Platinum catalyzed c-h activation and the effect of metal-support interactions

Article abstract of DOI:10.1021/acscatal.9b03807

Catalytic C-H bond activation of methane and ethane on a series of silica supported platinum catalysts (Pt/SiO₂) was studied by using hydrogen/deuterium (H/D) exchange. Kinetic experiments demonstrate that under the reaction conditions studied, the rate of C-H bond activation shows approximate first order dependence in alkane and inverse first order dependence in D₂. The rate of C-H activation is affected by the presence of sodium on the silica support, where sodium-free supports have the fastest rates of C-H activation, as assessed by H/D exchange. CO adsorption and FTIR studies indicate that the Pt particles on the sodium-free support are more electron-deficient, having the most blue-shifted linear CO stretch, while sodium-containing supports are more electron-donating, having the most red-shifted linear CO stretch. It is proposed, based on the results described in this article and previous work in the literature, that more electron-donating supports cause the Pt particles to be more electron-rich and to adsorb D? (or H*) more strongly, thereby stabilizing the ground state and resting state of the catalyst, resulting in a decreased rate of C-H activation.

Full text of DOI:10.1021/acscatal.9b03807

Research Article
Cite This: ACS Catal. 2020, 10, 710−720
pubs.acs.org/acscatalysis
Platinum Catalyzed C−H Activation and the Effect of Metal−Support
Interactions
Aaron Sattler,* Michele Paccagnini, Michael P. Lanci, Sabato Miseo, and Chris E. Kliewer
Corporate Strategic Research, ExxonMobil Research & Engineering Company, 1545 Route 22 East, Annandale, New Jersey 08801,
United States
*
S Supporting Information
ABSTRACT: Catalytic C−H bond activation of methane and
ethane on a series of silica supported platinum catalysts
(
Pt/SiO ) was studied by using hydrogen/deuterium (H/D)
2
exchange. Kinetic experiments demonstrate that under the
reaction conditions studied, the rate of C−H bond activation
shows approximate first order dependence in alkane and inverse
first order dependence in D . The rate of C−H activation is
2
affected by the presence of sodium on the silica support, where
sodium-free supports have the fastest rates of C−H activation, as
assessed by H/D exchange. CO adsorption and FTIR studies
indicate that the Pt particles on the sodium-free support are
more electron-deficient, having the most blue-shifted linear CO
stretch, while sodium-containing supports are more electron-
donating, having the most red-shifted linear CO stretch. It is proposed, based on the results described in this article and
previous work in the literature, that more electron-donating supports cause the Pt particles to be more electron-rich and to
adsorb D* (or H*) more strongly, thereby stabilizing the ground state and resting state of the catalyst, resulting in a decreased
rate of C−H activation.
KEYWORDS: H/D exchange, C−H activation, alkanes, mechanism, isotopes, deuterium
INTRODUCTION
C−H activation in both methane and ethane, and (ii)
demonstrated that the presence of sodium (Na) on a silica-
support, which acts to modify the properties of the support
thereby influencing metal−support interactions, affects the
material’s ability to activate C−H bonds. These results have
connections with other catalytic reactions that have been
studied in the past, where metal−support interactions have
been implicated, and demonstrate the high sensitivity that
H/D exchange in alkanes can have as a characterization tool
for heterogeneous catalysts.
■
Developing new technologies for converting alkanes selectively
to higher value products is a major challenge for industrial
catalysis, due to the relative kinetic and thermodynamic
stability of alkanes and their C−H bonds. Current routes
typically implement high temperatures, exemplified by steam
methane reforming to produce syngas (CO and H ) or ethane
steam cracking to produce ethylene. Oxidative routes remove
thermodynamic limitations and high temperature require-
1
2
ments, but overoxidation (e.g., to CO ) becomes a major
2
2
problem. New catalytic routes for alkane upgrading are,
RESULTS AND DISCUSSION
therefore, desired and understanding the mechanism(s) by
which C−H activation occurs, a necessary step in any alkane
transformation, can assist in catalyst development and
■
A series of three silica-supported Pt catalysts (Pt/SiO ) having
2
sodium contents of either 0 or ∼500 ppm of Na were
synthesized (see Supporting Information, SI, for more details).
All samples were loaded with ∼0.75 wt % Pt by incipient
wetness impregnation, using aqueous solutions of Pt
3
,4
discovery. Platinum (Pt) is a well-known and important
5
metal for hydrocarbon catalysis, specifically alkane con-
versions, as exemplified by its industrial use in catalytic
reforming to produce high-octane gasoline, propane dehy-
9
6
tetraammine nitrate and arginine at a 1:8 molar ratio, dried
7
and then calcined in air at 425 °C for 2 h. Calcination in air
completely oxidized the arginine, which was verified by
temperature-programmed oxidation and reduction experi-
drogenation to produce propylene, and hexane aromatization
8
to produce benzene. In this work, we sought to study the
C−H bond activation step itself, a step that precedes the
catalytic reactions mentioned above, and the effect of metal−
support interactions, by utilizing isotope exchange reactions
with hydrogen and deuterium (H/D). Specifically, on a series
ments. The samples were then reduced in the reactor in H2
Received: September 5, 2019
Revised: November 26, 2019
of silica supported Pt catalysts, Pt/SiO , we have (i) identified
2
a mechanism consistent with the observed kinetic data for
©
XXXX American Chemical Society
710
DOI: 10.1021/acscatal.9b03807
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ACS Catalysis
Research Article
a
Table 1. Sample Descriptions and Characterization of Pt Particle Size by Chemisorption
b
c
pt conc. (wt%)
alkali conc. (ppm)
dispersion O (%)
dispersion H (%)
2
2
Pt-0
Pt-500
Pt-500S
0.75
0.75
0.75
<16
479
38(5)
42(5)
43(5)
35(5)
46(5)
38(5)
500 (from IWI)
a
b
c
Numbers in parentheses indicate two-standard deviations, i.e., 95% confidence intervals. O chemisorption at 35 °C, assuming O:Pt = 1. H
2
2
s
chemisorption at 35 °C, assuming H:Pt = 1.
s
at 450 °C for 4 h. The 0 ppm of Na sample (Pt-0) used an
ultrapure silica supplied by PQ Corporation where the sodium
level was below the detection limit of the experimental
techniques (<16 ppm). Two samples with ∼500 ppm of Na
sample were synthesized, which corresponds to an approximate
Exchange rates were measured at conversions of 50% or less
and with excess D (generally here: 100 Torr CH and 800
2
4
Torr D ) to limit the influence of unproductive C−H
2
activation events (with HD or H ) that do not result in the
2
formation of new C−D bonds and the reverse reaction of
2
:1 Pt:Na molar ratio; the first used Davisil 646 (Pt-500),
CH D to form CH . At higher conversions, mixtures of D , H ,
3
4
2
2
where the 500 ppm of Na is introduced from impurities in the
commercial silica. The second ∼500 ppm sample (Pt-500S)
was synthesized by treating the ultrapure silica with 500 ppm
and HD exist (in addition to the different isotopologues of the
alkanes); this does not change the intrinsic rate of C−H
activation (ignoring isotope effects) but assessment by H/D
exchange becomes more challenging as the molecules approach
isotopic equilibration, and at equilibration no reaction can be
observed.
of NaNO , followed by calcination in air at 425 °C for 2 h,
3
thereby removing the nitrate groups. While Pt-500 and
Pt-500S both have the same loading of Na, the Na in Pt-
5
00S is expected to be on the surface of the SiO due to the
The H/D exchange reaction progressions are shown in
Figure 2 for CH /D , on Pt-500S, Pt-500, and Pt-0 catalysts,
2
synthetic procedure (S indicates surface in 500S). The samples
4
2
10
were characterized by H and O chemisorption (Table 1)
at the same catalyst loading (50 mg), temperature (275 °C),
2
2
and transmission electron microscopy (TEM), which indicate
similar Pt particle sizes (between 2.5 and 3.5 nm) in all the
samples (see SI).
and initial partial pressures of CH and D (100 and 800 Torr,
4
2
respectively). The three materials catalyze H/D exchange at
different rates, as seen by the change in CH concentration
4
The ability of the Pt/SiO materials to activate C−H bonds
2
(i.e., partial pressure, PCH4) over time, in the relative order Pt-0
in methane and ethane was studied by using H/D
>
Pt-500 > Pt-500S (Figure 2). Similar data are shown in the
1
1−13
exchange.
ethane experiments can be found in the SI. Using this
technique, d -methane (CH ) and D contact a heterogeneous
Methane experiments are detailed below, and
SI for methane/D exchange at other temperatures, in addition
2
to ethane experiments, demonstrating that catalysts that
contain sodium undergo H/D exchange more slowly compared
with catalysts that are sodium free, under the experimental
0
4
2
catalyst in a well-mixed batch reactor and undergo isotope
exchange. The extent of reaction was monitored by using GC−
MS (gas chromatography−mass spectrometry). H/D exchange
14
conditions studied.
The rate of disappearance of CH follows the first order
4
of alkanes (e.g., conversion of CH to CH D, Figure 1)
4
3
equation (eq 1), allowing us to obtain kobs for each experiment,
15
which are normalized on a per mole of surface Pt atom basis.
Experiments to assess reaction orders in CH and D , by
4
2
changing their partial pressures and keeping the total system
pressure constant, demonstrate that H/D exchange is
approximately first order in CH pressure and inverse first
4
Figure 1. H/D exchange in methane (top) and ethane (bottom) to
produce deuterated isotopologues.
order in D2 pressure, under the experimental conditions
16−18
studied (Figure 3).
Thorough studies on H/D exchange
in ethane have been previously reported by Zaera and co-
requires C−H bond activation and, therefore, the measured
exchange rates reflect a catalyst’s ability to cleave C−H bonds.
workers who made similar observations, finding a first order
19−22
dependence on ethane and −0.55 order in D2.
The focus
Figure 2. Monitoring H/D exchange between methane and D on Pt/SiO catalysts at 275 °C: CH (black ○), CH D (red □), CH D (blue ◊),
2
2
4
3
2
2
CHD (green Δ), and CD (magenta ▽).
3
4
7
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Figure 3. Partial pressure dependence studies to determine k . CH : 100 Torr, D : 800 Torr (red ○); CH : 50 Torr, D : 800 Torr (blue □); and
rxn
4
2
4
2
CH : 100 Torr, D : 400 Torr (black ◊).
4
2
of the work here is to understand the effect of the support on
C−H activation; although these data allow for analysis of rates
of secondary C−H activations (i.e., multiple exchange), as has
metal active site electron-density, and not attributable only to
minor differences in particle size as assessed by chemisorption
24
and TEM.
11,19
been shown previously,
present work.
this is not within the scope of the
A mechanism consistent with the observed rate law involves
reversible dissociation of D (k and k , K ) on the catalyst
2
1
−1
D
These data allow for the determination of turnover
surface to open up a set of sites (* = site), followed by C−H
bond cleavage via dissociative adsorption (k , the reverse of
which is k−2) to give R* (R = CH or C ) and H* (Figure
frequencies (TOFs), in units of mols of CH activated (i.e.,
2
4
mols of CH molecules to undergo H/D exchange) per mol of
3
H
2 5
4
surface Pt atom per second, which follow rate eq 2 based on
the pressure dependencies above, where krxn is related to kobs
by eq 3. Thus, H/D exchange is informing us on the catalytic
rate of C−H bond cleavage on this series of Pt catalysts, and
4). H*/D* scrambling is rapid on the catalyst surface, and with
an excess of D*, which is the situation at low conversions,
C−D bond formation occurs via associative desorption (k ) to
3
form product, which is a deuterated alkane. This mechanism
the k values obtained are listed in Tables 2 and 3 for the
can be described by a bimolecular Langmuir−Hinshelwood
rxn
19,18
process, as has been used in similar studies previously,
and
−
1
is shown in eq 4. Equation 4 can be transformed into eq 5
Table 2. Rate Constants (k , s ) Measured As a Function
rxn
under conditions where (i) D adsorption is significantly
of Temperature for Pt/SiO Catalysts
2
2
stronger than RH adsorption, (ii) we assume quasi-equilibrated
methane
ethane
and steady-state concentrations of adsorbed D* and CH *,
3
temp. (° C)
Pt-500S
Pt-500
Pt-0
Pt-500S
Pt-500
Pt-0
and (iii) that k and k are the same when isotope effects are
3 −2
x
ignored (i.e., both steps are C− H bond formations, where x =
or 2). Equation 5 reduces to eq 6 under these conditions and
1
1
2
2
2
2
3
50
75
00
25
50
75
00
0.6
1.3
7.1
24
1
0.5
1.3
5.8
0.2
1.3
4.7
18
0.2
0.7
2.2
9.6
is consistent with our observed rate law (eq 2). Thus, the rate
0.4
1.9
8.1
constant of H/D exchange (k ) is a function of the
rxn
0.2
1.1
3.9
equilibrium deuterium chemisorption (K ) and the rate
D
constant of C−H bond cleavage (k ) on the Pt surface (eq
2
7), which informs us of the rate of C−H bond activation, not
the rate of C−D bond formation, as k , the rate constant of
3
temperature dependence and partial pressure dependence
C−D bond formation is not in the rate law under the
23
studies, respectively. These results clearly demonstrate that
the support can affect the rate of C−H bond activation.
Previous work has studied the exchange rate as a function of
particle size and the differences in TOF observed here based
on support are significantly larger than the minor differences
experimental conditions studied.
This effect holds true as long as the most abundant surface
intermediate (MASI) is D*. Further evidence to support this is
provided by (i) the inverse dependence of D , which indicates
2
a D* covered surface that is energetically most favorable, (ii) if
the R* was energetically more favorable than H*, then the
surface would be primarily R* covered, which would be
expected to give a rate law that has a zero order dependence in
11c−e
previously observed due to particle size;
in fact, H/D
exchange was shown to be structure insensitive when Pt
11d
dispersions are above 10%.
These prior findings help to
2
5
support the notion that the different rates of C−H activation
reported here are largely a function of the support tuning the
alkane, which is not observed, and (iii) calorimetry
experiments done by Campbell and co-workers that are in
−
1
Table 3. Rate Constants (k , s ) Measured as a Function of Alkane and D Partial Pressure for Pt/SiO Catalysts
rxn
2
2
condition
methane
ethane
alkane (Torr) D (Torr) He (Torr) Pt-500S (275 °C) Pt-500 (250 °C) Pt-0 (225 °C) Pt-500S (225 °C) Pt-500 (200 °C) Pt-0 (175 °C)
2
1
1
5
00
00
0
800
400
800
0
400
50
1.1
0.9
1.1
2.9
2.8
2.7
1.2
1.1
1.3
0.54
0.44
0.58
1.3
1.3
1.4
1.3
1.3
1.3
7
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Figure 4. Proposed mechanism of C−H activation and H/D exchange on Pt/SiO catalysts (note: H* and D* are shown to represent the reaction
2
mechanism, and do not indicate the actual number of H*/D* species).
Figure 5. Monitoring H/D exchange between methane and D on Pt-500 at 225 °C, 250 °C, and 275 °C: CH (black ○), CH D (red □), CH D
2
2
4
3
2
(
blue ◊), CHD (green Δ), and CD (magenta ▽).
3
4
accord with a H* covered surface being more stable than a
k2PCH
4
2
6
TOF = K P , when KDPD2 ≫ KCH4
P
and 1
CH
4
CH * surface. On the basis of their thermochemical
3
D D
(6)
(7)
2
measurements, an H* covered surface is approximately 14
−
7
1
kcal mol more enthalpically stable than a CH /H covered
surface.
3
2
k2
krxn
=
KD
d(PCH4)
−
= k P
obs CH
4
The H/D exchange rate dependence on temperature was
studied (Figure 5). As expected, exchange rates increase with
temperature, and Arrhenius analyses (Figure 6) allow for the
determination of the apparent activation energies (Eapp) and
frequency factors (ln A), which are tabulated in Table 4. Pt-0
has the lowest Eapp for methane (28 kcal mol ), while Pt-500S
has the highest Eapp (35 kcal mol ). The E for methane is
higher than that of ethane, which correlates with the C−H
bond dissociation energies of the free alkanes (methane: 105.0
kcal mol , ethane: 100.5 kcal mol ). These results are
consistent with large bodies of literature on H/D exchange of
alkanes on metal catalysts, which show that H/D exchange of
dt
(1)
(2)
k
P
mols of CH activated
mols surface Pt atoms × sec
rxn CH4
4
TOF =
, where TOF =
PD2
−
1
−
1
i V y
j
z
app
krxn = k
j
zP
obsj
z D
28
2
kRT {
(
3)
−
1
−1 29
*
*
TOF = k [CH ][D ]
(4)
3
3
k2P
CH
13
4
ethane is faster than methane. This is also consistent with the
TOF =
KD =
, where
2
energy diagram in Figure 4, where the decreased rate in
methane exchange compared to ethane is due to the difference
in k , while K is not affected. It is interesting to compare the
i
K
P
y
j
CH4 CH4
1/2z
j1 +
+ (K P )
z
j
j
K P )1/2
D
D
z
z
(
2
D
D2
k
{
2
D
k
k2
1
, KCH4 = k , and k = k
Eapp here with previous work from Iglesia and co-workers on
(i) C−H activation of methane on bare Pt surfaces, where they
3
−2
k
(5)
−
1
−2
7
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Figure 6. Arrhenius analysis for methane/D H/D exchange on Pt/
2
SiO catalysts.
2
Figure 7. FTIR difference spectra of CO adsorbed on Pt/SiO2
materials (Pt-500S, red; Pt-500, black; Pt-0, blue).
‡
−1 30,31
measured ΔH of ∼19 kcal mol ,
and (ii) hydrogen
chemisorption isotherms, which indicate that H* adsorption is
−
1
32
44−57
∼
10 kcal mol . Thus, the sum of these two values is ∼29
(e.g., K, Cs) cause red-shifts in the CO adsorption band,
−
1
58
kcal mol , which are the two steps implicated in this work for
and this area has been reviewed by Barthomeuf. Dipole−
dipole interactions have also been reported to cause shifts in
the CO stretching frequency, and may be responsible for the
33,34
C−H activation, which is similar to the Eapp observed here.
The above catalytic data suggest that metal−support
interactions influence the material’s ability to activate C−H
bonds. To gain additional characterization on the Pt particles
59
different CO stretching frequencies observed. In this regard,
6
0
the CO stretching frequency as a function of coverage was
measured (Figure 8), and extrapolation to zero-coverage allows
for estimation of the singleton frequency (Figure 9), the CO
stretching frequency in the absence of CO−CO dipole−dipole
coupling interactions. As can be seen in Figure 8, all linear CO
stretching bands red-shift at lower coverage, such that Pt-500S
in the Pt/SiO samples, the samples were analyzed by FTIR
spectroscopy combined with CO adsorption (see SI for
The difference spectra (before and after
treatment with 5% CO) are shown in Figure 7, and clear
2
3
5−39
details).
40
differences can be observed. First, the linear CO stretching
−
1
band shifts progressively to lower energy in the sodium-
is still red-shifted compared to Pt-0 by about 23 cm , in fact
containing samples, from 2073 cm− for Pt-0 to 2061 cm for
Pt-500S. In general, bands at lower energies (red-shifted)
often indicate that the Pt particles are more electron-rich, as
the increased electron density on Pt can backbond into CO
antibonding orbitals, thereby decreasing the effective CO bond
order and stretching frequency. As described above, the
samples containing sodium are calcined prior to treatment with
the Pt precursor, such that a sodium oxide like species forms.
Sodium oxide species are more basic compared to silica, and
the more basic material is more electron donating, thereby
making the Pt particles more electron-rich and red-shifting the
CO band. Previous work consistent with our results showed
that potassium (K) on silica supported Pt materials caused red-
1
−1
even more so than at high coverage (Δcm = 12). These data
−1
support the hypothesis that sodium on the support results in
electronic modification of the Pt particles.
This work has led us to one main question, which is why is
C−H activation slower on Pt materials that contain sodium?
Analysis of the energy diagram in Figure 4 helps us to address
this question. Specifically, the rate of C−H activation is
dependent on both (i) the ground state energy of the D*
covered surface, which we can equate to an H* covered surface
when ignoring isotope effects, and (ii) the transition state
energy of an open set of sites interacting with a C−H bond to
cleave and form R* and H* (K and k , where K = K ).
H
2
H
D
Therefore, the samples containing sodium either (i) have lower
ground state D* (H*) surfaces, indicating stronger Pt−D(H)
interactions with less modulation of the transition state energy,
or (ii) have higher transition state energies where ground state
modulation is less. Previous measurements by Dumesic and co-
workers showed that hydrogen (and carbon monoxide) heats
4
1,42
shifts in the CO band.
Additional evidence for an
electronic effect is provided by analysis of the linear and
bridged CO species; as the support becomes more basic, the
ratio of linear to bridged CO has been shown to decrease,
which is observed for the Pt/SiO series here, as seen by the
43
2
−
1
−1
increase in the bridging CO band at ∼1800 cm for Pt-500S
of adsorption were ∼5 kcal mol greater for Pt particles on
61
and Pt-500 (Figure 7).
basic supports compared with acidic supports, which is in
accord with scenario (i) where the ground state D* (H*)
surface in Pt-500S is more stable than that of Pt-0. Campbell
has also reported calorimetry data on metal−support
In addition to silica systems, significant work has been done
on basic-zeolite systems with different alkali exchanged
zeolites, which has shown that exchange with alkali cations
a
Table 4. Arrhenius Analysis of H/D Exchange Reactions on Pt/SiO Catalysts
2
methane
ethane
temp. range (° C)
Eapp (kcal mol−1)
ln (A)
temp. range (° C)
Eapp (kcal mol−1
)
ln (A)
Pt-500S
Pt-500
Pt-0
250−300
225−275
225−275
35 (1)
32 (1)
28 (1)
32 (1)
31 (1)
29 (1)
225−275
175−225
150−225
28 (1)
22 (1)
21 (1)
28 (1)
24 (1)
24 (1)
a
Numbers in parentheses indicate two-standard deviations, i.e. 95% confidence intervals.
7
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Figure 8. FTIR difference spectra of CO adsorbed on Pt/SiO materials at varying CO coverages.
2
Figure 9. Extrapolation of linear CO stretching frequencies as a
function of CO coverage to obtain singleton frequencies.
Figure 10. Depiction of proposed ground state stabilization
(exaggerated for clarity) in Pt-500S catalyst due to stronger Pt-D*
interaction compared to Pt-500 and Pt-0. The Pt surfaces with two
open sites (middle species) have all been set to the same energy.
interactions, with the general finding that weaker metal−
support interactions result in stronger metal−adsorbate
62
interactions, influencing catalytic rates. This is in line with
our CO adsorption work above, as red-shifts in CO bands are
often indicative of stronger metal−CO interactions. Therefore,
as shown by both catalytic measurements and CO
73
adsorption. Additionally, H/D exchange studies have been
74
previously shown to be affected by changes in support.
it is proposed that Pt particles in the Pt/SiO series described
It should be noted, however, that metal−support inter-
2
75
here are electronically modified by the support, which results
largely in ground state stabilization of D* (H*) surfaces on
more basic supports, more so than transition state stabilization,
and thus slower rates of C−H activation when D* is the MASI,
as depicted in Figure 10.
actions have been a subject of debate. One catalytic reaction
studied in particular was n-hexane aromatization to ben-
7
6,77
zene,
a reaction which requires C−H bond activation. A Pt
on K exchanged LTL-zeolite (Pt/K−L) was reported as a
highly active and selective catalyst for conversion of n-hexane
to benzene; this led to questions of why was this material
8
Other work has been reported in favor of metal−support
effects. For example, Haller and co-workers demonstrated that
basic supports could influence the electron-richness of a Pt
particle as assessed by both catalytic reactions (e.g.,
better than others, and gave rise to many studies aimed to
understand Pt/K−L’s superior activity. Many explanations
were proposed, including the pore geometry of the
6
3
78−80
81
competitive toluene/benzene hydrogenation and hydro-
zeolite,
Pt particle size, selectivity as a function of Pt
6
4
82−85
genolysis ) and spectroscopy (e.g., X-ray spectroscopic
coking and deactivation,
as K−L is an electron-donating basic support.
and metal−support interactions,
6
5
63,75,86,87
measurement), in accord with spectroscopies on other
4
1−43
materials.
Correlations between the acidic/basic nature
Evidence for metal−support interactions in Pt/K−L were
provided by FTIR spectroscopy with CO adsorption, which
indicated that the Pt particles in Pt/K−L were electron-rich
of the support as assessed by CO adsorption and catalytic
activity have been reported; these include heptane reform-
6
6−68
69,70
44−46
ing,
hydrogenolysis,
aromatic hydrogenation,
compared to other more acidic supports, like our work
71
50,51,53,58,88
and catalyst deactivation studies. Catalytic studies on formic
acid decomposition and water−gas shift have also demon-
strated that sodium can influence activity and selectivity, in
some cases accelerating rates due to the weakening of the
formate C−H bond. Supported organometallic complexes
have also been reported to be greatly modified by the support,
above.
Platinum on a nonzeolitic basic support,
aluminum stabilized MgO, by Davis and Derouane, displayed
similar conversions and selectivities compared with the
8
9−92
aforementioned Pt/K−L catalyst,
and was originally
72
proposed to behave similarly due to the basic nature of the
MgO support; FTIR spectroscopy and CO adsorption
7
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93
demonstrated red-shifts in the CO bands, in accord with the
basic nature of the support. Thus, there is a rich history of
work on metal−support effects and the reported consequences
they can have on catalytic activity, and our work provides
additional data to demonstrate their potential effect on
catalytic reactions. Our results do not rule out other effects,
which may also play a significant role in influencing the activity
of a catalytic metal.
Knaeble, and Elaine Gomez for helpful discussions. We thank
Jarid Metz for help with the Pt/SiO syntheses.
2
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ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acscatal.9b03807.
4
492−4501. (b) Ji, Y. Y.; van der Eerden, A. M. J.; Koot, V.;
■
*
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D. C. Influence of support ionicity on the hydrogen chemisorption of
Pt particles dispersed in Y zeolite: consequences for Pt particle size
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Text and figures giving experimental details, character-
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AUTHOR INFORMATION
Corresponding Author
E-mail: aaron.sattler@exxonmobil.com.
ORCID
Aaron Sattler: 0000-0001-5871-8646
Michele Paccagnini: 0000-0003-3511-9231
Michael P. Lanci: 0000-0001-8176-8895
■
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank Jay Winkler (Caltech), Enrique Iglesia (UC
Berkeley), Stu Soled, Pedro Serna, Wesley Sattler, William
■
7
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