Supporting Information

© Wiley-VCH 2007

69451 Weinheim, Germany

High Activity Single-Site Mesoporous Pd/Al2O3 Catalysts for Allylic Alcohol Selox Simon F.J. Hackett, Rik M. Brydson, Mhairi H. Gass, Ian Harvey, Andrew D. Newman, Karen Wilson

and Adam F. Lee* Extended X-ray Absorption Fine Structure (EXAFS) Pd K-edge EXAFS measurements were made on Station 9.3 of the Daresbury SRS facility, using a Si(220) double-crystal monochromator with a beam current/energy of 150 mA / 2 GeV. Transmission Pd (24.35 keV) K-edge spectra were acquired using powdered catalysts mounted in a stainless steel cell. The lowest loading samples (≤1 wt% Pd) were measured in fluorescence mode using a 9-channel Ortec ctrain germanium solid-state detector. Spectra were fitted using the Daresbury EXSPLINE and EXCURV98 packages for background subtraction, and phaseshift determination and fitting respectively. Reference transmission spectra of PdO powder (>99 % Lancaster) and a 10 µm Pd foil standard were also recorded. XANES fitting was undertaken using the ATHENA 0.8.050 application from the IFEFFIT Open Source software suite (http://cars9.uchicago.edu/iffwiki/Ifeffit). Normalized absorbances for the Pd/meso-Al2O3 series are shown below, together with an exemplar least squares fitting of the 0.033 wt% Pd/meso-Al2O3 XANES spectrum to weighted Pd foil and PdO standards, and a comparison between the fresh and spent 0.033 wt% Pd/ meso-Al2O3 sample:

-50 50 150 250 350 450 550 650

Energy above Pd K-edge / eV

Pd foil

PdO

4.7 wt%

2.4 wt%

1.03 wt%

0.06 wt%

0.03 wt%

Nor

mal

ised

µ

-100 0 100 200 300 400 500

Energy above Pd K-edge / eV

Spent (24 h reaction at 60 °C)

Fresh

Nor

mal

ised

µ

0.033 wt% Pd meso-Al2O3

http://cars9.uchicago.edu/iffwiki/Ifeffit

k3-weighted χ data for the Pd/meso-Al2O3 series are show below (raw experimental: thick line, fit: thin line):

-14

-10

-6

-2

2

6

10

14

3 6 9 12 15-14

-10

-6

-2

2

6

10

14

3 6 9 12 15

-14

-10

-6

-2

2

6

10

14

3 6 9 12 15-14

-10

-6

-2

2

6

10

14

3 6 9 12 15

-14

-10

-6

-2

2

6

10

14

3 6 9 12 15

Wavenumber / Å

Wavenumber / Å

Wavenumber / Å

Wavenumber / Å Wavenumber / Å

4.7 wt% Pd 2.4 wt% Pd

1.03 wt% Pd 0.06 wt% Pd

0.03 wt% Pd

k3-w

eigh

ted

χ

k3-w

eigh

ted

χ

k3-w

eigh

ted

χ

k3-w

eigh

ted

χ

k3-w

eigh

ted

χ

The corresponding fitted parameters for Pd/meso-Al2O3 series are given in the table below along with Pd standards:

Sample CN1 Pd-Pd

CN2 Pd-Pd

CN3 Pd-Pd

CN4 Pd-Pd

CN Pd-O

R1 Pd-Pd

R2 Pd-Pd

R3 Pd-Pd

R4 Pd-Pd

R5 Pd-0

σ1 Pd-Pd

σ2 Pd-Pd

σ3 Pd-Pd

σ4 Pd-Pd

σ5 Pd-O R-Factor

Pd foil 12 6 24 12 - 2.74 3.87 4.763 5.379 - 0.010 0.014 0.021 0.019 - 22.1

4.70wt% 10.02 6.90 13.22 10.00 - 2.75 3.89 4.77 5.51 - 0.02 0.03 0.03 0.03 - 29.70

2.37wt% 9.52 8.48 14.06 8.52 - 2.74 3.84 4.78 5.38 - 0.02 0.03 0.02 0.02 - 19.56

1.03wt% 5.60 5.96 7.25 5.70 1.70 2.74 3.85 4.77 5.40 2.02 0.02 0.03 0.02 0.02 0.01 25.51

0.066wt% 4.23 4.86 5.76 3.17 2.12 2.74 3.84 4.76 5.37 2.01 0.01 0.03 0.02 0.02 0.01 27.18

0.033wt% - - - - 4.00 - - - - 2.00 - - - - 0.01 40.32

PdO 8 2 - - 4 3.07 3.45 - - 2.03 0.017 0.005 - - 0.007 32.30 Fourier transforms of the χ data (radial distribution functions) for the Pd/meso-Al2O3 series are show below:

0 2 4 6 8

Porosimetry/Surface Areas Porosity and surface areas were determined on a Micromeritics ASAP 2010 instrument by N2 adsorption. Surface areas were calculated using the BET equation over the pressure range P/P0 = 0.020.2, where a linear relationship was maintained, while pore-size distributions were calculated using the BJH model up to P/P0 = 0.6. Surface areas of processed catalysts were 300 ± 20 m2g-1. Metal dispersions were measured using a Micromeritics PulseChemisorb 2700 surface area analyzer by H2 chemisorption on samples pre-reduced at 400 ºC under flowing H2 for 1 h. The resulting dispersion were cross-checked against the theoretical dispersions derived for cubeoctahedral particles of diameters determined from TEM (shown later).

Interatomic Distance / Å

Pd foil

4.7 wt%2.4 wt%

1.03 wt%0.06 wt%0.03 wt%

PdO

Four

ier T

rans

form

Pore Diameter / Å

dV/d

D /

cm3 .g

-1.Å

-1

0.03 wt% Pd/meso- Al2O3

0

0.005

0.01

0.015

0.02

0.025

10 100 10000

50

100

150

200

250

300

0 0.2 0.4 0.6 0.8 1P/P0

Vol

ume

Ads

orbe

d/ c

m3 .g

-1.S

TP

0.03 wt% Pd/meso- Al2O3

Powder X-ray Diffraction (XRD) Powder X-ray patterns were recorded using a Bruker AXS D8 diffractometer with a Cu Kα X-ray source. Data were collected in theta-two theta mode over a 2θ range of 10 70 ° with a step size of 0.02 ° and dwell time of 50 s per point. Low angle patterns were recorded between 2θ = 0.1 - 5°, with a step size of 0.01 ° and dwell time of 2 s per point.

36 37 38 39 40 41 42 43 44

X-ray Photoelectron Spectroscopy (XPS) X-ray photoelectron spectra were acquired at normal emission on a Kratos AXIS HSi spectrometer equipped with a charge neutralizer and Mg Kα excitation source (1253.6 eV). Binding energy (BE) referencing was employed using the adventitious carbon peak (285 eV) and valence band. Wide scans were recorded for surface elemental analysis (pass energy 160 eV), with high resolution spectra recorded at 40 eV pass energy. For the lowest loading sample, 50 scans were necessary to obtain good signal:noise statistics. Spectral fitting was performed using CasaXPS Version 2.3.5 with a common lineshape adopted for all Pd components.

2ϑ / degrees

Inte

nsity

0.27 wt% Pd

0.54 wt% Pd

1.03 wt% Pd

2.4 wt% Pd

4.7 wt% Pd

(111) reflection of fcc Pd

Pd 3

d X

P In

tens

ity

Binding Energy / eV

x 20

x 40

0.06 wt% Pd

0.03 wt% Pd

4.7 wt% Pd Pd0

PdII

331336341346

Transmission Electron microscopy High angle annular dark field (HAADF) images were acquired at the SuperSTEM 1 facility using a scanning transmission electron microscope (STEM). This instrument is based on a 100 keV VG HB501 with a cold-field emission source, a high-resolution pole piece and Nion Mark II spherical aberration corrector [1] capable of achieving a spatial resolution of 0.1nm. The HAADF image is formed by collecting transmitted electrons on a high-angle annular dark-field detector with an angular range from 70 to 210 mrad. These images are sensitive to atomic number and are often referred to as Z-contrast images [2], hence the technique is very valuable at identifying small quantities of heavy element on a lighter elemental substrate. Standard sample preparation was used for microscopy. The powdered sample was dispersed in ethanol, sonicated for 10 minutes and a drop put onto a lacey carbon film suspended over a copper grid. The figure below shows the unprocessed image (Figure 2, main text), confirming that the individual atoms are visible. In some instances there appear to be two atoms very close together, this could be an artifact of the technique as the atoms are very mobile under the beam; it is possible that as the beam scans the image area, an atom is excited and moves into the path of the beam causing it to be imaged again. This has been confirmed by taking a series of images consecutively and observing the movement of the atoms.

The figures below show a smoothed HAADF image (left) of a different area of the same sample. Again, individual atoms are visible. The corresponding bright field (BF) image (right) is also shown. The latter reveals strong diffraction contrast and lattice spacings from the alumina support, demonstrating that conventional BF imaging cannot be used, particularly in these low Pd-loaded samples.

(1) Krivanek, O.L.; Dellby, N.; Lupini, A.R. Ultramicroscopy 1999, 78, 1. (2) Pennycook, S.J.; Boatner, L.A. Nature 1998, 336, 565.

Associated particle size-distributions for the 0.03 wt%, 1.03 wt% and 2.37 wt% Pd/meso-Al2O3 samples are given below:

Comparative average particle sizes and total PdII content for supported palladium over mesoporous and amorphous aluminas:

Pd loading / wt%

Pd cluster sizea / nm

Total PdII / %

Surface PdII / %

Mesoporous Al2O3 0.03 0.13 85 76.6 0.06 0.8 59 57.2 0.27 1.0 - 61.3 0.54 1.1 - 55.0 1.03 1.3 43.4 44.1 2.37 2.0 23.6 22.2 4.70 4.4 17.8 10.2 Amorphous γ-Al2O3b 0.06 2.7 71.2 65.1 0.44 2.8 45.7 42.1 0.84 2.2 32 33.0 1.48 3.6 28 30.7 2.02 4.6 22.6 19.2 4.72 4.2 18.5 4.3 8.54 7.8 7.5 0 a Average determined from EXAFS 1st shell coordination number, X-ray line-broadening and TEM bValues taken from Green Chem. 2006, 8, 549-555. Catalyst synthesis Mesoporous alumina was prepared from an aluminum hydroxide suspension was obtained by hydrolysis of 87.5 g of aluminum sec-butoxide (Sigma-Aldrich >95 %) with 20.6 g of de-ionized water in 550 g of propan-1-ol. After 1 hr stirring 21.6 g of lauric acid (Sigma-Aldrich 98 %) was added. The mixture was then aged (static) at room temperature for 24 hrs, and then heated for 48 hours at 110 oC. The solid was then filtered and washed with ethanol and dried at room temperature. Template was removed by calcination under static air. The heat was ramped at 25 o C.min-1 to 250 oC and then ramped to 550 oC at 5 oC.min-1 (note this reaction is highly exothermic). The sample was calcined at 550 oC for 2.5 hrs. Supported palladium catalysts were prepared from the above mesoporous alumina using tetraamine palladium(II) nitrate solution (Johnson Matthey assay 4.16 % Pd) by the incipient wetness technique. Dried samples were calcined at 500 oC in static air for 2 h, then reduced under flowing H2 (10 cm3.min-1) at 400 oC for 2 h. Catalysts were stored in air and not re-activated prior to use. Amorphous alumina supported catalysts were prepared by the same method using a commercially available Degussa C γ-alumina support (surface area 180 m2g-1).

0102030405060708090

100

0-0.20.2-0.40.4-0.60.6-0.80.8-11-1.21.2-1.41.4-1.61.6-1.81.8-22-2.2

Size / nm

Perc

enta

ge n

umbe

r of

par

ticle

s

0

5

10

15

20

25

30

0.2-0.40.4-0.60.6-0.80.8-11-1.21.2-1.41.4-1.61.6-1.81.8-22-2.22.2-2.42.4-2.6

Size / nm

Perc

enta

ge n

umbe

r of

par

ticle

s

0

5

10

15

20

25

0.2-0.40.4-0.60.6-0.80.8-11-1.21.2-1.41.4-1.61.6-1.81.8-22-2.22.2-2.42.4-2.6

Size / nm

Perc

enta

ge n

umbe

r of

par

ticle

s0.03 wt% 1.03 wt% 2.37 wt%

Catalyst performance Kinetic profiles for crotyl alcohol aerobic selective oxidation are shown below for representative Pd/meso-alumina samples at 100 ºC: Effect of pre-reduction temperature on 1.03 wt% Pd/meso-Al2O3 catalyst activity.

0

20

40

60

80

100

0 20 40 60 80 100 120 140

Time / min

Con

vers

ion

/ % 0.03wt% 0.07wt% 1.03wt% 4.7wt%

0.03wt%0.54wt%1.03wt%4.7wt%

Unreduced

Initi

al ra

te C

innO

H /

mol

.h-1

Initial rate CrotO

H / m

ol.h-1

Reduction temperature / ºC

0

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

0.0008

0.0009

0.001

0 100 200 300 400 5000

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

0.0016

0.0018

CinnOHCrotOH

Initial rate and TOF versus Pd loading for crotyl alcohol oxidation at 60 ºC. Apparent activation energy of Pd/Meso-Al2O3 catalysts in aerobic oxidation of crotyl alcohol as a function of Pd loading.

Pd/meso-Al2O3 ∆∆∆∆Eact / kJmol-1 0.03 wt% 10 0.06 wt% 37 1.03 wt% 45 4.7 wt% 54

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

0.0016

0 1 2 3 4 50

1000

2000

3000

4000

5000

6000

7000

8000

Initi

al ra

te /

mol

.h-1

TOF / m

mols.h

-1.surfacePd-1

Pd loading / wt%