Methanol oxidation over silica-supported Pt and Ag nanoparticles: Toward selective production of hydrogen and carbon dioxide

Article abstract of DOI:10.1016/j.catcom.2012.08.026

Pt, Ag, and Pt-Ag nanoparticles smaller than 5 nm were synthesized by a simple, alcohol reduction. These and similar materials may have many applications including photocatalysis because of the ability to tune the plasmonic and catalytic properties. After immobilization onto silica, the particles were tested for methanol decomposition and partial methanol oxidation. For methanol decomposition, Ag/silica was the more active than Pt/silica. This result was in agreement with product poisoning (CO) limiting turnover and CO generally binding more weakly to Ag than Pt surfaces. The properties of the bimetallic Pt-Ag were between the parent catalysts, but different than their physical mixture, which indicated Pt-Ag bimetallic formation. The catalytic activity for partial methanol oxidation was greater than methanol decomposition for all catalysts. The Pt/silica catalyst demonstrated the best hydrogen and carbon dioxide yields when oxygen was added. The results are discussed in the discussion of a two-step process in which methanol is decomposed to carbon monoxide and hydrogen and then these species are oxidized to water and carbon dioxide. Further work is needed to refine the process and the catalyst to achieve CO-free hydrogen from methanol and oxygen.

Full text of DOI:10.1016/j.catcom.2012.08.026

Catalysis Communications 28 (2012) 128–133
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Methanol oxidation over silica-supported Pt and Ag nanoparticles: Toward selective
production of hydrogen and carbon dioxide
Erum Qayyum a, Vanessa A. Castillo a, Kneath Warrington a, Mohamed A. Barakat b,c, John N. Kuhn a,
⁎
a
Department of Chemical & Biomedical Engineering, University of South Florida, 4202 East Fowler Avenue, ENB 118, Tampa, FL 33620, United States
Environmental Sciences Department, Faculty of Meteorology and Environment, King Abdulaziz University (KAU), Saudi Arabia
b
c
Central Metallurgical R& D Institute, P.O. Box 87 Helwan 11421, Cairo, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 April 2012
Received in revised form 16 August 2012
Accepted 24 August 2012
Available online 31 August 2012
Pt, Ag, and Pt–Ag nanoparticles smaller than 5 nm were synthesized by a simple, alcohol reduction. These
and similar materials may have many applications including photocatalysis because of the ability to tune
the plasmonic and catalytic properties. After immobilization onto silica, the particles were tested for metha-
nol decomposition and partial methanol oxidation. For methanol decomposition, Ag/silica was the more ac-
tive than Pt/silica. This result was in agreement with product poisoning (CO) limiting turnover and CO
generally binding more weakly to Ag than Pt surfaces. The properties of the bimetallic Pt–Ag were between
the parent catalysts, but different than their physical mixture, which indicated Pt–Ag bimetallic formation.
The catalytic activity for partial methanol oxidation was greater than methanol decomposition for all cata-
lysts. The Pt/silica catalyst demonstrated the best hydrogen and carbon dioxide yields when oxygen was
added. The results are discussed in the discussion of a two-step process in which methanol is decomposed
to carbon monoxide and hydrogen and then these species are oxidized to water and carbon dioxide. Further
work is needed to refine the process and the catalyst to achieve CO-free hydrogen from methanol and
oxygen.
Keywords:
Platinum
Silver
Bimetallic
Hydrogen
Fuel cells
Selectivity
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
partial methanol oxidation to generate hydrogen with minimal car-
bon monoxide production. Oxygen is added to methanol to aid in its
The ability to supply pure hydrogen is instrumental to a number of
applications including fuel cells, hydrotreating, and ammonia synthe-
sis. For example, even sub-10 ppm levels of carbon monoxide poison
proton exchange membrane fuel cell (PEMFC) anodes [1] and ammo-
nia synthesis catalysts [2]. Since most hydrogen is generated from
carbon-based sources, cleanup and separation of carbon species is a
key part of the processing. Whereas stationary technology permits
the use of the incredible useful water-gas shift reaction, [2] this puri-
fication process is equilibrium limited. The need for multiple, large re-
actors often results. A further non-WGS reactor is also needed to
provide a purity level not provided through its equilibrium limita-
tions. This step is often methanation, [2] but the preferential oxida-
tion of carbon monoxide in the presence of hydrogen or simply
PROX catalysis [3,4] is gaining attention as an alternative means. An
advantage of using PROX rather than methanation is that hydrogen
is not used as a reactant to remove the unwanted carbon monoxide
in the PROX reaction. Instead, oxygen is added and the important
element is the selectivity of the oxidation catalysis.
decomposition to the desired products of hydrogen and carbon diox-
ide. Similar to PROX catalysis, the key feature is the selective oxida-
tion of carbon monoxide to carbon dioxide rather than hydrogen to
water. This technology takes advantage of the commercial availability
of methanol [5] and its proposed [1] use as a as a hydrogen carrier.
The application of this technology is not to replace hydrogen purifica-
tion in large-scale plants, but rather to apply toward niche fuel cell
applications where simplicity, foot-print restrictions, and possibly
auxiliary processes to recover the waste heat of the exothermic reac-
tions exist making the loss of hydrogen generated by the water-gas
shift tolerable.
In this study, partial methanol oxidation is demonstrated using sil-
ica supported transition metal catalysts. For this initial effort, plati-
num (Pt) and silver (Ag) catalysts are being employed. Pt and Ag
are among the most popular transition metal catalysts for oxidation
catalysis [6–9]. The unique properties of precious metals such as Pt
allow the concentration of molecules at the surface to increase reac-
tion rates, but also to be resistant to formation of strong adsorption
and/or bulk phase transitions [9]. Pt and Pt-based catalysts are com-
monly studied for PROX catalysis [4,10–12]. Since Ag is a metal with
unique oxygen catalysis capabilities, coupling Ag with Pt may lead
to interesting catalytic properties including the development of
CO-tolerant catalysts, [13] which would be important for other
The main focus of this effort is to demonstrate that methanol
decomposition can be combined with PROX catalysis for selective,
⁎
Corresponding author. Tel.: +1 813 974 6498.
E-mail address: jnkuhn@usf.edu (J.N. Kuhn).
1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2012.08.026

E. Qayyum et al. / Catalysis Communications 28 (2012) 128–133
129
applications including PEMFC anode electrocatalysts. Pt and Ag bime-
tallic catalysts have been reported as interesting catalysts for the con-
trol activity and selectivity through ligand and bifunctional effects
[13,14]. Although support effects enhance methanol oxidation rates
on Pt and Ag monometallic catalysts [15–17], this initial effort is
focused on modifying the metal function directly to control the activ-
ity and selectivity.
was purged in 50 SCCM of He at 110 °C for 30 min. A temperature
program from room temperature to 110 °C with a rate of 5 °C/min
was used. The sample was then cooled to 50 °C under the same gas
flow. For experiments without oxygen, a total flow of 50 SCCM was
used and it was comprised of 5 SCCM of methanol and 45 SCCM of
helium. For experiments with oxygen, a total flow of 50 SCCM was
used and it was comprised of 5 SCCM of methanol, 2.5 SCCM of oxy-
gen and 42.5 SCCM of helium. The combined gases were introduced
into the reactor at atmospheric pressure and the composition of the
effluent stream of the reactor was analyzed on-line by a mass spec-
trometer (MKS Cirrus) using an electron multiplier detector. Calibra-
tions were performed to convert the raw signals into concentrations.
A temperature program from 50 to 350 °C with a ramp rate of 10 °C/min
and a 1 h hold at 350 °C was used. An extended time-on-stream study
was performed with the same conditions as above except the hold was
9 h. A post-experiment temperature-program oxidation (TPO) was
performed for this case to assess coke formation. For the TPO, the catalyst
was cooled to 50 °C in He (50 SCCM) following the reaction. Then, the
catalyst was heated at 10 °C/min to 600 °C in 10% O2/He (50 SCCM)
while the mass spectrometer was used to measure the effluent gases.
TOFs were calculated from the methanol conversion (from m/z=31)
normalized per surface metal atom using the size-calculated dispersion
to correct for the surface to bulk ratio. All of the oxygen-free rates and ac-
tivities were obtained under differential conditions (less than 10% con-
version). For partial methanol oxidation, the conversions will be
denoted in the results section. Only carbon monoxide (m/z=28), carbon
dioxide (m/z=44), water (m/z=18), and hydrogen (m/z=2) were
observed as products. Selectivity toward hydrogen was calculated by
selectivity (hydrogen)=hydrogen concentration * 100 % / (hydrogen
concentration+water concentration). A similar equation for used for
carbon dioxide selectivity using concentrations of carbon monoxide
and carbon dioxide. No conversion was obtained using silica (no
metal) as a catalyst under same conditions.
2. Experimental section
All solvents were research grade from Sigma-Aldrich unless other-
wise noted. All compressed gases were purchased from Airgas in the
highest purity available.
2.1. Nanoparticle synthesis and characterization
The nanoparticles capped by polyvinlypyrrolidone (PVP) were
prepared by established colloidal routes existing in the literature
[18–22]. Chloroplatinic acid (H2PtCl6 • 6H2O, 99.9% pure on metals
basis), silver nitrate (AgNO3, 99% pure), and polyvinlypyrrolidone
(PVP) with a molecular weight of 40,000 were purchased from
Sigma-Aldrich. First, an appropriate amount of chloroplatinic acid
and/or silver nitrate were measured and dissolved into DI water to
achieve a volume of 20 mL. The concentrations were 6.0 mM for the
monometallic Ag and Pt particles and 3.0 mM each of Pt and Ag for
the bimetallic Ag–Pt (1:1) particles. This solution was then diluted
with 180 mL of methanol. PVP (133 mg) was dissolved into this
mixture, which was then refluxed for 3 h. The combined solution
was heated to 110 °C in a reflux apparatus to arrive at the reduced
nanoparticles. After cooling, the suspension was triple washed (cycles
of hexane and ethanol with intermediate centrifugation) to remove
excess capping agent with the surfactant. The cleaned particles were
re-dispersed in an ethanol suspension.
The morphology and size of particles was measured by transmis-
sion electron microscopy (TEM). TEM images were acquired at accel-
eration voltages of 60 kV using an FEI Morgagni 268D microscope. For
each synthesis, the average particle size and a particle size histogram
was measured by counting the particle size of 100 particles.
3. Results and discussion
3.1. Synthesis and characterization of Pt, Ag and Pt–Ag nanoparticles
Colloidal routes are successful methods for the synthesis of metal
nanoparticles with well-defined morphology [23–26]. Here, a synthe-
sis adopted from the synthesis of ~3 nm Pt particles [19,22,27] is
applied to the synthesis of Ag, and Ag–Pt bimetallic catalysts. During
the syntheses, for the Pt and Pt–Ag nanoparticles, the precursor solu-
tion turned black indicating the formation of metal nanoparticles. For
the Ag nanoparticles, the solution turned a shade of orange. Such a
color change is expected for Ag nanoparticles due to their character-
istic plasmonic properties in visible light [28]. The TEM images of Pt,
Ag, and Pt–Ag (1:1) nanoparticles are presented in Fig. 1. From
these images, an average particle size and a distribution was deter-
mined (Table 1) by measuring the size of 100 particles and statistical-
ly analyzing the resulting histograms. The Pt nanoparticles had an
average size slightly smaller than 3 nm and a size deviation of rough-
ly 20%, which both agreed with the literature results [19,22] for this
synthesis. The monometallic Ag particle resulted in both a larger
size (3.34 nm) and a larger deviation (40%) as compared to the Pt
particles. The result can be attributed to using a higher temperature
(110 °C) than needed for the reduction and then forcing Ostwald rip-
ening to simultaneously occur. Ag nanoparticles are typically synthe-
sized at low temperatures to achieve small particles [29] because
elevated temperature result in 50+ nm sizes [30]. Interestingly, the
Pt–Ag bimetallic nanoparticles demonstrated the smallest size
(2.52 nm) of the three particles and a deviation similar to the Pt
nanoparticles. This finding suggested an interesting nucleation and
reduction behavior of combined metal ions and that bimetallic parti-
cles resulted. A possible explanation is that Ag ions nucleated and
then Pt coated the Ag particles preventing agglomeration. However,
2.2. Supported catalyst synthesis and characterization
The metal nanoparticles were loaded at value of 2 wt. percent on silica
(Cab-O-Sil; ~210 m2/g). For typical synthesis, the nanoparticle-ethanol
suspension was added to an appropriate mass of silica based on the
mass of Ag and/or Pt in the suspension. The slurry was sonicated at
room temperature for 2 h. The silica-immobilized nanoparticles were
separated from solution by centrifuging for 15 min at 5000 rpm. The
clear supernatant was decanted. The final catalysts were obtained by dry-
ing first at ambient conditions and then at 100 °C. The physical mixture of
Pt and Ag supported on silica was prepared by mixing the monometallic
suspensions to arrive at a catalyst with an equimolar ratio of Pt:Ag of 1:1.
The catalysts were characterized by nitrogen physisorption on an
Autosorb IQ (Quantachrome Instruments). Catalysts were degassed
at 200 °C prior to analysis. Nitrogen isotherms were acquired at
77 K. Standard BET analyses was performed to get the specific surface
area from the adsorption isotherm.
2.3. Methanol decomposition and partial oxidation catalytic studies
Catalytic methanol decomposition and oxidation were performed
with a laboratory-scale, fixed-bed flow reactor enclosed within a
Thermolyne furnace. The catalysts (50 mg) were loaded into a quartz
U-tube reactor between plugs of quartz wool. A type-K thermocouple
was used to measure the temperature near the bottom of the catalyst
bed. Gas flowrates were controlled by calibrated mass flow control-
lers (Alicat Scientific). Prior to the catalytic reaction, the catalyst

130
E. Qayyum et al. / Catalysis Communications 28 (2012) 128–133
Table 1
Particle size distributions from statistical analysis of TEM images and corresponding
dispersions.
Metal
Size (nm)a
Dispersion (%)b
Pt
Ag
Pt–Ag
2.84 0.61
3.34 1.33
2.52 0.51
38
33
43
a
Determined from counting 100 particles.
From average particle size using geometric model.
b
these particles may be expected to have interesting and unique cata-
lytic and optical properties.
3.2. Immobilization of nanoparticles onto silica and characterization of
supported catalysts
After washing, the nanoparticles were immobilized onto silica
during sonication in an ultrasonic bath. The TEM images in Fig. 1
were taken after washing as well. The nitrogen porosimetry results
are presented in Table 2. The results are well aligned with those
values measured for the silica support alone, which indicates no clog-
ging of the pores during the immobilization step. Previous results [32]
have demonstrated that washing effectively removes the polymer
stabilizing agent by comparing carbon dioxide profiles generated by
temperature-programmed oxidation experiments of washed (no
CO2 produced) and unwashed (CO2 produced) Pt particles prepared
by a similar method as here. Ethylene hydrogenation, a well-studied
structure insensitive catalytic reaction over Pt, [33–36], was also
performed on the Pt/silica catalyst. A turnover frequency of 12 s−1
was measured at T=40 °C. Correcting this value to those values pre-
viously used in a correlation, [37] a dispersion of 23% was determined.
This dispersion is in good agreement with the results calculated from
the average particle size of the Pt nanoparticles (Table 1) and previ-
ous [22] chemisorption results. By these arguments, the dispersion
calculated from the average particle sizes is used for the calculation
of turnover frequencies for methanol decomposition described below.
3.3. Catalysis activity for methanol decomposition and oxidation
Methanol conversion to syngas was measured with and without
oxygen added. The reaction onset temperature, based on the hydro-
gen signal (m/z=2) for the Pt/silica was 110 °C, which is lower, but
comparable, to the temperature of ~150 °C [17,38] previously
reported for a similar catalyst. The shift toward the lower onset tem-
perature in the present study as compared to the previous work
[17,38] may be due to the extensive washing protocol used in this
study, which is assumed as effective as discussed in Section 3.2. This
analysis is supported because high calcination temperatures were
needed in the previous studies [17,38] whereas only a low tempera-
ture treatment (110 °C) to remove water vapor was conducted in
this study. From the carbon monoxide signal (m/z=28), a high
onset temperature (180 °C) was observed relative to that of hydro-
gen. This finding is in agreement with methanol TPD studies [8,39]
performed on Pt (111) single crystals that showed carbon monoxide
desorbed at a temperature 70 to 90 °C higher than hydrogen. It also
Fig. 1. TEM images of (a) Pt, (b), Ag, and (c) Pt–Ag nanoparticles.
Table 2
Nitrogen porosimetry results of supported catalysts.
Catalyst
Specific surface
Pore volume
(cm3/g)
Pore diameter
(nm)
(m2/g)
computational studies [31] predict, in the absence of adsorbates, the
Ag segregation to the surface for both Pt in a host Ag structure and
Ag in a host Pt structure. With the water, methanol, and organic cap-
ping in solution, the more labile Pt may prefer to segregate to the
nanoparticle surface. With the particle sizes on the nanometer scale,
sufficiently low diffusion lengths provide the possibility of atomic
transport under reaction conditions. From these results and insights,
Pt/silica
Ag/silica
Pt–Ag/silica (bimetallic)
(Pt:Ag=1:1)
Pt–Ag/silica (mixture)
(Pt:Ag=1:1)
180
206
214
0.08
0.09
0.09
1.7
1.6
1.7
206
0.09
1.7

E. Qayyum et al. / Catalysis Communications 28 (2012) 128–133
131
suggested that the kinetically limiting step is linked to carbon monox-
ide desorption, which was previously found [40] for Pd/silica cata-
lysts. Once higher temperatures were reached, the reaction products
reached the stoichiometric amounts (twice as much hydrogen as car-
bon monoxide). The reaction rates and turnover frequencies for the
catalysts are compared in Fig. 2. From these results, the Ag/silica cat-
alyst is observed to be more active than the Pt/silica catalyst. On Pt
single crystals, molecularly adsorbed carbon monoxide [41] is the
most stable adsorbate out of molecularly adsorbed methanol [39],
dissociatively adsorbed methanol [39], and dissociatively adsorbed
hydrogen [41]. As mentioned above, carbon monoxide is a key adsor-
bate in the catalytic cycle and the trend just described from the sur-
face science approach fits with the results obtained here for Pt and
Ag catalysts surfaces. Both of the Pt–Ag/silica catalysts yield activities
between the two monometallic catalysts (Fig. 2). Since the physical
mixture of the monometallic nanoparticles behaved differently than
the Ag–Pt bimetallic nanoparticles of the same composition, it sug-
gests the bimetallic particles have modified electronic structures
through both Ag and Pt being in the same particle. With regards to
stability, little deactivation occurred during the hold at T=350 °C
for the three Pt-containing catalysts. For the Ag/silica catalyst, rough-
ly 30% of its activity was lost during the 1 h hold. Furthermore, mul-
tiple cycles conducted on the Ag–Pt/silica catalyst demonstrated the
profiles and stability obtained on the first cycle were reproducible
in subsequent cycles.
With the performances of the catalysts for methanol decomposi-
tion now established, the performances for partial methanol oxida-
tion are now discussed. Since the conversions of methanol and
oxygen (Fig. 3) were no longer limited to differential reactor condi-
tions under the same space velocities used for the oxygen-free exper-
iments, the conversions and apparent rates will be used. At 350 °C,
oxygen consumption was high over all catalysts. Moreover, the per-
formance was stable over the 1 h hold at this temperature. An ex-
tended time-on-stream study was performed for the Pt–Ag/silica
catalyst as shown in Fig. 4. Over the nearly 9 h on stream, the conver-
sion decreased from 40 to 25%. A post-reaction TPO indicated 0.4 g
coke formed/(g cat∗h) from the time-on-stream at T=350 °C,
which was presumed as the source of deactivation. Methanol conver-
sion was greatly increased by the addition of oxygen with Ag/silica
again being more active than Pt/silica. The effect of the oxygen addi-
tion on the methanol conversion rate is directly compared in Fig. 5
and indicates an order of magnitude increase in the rate in the pres-
ence of oxygen for all catalysts. This finding is in agreement with
the concept the carbon monoxide poisoning because oxygen aids in
the formation of carbon dioxide and water (ideally, just carbon diox-
ide), which are more likely to have weaker chemical bonds with
the metal surfaces. This explanation is in agreement with carbon
Fig. 3. Oxygen and methanol conversion (%) for partial methanol oxidation at T=350 °C
over Pt/silica, Ag/silica, Ag–Pt/silica, and a physical mixture of Pt/silica and Ag/silica.
monoxide being molecularly bound more strongly on Ag and Pt sur-
faces than carbon dioxide [41].
There was a decrease in the oxygen conversion for the Pt–Ag/silica
catalyst as compared to the parent materials and the physical mixture
of them. Since oxygen more strongly bounds to model Pt surfaces
than Ag surfaces [41] and the binding strength of dissociatively
adsorbed oxygen on Pt surfaces is the stronger than methanol, carbon
monoxide, water, hydrogen, and carbon dioxide [39,41], Pt enrich-
ment at the surface remains the most likely scenario. In that case, car-
bon monoxide and oxygen now appear to dictate the conversion
process. A Pt overlayer on Ag would weaken the adsorption of oxygen
(dissociative) and carbon monoxide (molecular) compared to a pure
Pt surface. However, this discussion would still require oxygen con-
version of the bimetallic Pt–Ag surface to be between the parent sur-
faces. Incorporation of the other reaction species is needed to capture
the full picture.
The methanol conversion selectivities toward the desired products,
hydrogen and carbon dioxide, are presented in Fig. 6. As compared to
Pt/silica, the higher activity for oxygen conversion for Ag/silica resulted
in less hydrogen (more water) and carbon dioxide, which infers that Ag
is better at oxidizing hydrogen than carbon monoxide compared to Pt.
The lower oxygen conversion of Pt–Ag/silica catalyst resulted in primar-
ily less carbon dioxide forming compared to the other three catalysts.
Additionally, the bimetallic Pt–Ag/silica had similar hydrogen selectivi-
ty as the Pt/silica catalyst. These results suggested a change in surface
coverage as the Ag amount would be increased. Based on computational
studies [41] in model systems, a transition of the dissociatively
adsorbed hydrogen from negative to positive should occur as the
amount of Ag in the Pt–Ag surface increases. Once the value becomes
Fig. 2. Reaction rate and turnover frequency for methanol decomposition at T=350 °C
over Pt/silica, Ag/silica, Ag–Pt/silica, and a physical mixture of Pt/silica and Ag/silica.
Fig. 4. Time-on-stream examination of the Ag–Pt/silica catalyst at T=350 °C.

132
E. Qayyum et al. / Catalysis Communications 28 (2012) 128–133
was added. Further work is needed to refine the process and the
catalyst to optimize these yields. The overall effort of this contribution
demonstrated a platform to produce CO-free hydrogen from metha-
nol by adding oxygen as a reactant. The technology may be used in
niche applications where pure hydrogen is needed from a small foot-
print reactor.
A subsequent goal of this effort is to use these nanoparticles, demon-
strated here as active catalysts, for phototcatalysis when supported on
titania. The combination of properties of Pt (catalytic and electron
trap), Ag (catalytic and photocatalytic [42–44] and plasmonic [28]),
and titania (photocatalytic and support) to achieve a high performing
photocatalyst for environmental remediation. As with other titania-
based catalysts modified by materials and molecules that absorb visible
light, the use of a broader spectrum of light is expected through synergis-
tic combination of the metal and titania materials. The application of the
metal nanoparticles for the photo-degradation of phenol and phenol
derivatives in aqueous solution is the focus of future examination.
Fig. 5. Comparison of reaction rates for methanol decomposition (MeD) and partial
methanol oxidation (MeOx) at T=350 °C over Pt/silica, Ag/silica, Ag–Pt/silica, and a
physical mixture of Pt/silica and Ag/silica.
Acknowledgment
positive, it is much less likely than hydrogen would become oxidized
because its combination and dissociation rates should increase rapidly.
Then, there is a window of parameter space in the particle restructuring
dynamics (which also depend on conditions and particle composition
and size) in which enhanced hydrogen selectivity with low carbon
dioxide selectivity would exist. Even though this result was not what
was sought, the use of bimetallic catalysts to tune the selectivities to
the desired products in partial methanol oxidation to CO-free hydrogen
is possible. However, the initial selection of materials warrants further
investigation into the desired formulation to maximize hydrogen and
carbon dioxide yields.
The authors gratefully acknowledge funding from King Abdulaziz
University and internal funding from the University of South Florida.
Partial support from NSF award number 0851973 is also appreciated.
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Fig. 6. Selectivity of hydrogen and carbon dioxide generation from partial methanol
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