Tailoring the framework composition of carbon nitride to improve the catalytic efficiency of the stabilised palladium atoms

Article abstract of DOI:10.1039/c7ta04607c

Graphitic carbon nitride (g-C₃N₄) exhibits unique properties for the preparation of single-atom heterogeneous catalysts (SAHCs) due to the presence of sixfold nitrogen-based coordination sites in the lattice. Despite the potential to profoundly affect the metal stabilisation and resulting catalytic properties, no work has previously investigated the effect of modifying the carrier composition. Here, we study the impact of doping carbon in g-C₃N₄ on the interaction with palladium. This is achieved by introducing carbon-rich heterocycles (barbituric acid or 2,4,6-triaminopyrimidine) during the synthesis of bulk and mesoporous g-C₃N₄. Palladium is subsequently introduced via microwave-irradiation-assisted deposition, which emerges as a highly effective route for the dispersion of single atoms. Detailed characterisation confirms the controlled variation of the C/N ratio of the lattice and reveals the complex interplay with the crystal size, surface area, amount of defects, basic properties and thermal stability of the carrier. Atomic dispersions of palladium with similar surface densities could be obtained on both the stoichiometric and carbon-doped carriers in mesoporous form, but appreciable differences are observed in the ratio of Pd²⁺/Pd⁴⁺. The latter, which provides a measure of the degree of electron transfer from the metal to the carrier, is found to correlate with the activity in the continuous flow semi-hydrogenation of 2-methyl-3-butyn-2-ol. Density functional theory calculations support the decreased adsorption energy of palladium upon doping with carbon and reveal the potentially significant impact of oxygen-containing defects. The findings demonstrate the importance of understanding the metal-carrier interaction to optimise the catalytic efficiency of SAHCs.

Full text of DOI:10.1039/c7ta04607c

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Ramirez, J. Mater. Chem. A, 2017, DOI: 10.1039/C7TA04607C.
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ISSN 2050-7488
PAPER
Kun Chang, Zhaorong Chang et al.
Bubble-template-assisted synthesis of hollow fullerene-like
MoS2 nanocages as a lithium ion battery anode material
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Tailoring the framework composition of carbon nitride to improve
the catalytic efficiency of the stabilised palladium atoms
E. Vorobyeva,a Z. Chen,a S. Mitchell,a R. K. Leary,b P. Midgley,b J. M. Thomas,b R. Hauert,c E. Fako,d
N. Lópezd and J. Pérez-Ramírez*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Graphitic carbon nitride (g-C3N4) exhibits unique properties for the preparation of single-atom
heterogeneous catalysts (SAHCs) due to the presence of sixfold nitrogen-based coordination sites in the
lattice. Despite the potential to profoundly affect the metal stabilisation and resulting catalytic properties, no
work has previously investigated the effect of modifying the carrier composition. Here, we study the impact
of doping carbon in g-C3N4 on the interaction with palladium. This is achieved by introducing carbon-rich
heterocycles (barbituric acid or 2,4,6-triaminopyrimidine) during the synthesis of bulk and mesoporous
g-C3N4. Palladium is subsequently introduced via microwave-irradiation-assisted deposition, which emerges
as a highly effective route for the dispersion of single atoms. Detailed characterisation confirms the
controlled variation of the C/N ratio of the lattice and reveals the complex interplay with the crystal size,
surface area, amount of defects, basic properties and thermal stability of the carrier. Atomic dispersions of
palladium with similar surface densities could be obtained on both the stoichiometric and carbon-doped
carriers in mesoporous form, but appreciable differences are observed in the ratio of Pd2+/Pd4+. The latter,
which provides a measure of the degree of electron transfer from the metal to the carrier, is found to
correlate with the activity in the continuous flow semi-hydrogenation of 2-methyl-3-butyn-2-ol. Density
functional theory calculations support the decreased adsorption energy of palladium upon doping with
carbon and reveal the potentially significant impact of oxygen-containing defects. The findings demonstrate
the importance of understanding the metal-carrier interaction to optimise the catalytic efficiency of SAHCs.
www.rsc.org/
per atom and reduce the amount of metal required. Enhanced
performance has been observed over single-atom
heterogeneous catalysts (SAHCs) in several relevant processes
Introduction
Catalytic processes remain heavily reliant on precious metals
due to their unparalleled active, selective and stable character.
The development of catalysts based on single atoms is of great
interest for the efficient utilisation of these metals.1-5
Compared to state-of-the-art nanoparticle-based catalysts,
which only expose a small fraction of surface atoms that can
including hydrogenation,4 oxidation6 and water-gas-shift
reactions.7,8 However, the fabrication of SAHCs is a major
challenge because of the tendency of atoms to aggregate into
clusters and nanoparticles.9,10 For this reason, the use of a
carrier which provides abundant well defined anchoring sites
that can strongly bind metal atoms plays a crucial role in their
stabilisation.11-14
contribute to the activity, achieving
a metal dispersion
(defined as the number of surface atoms/total number of
atoms) of unity is critical to maximise the catalytic efficiency
One material that exhibits a highly attractive set of
features as a sustainable carrier is graphitic carbon nitride
(g-C3N4), which can robustly coordinate metal species within
sixfold coordination sites in the lattice.15 The presence of these
small, nitrogen-rich crystallographic interstices provides a
stability unmatched by the broad related family of N-doped
carbons. As well as having demonstrated scalability and being
composed of inexpensive, nontoxic, and earth-abundant
elements, g-C3N4 possesses high chemical and thermal stability
and can be prepared with flexible morphology and surface
area. Besides, the composition can be easily tuned by using
other heteroatom sources.16 Various metals, including Pd, Pt,
Ir and Ag, have been successfully stabilised as single atoms on
a.Institute for Chemical and Bioengineering, Department of Chemistry and Applied
Biosciences, ETH Zurich, Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland.
E-mail: jpr@chem.ethz.ch
b.Department of Materials Science and Metallurgy, University of Cambridge, 27
Charles Babbage Road, Cambridge, CB3 0FS, United Kingdom.
c. EMPA, Swiss Federal Laboratories for Materials Science and Technology,
Uberlandstrasse 129, CH-8600 Dubendorf, Switzerland.
d.Institute of Chemical Research of Catalonia (ICIQ) and The Barcelona Institute of
Science and Technology, Av. Països Catalans 16, 43007 Tarragona, Spain.
Electronic Supplementary Information (ESI) available: Additional characterisation
of the carriers and Pd-containing catalysts including chemical composition, XRD
patterns, N2 isotherms, TGA profiles, further microscopy images, Pd 3d XPS
spectra, 13C CP-MAS NMR spectra, DRIFT spectra, CO2-TPD, EXD mapping, DFT and
additional catalytic data. See DOI: 10.1039/x0xx00000x
this carrier.17 The catalytic superiority of Pd
/g-C3N4 SAHCs has
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been evidenced in selective hydrogenation reactions, central
to the production of many fine chemical and pharmaceutical
intermediates, offering an ecological alternative to classical
Lindlar-like catalysts that contain high amounts of precious
metals and require the use of harmful additives as lead.18
Atomically-dispersed silver on g-C3N4 also out-performed the
other Ag-based selective hydrogenation catalysts,19 while
single atom platinum catalysts exhibited remarkable
photocatalytic hydrogen evolution activity.20
Analogous to the effects widely discussed for catalysts
based on deposited metal nanoparticles,21-23 the interaction
with the carrier determines the stability and further impacts
the electronic properties of metal atoms.22,23 However, only
very few attempts have been made to modify the carrier
structure and correlate the impact on the metal binding
strength and performance of SAHCs.24-26 The effect of the
carriers on the electronic properties of the SAHCs is difficult to
assess. Experimentally, this is most commonly probed by X-ray
photoelectron spectroscopy, fitting the observed signals to
species with different oxidation states assuming that the shifts
are only related to charge-transfer effects. However, other
factors can also affect the peak position including the
reduction of the coordination number (from a bulk material to
a single atom) and the extent of covalency, and the presence
of electric fields. In turn, theoretical models typically compute
charges through a Bader-type analysis27 and they are always
lower than the formal ones. In relation to SAHCs, theoretical
studies have revealed that some charge transfer and electron
sharing occurs when a metal is atomically dispersed on a
carrier, these are mapped to the ‘high-valent metal species’
assigned by X-ray photoelectron spectroscopy.11,28 However,
this does not reflect the marginal differences in the calculated
Bader charges and, in general, XPS low-valent metal species
correspond to surface atoms and high-valent ones to isolated
metals buried in the bulk of g-C3N4. Pt, Ir, Pd and Ag were all
shown to be have a slight positive charge when isolated on
g-C3N4.17 For other polar carriers this assignment is easier, for
example as Pt replaces Fe cations on the surface of Fe2O3 the
resulting substitutional impurities carry considerable positive
charges, which was linked to the remarkable CO oxidation
activity of this catalyst.1 Similarly, Pt was predicted to be
trapped as Pt2+ on (100) nanofacets of CeO2 and was detected
as Pt2+ and Pt4+ (the corresponding Bader charges were not
shown).29 On the other hand, Au atoms located at the top sites
of Pd55 nanoclusters were predicted to be negatively charged
(-0.11 |e|).30
Fig. 1 Steps in the polymerisation of the stoichiometric and C-doped g-C3N4 and
subsequent introduction of palladium by microwave-irradiation-assisted metal
deposition. Additional C atoms in the modified lattice are highlighted by a purple
glow. Yellow shaded areas connect N atoms within the coordination sites.
is subsequently approached via microwave-irradiation
assisted-deposition. Characterisation by multiple techniques
confirms the gradually increase C/N ratio of the carriers, that
has a strong impact on the surface area, crystal size, thermal
stability, and basic properties, and as a result, the ability to
adsorb and stabilize single metal atoms. The latter was
evaluated based on metal-carrier charge transfer, dispersion
and areal density of the metal. Density functional theory
calculations support the decreased adsorption energy of
palladium in the C-doped lattice and highlight the potentially
significant impact of oxygen-containing defects. To determine
the influence on the catalytic efficiency, the resulting SAHCs
were subsequently evaluated in the continuous-flow three-
phased semi-hydrogenation of 2-methyl-3-butyl-2-ol, an
important reaction in fine chemical and pharmaceutical
manufacture.
To gain insight into the role of the support, this work
studies the effect of modifying the C/N ratio of g-C3N4 on the
stabilisation, electronic properties and associated catalytic
performance of palladium. For this purpose, a series of carbon-
doped carriers were prepared by copolymerising the
conventional cyanamide precursor with different amounts of
barbituric acid (BA)31,32or 2,4,6-triaminopyrimidine (TAP)33,34
(Fig. 1). To assess the effect of the surface area, the C-doped
materials were prepared in bulk and mesoporous forms. In
view of the widely-cited benefits in terms of enhanced size
control and uniform dispersion, the introduction of palladium
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The pore size distribution was calculated using a non-local
density functional theory (NLDFT) model for carbon with a slit-
shaped pore geometry. X-ray photoelectron spectroscopy
(XPS) was measured in a Physical Electronics Instruments
Experimental
Carrier preparation
Bulk carbon nitride (BCN) was prepared by calcining
dicyandiamide (10 g) at 823 K for 4 h (2.3 K min-1 ramp rate)
under a nitrogen flow (15 cm3 min–1). Mesoporous carbon
nitride (MCN) was prepared by adding cyanamide (2.5 g) to an
aqueous dispersion of SiO2 particles (40 wt.%, 12 nm diameter,
Ludox HS-40) with an SiO2:cynamide mass ratio of 1, and the
mixture was stirred at 373 K until the water had completely
evaporated. The resulting solids were ground with a mortar
and pestle and then calcined as described for BCN. The silica
template was subsequently removed by treating the resulting
brown-yellow powder in an aqueous solution of NH4HF2 (4 M,
40 cm3 gSiO2-1) for 48 h. The template-free MCN was then
filtered, washed thoroughly with distilled water and ethanol
and dried at 333 K overnight. Bulk (coded BCN-BA-z) and
mesoporous (coded MCN-BA-z and MCN-TAP-z) C-doped
materials were prepared by copolymerisation of cyanamide
with barbituric acid (BA) or 2,4,6-triaminopyrimidine (TAP) in
varying mass ratios (z = 0.02, 0.2 or 0.9) following the
procedures described above. For reference, BA and TAP were
carbonised in pure form (6 g) by calcination under the same
conditions resulting in bulk BBA and BTAP materials.
Quantum 2000 spectrometer using monochromatic Al k
α
radiation generated from an electron beam operated at 15 kV
and 32.3 W. The spectra were collected under ultra-high
vacuum conditions (5×10−8 Pa) at a pass energy of 46.95 eV. All
spectra were referenced to the N 1s peak of the ring nitrogen
at 398.6 eV. 13C solid-state cross-polarisation/magic angle
spinning nuclear magnetic resonance (CP/MAS NMR) spectra
were recorded on a Bruker AVANCE III HD NMR spectrometer
at a magnetic field of 16.4 T corresponding to a 1H Larmor
frequency of 700.13 MHz. A 4 mm double resonance probe
head at
a spinning speed of 10 kHz was used for all
experiments. The 13C spectra were acquired using a cross
polarisation experiment with a contact time of 2 ms and a
recycle delay of 1 s. A total of 64×103 scans were added for
each sample. Between 39×103 and 96×103 scans were acquired
depending on the sample. 13C experiments used high-power 1H
decoupling during acquisition using a SPINAL-64 sequence.
Thermogravimetric analysis (TGA) was conducted in a Mettler
Toledo TGA/DSC 1 Star system connected to a Pfeiffer Vacuum
ThermoStar GSD 320 T1 Gas Analysis mass spectrometer. The
analysis was performed in air or N2 (40 cm3 min-1), heating the
sample from 298 K to 1273 K at a rate of 5 K min-1. The mass
signals of H2O (m/z = 18) and CO2 (m/z = 44) were continuously
monitored. Scanning electron microscopy (SEM) was
undertaken in an FEI Magellan 400 microscope working at
30 kV and 50 pA. Samples for transmission electron
microscopy (STEM) studies were prepared by dusting
respective powders onto lacey-carbon coated copper grids.
Conventional TEM imaging and STEM energy dispersive X-ray
spectroscopy (EDX) measurements were performed on a Talos
F200X instrument operated at 200 kV and equipped with an
FEI SuperX detector. Aberration-corrected (AC-)STEM was
performed using an FEI Titan Cubed microscope equipped with
XFEG electron source and CEOS probe aberration corrector,
operated at 300 kV. STEM high-angle annular dark-field
(HAADF) images were acquired with an illumination angle of
17 mrad and detector inner angle of 35 mrad, chosen to
minimise any possible Bragg diffraction contrast and maximise
overall image signal, and especially atomic number (Z) contrast
between Pd atoms/clusters and the underlying support. Per
Metal introduction
The incorporation of palladium into carriers was approached
by postsynthetic microwave irradiation assisted deposition.
The carrier (0.5 g) was firstly dispersed in H2O (20 cm3) with
the assistance of sonication. Then, a solution of Pd(NH3)4(NO3)2
containing 5 wt.% Pd (50 ꢀL) was added, targeting a metal
loading of 0.5 wt.% relative to the carriers. The resulting
solution was then placed in a microwave reactor (CEM
Discover SP), applying a cyclic program of 15 s irradiation and
3 min cooling with 20 repetitions using a power of 100 W. The
resulting powder was washed with distilled water and ethanol
and dried at 333 K overnight.
Catalyst characterisation
Elemental analysis of C, H, N and O was determined by
infrared spectroscopy using a LECO CHN-900 combustion
furnace. Inductively coupled plasma-optical emission
spectrometry (ICP-OES) was conducted using a Horiba Ultra 2
instrument equipped with photomultiplier tube detection. The
solids were dissolved in a piranha solution and left under
sonication until the absence of visible solids in the solution.
Powder X-ray diffraction (XRD) was performed in a PANalytical
X’Pert PRO-MPD diffractometer operated in Bragg Brentano
pixel dwell times of 5-10 ꢀs and probe currents 40-60 pA were
selected to achieve sufficient signal-to-noise for single Pd atom
visibility whilst minimising beam induced changes, providing
images representative of the Pd atom species and their
distribution on the CN supports. Scanning electron
micrographs of the uncoated samples were acquired using a
Zeiss Gemini 1530 FEG SEM operated at 1 kV. CO2
temperature-programmed desorption (CO2-TPD) was carried
out in a Micromeritics Autochem II 2920 equipped with a
thermal conductivity detector coupled to MKS Cirrus 2 mass
spectrometer. The samples were first activated at 473 K for 1 h
under a helium atmosphere. Then the temperature was
reduced to 323 K and the samples were saturated with CO2 for
geometry using Ni-filtered Cu Kα
Data were recorded in the range of 5-70° 2
(λ
= 0.1541 nm) radiation.
with an angular
θ
step size of 0.05° and a counting time of 2 s per step. The
variation of the crystal size in the stacking direction was
estimated from the broadening of the (002) reflection by using
the Scherrer equation with a shape factor, K = 0.9. The
interlayer staking distance was determined from the position
of the (002) reflection using the Bragg equation. Nitrogen
sorption was measured at 77 K in a Micrometrics 3Flex
instrument, after evacuation of the samples at 423 K for 10 h.
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1.5 h before flushing with helium to remove physisorbed
molecules. This procedure was repeated twice. Once the
baseline was flat, the temperature was increased to 773 K at a
rate of 10 K min-1 to obtain the CO2 desorption curves. Diffuse
reflectance infrared Fourier transform spectroscopy (DRIFTS)
was performed using a Bruker Optics Vertex 70 spectrometer
equipped with a high-temperature DRIFT cell (Harrick) and an
HgCdTe (MCT) detector. Spectra were recorded in the range of
4000-400 cm−1 at room temperature under a N2 flow by
coaddition of 200 scans with a nominal resolution of 4 cm−1.
Density functional theory
The Vienna ab-initio simulation package35 was employed to model
the structure of the Pd SAHCs based on the modified g-C3N4
carriers, using the Perdew–Burke–Ernzerhof functional together
with dispersion terms D3.36,37 The projector augmented wave
method38,39 was employed to represent core electrons and the
valence was expanded in plane waves with a cutoff energy of
450 eV. The C6N8 (melon) moieties were built in a graphitic form
and the optimised interlayer structure is 3.5 Å. Four layered slabs of
the (0001) surface were built with p(2×2) supercells (Fig. S13 and
S14). The incorporation of metal atoms was assessed on one side of
the slab.
Catalyst testing
The hydrogenation of 2-methyl-3-butyl-2-ol (Acros Organics,
98%) was carried out in a continuous-flow flooded-bed
micro-reactor (ThalesNano H-Cube ProTM), in which the liquid
feed (containing 5 vol.% of substrate and toluene (Fischer
Chemicals, 99.95%) and gaseous hydrogen (generated in situ
by Millipore water electrolysis) flow concurrently upward
through a cylindrical cartridge (3.5 mm internal diameter)
containing a fixed bed of catalyst (0.1 g) and silicon carbide
(0.12 g) particles, both with a size of 0.2-0.4 mm. The reactions
were conducted at various conditions of temperature
(303-363 K), total pressure (1-8 bar), liquid (1 cm3 min−1) and
H2 (40 cm3 min−1) flow rates. The products were collected
every 15 min after reaching steady state and analysed offline
using a gas chromatograph (HP-6890) equipped with a HP-5
Fig. 2 (a) XRD patterns, (b) 13C MAS NMR spectra, (c) C 1s XPS spectra and (d)
N 1s XPS spectra of the stoichiometric and C-doped mesoporous g-C3N4 carriers.
In (c,d), solid black lines show the result of fitting the raw data (open symbols),
the dashed lines correspond to the individual peaks after deconvolution. Blue
lines indicate the background applied.
compatible functionality to copolymerise with this molecule to
form the standard tri-s-triazine units via the elimination of
ammonia or water.31-34 To demonstrate the flexibility of this
approach and to study the impact of surface area, C-doped
carriers have been prepared in both bulk and mesoporous
forms, the latter obtained by applying colloidal silica as a hard
template during the synthesis. The resulting samples are
capillary column and
a flame ionisation detector. The
conversion (X) of the substrate was determined as the amount
of reacted substrate divided by the amount of substrate at the
reactor inlet. The selectivity (S) to each product was quantified
as the amount of the particular product divided by the amount
of reacted substrate. The reaction rate (r) was expressed as
moles of product per mole of Pd and unit of time.
coded x-y-z, where
(bulk - BCN or mesoporous - MCN), y corresponds to the
dopant applied (BA or TAP) and indicates the
x denotes the carrier morphology
z
cyanamide/dopant mass ratio (0.02, 0.2 or 0.9). For reference
purposes, the stoichiometric g-C3N4 carrier was also
synthesised in bulk (BCN) and mesoporous (MCN) form and
the individual dopants were also polymerised in bulk form
leading to the BBA and BTAP materials.
Results and Discussion
Various techniques were applied to characterise the
properties of the modified carriers. The framework
composition of all carriers was determined based on elemental
analysis after correction for the possible adsorption of gases
by the material (vide infra). Upon introduction of BA or TAP
during the synthesis an increased amount of carbon is
observed (Table S1), consistently, the C/N ratio rises from 0.6
in the stoichiometric materials to close to 1 in the C-doped
analogues. Comparison of the X-ray diffraction (XRD) patterns
Carrier properties
The preparation of carbon-doped g-C3N4 carriers was
approached by copolymerising the conventional cyanamide
precursor with barbituric acid (BA) or 2,4,6-triaminopyrimidine
(TAP). These compounds both contain carbon-rich
heterocycles with respect to the six-membered ring of
melamine, the smallest aromatic unit of the condensed
structure of graphitic carbon nitride, and ideally have
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reflection at 2θ = 27.3° (Fig. S2). Moreover, the (100) reflection
at 2 = 13.1° corresponding to the in-plane order of tri-s-
θ
triazine units within the g-C3N4 sheets, is not visible in the
carbon-doped samples, suggesting an increased distortion of
g-C3N4 layers.40 Estimation using the Scherrer equation
(
Table S2), confirmed a decrease of the crystal size in the
stacking direction of the lattice with increasing C/N ratio from
9 nm in the stoichiometric MCN carrier to 2 nm in MCN-TAP-
0.9 and MCN-BA-0.9 (Fig. S3), indicating that the presence of
both dopants hinders the polymerisation of cyanamide. Note
that the values of crystal size should only be used for
qualitative comparison since doping of the lattice with carbon
can also introduce lattice distortion and structural defects
leading to peak broadening, which is difficult to decouple from
the purely size related effect. The slight shift of the (002)
reflection indicates a small concomitant increase in the
interlayer stacking from 0.326 nm in MCN to 0.332 nm in
MCN-BA-0.9.34 In fact, the substitution of one or more
nitrogen atoms in the framework of g-C3N4 leads to a
decreased strength of hydrogen bonds, which is known to
reduce the stability and structural regularity in g-C3N4
materials.32 Comparatively, the observation of a single broad
reflection at 2θ = 27.3° in the materials obtained upon the
direct thermal condensation of barbituric acid (BBA) or
2,4,6-triaminopyrimidine (BTAP) indicates that they adopt a
layered structure similar to that of the conventional graphitic
carbon nitride (BCN).
To further confirm the successful incorporation of carbon
into the g-C3N4 lattice, the mesoporous samples were studied
by magic-angle spinning nuclear magnetic resonance (MAS
NMR) and X-ray photoelectron (XPS) spectroscopy. The two
main signals at 164 and 157 ppm in the 13C MAS NMR
spectrum of MCN are attributed to CN2(NHx) and CN3 moieties,
respectively (Fig. 2b).41 The gradual coalescence of these peaks
with increased amount of BA or TAP (Fig. S4) can be related to
Fig. 3 (a) N2 isotherms and corresponding NLDFT pore size distributions (inset),
(b) TGA profiles in air and (c) the variation of the BET surface area (circles) and
the amount of CO2 adsorbed (squares) with the C/N ratio of the stoichiometric
MCN (green) and C-doped carriers modified with TAP (red) and BA (blue).
of the mesoporous (Fig. 2) and bulk (Fig. S1) carriers reveals
that the incorporation of carbon was accompanied by a
disturbance of the graphitic carbon nitride lattice. In particular,
increasing the cyanamide/dopant ratio was associated with a
broadening and reduced intensity of the (002) stacking
Fig. 4 Bright field-TEM images of mesoporous and bulk g-C3N4 copolymerised with BA
or TAP. The 100 nm scale bar applies to all images.
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the decreased crystalline order of the tri-s-triazine moieties. In hysteresis loop at p/p0 = 0.3-0.9, suggesting the presence of
addition, a new peak centred at 95 ppm appears, which smaller crystalline domains and/or a higher number of defects
reflects the desired incorporation of -C-C=N- units into the in these samples (Fig. S1). Examination of the carriers by
framework.32 Consistently, MCN-BA-0.9 and MCN-TAP-0.9 transmission electron microscopy (TEM) demonstrates that
samples evidence a strong peak at 287.3 eV in the C 1s XPS the inclusion of BA or TAP does not radically alter the
spectra
(Fig. 2c) that is attributed to C-doped -C-C=N- morphology up to a mass ratio of 0.9 (Fig. 4 and S5). All
moieties,42 while the peak at 284.8 eV that represents C-C mesoporous carriers exhibit the extensive presence of
bond formation also increases. The latter could result from the spherical mesopores of sizes around that of the 12 nm
formation of an amorphous carbon phase during the diameter of the colloidal silica template, while the bulk carriers
polymerisation.43 The existence of the tri-s-triazine units was exhibit a reduced more uniform beam transparency. Scanning
confirmed by the presence of the peak at 288.1 eV (CN3).44 electron microscopy (SEM) images of MCN also reveal the
Deconvolution of N 1s XPS spectra (Fig. 2d) identifies the presence of macropores with the size of around 500 nm, which
presence of nitrogen species, typical for the g-C3N4 structure. are not observed in the large particles of BCN. Analysis by
Three main peaks at 398.6 eV (ring nitrogen, C-N=C), 399.5 eV selected area electron diffraction confirmed the polycrystalline
(tertiary nitrogen, NC3) and 400.6 eV (NHx groups) are nature of the material (Fig. S5). Note that the observation of
observed in all spectra. The presence of tertiary nitrogen and large meso-/macropores in BBA agrees with the higher surface
the C-N=C/NC3 ratio of 6 for MCN carrier confirms that the area of this material.
structure is based on tri-s-triazine building block.45 The
The impact of carbon doping on the thermal stability of the
C-N=C/NC3 ratio drops to 3.7 and 3.5 for MCN-TAP-0.9 and carrier and the propensity to adsorb gases was assessed by
MCN-BA-0.9, respectively, indicating a decreased amount of thermogravimetric analysis (TGA) in air and in nitrogen,
the ring nitrogen in the carbon-doped carriers and evidencing respectively, following the evolution of volatile species by
the successful substitution of nitrogen by carbon in the sixfold mass spectrometry (MS). The thermal stability was improved
cavity of the g-C3N4 structure.
after carbon introduction. For example, the temperature for
As evidenced by nitrogen sorption (Fig. 3a), MCN-BA-0.9 50% weight loss of MCN-BA-0.9 or MCN-TAP-0.9 is 50 K higher
and MCN-TAP-0.9 display an enhanced surface area compared compared to MCN (Fig. 3b and S2), which also applies for the
to pure MCN (Table S2). The prominent hysteresis loops bulk carriers (Fig. S1). In line with the fact that carbon nitride is
observed in all isotherms evidence the presence of connected weakly basic and has previously been studied for CO2 capture,
spherical or cylindrical mesopores. Corresponding pore size weight losses below 573 K primarily resulted from the
distributions (Fig. 3a, inset) display two pronounced peaks, desorption of CO2
centred at 1.5 and 10 nm, the latter close to the size of the surface area, a strong correlation was observed between the
SiO2 template. The increased surface area with increasing C/N CO2 uptake and the C/N ratio of the carrier Fig. 3c).
ratio is in agreement with the reduced crystalline order. Interestingly, more significant increase resulted upon
(Fig. S6). Consistent with the enhanced
(
a
Interestingly, distinctions are visible between the application modification with BA that TAP, suggesting possible differences
of BA and TAP (Fig. S3), the former resulting in a greater in the basicity of these samples. To study this, temperature-
enhancement in the surface area with decreasing crystal size. programmed reduction measurements of CO2 (CO2-TPD)
As expected, the BCN and BTAP carriers exhibit surface areas monitored by MS were conducted. Two desorption peaks were
lower than 10 m2 g-1 consistent with the densification of the observed in the CO2-TPD profiles, the first centred at 373 K
polymerised structures in the absence of a template. In
(Fig. S7) corresponding to the presence of weak Lewis
comparison, BBA and BCN-BA-0.9 display relatively high basicity46 and as second broader peak around 533 K, attributed
specific surface areas of 45 and 48 m2 g-1, respectively, with a to stronger basic sites. Comparatively, MCN-TAP-0.9 was seen
Fig. 5 AC-STEM images of the metal speciation in Pd-containing SAHCs based on the C-doped carriers, evidencing single atom dispersion. Pd-BCN-BA-0.9 also contains small
ca. 1 nm clusters, as highlighted inset.
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to exhibit a higher concentration of weak basic sites, while
MCN-BA-0.9 contained more strong basic sites, which can
explain the higher CO2 uptake of the latter sample.
Based on the amount of CO2 adsorbed it is clear that this
accounts for the majority of oxygen detected by elemental
analysis. Correction of the chemical composition reveals that
the amount of oxygen in the lattice of the C-doped carriers is
relatively low (<2.4 mol%) and is not significantly impacted by
the presence of mesoporosity. The fact that no adsorbed H2O
was detected indicates that the hydrogen evidenced in the
carriers most likely relates to defects such as tertiary or
secondary amines. Attempts to identify the possible origin of
oxygen-related defects by assessment of the surface
properties by diffuse reflectance infrared Fourier transform
spectroscopy (DRIFTS) were complicated by the overlapping
signals associated with the g-C3N4 lattice
(Fig. S8).
Nonetheless, comparison of the spectra did confirm higher
numbers of secondary amine defects in the C-doped carriers
with respect to the stoichiometric MCN.
Palladium stabilisation on the carriers
Fig. 6 (a) Comparison of the Pd 3d core level XPS spectra of the catalysts based
on the mesoporous carriers. Solid black lines show the result of fitting the raw
data (open symbols), the dashed lines correspond to the individual peaks after
deconvolution. Blue lines indicate the background applied. Vertical grey lines
correspond to the deconvoluted components, which are assigned based on the
shifts expected for bulk species. (b) The correlation between Pd surface
concentration and BET surface area. (c) The correlation between Pd2+/Pd4+ ratio
and Pd surface concentration. In (b), (c) and the intermediate samples MCN-BA-
0.2 and MCN-TAP-0.2 are included. Green symbol refers to the MCN carrier,
while red and blue symbols denote carriers modified with TAP and BA,
respectively.
The stabilisation of palladium on the carriers via microwave-
irradiation-assisted deposition attained a metal loading close
to the targeted value of 0.5 wt.% in all cases (Table S3). Careful
examination of the metal speciation by aberration-corrected
(AC-)STEM, confirmed the single atom dispersion (Fig. 5 and
S9) and the absence of Pd nanoparticles in all of the catalysts
based on the mesoporous C-doped carriers (as summarised in
Table S3). Energy-dispersive X-ray spectroscopy (EDX) mapping
also supported the uniformity of the Pd distribution over these
the synthesis, much more drastic increases in Pdsurface were
observed in catalysts based on the low-surface bulk carriers
(11-24 times) with respect to the mesoporous analogues
(2-4 times). Nonetheless, opposite behaviour is observed on
comparison of the series of catalysts based on the mesoporous
C-doped carriers, which display an appreciable increase in
Pdsurface with surface area (Fig. 6b). This suggests that doping
the lattice with carbon either hinders the diffusion of
palladium into subsurface layers or creates stronger
adsorption sites at the surface with respect to the
stoichiometric lattice.
carriers (Fig. S10). However, some metal clusters of
∼1 nm
were observed in Pd-BCN-BA-0.9 (Fig. 5, inset). High metal
dispersions were also observed in Pd-BCN (Fig. S11). This is
noteworthy as previous attempts at depositing palladium on
BCN led to significant nanoparticle formation,17 pointing
toward the benefits of using microwave-irradiation to improve
the stabilisation of single atoms on low surface area carriers In
contrast, extensive formation of Pd clusters and small
nanoparticles was evidenced in Pd-BBA, which has the highest
surface area of the bulk carriers (61 m2 g-1). Thus, the metal
speciation appears to be more strongly dependent on the
structure and binding strength of the coordination sites within
the material rather than the surface area. Since the
polymerisation of BA and TAP does not result in crystalline
materials based on tri-s-triazine networks, these carriers
behave more like nitrogen-doped carbons and are unable to
effectively stabilise isolated metal centres
Deconvolution of the Pd 3d5/2 spectra identified two peaks
at 338.5 eV and 336.9 eV in all samples (Fig. 6a), which are
tentatively assigned to Pd4+ and Pd2+, respectively. Notably, no
peak corresponding to metallic Pd around 335.0 eV was
observed in any of the spectra.47 Interestingly, significant
variation is observed in the relative peak intensity, the
Pd2+/Pd4+ ratio changing from 0.24 for Pd-MCN-BA-0.9 to 1.04
for Pd-MCN-TAP-0.9, while Pd-MCN shows intermediate value
0.53 (Table S3). Replacing the nitrogen atoms with carbon in
the stoichiometric g-C3N4 structure, a weaker metal-carrier
interaction, which is corroborated by the reduced adsorption
energies of isolated Pd atoms by 0.2-0.5 (vide infra) and thus a
higher Pd2+/Pd4+ ratio is expected, as in the case of Pd-MCN-
TAP-0.9. In contrast to this, a lower Pd2+/Pd4+ ratio was
observed in Pd-MCN-BA-0.9. Attempts to correlate the
differences in the relative amounts of high- and low-valent
metal with a bulk compositional parameter (e.g., the C/N ratio,
Further insight into the interaction of palladium with the
C-doped carriers was obtained by analysis by X-ray
photoelectron spectroscopy (XPS), which enabled comparison
of the impact of varying the composition on the surface
concentration (Pdsurface) and formal oxidation state of the
metal (Fig. 6a and S12). Surface enrichment of Pd was
observed in all samples (Table S3), which agrees with the high
barriers for the diffusion of Pd atoms into sub-subsurface
layers predicted by previous DFT calculations.17 In line with the
higher local surface metal concentrations experienced during
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the binding sites defined by the tri-s-triazine (C6N8) units
considering two possible stacking arrangements (Fig. S13). As
illustrated in Fig. S14
,
chemical defects have been
incorporated into the structure by replacing some of the
nitrogen atoms by CH or by CO and a nearby H. The former
comprises the targeted substitution in the C-doped structures,
while the latter represents
a possible type of oxygen-
containing defect that may form due to the oxidation of the
material during synthesis.48 The metal stabilisation was
subsequently studied by placing Pd atoms at different depths
within the modified interstices (Fig. S14).
The adsorption of palladium in the stoichiometric
(defect-free) compound ranges from 2 eV for the bulk of the
material to 1.7 eV at the surface. C-doped materials are less
prone to adsorb Pd and the adsorption energy is reduced by
0.25-0.5 eV on the surface close to a defect (Table S4). The
computed XPS shifts show that the analysis is complex. The 3d
levels of Pd atoms adsorbed at the surface are shifted towards
smaller binding energies by about 0.4 eV. Thus, qualitative
analysis of the XPS data indicates that both Pd4+-like (in the
bulk) and Pd2+-like (at the surface) atoms can be formed.
However, calculated Bader charges are small (ca. 0.5|e-|) due
to the large covalency between the metal atom and the lattice.
The C-doped structures present similar features, but with one
noticeable difference in the XPS signature related to Pd in
close contact with O defects. Pd adsorbed in these sites are
closer to the Pd4+ feature, exhibiting -0.50 eV higher binding
energies with respect to Pd atoms in the bulk of the
stoichiometric C3N4 reference. Comparatively, the weakest
interaction is identified upon replacing N with a CH defect,
while close to an O-defect Pd atoms are more stable with
respect to the stoichiometric sites. This implies that Pd is
better anchored at the O-defect sites in a strongly cationic
configuration, which could explain the higher Pd4+/Pd2+ ratios
observed in the BA-modified materials, whereas the
TAP-modified carriers behave more like an ideal C-doped
carbon nitride due to the lower adsorption energy, leading to a
higher concentration of “effective” palladium close to the
surface.
Fig. 7 (a) Reaction scheme of the selective hydrogenation of 2-methyl-3-butyn-
2-ol to 2-methyl-3-buten-2-ol and the unselective over-hydrogenation to 2-
methyl-3-butan-2-ol. (b) Reaction rate (left column, in 103 mol2-methyl-3-buten-2-
ol molPd−1 h−1) and selectivity to 2-methyl-3-buten-2-ol (right column, in %) at
different temperature and pressure over Pd-based catalysts on g-C3N4. The
contour plots were obtained through spline interpolation of 14 experimental
points. Reaction conditions: Wcat = 0.1 g, FL (2-methyl-3-butyn-2-ol + toluene) = 1
cm3 min-1 and FG (H2) = 36 cm3 min-1.
O content or lattice electronegativity) did not uncover any
general relationship. This is perhaps unsurprising considering
that the metal is primarily located in the surface layers of the
carrier and therefore most likely to depend on the specific
termination of the lattice and presence of surface defects. The
distinct variations in the CO2 uptake and basicity of the C-
doped carriers already points towards differences in the
surface properties depending on the dopant applied.
Importantly, comparison of the Pd2+/Pd4+ ratio versus Pdsurface
confirms that the variation does not result from differences in
the areal density of palladium between the samples (Fig. 6c).
The absence of the metallic Pd signal in the Pd 3d spectra of
Pd-BBA and Pd-BTAP conflicts with the presence of small
clusters as confirmed by STEM analysis, which can be explain
by bathochromic shift due to the quantum effects appears for
particles smaller than 2 nm.27 These results highlight the
current analytical challenges faced to describe the metal-
carrier interaction with respect to understanding both the XPS
response and the precise surface structure.
Catalytic performance
The performance of the Pd-SAHCs based on the C-doped
carriers
was
evaluated
in
the
continuous-flow
Fig. 7a). To
semi-hydrogenation of 2-methyl-3-butyn-2-ol
(
decouple the impact of the carrier composition, the tests
focused on the catalysts based on the mesoporous carriers,
which exclusively contain isolated Pd atoms in comparably low
areal density (0.47±0.09 ꢀ
molPd m-2). The contour maps in
Fig. 7b depict the rate and selectivity to 2 methyl-3-buten-2-ol
over selected catalysts at different temperatures and
pressures. Under the conditions investigated, the conversion
of 2-methyl-3-butyn-2-ol ranged between 3 and 60% in all
cases. The high chemoselectivity of the single atoms was
clearly evidenced by the selectivity to the alkenol product in
excess of 95%. Interestingly, the application of BA or TAP to
prepare C-doped carriers is seen to have opposite effects;
Modelling
To gain molecular insight into the impact of carbon doping on
the interaction of palladium with carbon nitride, density
functional theory (DFT) calculations have been carried out for
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for the comparative evaluation of catalysts based on the bulk
carriers. In particular, the difficulty in quantifying the amount
and properties of nanoclusters and single atoms, which cannot
be assessed by standard chemisorption techniques, highlights
the need for improved methods to precisely control and
characterise the distribution and dispersion of metals in g-
C3N4.
Conclusions
This study has assessed the impact of varying the elemental
composition of graphitic carbon nitride on the stabilisation and
catalytic efficiency of palladium species on this carrier.
Controlled modification of the C/N ratio could be achieved by
the copolymerisation of cyanamide with carbon-rich
heterocycles. The substitution of nitrogen by carbon in the
lattice was confirmed by elemental analysis, XPS and 13C NMR
spectroscopy and was found to concomitantly enhance the
surface area and thermal stability. Microwave-irradiation-
assisted deposition was shown to be an effective route for
dispersing metals as single atoms even on low surface area
carriers. As evidenced by XPS and AC-STEM, both the
speciation and oxidation state of palladium was influenced by
the specific dopant applied. The incorporation of
2,4,6-triaminopyrimidine led to the weakening of the metal-
carrier interaction expected due to the reduced coordination
number of the binding sites, but an increased binding strength
was observed upon incorporation of barbituric acid.
Experimental and theoretical observations pointed towards
differences in the surface properties, possibly related to the
presence of oxygen-related defects. The metal oxidation state
assigned from XPS in the resulting catalysts was found to be an
important indicator for the semi-hydrogenation of 2-methyl-3-
butyn-2-ol with an enhanced catalytic efficiency observed over
catalysts containing higher fractions of lower-valence Pd2+
species, which according to the calculations correspond to Pd
atoms at the surface or near CH defects. The findings
demonstrate the possibility of improving the efficiency of
SAHCs by tailoring the carrier properties.
Fig. 8 Correlation of the rate of alkenol formation in the semi-hydrogenation of
2-methyl-3-butyn-2-ol as a function of the (a) temperature (P = 1 bar) or (b)
pressure (T = 363 K) of reaction with the Pd2+/Pd4+ ratio over Pd-MCN (squares)
or over the SAHCs based on the mesoporous C-doped carriers modified with BA
(triangles) or TAP (circles).
Pd-MCN-BA-0.9 appears less active than Pd-MCN, while higher
rates are achieved over Pd-MCN-TAP-0.9.
Comparison of the rate or alkenol formation over all of the
mesoporous SAHCs as a function of the Pd2+/Pd4+ ratio at
different temperatures (Fig. 8a) and pressures (Fig. 8b) reveals
a strong dependence on the relative amount of the lower-
valent metal species. In particular, at 1 bar and 343 K, the
conditions of highest practical relevance, over
a 3-fold
Acknowledgements
variation in the reaction rate is observed. Tests of selected
catalysts based on the bulk carbon nitride evidenced
significantly higher rates than those observed over the SAHCs
based on the mesoporous carriers (Fig. S15), which can be
attributed to the much higher surface density of metal in these
This research has received funding from the Swiss National
Science Foundation (Grant No. 200021-169679) as well as the
European Research Council under the European Union's
Seventh Framework Programme (FP7/2007–2013)/ERC grant
agreement 291522–3DIMAGE and the European Union
Seventh Framework Programme under Grant Agreement
312483-ESTEEM2 (Integrated Infrastructure Initiative -I3). Dr
Réne Verel (ETH Zurich) is thanked for assistance with 13C
MAS-NMR. ScopeM at ETH Zurich is acknowledged for
providing access to its facilities. R.K.L. acknowledges a Junior
Research Fellowship from Clare College.
samples (110 and 15.5 ꢀ
molPd m-2 for Pd-BCN-BA-0.9 and Pd-
BBA respectively). Despite containing visible Pd nanoclusters,
Pd-BCN-BA-0.9 preserved fully selective character to the
alkenol. In contrast, a high degree of overhydrogenation was
evidenced over Pd-BBA, which is ascribed to the extensive
formation of Pd clusters and small nanoparticles. These
findings point toward the importance of tuning the metal-
carrier interaction for the design of highly efficient SAHCs. The
significant variation in the surface density of metal and the
heterogeneous metal speciation present significant challenges
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24.
25.
F. Besenbacher, I. Chorkendorff, B. S. Clausen, B. Hammer,
A. M. Molenbroek, J. K. Nørskov and I. Stensgaard,
Science, 1998, 279, 1913-1915.
F. R. Lucci, J. Liu, M. D. Marcinkowski, M. Yang, L. F. Allard,
M. Flytzani-Stephanopoulos and E. C. H. Sykes, Nat.
Commun., 2015, 6:8550.
M. Mavrikakis, P. Stoltze and J. K. Nørskov, Catal. Lett.,
2000, 64, 101-106.
Y. Sun, Y. Wang, J. S. Pan, L.-l. Wang and C. Q. Sun, J. Phys.
Chem. C, 2009, 113, 14696-14701.
G. Vilé, D. Albani, M. Nachtegaal, Z. Chen, D. Dontsova, M.
Antonietti, N. López and J. Pérez-Ramírez, Angew. Chem.
Int. Ed., 2015, 54, 11265-11269.
A. Bruix, Y. Lykhach, I. Matolínová, A. Neitzel, T. Skála, N.
Tsud, M. Vorokhta, V. Stetsovych, K. Ševčíková, J.
Mysliveček, R. Fiala, M. Václavů, K. C. Prince, S. Bruyère, V.
Potin, F. Illas, V. Matolín, J. Libuda and K. M. Neyman,
Angew. Chem. Int. Ed., 2014, 53, 10525-10530.
H. Zhang, T. Watanabe, M. Okumura, M. Haruta and N.
Toshima, Nat. Mater., 2012, 11, 49-52.
M. Shalom, M. Guttentag, C. Fettkenhauer, S. Inal, D.
Neher, A. Llobet and M. Antonietti, Chem. Mater., 2014,
26, 5812-5818.
J. Zhang, X. Chenꢀ, K. Takanabe, K. Maeda, K. Domen, J. D.
Epping, X. Fu, M. Antonietti and X. Wang, Angew. Chem.
Int. Ed., 2010, 49, 441-444.
W. Ho, Z. Zhang, W. Lin, S. Huang, X. Zhang, X. Wang and
Y. Huang, ACS Appl. Mater. Interfaces, 2015, 7, 5497-5505.
M. K. Bhunia, K. Yamauchi and K. Takanabe, Angew.
Chem., 2014, 126, 11181-11185.
G. Kresse and J. Furthmüller, Comput. Mater. Sci., 1996, 6,
15-50.
J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett.,
1996, 77, 3865-3868.
S. Grimme, J. Antony, S. Ehrlich and H. Krieg, J. Chem.
Phys, 2010, 132, 154104.
P. E. Blöchl, Phys. Rev. B, 1994, 50, 17953-17979.
G. Kresse and D. Joubert, Phys. Rev. B, 1999, 59, 1758-
1775.
F. Goettmann, A. Fischer, M. Antonietti and A. Thomas,
Angew. Chem. Int. Ed., 2006, 45, 4467-4471.
B. V. Lotsch, M. Döblinger, J. Sehnert, L. Seyfarth, J.
Senker, O. Oeckler and W. Schnick, Chem. Eur. J., 2007,
13, 4969-4980.
M. K. Bhunia, S. Melissen, M. R. Parida, P. Sarawade, J.-M.
Basset, D. H. Anjum, O. F. Mohammed, P. Sautet, T. Le
Bahers and K. Takanabe, Chem. Mater., 2015, 27, 8237-
8247.
Q.-F. Deng, L. Liu, X.-Z. Lin, G. Du, Y. Liu and Z.-Y. Yuan,
Chem. Eng. J., 2012, 203, 63-70.
References
1.
2.
3.
4.
B. Qiao, A. Wang, X. Yang, L. F. Allard, Z. Jiang, Y. Cui, J.
Liu, J. Li and T. Zhang, Nat. Chem., 2011, 3, 634-641.
X.-F. Yang, A. Wang, B. Qiao, J. Li, J. Liu and T. Zhang, Acc.
Chem. Res., 2013, 46, 1740-1748.
S. Liang, C. Hao and Y. Shi, ChemCatChem, 2015, 7, 2559-
2567.
G. Kyriakou, M. B. Boucher, A. D. Jewell, E. A. Lewis, T. J.
Lawton, A. E. Baber, H. L. Tierney, M. Flytzani-
Stephanopoulos and E. C. H. Sykes, Science, 2012, 335,
1209-1212.
26.
27.
28.
5.
6.
J. M. Thomas, Nature, 2015, 525, 325-326.
M. Moses-DeBusk, M. Yoon, L. F. Allard, D. R. Mullins, Z.
Wu, X. Yang, G. Veith, G. M. Stocks and C. K. Narula, J. Am.
Chem. Soc., 2013, 135, 12634-12645.
29.
7.
8.
Q. Fu, H. Saltsburg and M. Flytzani-Stephanopoulos,
Science, 2003, 301, 935-938.
Y. Zhai, D. Pierre, R. Si, W. Deng, P. Ferrin, A. U. Nilekar, G.
Peng, J. A. Herron, D. C. Bell, H. Saltsburg, M. Mavrikakis
and M. Flytzani-Stephanopoulos, Science, 2010, 329,
1633-1636.
30.
31.
9.
S. Sun, G. Zhang, N. Gauquelin, N. Chen, J. Zhou, S. Yang,
W. Chen, X. Meng, D. Geng, M. N. Banis, R. Li, S. Ye, S.
Knights, G. A. Botton, T.-K. Sham and X. Sun, Sci. Rep.,
2013, 3, 1775.
32.
10.
11.
A. Uzun, V. Ortalan, Y. Hao, N. D. Browning and B. C.
Gates, ACS Nano, 2009, 3, 3691-3695.
M. Yang, J. Liu, S. Lee, B. Zugic, J. Huang, L. F. Allard and
M. Flytzani-Stephanopoulos, J. Am. Chem. Soc., 2015, 137,
3470-3473.
33.
34.
35.
36.
37.
12.
13.
A. L. Yakovlev, K. M. Neyman, G. M. Zhidomirov and N.
Rösch, J. Phys. Chem., 1996, 100, 3482-3487.
J. Lin, A. Wang, B. Qiao, X. Liu, X. Yang, X. Wang, J. Liang, J.
Li, J. Liu and T. Zhang, J. Am. Chem. Soc., 2013, 135,
15314-15317.
14.
H. Wei, X. Liu, A. Wang, L. Zhang, B. Qiao, X. Yang, Y.
Huang, S. Miao, J. Liu and T. Zhang, Nat. Commun., 2014,
5, 5634.
38.
39.
15.
16.
Z. Zhao, Y. Sun and F. Dong, Nanoscale, 2015, 7, 15-37.
Y. Zheng, J. Liu, J. Liang, M. Jaroniec and S. Z. Qiao, Energy
Environ. Sci., 2012, 5, 6717-6731.
40.
41.
17.
Z. Chen, S. Mitchell, E. Vorobyeva, R. K. Leary, R. Hauert,
T. Furnival, Q. M. Ramasse, J. M. Thomas, P. A. Midgley, D.
Dontsova, M. Antonietti, S. Pogodin, N. López and J.
Pérez-Ramírez, Adv. Funct. Mater., 2017, 27, 1605785.
X. Huang, Y. Xia, Y. Cao, X. Zheng, H. Pan, J. Zhu, C. Ma, H.
Wang, J. Li, R. You, S. Wei, W. Huang and J. Lu, Nano Res.,
2017, DOI: 10.1007/s12274-016-1416-z, 1-11.
Z. Chen, S. Pronkin, T.-P. Fellinger, K. Kailasam, G. Vilé, D.
Albani, F. Krumeich, R. Leary, J. Barnard, J. M. Thomas, J.
Pérez-Ramírez, M. Antonietti and D. Dontsova, ACS Nano,
2016, 10, 3166-3175.
42.
18.
19.
43.
44.
A. Thomas, A. Fischer, F. Goettmann, M. Antonietti, J.-O.
Müller, R. Schlögl and J. M. Carlsson, J. Mater. Chem.,
2008, 18, 4893-4908.
20.
21.
22.
X. Li, W. Bi, L. Zhang, S. Tao, W. Chu, Q. Zhang, Y. Luo, C.
Wu and Y. Xie, Adv. Mater., 2016, 28, 2427-2431.
S. J. Tauster, S. C. Fung, R. T. K. Baker and J. A. Horsley,
Science, 1981, 211, 1121-1125.
G. N. Vayssilov, Y. Lykhach, A. Migani, T. Staudt, G. P.
Petrova, N. Tsud, T. Skála, A. Bruix, F. Illas, K. C. Prince, V.
Matolı´n, K. M. Neyman and J. Libuda, Nat. Mater., 2011,
10, 310-315.
45.
46.
47.
C. Fettkenhauer, G. Clavel, K. Kailasam, M. Antonietti and
D. Dontsova, Green Chem., 2015, 17, 3350-3361.
Q. Li, J. Yang, D. Feng, Z. Wu, Q. Wu, S. S. Park, C.-S. Ha
and D. Zhao, Nano Res., 2010, 3, 632-642.
L. S. Kibis, A. I. Stadnichenko, S. V. Koscheev, V. I.
Zaikovskii and A. I. Boronin, J. Phys. Chem. C, 2012, 116,
19342-19348.
48.
S.-W. Bian, Z. Ma and W.-G. Song, J. Phys. Chem. C, 2009,
113, 8668-8672.
23.
A. Kumar and V. Ramani, ACS Catal., 2014, 4, 1516-1525.
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Journal of Materials Chemistry A
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DOI: 10.1039/C7TA04607C
Table of Contents entry
Tailoring the framework composition of carbon nitride to improve the catalytic
efficiency of stabilised palladium atoms
E. Vorobyeva, Z. Chen, S. Mitchell, R. K. Leary, P. Midgley, J. M. Thomas, R. Hauert, E. Fako,
N. López and J. Pérez-Ramírez*
The C/N ratio of the carbon nitride lattice is tailored by doping with carbon to assess the impact on the
stabilisation of palladium atoms and their catalytic efficiency in the selective hydrogenation of 2-methyl-
3-butyn-2-ol.