Active Pd(II) complexes: Enhancing catalytic activity by ligand effect for carbonylation of methyl nitrite to dimethyl carbonate

Article abstract of DOI:10.1039/c7cy01305a

Palladium (Pd)-based catalysts have been widely used for carbonylation of methyl nitrite to dimethyl carbonate (DMC), but a high-performance chloride free catalyst combining both excellent carbon monoxide (CO) conversion and DMC selectivity has not been developed yet. In this work, a chloride free, Pd-based catalyst with good activity and selectivity (conversion of CO: 60.1%, selectivity to DMC: 99.9%) has been successfully fabricated. By thorough characterization and analysis, it is found that the good catalytic activity is positively correlated with the high oxidation states of the Pd species, which could be tuned by their ability to accept the backdonation electron of the ligands. The strong electron backdonation from Pd to π? antibonding orbitals of the ligand in the palladium acetylacetonate [Pd(acac)₂] complex accelerates the step where Pd^δ+ reoxidizes to Pd(ii), resulting in the higher catalytic activity. In addition, a catalytic mechanism was proposed based on the results of X-ray photoelectron spectroscopy and in situ diffuse reflectance infrared spectroscopy. This work not only explains the positive relationship between the catalytic activity and the oxidation state of the Pd species, but also provides a new way to enhance catalytic performance by utilizing the abilities of accepting the backdonation electron of the ligands.

Full text of DOI:10.1039/c7cy01305a

View Article Online
View Journal
Catalysis
Science &
Technology
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: H. Tan, Z. Wang,
Z. Xu, J. Sun, Z. Chen, Q. Chen, Y. chen and G. Guo, Catal. Sci. Technol., 2017, DOI:
10.1039/C7CY01305A.
This is an Accepted Manuscript, which has been through the
Volume 6 Number 1 7 January 2016 Pages 1–308
Royal Society of Chemistry peer review process and has been
accepted for publication.
Catalysis
Science &
Technology
Accepted Manuscripts are published online shortly after
www.rsc.org/catalysis
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
ISSN 2044-4753
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
PAPER
Qingzhu Zhang et al.
Catalytic mechanism of C–F bond cleavage: insights from QM/MM
analysis of fluoroacetate dehalogenase
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
rsc.li/catalysis

Please do not adjust margins
Catalysis Science & Technology
Page 1 of 7
View Article Online
DOI: 10.1039/C7CY01305A
Journal Name
ARTICLE
Active Pd(II) Complexes: Enhancing Catalytic Activity by Ligand
Effect for Carbonylation of Methyl Nitrite to Dimethyl Carbonate
Hong-Zi Tan,ab Zhi-Qiao Wang,*ab Zhong-Ning Xu,*ab Jing Sun,a Zhe-Ning Chen,a Qing-Song Chen,a
Yumin Chen,a and Guo-Cong Guo*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Pd-based catalysts have been widely used for carbonylation of methyl nitrite to dimethyl carbonate, but a high-
performance chloride-free catalyst combining with both excellent CO conversion and DMC selectivity has not been
developed yet. In this work, a chloride-free Pd-based catalyst with good activity and selectivity (conversion of CO: 60.1%,
selectivity to DMC: 99.9%) has been been successfully achieved. By the thorough characterizations and analysis, it is found
that the good catalytic activity is positively correlated with high oxidation states of Pd species, which could be tuned by the
abilities of accepting back-donation electron of ligands. The strong electron back-donation from Pd to π* antibonding
orbitals of ligand in the Pd(acac)2 complex accelerates the step of Pdδ+ re-oxides to Pd(II), resulting in the higher catalytic
activity. In addition, the catalytic mechanism was proposed based on the results of XPS and in-situ DRIR spectroscopy. This
work not only sheds light on the positive relationship between the catalytic activity and the oxidation state of Pd species,
but also provides a brand new way to enhance catalytic performance by utilizing the abilities of accepting back-donation
electron of ligands.
www.rsc.org/
In recent years, much attention has been attracted to the
research and development of DMC synthesis. Considerable
efforts have been devoted to the route of vapor-phase methyl
1. Introduction
Dimethyl carbonate (DMC) is an important and
environmentally friendly chemical raw material and
nitrite carbonylation to DMC developed by UBE industries
owing to its unique advantages.13, 14 This route avoids using
toxic phosgene. In addition, the byproduct of NO can be
recycled to produce the raw material of methyl nitrite.
However, this route does not implement industrialization at
present, owing to the lack of high-performance catalyst for
carbonylation of methyl nitrite to DMC.
2
intermediate.1, Owing to its plentiful methyl group and
carbonyl group, nontoxic, excellent solubility3, DMC has been
widely used in polymer synthesis3, 4, fuel additives3, and
5
solvent1. Additionally, it has been used as an important solvent
in the electrolyte of lithium battery due to its high dielectric
constant.6 Currently, there are several industrial processes for
Many catalysts have been developed for the route of
production
of
DMC,
9
,
such
as
oxycarbonylation10-12
.
phosgenation7,
vapor-phase carbonylation of methyl nitrite to DMC. In the
15
transesterification8,
methanol
early stages, a chloride-containing catalyst, Pd-CuCl2/γ-Al2O3
,
However, there are some disadvantages for these routes. The
phosgenation route adopts the hypertoxic phosgene as raw
material. Oxacyclopropane and epoxy propane used in the
transesterification route are from crude oil, resulting in a high
cost of production. In addition, the route of methanol
oxycarbonylation not only owns a low methanol conversion,
but also magnifies the danger of explosion owing to the
introduction of oxygen. Therefore, it is of great importance to
explore a new route for DMC synthesis.
presents perfect activity with 71% CO conversion and 99%
DMC selectivity. But its catalytic activity was almost
completely lost after several hours due to the loss of chloride,
showing a poor stability. What’s more, the chloride-containing
catalysts also suffer from other problem, such as the purity of
DMC and the corrosion of reaction apparatus.13 Therefore,
many chloride-free catalysts have been developed.
A
representative chloride-free catalyst of Pd(0)/NaY exhibited a
good stability.13 However, the catalytic activity is not high
enough (21% CO conversion and 90% DMC selectivity).13
Therefore, it is very essential and urgent to develop a high-
performance chloride-free catalyst for methyl nitrite
carbonylation to DMC.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 2 of 7
View Article Online
DOI: 10.1039/C7CY01305A
Journal Name
ARTICLE
Table 1 The correspondences between different catalysts and Pd complexes.
Number
C1
C2
C3
C4
C5
C6
Catalysts
Pd(II)/NaY
Pd(acac)2
Pd(II)/NaY
Pd(OAc)2
Pd(II)/NaY
Pd(NO3)2
Pd(0)/NaY
Pd(acac)2
Pd(0)/NaY
Pd(OAc)2
Pd(0)/NaY
Pd(NO3)2
Precursors
Preparation of Pd(0)/NaY catalysts:
C1 C2 and C3 catalysts were reduced at 120 °C under pure
H2 atmosphere to obtain Pd(0)/NaY [Pd(acac)2], Pd(0)/NaY
In this work, we developed a high-performance chloride-
free Pd(II)-based catalyst. It exhibits more than 60.1% CO
conversion and 99.9% DMC selectivity for methyl nitrite
carbonylation to DMC. A series of characterizations, TEM, XPS,
and in-situ DRIRS, were performed to investigate the origin of
the high catalytic activity. Ligand effect was proved to be
responsible for the enhancing catalytic activity by impacting
the Pd valence state. In addition, a catalytic mechanism was
proposed based on the results of catalysts characterization
and performance evaluation.
,
[Pd(OAc)2] and Pd(0)/NaY [Pd(NO3)2] catalysts, denoted as C4
,
C5 and C6, respectively.
Preparation of unsupported Pd(acac)2 and Pd powder catalysts:
Pure Pd(acac)2 and Pd powder were dispersed on silica
wool used as contrast catalysts without support.
2.3 Catalyst Characterization
Inductively coupled plasma (ICP) spectroscopy was
performed with an Ultima 2 plasma emission spectrometer
from Jobin Yvon.
2. Experimental Section
2.1 Materials
The Brunauer-Emmett-Teller (BET) surface areas were
calculated from the N2 adsorption-desorption isotherms with
the BET method, which were performed on Micromeritics
ASAP 2020 at liquid nitrogen temperature (77 K).
Pd(acac)2 (AR; Sino-Platinum Co., Ltd., China); Pd(OAc)2 (AR;
Sino-Platinum Co., Ltd., China); Pd(NO3)2·2H2O (AR; Sino-Platinum
Co., Ltd., China); Pd powder (AR; Sino-Platinum Co., Ltd., China);
NaY zeolite (Nankai Catalyst Factory) and deionized water (18
MΩ·cm) were used throughout the experiments. All chemicals were
used as received without further purification.
X-ray photoelectron spectroscopy (XPS) analysis was
performed with a VG Escalab 250 spectrometer equipped with
an X-ray source by employing an Al-Kα (1486.7 eV) anode.
Transmission electron microscopy (TEM), high angle
annular dark field scanning transmission electron microscopy
(HAADF-STEM) and high angle annular dark field scanning
transmission electron microscopy-energy dispersive X-ray
(HAADF-STEM-EDX) mapping were performed on a Tecnai G2
F20 field-emission transmission electron microscope operating
at an acceleration voltage of 200 kV. All catalyst samples were
dispersed in ethanol by ultrasonic, then dropped it onto
carbon-coated copper grids for the above measurements.
In-situ diffuse reflectance infrared spectroscopy (DRIRS)
measurements were performed on a Nicolet 6700 diffuse
reflectance infrared spectrometer equipped with a stainless
steel in-situ IR flow cell. The powder samples were placed into
the cell, and pretreated in N2 flow for 30 min at 180 °C. After
cooling down to the 120 °C, a reference spectrum was
recorded. Then, the reactants were introduced in constant
flowing, and the spectra were recorded at a resolution of 4 cm-
2.2 Catalyst Preparation
In order to investigate ligand effect, a series of chloride-
free Pd-based catalysts have been prepared by wet
impregnation as follows to ensure consistent parameters.
Preparation of Pd(II)/NaY catalysts:
Pd(acac)2/NaY catalyst was prepared as below. Defined
amount of Pd(acac)2 was dispersed in 10 mL of deionized
water. 1.0 g NaY zeolite was subsequently added into the
solution and stirred for overnight. Then, the precipitate dried
at 80 °C in vacuum for 10 h. The catalyst precursor was
calcined at 150 °C for 4 h in air to obtain Pd(II)/NaY [Pd(acac)2]
catalyst, denoted as C1 (Table 1).
Adopting Pd(OAc)2 and Pd(NO3)2·2H2O as the palladium
source, we prepared Pd(II)/NaY [Pd(OAc)2] and Pd(II)/NaY
[Pd(NO3)2] catalysts with the similar process to that of
Pd(II)/NaY [Pd(acac)2] catalyst. These two catalysts were
denoted as C2 and C3, respectively.
1
.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 2
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 3 of 7
View Article Online
DOI: 10.1039/C7CY01305A
Journal Name
ARTICLE
2.4 Catalytic Activity Evaluation
Catalytic activities of catalysts for vapor-phase
carbonylation of methyl nitrite to DMC were measured using a
fixed-bed quartz tubular reactor. The center of the quartz
tubular reactor was loaded with 200 mg of catalysts. This
reaction was performed under atmospheric pressure using
reactant gases composed of 16.9% CO, 51.6% MN (methyl
nitrite), 2.4% Ar (as an internal standard), and 29.1% N2 (as a
balance gas) at a weight hour space velocity (WHSV) of 1440
L·kgcat.-1·h-1 and a temperature of 120 °C. The composition of
the reactant gases and reaction products were monitored
using an on-line Shimadzu GC-2014 gas chromatograph
equipped with a thermal conductivity detector and a flame
ionization detector.
Fig. 1 The conversion of CO and selectivity to DMC over Pd(II)/NaY catalysts (C1, C2 and
C3) for carbonylation of methyl nitrite to DMC at 120 °C and 0.1 MPa. Reaction
conditions: 200 mg catalyst, weight hour space velocity (WHSV) = 1440 L·kgcat.-1·h-1, CO:
MN: Ar : N2 = 16.9 : 51.6 : 2.4 : 29.1 (volume).
The conversion of CO, the selectivity to DMC and the
weight-time yields (WTY) of DMC were calculated using the
following formulas:
Furthermore, the comparison of catalytic activity and
selectivity over Pd(II)/NaY and Pd(0)/NaY catalysts were shown
Conversion of CO (%) = ([CO]in / [Ar]in − [CO]out / [Ar]out) / ([CO]in
/ [Ar]in) × 100%
in Table S1. The conversion of CO over C4
46.8% and 39.6%, which are lower than those of C1
However, although C4 C5 and C6 catalysts have a certain
amount of CO conversion, the main product is DMO not DMC.
Due to the palladium precursors of C1 and C4 C2 and C5 C3
,
C5 and C6 are 52.1%,
,
C2 and C3
.
,
Selectivity to DMC (%) = (SDMC × R-FDMC) / (SDMC × R-FDMC + SDMO
× R-FDMO) × 100%
,
,
and C6 are the same respectively, we confirmed that Pd(II)
species are beneficial to DMC and Pd(0) species are beneficial
to DMO for vapor-phase carbonylation of methyl nitrite
reaction.
WTY of DMC (g·kgcat.−1·h−1) = conversion of CO (%) × selectivity
to DMC (%) × WHSV of CO (L·kgcat.-1·h-1) × 90.08 g·mol-1 / (22.4
L·mol−1)
To gain more insights into the effect of active species on
the product selectivity, unsupported Pd(acac)2 and Pd power
were used as contrast catalysts for the carbonylation reaction
of methyl nitrite. The tendencies of product selectivity in the
contrast experiments were shown in Fig. 2. For unsupported
Pd(acac)2 catalyst, the selectivity to DMC shows an obvious
decline at the beginning, and decreases to a stable value at the
last stage. On the contrary, the selectivity to DMO exhibits a
significant increase at first, and increases to a steady state at
last. And while for unsupported Pd powder catalyst, the
selectivity to DMC holds a low value (approximately 25%) all
the time, which is close to that of Pd(acac)2 in the late stage.
Whereas the selectivity to DMO can be stable around 75%.
Therefore, these results convincingly again demonstrate that
Pd(II) and Pd(0) are the catalytic active species for DMC and
DMO, respectively.
Where [Ar]in and [Ar]out are the concentrations of Ar at the
inlet and outlet, [CO]in and [CO]out are the concentrations of
CO at the inlet and outlet, respectively. SDMC and SDMO are the
peak areas of dimethyl carbonate and dimethyl oxalate, R-FDMC
and R-FDMO are the relative correction factors of dimethyl
carbonate and dimethyl oxalate, respectively.
3. Results and Discussion
3.1 Catalytic Activity
Three Pd(II)/NaY catalysts (C1, C2 and C3) were synthesized
under the same conditions except using different palladium
complexes [Pd(acac)2, Pd(OAc)2, Pd(NO3)2·2H2O], respectively.
Three Pd(0)/NaY catalysts (C4, C5 and C6) were synthesized by
reducing the corresponding Pd(II)/NaY catalysts, respectively.
The evaluation of catalytic activity over Pd(II)/NaY catalysts
and Pd(0)/NaY catalysts for vapor-phase carbonylation of
methyl nitrite to DMC was carried out in a home-made
catalytic evaluation device.
3.2 Insight into ligand effect
Now we learnt that different Pd(II) complexes with
different ligands brought with definitely different catalytic
activities. It could be called ligand effect. But how did it
happen?
The catalytic performances of Pd(II)/NaY catalysts were shown
in Fig. 1. All Pd(II)/NaY catalysts presented quite high
Table 2 The actual Pd loading and BET surface area of all catalysts
selectivity to DMC (>99%). The conversion of CO over C1, C2
Catalysts
Actual Pd loading (%)
SBET (m2·g-1)
590.3
and C3 catalysts are 60.1%, 56.1% and 53.9%, respectively,
C1
C2
C3
1.59
1.68
1.65
suggesting that the order of catalytic activities for vapor-phase
516.7
carbonylation of methyl nitrite to DMC is C1 > C2 > C3.
483.8
SBET: BET surface area of catalysts.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 4 of 7
View Article Online
DOI: 10.1039/C7CY01305A
ARTICLE
Journal Name
To get insight into the origin, we firstly investigated the O-K for the fresh C1 catalyst were further measured and
physicochemical properties of Pd(II)/NaY catalysts. As listed in shown in Fig. 3c, 3d, 3e and 3f, respectively. It is clear that all
Table 2, the actual Pd loadings for the Pd(II)/NaY catalysts measured elements are uniformly distributed, further
determined by ICP are close, which eliminates the influence of demonstrating an atomically dispersion of Pd species on the
Pd loading on the catalytic activity. The BET surface area of C1 support of NaY zeolite.
is 590.3 m2·g-1, which is higher than that of C2 (516.7 m2·g-1)
Electronic state of active species is a key parameter in
and C3 (483.8 m2·g-1). The order of the BET surface area (C1 > catalytic process. Therefore, the oxidation states of Pd species
C2 > C3) is consistent with that of the catalytic activity, in different catalysts were investigated to get insight into the
indicating that the larger BET surface area may be beneficial origin of ligand effect. As shown in Fig. 4, the binding energy
for the catalytic activity.
(BE) of Pd 3d5/2 peaks of fresh C1, C2 and C3 catalysts are
338.21 eV, 338.05 eV and 337.71 eV, respectively, decreasing
from C1 to C3. Higher binding energy means higher oxidation
state. It is clear that the trend of Pd species oxidation state in
different catalysts is C1 > C2 > C3, which is consistent with that
of their catalytic activities, indicating that the Pd species with
higher oxidation state showed higher catalytic activity. It
means that Pd species from Pd(acac)2 have higher valence
state than those of Pd(OAc)2 and Pd(NO3)2. This phenomenon
could be explained by the abilities of accepting electron back-
donation of different ligands. Considering the difference of
coordination structure and coordination numbers in three
Fig. 2 The tendencies of product selectivity over unsupported (a) Pd(acac)2 and (b) Pd
powder for carbonylation reaction of methyl nitrite at 120 °C and 0.1 MPa. Reaction
conditions: 20 mg catalyst, weight hour space velocity (WHSV) = 1440 L·kgcat.-1·h-1, CO:
MN: Ar : N2 = 16.9 : 51.6 : 2.4 : 29.1 (volume).
Fig. 4 Pd 3d XPS spectra of Pd(II)/NaY catalysts: (a) C1, (b) C2 and (c) C3.
In order to investigate the distribution of the palladium
active component, TEM, HAADF-STEM and HAADF-STEM-EDX
mapping of C1 catalyst were performed. As shown in Fig. 3a
and 3b, there is no obvious nanoparticle in the TEM and
HAADFF-STEM images of the fresh C1 catalyst, while EDX
(shown in Fig. S1) of the image indicated the presence of Pd,
thus providing direct evidence on Pd species dispersed on the
support. The HAADF-STEM-EDX mapping of Pd-L, Si-K, Al-K and
Fig. 3 TEM image (a), HAADF-STEM image (b), and HAADF-STEM-EDX mapping of Pd-L
(c), Si-K (d), Al-K (e), O-K (f) of fresh C1 catalyst.
Fig. 5 Pd 3d XPS spectra of (a) fresh and (b) engaged Pd(II)/NaY (C1) catalyst.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 5 of 7
View Article Online
DOI: 10.1039/C7CY01305A
Journal Name
ARTICLE
palladium complexes [Pd(acac)2, Pd(OAc)2, and Pd(NO3)2], the there is only small amount CO adsorbed in top-site (peak at
higher electronegativity of coordination O atom and the 2111 cm-1) after N2 sweeping, indicating that CO adsorbed on
chelate structure in Pd(acac)2 complex16 lead to a strong Pd(II) in linear mode insert to form the carbonyl methoxy
accepting electron back-donation ability of acac ligand. Owing intermediate.
to the stronger ability of accepting electron back-donation
The in-situ DRIRS of the reaction of CO and MN on C1
from Pd to π* antibonding orbitals of acac- ligand than that of catalyst has been measured at 120 °C (Fig. 6). The peaks at
-
OAc- and NO3 ligands, Pd species in C1 catalyst show higher 1546 cm-1 and 1392 cm-1 are corresponding to the symmetric
oxidation state, which leaded to the best catalytic and anti-symmetric stretching of O-C-O species in MMC
(namely CH3OCO-), respectively.15 As the increasing of reaction
performance.
In order to better understand the ligand effect, density time from 2 min to 15 min, the stretching strength of O-C-O
functional theory (DFT) calculations were performed to
elucidate the electronic nature of C1, C2 and C3 catalysts. Our
calculations show that the ionization potentials (IPs) follow the
trend Pd(acac)2 (7.7 eV) < Pd(OAc)2 (9.7 eV) < Pd(NO3)2 (11.2
eV), in antiparallel to the activity of catalysts. This can be
rationalized by considering that the oxidation of palladium
center is critical for the catalytic process, which should benefit
from the low IP. Therefore, the acac- ligand with a strong
accepting ability facilitates the electron donation from
palladium center, which stabilizes the palladium in a high
oxidation state, and further promotes the catalytic reaction to
DMC.
It can be concluded that Pd species with high oxidation
state are the active center for vapor-phase carbonylation of
methyl nitrite to DMC. The ligand with strong ability of
accepting electron-donation is vital to obtain high catalytic
activity, which is the ligand effect.
Fig. 6 In-situ DRIR spectra of the reaction between CO and MN on C1 catalyst at 120 °C.
species have been increasing. The band from 1224 to 1143 cm-
3.3 Catalytic mechanism
1
should be assigned to the vibration of C-O-C species in
Pd 3d XPS spectra of the fresh and engaged C1 catalysts
were measured and shown in Fig. 5. The binding energy of Pd
3d5/2 and Pd 3d3/2 peaks of the fresh Pd(II)/NaY catalyst (Fig.
5a) are 338.21 eV and 343.58 eV respectively, indicating that
the state of Pd in the fresh Pd(II)/NaY catalyst is Pd(II).13, 17-19 In
the engaged Pd(II)/NaY C1 catalyst (Fig. 5b), two peaks at
337.15 eV and 342.15 eV belong to Pd(II) species, while two
new peaks at 335.04 eV and 340.33 eV should be assigned to
the reduced Pd species (Pdδ+, 0 < δ < 2), which may be the
result of CO reduction during the catalytic process. Moreover,
the proportion of Pd(II) and Pdδ+ species in the engaged
catalyst is 60.47% and 39.53%, respectively. It could be verified
that the major Pd(II) is the catalytic active species for DMC
synthesis. Owing to the existence of oxidative CH3ONO, a
procession of Pd nanoparticle re-oxide to palladium complexes
would be existed, in which the effect of ligands was significant.
Two kinds of Pd species with different oxidation state might be
related with the catalytic reaction mechanism.
MMC.22, 23 More interestingly, a couple of new peaks appear at
1780 and 1298 cm-1 with the pass of time, which are
corresponding to the C=O and C-O species in gaseous DMC,
respectively.22 Moreover, the peaks at 2869 cm-1 (shown in Fig.
S3) and 1462 cm-1 (shown in Fig. 6) are assigned to the
symmetric stretching and deformation C-H vibration of the
CH3- in DMC.22
Combined with the results of in-situ DRIR spectra, the
catalytic mechanism of DMC formation on Pd(II)/NaY catalyst
was reasonably proposed. The pivotal intermediate of
CH3OCO- was formed first, then intermolecular coupling
elimination occurs between the CH3OCO- intermediate and
another CH3ONO, which result in the formation of DMC and
the recycle of Pd(II)L2 active species. Rivetti and Romano have
also proposed that DMC is produced from
a mono-
methoxycarbonyl Pd complex upon nucleophilic attack of
methoxy ion.24, 25
However, part of Pd(II)L2 were reduced by the CO feed
gas to form the Pdδ+ species. The process of Pd nanoparticle
re-oxide to palladium complexes by CH3ONO would be existed,
which protrude the effect of ligand in this process.
The in-situ DRIRS has become an important technique to
identify the intermediates in catalytic reactions and predict the
reaction mechanism. So, the corresponding in situ DRIRS were
further performed for analysing the reaction process. As
shown in Fig. S2, adsorption of CO on the C1 catalyst was
investigated using in situ DRIRS, which was operated at the
temperature of 10 °C to prevent Pd(II) species being reduced
by CO. Before N2 sweeping, the peaks at 2167 and 2122 cm-1
are attributed to the bimodal of CO in gas phase 20, 21, while
the peak at 2353 cm-1 is attributed to CO2 in air. However,
According to the distinction of product selectivity and CO
conversion over Pd(II)/NaY and Pd(0)/NaY catalyst in the same
palladium complex system, it could be proposed that Pd(II) is
the active species and Pdδ+ is an intermediate species to be re-
oxidized to Pd(II), which is consistent with the XPS results of
engaged Pd(II)/NaY C1 catalyst. Therefore, we can reasonably
concluded that the strong ability of accepting electron-
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 6 of 7
View Article Online
DOI: 10.1039/C7CY01305A
ARTICLE
Journal Name
12 M. J. Schneider, M. Haumann, M. Stricker, J. Sundermeyer
and P. Wasserscheid, J. Catal., 2014, 309, 71–78.
13 Y. Yamamoto, T. Matsuzaki, S. Tanaka, K. Nishihira, K. Ohdan,
A. Nakamura and Y. Okamoto, J. Chem. Soc., Faraday Trans.,
1997, 93, 3721–3727.
donation from Pd to π* antibonding orbitals of ligand in the
Pd(acac)2 complex accelerate the step of intermediate Pdδ+ re-
oxidized to Pd(II), resulting in the higher catalytic activities
than Pd(OAc)2 and Pd(NO3)2 complexes.
14 T. Matsuzaki and A. Nakamura, Catal. Sur. Japan, 1997, 1,
77–88.
15 D.-M. Lv, Z.-N. Xu, S.-Y. Peng, Z.-Q. Wang, Q.-S. Chen, Y. Chen
and G.-C. Guo, Catal. Sci. Technol., 2015, , 3333–3339.
16 W.-P. Liu, L. Guang, S.-P. Pu, W.-G. Gao and G.-X. Yan,
Precious Metals, 2004, 25, 12–16.
17 Y.-Y. Dong, Y.-L. Shen, Y.-J. Zhao, S.-P. Wang and X.-B. Ma,
4. Conclusions
5
In summary, a high-performance (conversion of CO: 60.1%,
selectivity to DMC: 99.9%) Pd(acac)2/NaY catalyst (C1) for
carbonylation of methyl nitrite to DMC has been successfully
ChemCatChem, 2015,
18 Z.-N. Xu, J. Sun, C.-S. Lin, X.-M. Jiang, Q.-S. Chen, S.-Y. Peng,
M.-S. Wang and G.-C. Guo, ACS Catal., 2013, , 118–122.
7, 2460–2466.
synthesized. For comparison, a series of Pd(II)/NaY (C2 and C3
)
and Pd(0)/NaY (C4, C5 and C6) catalysts also been synthesized.
3
ICP measurement eliminates the influence of Pd loading on the
catalytic activity. TEM, HAADF-STEM and HAADF-STEM-EDX
measurements proved that the Pd indeed atomically
distributed on the support of NaY zeolite. Based on the XPS
and in situ DRIR spectroscopy, the catalytic mechanism of DMC
formation on Pd(acac)2/NaY catalyst was also proposed that
Pdδ+ may be an intermediate species and strong electron back-
donation effect between Pd species and acac- ligand in the
Pd(acac)2 complex may accelerate the step of intermediate
Pdδ+ re-oxidized to Pd(II). This work would provide insights for
developing industrial catalysts for vapor-phase carbonylation
of methyl nitrite to DMC.
19 R.-X. Jiang, Y.-J. Wang, X.-Q. Zhao, S.-F. Wang, C.-Q. Jin and C.
Zhang, J. Mol. Catal. A-Chem., 2002, 185, 159–166.
20 M. Jabłońska, A. Król, E. Kukulska-Zajac, K. Tarach, L.
Chmielarz and K. Góra-Marek, J. Catal., 2014, 316, 36–46.
21 T. Baidya, P. Bera, B. D. Mukri, S. K. Parida, O. Kröcher, M.
Elsener and M. S. Hegde, J. Catal., 2013, 303, 117–129.
22 J.-X. Yang, W. Cheng, G. Liu, W. Li and W.-D. Xiao, J. Mol.
Catal. A-Chem., 2009, 314, 63–70.
23 X.-G. Zhao, Q. Lin and W.-D. Xiao, Applied Catalysis A:
General, 2005, 284, 253–257.
24 U. R. Franco and Rivetti, J. Organomet. Chem., 1979, 174
221–226.
,
25 U. R. Franco and Rivetti, J. Organomet. Chem., 1978, 154
323–326.
,
Conflicts of interest
There are no conflicts of interest to declare.
Acknowledgements
This work was supported by the National Key R&D Program of
China (2017YFA0206802), the National Natural Science
Foundation of China (91545201, 91645116, 21403237), the
Programs of the Chinese Academy of Sciences (XDB20010100,
ZDRW-CN-2016-1), and China Postdoctoral Science Fundation
(2016LH0018).
Notes and references
1
B. Schaffner, J. Holz, S. P. Verevkin and A. Borner,
ChemSusChem, 2008, , 249–253.
1
2
3
P. Tundo and M. Selva, Acc. Chem. Res., 2002, 35, 706–716.
N. Keller, G. Rebmann and V. Keller, J. Mol. Catal. A-Chem.,
2010, 317, 1–18.
4
5
6
J.-C. C. T. Sakakura, and H. Yasuda, Chem. Rev., 2007, 107,
2365–2387.
M. A. Pacheco and C. L. Marshall, Energy & Fuels 1997, 11, 2–
29.
M. S. Park, G.-X. Wang, Y.-M. Kang, D. Wexler, S.-X. Dou and
H.-K. Liu, Angew. Chem. Int. Ed., 2007, 46, 750–753.
H. Babad and A. G. Zeiler, Chem. Rev., 1972, 73, 75–91.
J. Xu, K.-Z. Long, T. Chen, B. Xue, Y.-X. Li and Y. Cao, Catal.
7
8
Sci. Technol., 2013,
J.-Q. Wang, J. Sun, W.-G. Cheng, C.-Y. Shi, K. Dong, X.-P.
Zhang and S.-J. Zhang, Catal. Sci. Technol., 2012, , 600–605.
10 A. Bansode and A. Urakawa, ACS Catal., 2014, , 3877–3880.
3, 3192–3199.
9
2
4
11 T. Sakakura and K. Kohno, Chem. Commun., 2009, 1312–
1330.
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 7
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C7CY01305A
161x118mm (300 x 300 DPI)