New Cu-Based Catalysts Supported on TiO2 Films
FULL PAPER
ed) tube at l=1.5404 ꢄ (CuKa) in the range 2V=5–808 and with scan-
ning speed of 0.23 8minꢀ1 (CuZn) and 0.098minꢀ1 (Cu). The powder sam-
ples were prepared by solvent evaporation from the colloidal suspensions
deposited on a glass plate (PW3071/60Bracket).
quots. The data were compared with literature data and with previously
acquired, qualitative GC-MS measurements.
Catalyst surface area, pore sizes, and metal dispersion were determined
by physisorption and chemisorption techniques (see the Supporting Infor-
mation). The catalytic activity is presented in terms of amount of the re-
action product obtained per unit time per catalyst weight (not accounting
XPS data were obtained with
a Kratos AXIS Ultra spectrometer
equipped with a monochromatic Al Ka X-ray source and a delay-line de-
tector (DLD). Spectra were obtained by using an aluminium anode
(Al Ka=1486.6 eV) operating at 150 W. For survey and region scans, con-
stant pass energies of 160 and 40 eV were used, respectively. The back-
ground pressure was 2ꢃ10ꢀ9 mbar. Samples were prepared in a glovebox
(d= <10 ppm O2) and transported in a closed sample holder for oxygen-
free XPS analysis.
for the weight of glass beads). The initial reaction rate (rinit
) in
molprod gcatꢀ1 sꢀ1 was determined from the product concentration after a
reaction time of 5 min (Equation 2).
C ꢂ VL
ð2Þ
rinit
¼
Dt ꢂ wcat
HRTEM images were recorded using a FEI Tecnai G2 Sphera transmis-
sion electron microscope at an acceleration voltage of 200 kV. For TEM
analyses, 250 mg of the solid catalyst was pulverized and suspended in
ethanol. A volume of 30 mL of the suspension was dip-coated onto a 200
mesh molybdenum grid (carbon holey film) and subsequently dried at
ambient temperature and pressure. Support surface morphology was ana-
lyzed on a FEI Quanta series FEG 3D G2 SEM using an acceleration
voltage of 5 kV and magnifications of between 5,000x–100,000x, provid-
ing a maximum lateral resolution of 50 nm2. Catalyst elemental composi-
tions were elucidated by EDX analysis at a spot size of 50 nm2 at an in-
teraction-volume of 100 mm.
In which C is the concentration of 4-phenoxypyridine in mol Lꢀ1after re-
action time of 5 min, VL is the solvent volume in L, Dt is the time interval
(300 s) in s, and w is the catalyst weight in g.
The catalytic activity was measured for the three catalyst types: the un-
supported CuZn nanoparticles (CuZn NPs), Cu supported on non-porous
titania (Cu/np-TiO2) and Cu supported on structured mesoporous titania
(Cu/meso-TiO2). The catalyst deactivation was studied in a fixed-bed re-
actor at different processing times.
Magic-angle-spinning (MAS) 63Cu NMR spectra were recorded at room
temperature on a Bruker DMX500 spectrometer, operating at a frequen-
cy of 132.57 MHz. A 4 mm MAS probe head was used with a sample ro-
tation rate of 6 kHz. To suppress baseline artifacts resulting from probe
ringing, 63Cu NMR spectra were recorded by use of a three-pulse pulse
sequence q+x–qꢁx–t–qy–d1 with short pulses of 1 ms pulse length (corre-
sponding to an excitation angle of 188), an interpulse delay of 0.1 ms, and
an interscan delay of 100 ms. Typically 8192 scans were recorded. The
radio-frequency carrier position was chosen close to the resonance fre-
quency of microcrystalline copper(I) chloride powder. Following the con-
vention in several solid-state 63,65Cu NMR studies,[24] solid CuCl was also
used as external reference for the chemical shift d=0 ppm. The 63Cu
NMR spectrum of the NMR coil alone (without sample) consisted of a
single d=90 ppm wide signal (at half height) without MAS sidebands,
and this was subtracted from the MAS NMR spectra of the catalysts as
background correction. The fact that the MAS NMR signal of Cu0 in the
fresh catalyst was narrower and had spinning sidebands, made an unam-
biguous subtraction possible.
Catalyst pretreatment: Prior to experiments, the catalysts were pretreated
in a flow of dimethylacetamide (5 mLminꢀ1) for 4, 8, or 12 h (the same
duration as the subsequent experiment). In catalyst stability experiments,
potassium phenolate was dissolved in the solvent. In the oxidation stabili-
ty experiments, 4-chloropyridine was added to the solvent at 1408C. De-
tails on the experimental setup are provided in the the Supporting Infor-
mation.
Derivation of kinetic model: Experiments were carried out over the tem-
perature range 110–1408C by using metallic copper (99%, Aldrich). The
catalyst loading (1–10 mol% with respect to 4-chloroACHTUNGTNERpUNNG yrACHUNTRTGENNUNGiACHUTGTNRENNUGdine), initial re-
actant concentrations (potassium phenoxide 0.3–0.75 molLꢀ1 and 4-chlor-
opyridine 0.2–0.5 molLꢀ1), initial product concentrations (4-phenoxypyri-
dine 0.05–0.25 molLꢀ1) and the crown ether concentration (1–10 mol%
of 18-crown-6 ether with respect to potassium phenoxide) were varied.
The mole ratios of potassium phenoxide and 4-chloropyridine were
varied from 0.5 to 4.[25]
The metal loading was determined by ICP-OES on a SPECTRO CIR-
OSCCD spectrometer.
Acknowledgements
For temperature-programmed oxidation a quartz glass tube (outer diame-
ter: 6 mm, inner diameter: 3 mm) was filled with a known amount of sup-
ported catalyst, sealed, and pretreated in a convection oven under hydro-
gen flow for 6 h at 3508C. After cooling, an oxygen flow (4 vol% in He)
was applied at a flow rate of 8 mLminꢀ1 and heated to 3008C at a rate of
18Cminꢀ1. During the temperature desorption step, a hydrogen flow
(4 vol% in N2) was passed over the catalyst bed from RT to 4008C at a
rate of 108Cminꢀ1. A commercial copper catalyst (BTS-catalyst 30 wt%
CuO/SiO2, 125–250 mm, R3–11, lot nr. 0849, BASF) was used as reference
standard.
We thank the Dutch Technology Foundation STW (project MEMFiCS
GSPT-07974), DSM Research, Friesland Campina, LioniX, IMM (Ger-
many), Milestone s.r.l. (Italy) for their financial and in-kind support. We
also acknowledge the European Commission (project NoE EXCELL
NMP3-CT-2005–515703) and The Royal Society (International Joint Proj-
ect 2008/R4 ꢁꢁSmart Structured Multiphase Reactors for Process Intensifi-
cationꢁꢁ). Thanks go to Prof. Dr. Bert W. Meijer and Dr. Jef A. J. M.
Vekemans for the analytical equipment and fruitful discussions.
Catalytic activity measurements: Potassium phenolate and 4-chloropyri-
dine were separately prepared as described elsewhere.[23] A mixture con-
taining an accurate amount of 4-chloropyridine (0.75 mol), potassium
phenolate (0.90 mol), and 18-crown-6 as appropriate (ca. 0.01 molequiv
with respect to phenolate), was stirred in a baffled glass reactor (75 mL)
loaded with DMA (15–25 mL) at 458C until dissolution was complete.
After heating the reaction mixture to the desired temperature, an appro-
priate amount of catalyst was added to the reactor, which was mechani-
cally stirred at 500 or 1500 rpm. The procedure was carried out in an
argon atmosphere and the resulting slurry was heated. Due to the differ-
ent synthetic protocols different copper loadings resulted; therefore the
amount of catalyst in the reactor was adjusted for each catalyst type to
provide similar Cu metal loadings. The solvent temperature during the
reaction was measured using a thermocouple. The yield of 4-phenoxypyr-
idine was determined by recording the 1H NMR spectra of reaction ali-
[1] a) J. M. Campelo, D. Luna, R. Luque, A. A. Romero, Chem
Chem 2009, 2, 18–45; b) R. Ferrando, J. Jellinek, R. L. Johnston,
[2] C. N. R. Rao, G. U. Kulkarni, P. J. Thomas, P. P. Edwards, Chem.
[4] W. J. Zhang, Y. Liu, R. G. Cao, Z. H. Li, Y. H. Zhang, Y. Tang, K. N.
ton, B. F. G. Johnson, A. E. H. Wheatley, J. C. Schouten, Lab Chip
[6] V. Engels, F. Benaskar, D. A. Jefferson, B. F. G. Johnson, A. E. H.
Wheatley, Dalton Trans. 2010, 39, 6496–6502.
ACHTUNGTRENNUNGSus-
AHCTUNGTRENNUNG
Chem. Eur. J. 2012, 18, 1800 – 1810
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1809