes with the increase of reaction temperature as for copper
catalysts is observed. The obtained palladium catalyst shows
more advantageous catalytic properties at high temperatures.
Low selectivity of PdZnCrOx catalyst to CO can be in part related
to the redox properties of ZnCrOx support, resulted from the
improved oxygen transfer to the partially dehydrogenated
intermediate surface species.[56] However further studies are
necessary for detailed explanation of such effects. The increase
in CO selectivity at high temperatures and the drop of water
conversion (Figure 4c) can be related to the increase of the rate
of the reverse water-gas shift reaction (CO2 + H2 ⇆ CO + H2O)
and methanol decomposition (CH3OH ⇆ CO +2H2). Overall, it can
be concluded that the commercial CuZnAlOx catalyst is the most
active and selective one towards hydrogen production in the
temperature region of 180-300 oC. Palladium-based catalyst is
slightly more active than the CuMnAlOx catalyst in the low
temperature range and more selective to CO2 at high
temperatures.
Hydrogen concentration / %
Hydrogen concentration / %
e)
f)
Hydrogen concentration / %
Hydrogen concentration / %
Hydrogen and carbon dioxide are the main reaction products of
the steam reforming of methanol. Hence both components may
influence the course of the SRM reaction. SRM processes are
often carried out in non-gradientless reactors, hence the increase
of methanol conversion along the catalytic bed leads to the
Figure 5. Hydrogen inhibition effects
concentration in the feed and methanol conversion and CO selectivity for
CuZnAlOx (a,b), CuMnAlOx (c,d) and PdZnCrOx (e,f) catalysts.
-
relation between total hydrogen
This article is protected by copyright. All rights reserved.

10.1002/cctc.201900738
ChemCatChem
FULL PAPER
An introduction of hydrogen to the reaction feed stream leads to
the drop of methanol conversion. This effect is more intense at
low temperatures and low methanol conversions for all three
catalysts On the other hand, when methanol conversion is close
to the 90% under specified reaction conditions (high activity of
catalysts), this negative trend becomes less evident The
presence of additional amounts of hydrogen in the reaction
mixture has a minor effect on CO selectivity at low temperatures
and becomes more intense at high temperatures, where methanol
conversion gets high values. It has to be noted that palladium-
based catalyst presents lower CO selectivity as compared with
copper-based catalysts, thus less affected by hydrogen presence
at high temperatures. Copper catalysts supported on modified
zinc oxide are known as active low-temperature WGS catalysts.
Hence this effect can be partially explained taking into account
higher activity of catalysts in WGS reaction. Accordingly to the
RWGS reaction equation (3), an introduction of hydrogen to the
reaction zone should lead to the shift of the equilibrium to the right
side, i.e. production of carbon monoxide. An increase of the slope
with respect to the hydrogen concentration as temperature
increase may be due to kinetic reasons – higher activity of
catalysts in WGS reaction.
between 250 and 400 oC. Low-temperature peak positions are not
strongly influenced by the presence of hydrogen in the carrier gas
a)
b)
Temperature / o
C
Temperature / o
C
c)
d)
Dissociative adsorption of methanol on the surface of catalysts is
commonly regarded as the initial step in SRM process. In this
work, formation of successive surface species on the copper and
palladium catalysts and transformation towards gaseous products
was studied by means of methanol temperature-programmed
desorption techniques with respect to the hydrogen presence in
the gas stream. Online monitoring of evolved gases in the
presence and absence of hydrogen in the inlet stream was
performed via a mass spectrometry, and the obtained signal lines
are presented in Figure 6. The main products detected during
TPD in the outlet gas stream are hydrogen (indicated by signal
changes of m/z = 2), water (m/z = 18), carbon monoxide (m/z =
28), formaldehyde (m/z = 29), methanol (m/z = 31) and carbon
dioxide (m/z = 44). The intensity of desorbed methanol under
helium flow is very weak for all catalysts, suggesting the
transformation of adsorbed methanol species at temperatures as
Temperature / o
C
Temperature / o
C
e)
f)
Temperature / o
C
Temperature / o
C
o
low as 100 C to the specified surface intermediate species. In
contrary, the intensity of desorbed methanol under the flow of
H2/He gas stream is much stronger. Two temperature regions of
Figure 6. Temperature-programmed desorption of methanol from the surface
of catalysts. The intensity of selected ions in mass spectrometry analysis.
Dashed lines – desorption in the flow of He, solid lines desorption in the flow of
the mixture H2/He.
o
methanol desorption can be found, i.e. (i) 100 – 250 C and (ii)
o
300 – 400 C (Figure 6a). The position of the low temperature
maximum ascribed to the weakly interacted methanol with the
surface of catalysts is almost the same for all three samples. One
can also observe formation of higher amounts of formaldehyde in
the flow of H2/He stream (the recorded signal resulted in part from
fragmentation of formaldehyde and methanol in the mass
spectrometer, Figure 6b). This effect can be related to the
retardation of the deep transformation of adsorbed methanol
molecules and reversible reaction of surface species with
hydrogen as result of new hydrogen adsorption/desorption
balance or changes in the oxidation state of Cu surface sites. A
similar effect of hydrogen is visible in palladium catalyst. The
maximum of the first desorption peak of hydrogen can be found
at ca. 200 oC (Figure 6c). The high temperature peaks are located
The lowest temperatures of corresponding hydrogen maxima are
observed for CuZnAlOx catalyst. However, hydrogen is evolved
from suitable active sites located on the surface of palladium-
based catalyst at higher temperatures. This is in good correlation
with the data obtained from TPD of hydrogen experiments, as
discussed above. Small amounts of CO are desorbed at low
temperatures (100 – 200 oC) (Figure 6d). The strong peaks of CO
o
are observed for all the catalysts between 200 and 400 C. The
highest temperature of CO maximum desorption peak is visible
for palladium-based catalyst. It is interesting that the presence of
hydrogen slightly shifts the desorption maxima to higher
temperatures, indicating inhibition of the transformation of surface
This article is protected by copyright. All rights reserved.

10.1002/cctc.201900738
ChemCatChem
FULL PAPER
species also to carbon monoxide. CO2 is desorbed from the
surface of the catalysts within the temperature range of 150 - 350
oC (Figure 6e). Two well resolved maxima are observed for
CuZnAlOx catalyst. An introduction of hydrogen into the carrier
gas leads to the decrease of the intensity of low-temperature
peaks and increase of the desorption temperatures of CO2.
Similar effect is observed for CuMnAlOx catalyst. In the case of
palladium-based catalyst, the maximum is shifted from about 200
to 250 oC. The changes of peaks positions are smaller for copper-
based catalysts. Formation of CO via methanol decomposition
or/and RWGS reactions is affected by the presence of additional
amounts of hydrogen in the inlet stream. However, the influence
of hydrogen on the formation and subsequent desorption of CO2
is much more evident. Such effects can be connected with
retardation of the formation of CO2 as primary product of SRM
process or contribution of CO2 in the RWGS reaction.
and 1360 cm-1, respectively. Similar vibration bands are observed
for CuMnAlOx and PdZnCrOx catalysts.
The changes of the nature of the species formed on the surface
of copper and palladium-based catalysts during adsorption and
then desorption of methanol in the flow of inert gas (argon) and
hydrogen-argon mixture were studied by DRIFTS method. The
catalysts were pre-activated in a similarly way as described above.
The obtained DRIFTS spectra recorded at different desorption
temperatures are presented in Figures 7-9.
Wavenumber / cm-1
Figure 8. DRIFTS spectra of methanol desorption from the CuMnAlOx catalyst
in the flow of Ar (red) and H2/Ar mixture (blue).
It is worth to note that vibration bands of νas(OCO) are shifted to
lower wavenumbers (ca. 1580 cm-1) for these catalysts. One can
also observe different shape of individual peaks. An increase of
desorption temperature leads to the gradual decrease of the
intensities of IR vibrations of methoxy and formate species.
Spectra presented in the Figure 7 show that methoxy and formate
species are also formed in the presence of hydrogen in the gas
stream. However slightly higher ratio of methoxy to formate
vibration intensities is observed in the presence of hydrogen for
all three catalysts at low temperatures. This effect may indicate
slight retardation of subsequent transformation of methoxy to
formate intermediates.
Studies point out that methanol during adsorption on the surface
of copper- and palladium-based catalysts can be transformed to
methoxy and formate species at relatively low temperatures (100
oC). However taking into account that dissociative adsorption of
methanol with formation of methoxy and formate species may
also occur on oxide supports, such as ZnO, Al2O3, MnOx, CrZnOx,
one can expect that support may also participate in the formation
of intermediate surface species in the SRM process.[62-65] Almost
all proposed reaction mechanisms of SRM assume, that the
reaction takes place on the surface of catalysts via formation of
methoxy species, which are then transformed to the
formaldehyde, and next to formate or methyl formate
intermediates with stepwise hydrogen abstraction and/or
subsequent transformation of such species.[12,13] The largest
energy barrier has been often reported for the dehydrogenation of
methoxy to formaldehyde species.[66] Formation of methyl formate
was proposed in the literature as result of the surface reaction
between methoxy and formaldehyde species.[66-68] Such species
can be further transformed to CO2 via subsequent reaction with
hydroxyl groups, decomposition of formic acid as well as other
routes. Methyl formate was suggested as intermediate product,
Wavenumber / cm-1
Figure 7. DRIFTS spectra of methanol desorption from the CuZnAlOx catalyst
in the flow of Ar (red) and H2/Ar mixture (blue).
The absorption bands located at 2930 and 2820 cm-1 recorded at
100 oC after adsorption of methanol and then the flush of an inert
gas observed on the spectra of CuZnAlOx catalyst can be
ascribed to the asymmetric νas(CH3) and symmetric νs(CH3)
stretching vibrations.[62-65] Strong absorption band at 1055 cm-1
with weak shoulder at 1100 cm-1 is observed in the fingerprint
region and can be attributed to the stretching vibrations of ν(C-O)
in differently coordinated methoxy groups. The shoulder at ca.
2890 cm-1 together with ν(OCO) suitable vibration bands indicates
the presence of formate species. Stretching ν(CH) vibration bands
correspond with asymmetric νas(OCO) and symmetric stretching
vibrations of νs(OCO) in formate groups located at ca. 1600 cm-1
This article is protected by copyright. All rights reserved.

10.1002/cctc.201900738
ChemCatChem
FULL PAPER
which could be also transformed to CO in the following reactions: Conclusions
HCOOCH3 → 2CO + 2H2 and HCOOCH3 → CO + CH3OH.[69-70]
However, considering the influence of hydrogen on the changes
of CO selectivity discussed above, the last route in our opinion
can be rather diminished in the SRM process. An increase in CO
selectivity with the increase of hydrogen concentration was
recorded at elevated temperatures for all three catalysts. The
equilibrium of methyl formate decomposition reactions to CO and
H2 equilibrium should be shifted to the left side in the presence of
an excess of hydrogen.
The course of the steam reforming of methanol has been
investigated over three types of catalysts, i.e. novel chromium
modified zinc oxide palladium catalyst (PdZnCrOx), copper
supported on aluminum modified manganese oxide (CuAlMnOx)
and commercial catalyst (CuAlZnOx). All these catalysts showed
high activity and relatively low selectivity to carbon monoxide at
low reaction temperatures. Palladium catalyst exhibited more
favorable properties at high reaction temperatures, where lower
selectivity to CO than over copper-based catalysts was observed.
The influence of the inhibitory effects of hydrogen on the activity
and selectivity of different types of catalysts was demonstrated. In
order to better understand the effect of hydrogen on the steam
reforming of methanol over copper and palladium-based catalysts,
the catalytic tests were carried out in the presence of a reaction
mixture consisting of methanol and water vapor enriched with
hydrogen of different concentration. Studies indicated that the
presence of hydrogen in the gas stream may influence methanol
conversion and selectivity of catalysts to carbon monoxide. This
effect was related to the reaction temperature and nature of
catalysts. The drop of methanol conversion with an increase of
hydrogen concentration in the gas stream was especially visible
at low and moderate temperatures, whereas an increase of
selectivity to CO was manifested at higher temperatures.
Temperature-programmed desorption of hydrogen and methanol,
as well as diffuse reflectance infrared Fourier-transform
spectroscopy studies of methanol desorption indicated that the
course of surface reactions was influenced by the presence of
hydrogen in the feed stream. It was pointed out that strong
interactions of hydrogen with the surface of catalysts may retard
transformation of surface species formed under reaction
conditions into the SRM products. However, more detailed
experimental and computational studies of the mechanism of
reaction on copper and palladium-based catalysts in the absence
and presence of hydrogen in the gas stream are necessary in
order to elucidate the role of particular reaction products on the
course of individual surface reaction stages.
Wavenumber / cm-1
Figure 9. DRIFTS spectra of methanol desorption from the PdZnCrOx catalyst
in the flow of Ar (red) and H2/Ar mixture (blue).
The results of the present work indicate that the abstraction of
hydrogen atoms from the intermediate surface species adsorbed
on the metal crystallites or support sites by adjoining surface
centers probably located on metal crystallites can be hindered in
the presence of hydrogen in the fed stream. It is difficult to
unambiguously specify on the basis of the conducted studies,
which of the subsequent stages of dehydrogenation and surface
transformation of adsorbed species is most strongly inhibited by
hydrogen, and further detailed studies of the reaction mechanism
are required. However the obtained results indicate that surface
sites which strongly interact with hydrogen may facilitate
dehydrogenation reactions of surface species under SRM
conditions, but simultaneously, when hydrogen is present in the
fed stream, may also retard such transformation due to the strong
bonding of hydrogen from the gas phase. Taking into account that
methanol conversion and simultaneous production of hydrogen at
intermediate temperatures are high, this effect could be significant.
An increase in the reaction temperature leads to an increase in
the mobility of hydrogen atoms and the desorption of H2
molecules, but in the presence of strong adsorption sites on the
catalysts this effect can be still pronounced even at elevated
temperatures.
Experimental Section
Synthesis of catalysts
PdZnCrOx. The catalyst was synthesized by the impregnation of as-
prepared zinc oxide support modified with chromium. The ZnCrOx support
was obtained by the co-precipitation method.[56] 47.2 g of zinc acetate
(Zn(CH3COO)2, Sigma-Aldrich) and 39.5
g of chromium nitrate
(Cr(NO3)3∙9H2O, Sigma-Aldrich) were dissolved in 150 mL of water. 2 M
aqueous solution of ammonium carbonate ((NH4)2CO3) was dropped into
vigorously stirred mixed solution of salts maintained at the temperature of
40 oC up to pH = 8.5. After aging for 3 h at 55 oC, the precipitate was
filtrated and washed thoroughly with deionized water and then rinsed with
96% ethanol to remove NH4+ and any remaining salts. The precipitate was
dispersed in 100 mL of absolute ethanol under vigorous stirring, filtrated
and washed with ethanol. The obtained solid support was aged overnight
at room temperature, dried for 12 h at 110 oC and then calcined at 400 oC
for 6 h. Prior to the impregnation, the support was dried in air at 110 °C for
1 h, followed by suspension of 2 g with 150 mL of a 0.007 M of acetone
This article is protected by copyright. All rights reserved.

10.1002/cctc.201900738
ChemCatChem
FULL PAPER
solution of palladium (II) acetylacetonate (Pd(C5H7O2)2, Sigma-Aldrich)
and vigorously mixied at the room temperature for 2 h. After impregnation
the catalyst precursor was aged overnight at room temperature, dried at
110 °C for 12 h and calcined at 250 °C for 1 h in order to decompose
palladium precursor. Prior to the catalytic tests, the catalyst was activated
in H2 at 350 oC for 1 h.
mapping was carried out in the STEM mode by collecting point by point
EDS spectrum of each of the corresponding pixel in the map. Palladium
catalyst prior to the microscopic studies was reduced in the quartz flow
reactor in the flow of hydrogen at 350 oC for 1 h. After the decrease of the
temperature to 25 C, hydrogen was switched for inert gas, and then for
5%O2/He mixture.
o
CuMnAlOx. Synthesis of catalyst was carried out via urea-nitrates
combustion method.[27,28,53] Manganese nitrate (Mn(NO3)2∙6H2O), copper
nitrate (Cu(NO3)2∙3H2O), aluminium nitrate (Al(NO3)3∙9H2O) and urea
(CO(NH2)2) were mixed in the appropriate molar ratios in a minimum
volume of distilled water in order to obtain a transparent solution. Based
on our previous studies[27,28,53] the amount of urea was 75% larger than
stoichiometry, i.e. the amount corresponding to complete combustion of
urea by the nitrate anions present in the metal salts. The Cu/(Cu+Mn+Al)
molar ratio was equal to 0.30 (Al/(Al + Mn + Cu) = 0.07). The mixed solution
of urea with nitrate salts was autoignited in an open muffle furnace
preheated at 400 – 500 oC. To obtain pure, well-crystallized oxide catalyst,
the powder was further heated at 550 oC for 1 h.
Temperature-programmed reduction (TPR) and temperature-programmed
hydrogen desorption (H2-TPD) studies were carried out in the Autochem II
2920 apparatus (Micromeritics Instr. Corp.), equipped with U-tube quartz
reactor and TCD detector. Samples (m = 0.05 g) in both TPR and H2-TPD
studies were reduced under a flow of 5% H2 in Ar (total flow rate 30 mL
min-1). The ramp rate was 10 oC per min. Water produced in the reduction
was removed in a cold trap maintained in a liquid nitrogen-2-propanol
mixture at -89 oC. Reduction was performed at the same conditions as
before the SRM catalytic tests, i.e. at 220 oC for CuZnAlOx, 280 oC for
CuMnAlOx, and 350 oC for PdZnCrOx catalysts, depending on their
reducibility. In the case of TPD studies, the temperature after 1 h of
isothermal reduction was decreased to -60 oC for copper catalysts and to
100 oC for PdZnCrOx catalyst. Then, the hydrogen containing mixture was
replaced by argon and the temperature after 0.5 h of flushing was
increased with linear ramp rate 10 oC min-1 up to 600 oC. The reaction
mixture was passed through a cold trap. Different temperature adsorption
was used to avoid hydrogen absorption by palladium and formation of
palladium hydrate phase.
CuZnAlOx. Highly active HiFUEL® R120 methanol reforming catalyst (50.2
wt.% CuO, 18.7 wt.% Al2O3, 30.8 wt.% ZnO) was purchased from Johnson
Matthey in non-reduced form and was used as reference sample. [62] The
cylindrical pellets were crushed and sieved (0.09 < fraction < 0.18 mm).
Physicochemical characterization
Temperature-programmed desorption of methanol (MeOH-TPD) studies
were carried out in a reaction system equipped with U-tube quartz flow
reactor, electric furnace, gas mass flow controllers, valves, methanol
evaporator and mass spectrometer (HAL201RC, Hiden Analytical),
coupled with stainless steel heated capillary. The samples (m = 0.1 g) were
initially reduced under the flow of 15% H2/He (total flow rate = 30 mL min-
1, linear ramp rate of 10 oC min-1) up to the suitable reduction temperatures,
depending on catalyst. Hydrogen containing mixture after isothermal
reduction for 1 h was replaced with helium. Then the temperature was
decreased to 100 oC. Helium stream (30 mL min-1) was next passed
through saturator with methanol maintained at 15 oC and fed into the
reactor. Methanol was adsorbed for 30 min, and then the mixture was
replaced with helium, flushing for 30 min. Desorption profiles were
recorded under a linear ramp rate of 10 oC min-1. Similar experiments were
performed using the mixture of helium and hydrogen (15% H2/He with the
total flow rate of 30 mL min-1) during desorption stage. The reaction
products were analyzed by mass spectrometer, using multiple ion
detection mode. The intensity of selected ions was monitored (including
the ions with m/z = 2, 14, 15, 16, 18, 28, 29, 30, 31, 32, 44, 45, 60).
The composition of the catalysts was determined by the X-ray
fluorescence (XRF) method using AxiosmAX (PANalytical) spectrometer
and by Canberra 1510 analyzer. The specific surface area (SBET) was
evaluated by Brunauer–Emmett–Teller (BET) method from nitrogen
adsorption/desorption isotherms obtained volumetrically at -196 oC using
ASAP 2405N analyzer (Micromeritics Instr. Corp.). Samples were
outgassed under ~10-2 Pa at 130 oC. Mean pore diameter was determined
by applying the Barret–Joyner–Halenda (BJH) method from desorption
part of isotherm. The active surface area and mean size of palladium
crystallites were determined by hydrogen chemisorption studies using
ASAP 2020HD (Micromeritics Instr. Corp.) analyzer. Palladium catalyst
was reduced in situ with hydrogen at 350 oC for 1 h. After reduction
procedure the temperature was decreased to 110 oC under vacuum. The
sample was degassed up to 5x10-7 Pa and hydrogen chemisorption
measurement was conducted. The mean size of palladium crystallites
(dCh) was calculated on the basis of palladium content and total hydrogen
chemisorption. The uptake of hydrogen due to its chemisorption was
determined by extrapolating the straight-line portion of the isotherm (up to
the equilibrium pressure of 13.3 kPa) to zero pressure. Palladium
dispersion and active metal surface area were calculated taking into
account the atomic ratio H:Pd = 1:1 and the surface area occupied by one
hydrogen atom equal to 0.065 nm2. The active surface area of copper-
based catalysts was measured by the chemisorption method in the
AutoChem 2950 analyzer (Micromeritics Instr. Corp.). Small pulses of
chemisorbed N2O (100 L, containing 4.3 mol of N2O) at 20 °C oxidized
the surface atoms of metallic copper in the pre-reduced in-situ catalyst
sample, according to the reaction 2Cu + N2O → Cu2O + N2. Non-reacted
N2O was removed in a cold trap (immersed in a liquid nitrogen) placed in
front of a thermal conductivity detector TCD. The TCD detected amounts
of nitrogen formed. The surface area occupied by the single surface
copper atom was 6.85·10-20 m2 per Cu atom.
Diffuse reflectance infrared Fourier-transform spectroscopy studies
(DRIFTS) of methanol desorption were carried out in the integrated FT-IR
system equipped with an automated gas and vapour sampling unit
(Medson), FT-IR spectrometer (Nicolet 6700, Thermo Scientific) and
Praying Mantis High-temperature Reaction Chamber (Harrick) with ZnSe
windows. The spectrometer was equipped with LN2 cooled MCTA detector.
The background signal was obtained by the use of KBr. Samples were
placed in the reaction chamber equipped with K-type thermocouples.
Samples were subjected to the similar activation conditions as described
above. Samples after reduction were flushed with an inert gas and cooled
down. Following adsorption of methanol from the argon/methanol stream
for 30 min and then flushing with Ar, DRIFT spectra were collected at
selected temperatures over the range of 650 - 4000 cm-1 at the resolution
of 4 cm-1. The samples were heated up under a linear ramp of 10 oC min-
1 in the flow of Ar or H2-Ar mixture.
The morphology of selected catalysts was studied by the electron
transmission microscope Titan G2 60-300 kV (FEI Company). Particle size
distribution was obtained by measuring diameter of at least 200 particles
in different areas of the catalyst. Phase identification was performed by
using the FFT generated from high-resolution TEM images. The elements
Catalysts evaluation in SRM process
This article is protected by copyright. All rights reserved.

10.1002/cctc.201900738
ChemCatChem
FULL PAPER
∑
푐퐶푂 + 푐퐶푂 + 푐퐶퐻 + ⋯ + 푖 푐푖
푖 푐푖 − 푐푀푒
Catalytic studies in the SRM reaction were carried out in a fixed bed flow
reactor system (Microactivity Reference unit, PID Eng&Tech), working
under atmospheric pressure, and equipped with HPLC pump,
microchannel evaporator and mixer (Figure 10).
2
4
푋푀푒
=
100% =
100% (1)
∑
푖 푐푖
푐퐶푂 + 푐 + 푐
+ ⋯ + 푖 푐푖 + 푐푀푒
퐶푂2
퐶퐻4
where: ci – concentration of carbon containing component in the reaction
products mixture. Water conversion under reaction conditions was
calculated as follows:
∑
1.5 푖 푐푖 − 푐퐻
푂 100%
(2)
2
푋퐻
2푂
=
∑
1.5 푖 푐푖
The selectivity of the catalysts towards hydrogen, carbon dioxide and
carbon monoxide was calculated on a carbon balance basis as:
푐
퐻2
푆퐻
=
100% (3)
100% (4)
100% (5)
2
3(푐퐶푂 + 푐퐶푂 + 푐퐶퐻 + ⋯ + 푖 푐푖)
2
4
푐
퐶푂2
푆퐶푂
=
2
푐퐶푂 + 푐퐶푂 + 푐퐶퐻 + ⋯ + 푖 푐푖
2
4
푐퐶푂
푐퐶푂 + 푐퐶푂 + 푐퐶퐻 + ⋯ + 푖 푐푖
푆퐶푂
=
2
4
Figure 10. The schematic diagram of experimental device system for
investigating the course of the steam reforming - Mircoactivity Reference
Reactor (PID Eng&Tech), (R) microreactor, (C1-C6) mass flow controllers,
(L1,L2) HPLC pumps, (T1- T4) temperature control, (B1,B2) 6 port valves,
(B3) three-way valves.
Acknowledgements
Financial support from The Fuel Cells and Hydrogen Joint
Undertaking (FCH JU; Area SP1-JTI-FCH-2009.4.2; Grant
agreements no. 245202 and no. 325358) is gratefully
acknowledged. The research was carried out with the equipment
purchased thanks to the financial support of the European
Regional Development Fund in the framework of the Polish
Innovation Economy Operational Program (Contract no.
POIG.02.01.00-06-024/09 Center of Functional Nanomaterials).
The reaction products were analysed on-line by two gas chromatographs
equipped with thermal conductivity detectors (TCD) (Figure 11). The
analysis of CH3OH and H2O vapours was performed by GC-450 (Varian),
while dry gases including H2 (with argon as a carrier gas), CO, CH4 and
CO2 (with helium as carrier gas) were analysed by Micro-GC CP-4900
(Varian).
Keywords: Methanol steam reforming; Palladium catalyst;
Copper catalyst; Hydrogen inhibition
[1]
Y. Lwin, W.R.W. Daud, A.B. Mohamad, Z. Yaakob, Int. J. Hydrogen
Energy 2000, 25, 47.
[2]
[3]
N. Katiyar, S. Kumar, S. Kumar, Chem. Eng. Tech. 2013, 36, 581.
W. Tong, K. Cheung, A. West, K. Yu, S.C.E. Tsang, Phys. Chem. Chem.
Phys. 2013, 15, 7240.
Figure 11. The schematic diagram of the analytic system used in the
determination of activity and selectivity of catalysts in the steam reforming
of methanol; (a) gas dosing system, (b) Mircoactivity Reference Reactor
(PID Eng&Tech), (c) pressure stabilisation on the reactor outlet line, (d)
drying system of reaction products, (e) MicroGC-4900 (Varian), (f)
pressure stabilisation system on the microGC outlet line, (g) GC-450
(Varian), (h) pressure stabilisation system on the GC outlet line.
[4]
[5]
[6]
[7]
E. Kunkes, M. Behrens, Methanol Chemistry in Chemical Energy Storage,
(Eds.: R. Schlögl), de Gruyter, Berlin, 2013, pp. 413-442.
C.J. Jiang, D.I. Trimm, M.S. Wainwright, N.W. Cant, Appl. Catal. A 1993,
97, 145.
B.A Peppley, J.C. Amphlett, L.M. Kearns, R.F. Mann, Appl. Catal. A 1999,
179, 21.
B.A. Peppley, J.C. Amphlett, L.M. Kearns, R.F. Mann, Appl. Catal. A
1999, 179, 31.
The total flow rate of methanol/water mixture was 50 mL min-1 (molar ratio
MeOH/H2O = 1/1.5). The mixture was diluted with nitrogen (50 mL min-1).
The catalyst (0.1 g) was mixed with 0.9 g of quartz grains. The applied
volume hourly space velocity, expressed as the ratio of the volume flow
rate of methanol-water mixture VHSVmix to the weight of catalyst was 30 L
[8]
[9]
N. Takezawa, N. Iwasa, Catal. Today 1997, 36, 45.
S.T. Yong, C.W. Ooi, S.P. Chai, X.S. Wu, Int. J. Hydrogen Energy 2013,
38, 9541.
[10] J.K. Lee, J.B. Ko, D.H. Kim, Appl. Catal. A 2004, 278, 25.
[11] H. Xi, X. Hou, Y. Liu, S. Qing, Z. Gao, Z. Angew. Chem. Int. Ed. 2014,
53, 11886.
h-1gcat-1, while the value expressed as the ratio of the total volume flow rate
-1
of reaction mixture VHSVall to the weight of catalyst was 60 L h-1 gcat
.
Inhibition effect was studied via enrichment of the MeOH/H2O reaction
mixture (50 mL min-1, diluted with 50 mL min-1 of N2) with hydrogen (0 to
25 vol. %). The weight of catalyst sample in the studies of hydrogen
inhibition was 0.5 g and diluted with 0.5 g of quartz scraps. The catalysts
were reduced at suitable temperatures, as described above, and tested at
selected temperatures, from 180 oC to 420 oC. The activity of catalysts was
expressed in the term of methanol conversion (XMe):
[12] J. Papavasiliou, G. Avgouropoulos, T. Ioannides, Appl. Catal. B 2009, 88,
490.
[13] B. Frank, F.C. Jentoft, H. Soerijanto, J. Kröhnert, R. Schlögl, R.
Schomäcker, J. Catal. 2007, 246, 177.
[14] H. Purnama, T. Ressler, R.E. Jentoft, H. Soerijanto, R. Schlögl, R.
Schomäcker, Appl. Catal. A 2004, 259, 83.
This article is protected by copyright. All rights reserved.

10.1002/cctc.201900738
ChemCatChem
FULL PAPER
[15] S.R. Samms, R.F. Savinell, J. Power Sources 2002, 112, 13.
[16] A.Y. Kapran, S.M. Orlyk, Theor. Experim. Chem. 2017, 53, 3.
[17] S.K. Talkhoncheh, M. Haghighi, S. Minaei, H. Ajamein, M. Abdollahifar,
RSC Advances 2016, 6, 57199.
[53] G. Avgouropoulos, J. Papavasiliou, T. Ioannides, S. Neophytides, J.
Power Sources 2015, 296, 335.
[54] J. Papavasiliou, G. Słowik, G. Avgouropoulos, Energy Technol. 2018, 6,
1332.
[18] R. Shokrani, M. Haghighi, N. Jodeiri, H. Ajamein, M. Abdollahifar, Int. J.
Hydrogen Energy 2014, 39, 13141.
[55] J. Papavasiliou, C. Schutt, G. Kolb, S. Neophytides, G. Avgouropoulos,
Int. J. Hydrogen Energy 2019, 44, 12818.
[19] J.E. Park, S.D. Yim, C.S. Kim, E.D. Park, Int. J. Hydrogen Energy 2014,
39, 11517.
[56] W. Gac, W. Zawadzki, G. Słowik, M. Greluk, J. Pawlonka, A. Machocki,
J. Therm. Anal. Calorim. 2016, 125, 1205.
[20] M. Mrad, D. Hammoud, C. Gennequin, A. Aboukaïs, E. Abi-Aad, Appl.
Catal. A 2014, 471, 84.
[57] F. Arena, T. Torre, C. Raimondo, A. Parmaliana, Phys. Chem. Chem.
Phys. 2001, 3, 1911.
[21] W. Tong, A. West, K. Cheung, K.-M. Yu, S.C.E. Tsang, ACS Catalysis,
2013, 3, 1231.
[58] W. Gac, G. Słowik, W. Zawadzki, Appl. Surf. Sci. 2016, 370, 536.
[59] D. Łomot, W. Juszczyk, Z. Karpiński, F. Bozon-Verduraz, J. Chem. Soc.
Faraday Trans. 1997, 93, 2015.
[22] J. Papavasiliou, G. Avgouropoulos, T. Ioannides, Int. J. Hydrogen Energy
2012, 37, 16739.
[60] T. Conant, A.M. Karim, V. Lebarbier, Y.Wang, F. Girgsdies, R. Schlögl,
A. Datye, J. Catal. 2008, 257, 64.
[23] S.G. Sanches, J.H. Flores, R.R. De Avillez, M. Pais Da Silva, Int. J.
Hydrogen Energy 2012, 37, 6572.
[61] J. Pawlonka, W. Gac, M. Greluk, G. Słowik, J. Therm. Anal. Calorim.
2016, 125, 1265.
[24] C. Rameshan, W. Stadlmayr, S. Penner, M.H. Lorenz, N. Memmel, M.
Hävecker, R. Blume, D. Teschner, T. Rocha, D. Zemlyanov, A. Knop-
Gericke, R. Schlögl, B. Klötzer, Angew. Chem. Int. Ed. 2012, 51, 3002.
[25] M. Mrad, C. Gennequin, A. Aboukaïs, E. Abi-Aad, Catal. Today 2011,
176, 88.
[62] G. Avgouropoulos, A. Paxinou, S. Neophytides, Int. J. Hydrogen Energy
2014, 39, 18103.
[63] M.A.L. Vargas, G. Busca, U. Costantino, F. Marmottini, T. Montanari, P.
Patrono, F. Pinzari, G. Ramis, J. Mol. Catal. A 2007, 266, 188.
[64] S.T. Korhonen, M.A. Bañares, J.L.G. Fierro, A.O.I. Krause, Catal. Today
2007, 126, 235.
[26] M.-C. Tsai, J.-H. Wang, C.-C. Shen, C.-T. Yeh, J. Catal. 2011, 279, 241.
[27] G. Avgouropoulos, J. Papavasiliou, M.K. Daletou, J.K. Kallitsis, T.
Ioannides, S. Neophytides, Appl. Catal. B 2009, 90, 628.
[28] J. Papavasiliou, G. Avgouropoulos, T. Ioannides, Catal. Commun. 2005,
6, 497.
[65] A. Ueno, T. Onishi, K. Tamaru, Trans. Faraday Soc. 1971, 67, 3585.
[66] S. Lin, D. Xie, H. Guo, J. Mol. Catal. A 2012, 356, 165.
[67] K. Takahashi, N. Takezawa, H. Kobayashi, Chem. Lett. 1983, 7, 1061.
[68] J.-Y. Bo, S. Zhang, K.H. Lim, Catal. Lett. 2009, 129, 444.
[69] G.J. Millar, A.H. Rochester, K.C. Waugh, J. Chem. Soc. Faraday Trans.
1991, 87, 2795.
[29] J. Papavasiliou, G. Avgouropoulos, T. Ioannides, J. Catal. 2007, 251, 7.
[30] X. Xu, K. Shuai, B. Xu, Catalysts 2017, 7, 183.
[31] G. Avgouropoulos, J. Papavasiliou, T. Ioannides, Chem. Eng. J. 2009,
154, 274.
[70] I.A. Fisher, A.T. Bell, J. Catal. 1999, 184, 357.
[32] C.E. Barrios, M.V. Bosco, M.A. Baltanás, A.L. Bonivardi, Appl. Catal. B
2015, 179, 262.
[33] Y. Matsumura, Appl. Catal. A 2013, 468, 350.
[34] L. Yang, G.-D. Lin, H.-B. Zhang, Appl. Catal. B 2013, 455, 137.
[35] G. Avgouropoulos, Catal. Commun. 2009, 10, 682.
[36] Q. Zhang, R.J. Farrauto, Appl. Catal. B 2011, 395, 64.
[37] M. Armbrüster, M. Behrens, K. Föttinger, M. Friendrich, E. Gaudry, S.K.
Matam, H.R. Sharma, Catal. Rev. - Sci. Eng. 2013, 55, 289.
[38] K. Sun, W. Lu, M. Wang, X. Xu, Appl. Catal. A 2004, 268, 107.
[39] Y. Suwa, S. Ito, S. Kameoka, K. Tomishige, K. Kunimori, Appl. Catal. A
2004, 267, 9.
[40] Y. Liu, T. Hayakawa, T. Ishii, M. Kumagai, H Yasuda, K. Suzuki, S.
Hamakawa, K. Murata, Appl. Catal. A 2001, 210, 301.
[41] L.M. Gomez-Sainero, R.T. Baker, I.S. Metcalfe, M. Sahibzada, P.
Concepcion, J.M. Lopez-Nieto, Appl. Catal. A 2005, 294, 177.
[42] N. Iwasa, T. Mayanagi, W. Nomura, M Arai, N. Takezawa, Appl. Catal. A
2003, 248, 153.
[43] Y.H. Chin, R. Dagle, J.L. Hu, A.C. Dohnalkova, Y. Wang, Catal. Today
2002, 77, 79.
[44] R. L. Barbosa, V. Papaefthimiou, Y.T. Law, D. Teschner, M. Hävecker,
A. Knop-Gericke, R. Zapf, G. Kolb, R. Schlögl, S. Zafeiratos, J. Phys.
Chem. C 2013, 117, 6143.
[45] Y. Men, G. Kolb, R. Zapf, M. O’Connell, A. Ziogas, Appl. Catal. A 2010,
380, 15.
[46] J. Wang, H. Chen, Y. Tian, M. Yao, Y. Li, Fuel 2012, 97, 805.
[47] M. Saidi, Int. J. Hydrogen Energy 2017, 42, 16170.
[48] P. Ribeirinha, M. Abdollahzadeh, M. Boaventura, A. Mendes, Appl.
Energy 2017, 188, 409.
[49] A. Iulianelli, P. Ribeirinha, A. Mendes, A. Basile, Ren. Sust. Energy Rev.
2014, 29, 355.
[50] S. Liguori, A. Iulianelli, F. Dalena, V. Piemonte, Y. Huang, A. Basile, J.
Hydrogen Energy 2014, 39, 18702.
[51] C. Song, Catal. Today 2006, 115, 2.
[52] G. Avgouropoulos, T. Ioannides, J.K. Kallitsis, S. Neophytides, Chem.
Eng. J. 2011, 176-177, 101.
This article is protected by copyright. All rights reserved.

10.1002/cctc.201900738
ChemCatChem
FULL PAPER
FULL PAPER
Highly efficient Pd- and Cu-based
catalysts in the steam reforming of
methanol (SRM)
Wojciech Gac*, Witold Zawadzki,
Magdalena Greluk, Grzegorz Słowik,
Andrzej Machocki, Joan Papavasiliou,
George Avgouropoulos*
Drop of CH3OH conversion and
increase in CO selectivity with
increase of H2 content
Investigation of inhibiting role of
hydrogen in the steam reforming of
methanol
The presence of H2 inhibits in different
way the performance of catalysts
Inhibition effects related to the
presence of strong hydrogen
adsorption sites
This article is protected by copyright. All rights reserved.