www.sciencemag.org/content/351/6276/965/suppl/DC1

Supplementary Materials for

Palladium-tin catalysts for the direct synthesis of H2O2 with high selectivity

Simon J. Freakley,* Qian He, Jonathan Harrhy, Li Lu, David A. Crole, David J. Morgan, Edwin N. Ntainjua, Jennifer. K. Edwards, Albert F. Carley, Albina Borisevich,

Christopher J. Kiely, Graham J. Hutchings* *Corresponding author. E-mail: hutch@cf.ac.uk (G.J.H.), freakleys@cf.ac.uk (S.J.F.)

Published 26 February 2016, Science 351, 965 (2016) DOI: 10.1126/science.aad5705

This PDF file includes: Materials and Methods

Figs. S1 to S18

Tables S1 to S6

References

2

Materials and Methods

Catalyst Preparation

Monometallic tin and palladium and bimetallic Pd-Sn catalysts were prepared by

impregnating or co-impregnating aqueous solutions of metal salts onto either TiO2 (Degussa

p25) or SiO2 (Matrex 60A) supports. All the catalysts prepared had a nominal total metal

loading of 5 wt.% unless otherwise stated. A typical preparation of 1 g of 2.5 wt% Pd – 2.5

wt% Sn / TiO2 was as follows:- Pd(NO3)2.2H2O (0.0626 g, Sigma Aldrich) was first

dissolved in 2 ml of de-ionised water and heated to 80 ºC with stirring. SnCl4.5H2O (0.0738

g, Sigma Aldrich) was dissolved in 1 ml of water and added to the aqueous palladium

solution and left for 15 min under stirring. TiO2 (0.95 g, Degussa P25) was then added to the

solution and the water allowed to evaporate until the mixture had a paste-like consistency.

SiO2 (Matrex 60A) was also used as catalyst support. Samples were then dried (110 ºC for

16 h) and calcined (static air at various temperatures for 3 h with a ramp rate of 20 ºC min-1).

Selected samples were reduced at various temperatures under a flow of 5% H2/Ar for 2 h with

a ramp rate of 20 ºC min-1. Selected samples were then re-calcined under static air.

Catalyst Testing

Hydrogen peroxide synthesis and degradation activity was evaluated using a Parr

Instruments stainless steel autoclave with a nominal volume of 100 ml and a maximum

working pressure of 14 MPa. To test each catalyst for H2O2 synthesis, the autoclave was

charged with catalyst (0.01g) and 8.5 g solvent (5.6 g MeOH and 2.9 g H2O both HPLC

grade). The charged autoclave was then purged three times with 5% H2/CO2 (0.7 MPa) before

filling with 5% H2/CO2 to a pressure of 2.9 MPa at 20 oC. The pressure was allowed to drop

to 2.6 MPa as the gas dissolved in the solvent at 20 oC. This was followed by the addition of

25% O2/CO2 (1.1 MPa). The temperature was then allowed to decrease to 2 oC followed by

stirring (at 1200 rpm) of the reaction mixture for 30 mins. The H2O2 productivity was

determined by titrating aliquots of the final solution after reaction with acidified Ce(SO4)2

(0.01 M) in the presence of two drops of ferroin indicator. Catalyst productivities are reported

as mol H2O2 kgcat-1 h-1.

H2O2 degradation experiments were carried out in a similar manner to the H2O2

synthesis experiments, but in the absence of 1.1MPa 25%O2/CO2. Furthermore, H2O from the

8.5 g of solvent was replaced by a 50 vol% H2O2 solution to give a reaction solvent

containing between 4-16 wt% H2O2. The standard reaction conditions adopted for H2O2

degradation were as follows: 0.01 g catalyst, 8.5 g solvent (5.6 g MeOH, 2.22 g H2O and 0.68

g H2O2 (50 %)), 2.9 MPa 5%H2/CO2, 2 oC, 1200 rpm, 30 mins.

Catalyst Characterization

XPS measurements were carried out using a Kratos Axis Ultra DLD spectrometer using

monochromatic Al K radiation (source power 140 W). An analyser pass energy of 160 eV

was used for survey scans, and 40 eV for detailed acquisition of individual elemental regions.

Samples were heat treated ex situ prior to mounting using double-sided adhesive tape, and

binding energies referenced to the Ti(2p3/2) peak at 458.2 eV for TiO2 supported samples and

the Si(2p) peak at 103eV for SiO2 supported samples; these reference peaks were chosen over

the C(1s) signal of adventitious carbon to exclude any potential changes in the C(1s) signal

3

due to the reductive and oxidative treatment cycles. Spectra were quantified using CasaXPS

and surface compositions (quoted in atom %) of the different samples are presented in Table

S3. Due to the similar binding energies of SnO and SnO2, the Sn Auger peaks were recorded

and the Auger parameter (’) measured between the Sn(3d5/2) and Sn(MNN) peaks, where ’

= BE Sn(3d5/2) + KE Sn(MNN). Typical values of ’ are 922.3 eV (Sn0), 919.7 eV (Sn2+ in

SnO) and 919.0 eV (Sn4+ in SnO2), therefore an increase in the value of ’ indicates a shift

towards lower oxidation state. (22-24)

Samples for examination by electron microscopy were dry dispersed onto a holey carbon

TEM grid. Samples were either examined (i) at 200kV in an aberration corrected JEOL

ARM-200FS in Lehigh University and (ii) at 60kV in a Nion UltraSTEM-100 at Oak Ridge

National Laboratory, equipped with a Gatan Enfina EELS spectrometer. The EELS spectrum

images were analysed as illustrated in Figure SE1 below.

Figure SE1. Schematic diagram illustrating the EELS fitting procedure employed in this

study.

The black solid curve in Figure SE1 represents a typical experimental EELS spectrum

acquired in this work, which can contain features from several components, including Pd or

PdO (red), Sn or SnO2 (green) and TiO2 (blue). The PdO, SnO2 and TiO2 reference spectra

4

were obtained experimentally from standard materials, while the Pd and Sn reference spectra

were taken from the EELS atlas. The following steps were carried out in a typical analysis:-

Firstly, the Pd distribution was obtained by linearly fitting the Pd M edge and a power-

law background (dashed line) over the 360-420 eV energy range (denoted as region (1) in

Fig. SE1) where the difference between the Pd and PdO reference spectra is negligible. The

symbol * in Fig SE1 means that the spectrum is acquired from EELS atlas database.

Secondly, the Ti and Sn distributions were then obtained by linearly fitting the Ti L

edge, the Sn M edge and a power-law background (dotted line) over the 450-520 eV energy

range (shown as region (2) in Fig. SE1) which occurs before the onset of the O K edge.

Again, in this energy range the difference between the Sn and SnO2 reference spectra is

negligible.

Thirdly, the weighting factors obtained from the second step were used to remove the

TiO2 and the background components from a larger energy range from 450 to 600 eV

(denoted as region (3) in Fig. SE1). The remaining O K edge was considered to arise either

from Pd-oxide or Sn-oxide (shown in Figures S9 and S10). The direct multiple linear least

square fitting procedure does not work well in this latter case because the candidate oxides

materials could feasibly be ‘off-stoichiometry’ and therefore the component reference spectra

are unknown.

5

Figure S1.

Pd(3d) core-level spectra for (a–c) 3 wt% Pd - 2 wt% Sn / TiO2 and (d–f) 1 wt% Pd – 4 wt%

Sn / SiO2 bimetallic catalysts after different heat treatment regimens.

TiO2 support: (a) 500 °C / 3 h / air; (b) + reduced 200 °C / 2 h; (c) + 400 °C / 3 h / air

SiO2 support: (d) 500 °C / 3 h / air; (e) + reduced 200 °C / 2 h; (f) + 400 °C / 3 h / air

6

Figure S2.

Representative STEM-ADF grey scale images (a, b) and STEM-EELS (RGB) maps (c - f) of

a 3 wt% Pd – 2 wt% Sn / TiO2 catalyst after calcination at 500 oC for 3 h. The images show

the co-existence of thin surface films and PdO nanoparticles on the TiO2 support. The EELS

elemental maps show the surface film consists primarily of SnOx but contains patchy regions

of PdOx.

(a) (b)

(c)

(d)

(e)

(f)

7

Figure S3.

Representative STEM-ADF grey scale images (a, b) and STEM-EELS (RGB) maps (c - f) of

the larger (5 - 10 nm) supported particles in a 3 wt% Pd – 2 wt% Sn / TiO2 catalyst after

calcination at 500 oC for 3 h. The EELS elemental maps show these particles to be Pd-Sn

alloys. A complementary pair of BF- and ADF-STEM images of a typical Pd-Sn alloy

particle is shown in (g & h). The spacings and intersection angles of the lattice fringes seen in

the arrowed region in (h) are compatible with the [1-10] projection of cubic Pd3Sn or the

[100] or the [001] projections of orthorhombic Pd2Sn. They do not match well to PdO, SnO

or SnO2.

(a) (b) (c)

(d) (e)

(f)

(g) (h)

8

Figure S4.

Representative STEM-ADF images (a – c) of a 5 wt% Sn / TiO2 monometallic catalyst after

calcination at 500 oC for 3 h. It is clear that the Sn tends to spread out and wet the TiO2

support particles as thin SnOx films. Note also that there are far fewer sub-nm particles (noted

in Figures 1, S2, S3, S5, S6, S7 and S8) which suggests that these latter features are

associated primarily with the Pd component in the bimetallic catalyst.

(a) (b) (c) 10 nm 10 nm 10 nm

9

Figure S5.

Representative STEM-ADF grey scale images (a, b) and STEM-EELS (RGB) maps (c – f) of

a 3 wt% Pd – 2 wt% Sn / TiO2 catalyst after calcination at 500 oC for 3 h and then reduction

in 5% H2/Ar at 200 oC for 2 h. These show the co-existence of thin SnOx surface films on the

TiO2 support containing embedded/supported Pd nanoparticles.

(e)

(b)

(c)

(d)

(a)

(f)

10

Figure S6.

Representative STEM-ADF grey scale images (a, b) and STEM-EELS (RGB) maps (c - f) of

the larger (5 - 10 nm) supported particles a 3 wt% Pd – 2 wt% Sn / TiO2 catalyst after

calcination at 500 oC for 3 h and then reduction in 5% H2/ Ar at 200 oC for 2 h. The EELS

elemental maps show these particles to be Pd-Sn alloys. A complementary pair of BF- and

ADF-STEM images of a typical Pd-Sn particle is shown in (g & h). The spacings and

intersection angles of the lattice fringes seen in the arrowed region in (h) could in principle be

compatible with the [1-10] projection of cubic Pd3Sn, the [001] projection of orthorhombic

PdSn or the [3-62] projection of orthorhombic Pd2Sn. They do not match well to PdO, SnO or

SnO2.

(a) (b)

(c)

(d) (e)

(f)

(g) (h)

11

Figure S7.

Representative STEM-ADF grey scale images (a, b) and STEM-EELS (RGB) maps (c - f) of

the 3 wt% Pd – 2 wt% Sn / TiO2 catalyst after (i) calcination at 500 oC for 3 h, (ii) reduction

in 5% H2/ Ar at 200 oC for 2 h and then (iii) calcination at 400 oC for 3 h. The EELS

elemental maps reveal Pd-Sn alloy particles supported on an SnOx surface film which is in

turn supported on the TiO2.

12

Figure S8.

Representative STEM-ADF grey scale images (a, b) and STEM-EELS (RGB) maps (c - f) of

the larger (5 – 10 nm) supported particles in a 3 wt% Pd – 2 wt% Sn / TiO2 catalyst after (i)

calcination at 500 oC for 3 h, (ii) reduction in 5%H2/ Ar at 200 oC for 2 h and then (iii)

calcination at 400 oC for 3 h. The EELS elemental maps show these particles to be Pd-Sn

alloys. A complementary pair of BF- and ADF-STEM images of a typical Pd-Sn particle is

shown in (g & h). The spacings and intersection angles of the lattice fringes seen in the

arrowed region in (h) could in principle be compatible with the [12-4] or [1-53] projections of

orthorhombic PdSn or the [3-62] projection of orthorhombic Pd2Sn. They do not match well

to PdO, SnO or SnO2.

(a) (b)

(c)

(d) (e)

(f)

(g) (h)

13

Figure S9.

A comparison of EELS spectra obtained from the thin film regions of the three samples

shown in Figures S2, S4 and S7. (a) Shows EELS spectra over the 450-600 eV range after

removing the TiO2 component and the power-law background (see Figure SE1, third step).

(b), (c) and (d) are the RGB EELS maps, obtained from the SnOx thin films in 3wt% Pd –

2wt% Sn / TiO2 catalysts at (b) the calcined only, (c)the calcined + reduced and (c) the

calcined + reduced + calcined stages respectively. The spectra (b), (c) and (d) superimposed

on (a) were obtained from the dashed rectangular area indicated in the corresponding RGB

EELS map. The SnO2 reference spectrum was obtained from a SnO2 particle standard,

whereas the PdO and Sn reference spectra are taken from EELS atlas. Spectrum (b) provides

direct evidence of the existence of SnOx thin films. After the reduction treatment, the film can

be reduced, as evidenced by the absence of the O K edge in spectrum (c). The O K edge

reappears upon re-calcination, as shown in spectrum (d). The scale bars represent a distance

of 1nm.

14

Figure S10.

A comparison of EELS spectra obtained from the thin film regions of the three samples

shown in Figures S3, S5 and S8. (a) Shows EELS spectra over the 450-600 eV range after

removing the TiO2 component and the power-law background (see Figure SE1, third step).

(b), (c) and (d) are RGB EELS maps, obtained from the alloyed nanoparticles in 3 wt% Pd - 2

wt% Sn / TiO2 catalysts at (b) the calcined only, (c) calcined + reduced and (d) calcined +

reduced + calcined stages respectively. The spectra (b), (c) and (d) superimposed on (a) were

obtained from the dashed rectangular area indicated in the corresponding RGB EELS map.

The SnO2 reference spectrum was obtained from a SnO2 particle standard, whereas the PdO

and Sn reference spectra are taken from EELS atlas. In contrast to the situation shown in

Figure S9 for the thin films, no clear O K edge was observed in any of the three

nanoparticles. This confirms these nanoparticles to be metallic Pd-Sn alloys. Some slight

oxidation of the surface of these particles is possible but at a level that is below the

detectability limit of the EELS technique. The scale bars represent a distance of 1nm.

15

Figure S11.

Representative BF- and ADF-STEM image pairs (a & b: c & d: e & f) showing ultra-small

Pd/PdOx nanoparticles embedded in the amorpous SnOx thin films.

(a) (b)

(c) (d)

(e) (f)

16

Figure S12.

Complementary BF- & ADF-STEM images (a & b) and EELS maps (c - e) of a ‘model’ 5

wt% Pd / SnO2 monometallic catalyst after calcination at 500 oC for 3 h. The Sn intensities in

the SnO2 support area were saturated on purpose in order to show up any relatively weak

signals in the particle region. Note from the elemental maps that the supported PdOx particle

appears to be ‘clean’.

(a) (b) (c)

(d) (e)

17

Figure S13.

Another example of complementary BF- & ADF-STEM images (a & b) and EELS maps (c –

e) from a ‘model’ 5 wt% Pd / SnO2 monometallic catalyst after calcination at 500 oC for 3 h.

The Sn intensities in the SnO2 support area were saturated on purpose in order to show up

any relatively weak signals in the particle region. Note from the elemental maps that the

supported PdOx particle once again appears to be ‘clean’.

(a) (b) (c)

(d) (e)

18

Figure S14.

Complementary BF- & ADF-STEM images (a & b) and EELS maps (c - e) of a ‘model’ 5

wt% Pd / SnO2 monometallic catalyst after (i) calcination at 500 oC for 3 h, (ii) reduction in

5%H2/ Ar at 200 oC for 2 h and then (iii) calcination at 400 oC for 3 h. The Sn intensities in

the SnO2 support area were saturated on purpose in order to show up any relatively weak

signals in the particle region. Note that the elemental maps show that the supported PdOx

particle is decorated with SnOx due to the SMSI effect.

(a) (b) (c)

(d) (e)

19

Figure S15.

Additional example of complementary BF- & ADF-STEM images (a & b) and EELS maps (c

- e) of a ‘model’ 5 wt% Pd / SnO2 monometallic catalyst after (i) calcination at 500 oC for 3 h,

(ii) reduction in 5%H2/ Ar at 200 oC for 2 h and then (iii) calcination at 400 oC for 3 h. The

Sn intensities in the SnO2 support area were saturated on purpose in order to show up any

relatively weak signals in the particle region. Note that once again the elemental maps show

that the supported PdOx particle is decorated with SnOx due to the SMSI effect.

(a) (b)

(c)

(d)

(e)

(f)

(a) (b) (c)

(d) (e)

20

Figure S16.

0 2 4 6 8 10 12 14 16 18

0

1

2

3

4

5

6

H2O

2 d

estr

oyed / m

mol

wt% H2O

2

Hydrogenation activity of the 1 wt% Pd – 4 wt% Sn / SiO2 catalyst with increasing

concentration of H2O2 present.

1 wt% Pd – 4 wt% Sn / SiO2 (500 °C / 3 h / air - Reduced 200 °C / 2 h - 400 °C / 4 h / air )

Rate of H2O2 degradation calculated from the loss off H2O2 using standard reaction

conditions: 2.9 MPa 5%H2/CO2, 8.5 g solvent (5.6 g MeOH, 2.22 g H2O and 0.68 g 50%

H2O2), 0.01 g catalyst, 2 oC, 1200 rpm, 30 mins.

21

Figure S17.

Representative lower magnification grey scale STEM-ADF images (a, b) and STEM-EELS

(RGB) maps (c - f) of a 1 wt% Pd – 4 wt% Sn / SiO2 catalyst after (i) calcination at 500 oC

for 3 h, (ii) reduction in 5% H2/Ar at 200 oC for 2 h and then (iii) calcination at 400 oC for 3

h. The EELS elemental maps show a strong correlation between the Pd and Sn signals within

particles on the SiO2 support.

(a) (b) (c)

(d) (e)

22

Figure S18.

Representative higher magnification grey scale STEM-ADF images (a, b) and STEM-EELS

(RGB) maps (c - e) of a 1 wt% Pd – 4 wt% Sn / SiO2 catalyst after (i) calcination at 500 oC

for 3 h, (ii) reduction in 5% H2/Ar at 200 oC for 2 h and then (iii) calcination at 400 oC for 3

h. Note from the elemental maps that the ultra-small Pd components are preferentially

supported or embedded on the SnOx film which is partially wetting the SiO2 support.

(a) (b)

(c)

(d)

(e)

23

Table S1.

H2O2 productivity of monometallic Sn or Pd and bimetallic Sn-Pd catalysts supported on

TiO2 showing synergy between Sn and Pd. All catalysts were calcined in static air at 500 °C

for 3 h prior to use.

Catalyst H2O2 productivity

mol kg cat −1 h-1

5 wt% Pd / TiO2 41

5 wt% Sn / TiO2 18

2.5 wt% Pd – 2.5 wt% Sn / TiO2 62

2.5 wt% Pd / TiO2 20

2.5 wt% Sn / TiO2 6

Rate of hydrogen peroxide production was determined after reaction using the following

reaction conditions:- 5% H2/CO2 (2.9 MPa ) and 25% O2/CO2 (1.1 MPa) , 8.5 g solvent (2.9 g

HPLC water, 5.6 g MeOH) 0.01 g catalyst, 2 oC , 1200 rpm, 30 mins).

24

Table S2.

H2O2 hydrogenation over monometallic Sn or Pd and various composition bimetallic Sn-Pd

catalysts supported on TiO2. All catalysts were calcined in static air at 500 °C for 3 h prior to

use.

a) Rate of hydrogen peroxide production was determined after reaction using the following

reaction conditions:- 5% H2/CO2 (2.9 MPa ) and 25% O2/CO2 (1.1 MPa) , 8.5 g solvent (2.9 g

HPLC water, 5.6 g MeOH) 0.01 g catalyst, 2 oC , 1200 rpm, 30 mins).

b) Rate of H2O2 degradation was calculated from the loss of H2O2 using standard reaction

conditions: 5%H2/CO2 (2.9 MPa), 8.5 g solvent (5.6 g MeOH, 2.22 g H2O and 0.68 g 50%

H2O2), 0.01 g catalyst, 2 oC, 1200 rpm, 30 mins.

Catalyst H2O2

productivitya

mol kg cat −1 h-1

H2O2

hydrogenationb

mol kg cat −1 h-1

5 wt% Pd / TiO2 41 126

5 wt% Sn / TiO2 18 0

4 wt% Pd – 1 wt% Sn / TiO2 57 83

3 wt% Pd – 2 wt% Sn / TiO2 68 65

2.5 wt% Pd – 2.5 wt% Sn / TiO2 62 41

2 wt% Pd – 3 wt% Sn / TiO2 57 12

1 wt% Pd – 4 wt% Sn / TiO2 49 65

25

Table S3.

XPS derived molar ratios (at%) and oxidation states for optimal ratio Pd-Sn bimetallic samples supported on SiO2 and TiO2 for each heat

treatment regimen.

Catalyst Pd Sn O Ti Si

Pd(3d5/2)

Binding Energy /

eV Sn(3d5/2)

Binding Energy /

eV

Sn

Auger

Parameter

(') /

eV

Pd/Sn

Ratio

Pd(0) Pd(II)

1 wt% Pd – 4 wt% Sn /

SiO2

500 °C / 3 h / air 0.3 0.7 70.3 28.7 335.1 (5%) 336.6 (95%) 486.3 918.6 0.34

+ Reduced 200 °C / 2 h 0.3 5.3 69.5 24.9 335.1 (100%) Not detected 486.2 918.5 0.21

+ 400 °C / 3 h / air 0.2 0.8 70.6 28.5 334.8 (15%) 336.2 (85%) 486.3 918.7 0.26

3 wt% Pd – 2 wt% Sn /

TiO2

500 °C / 3 h / air 1.4 1.6 69.1 27.9 334.3 (6%) 336.5 (94%) 486.4 918.9 0.88

+ Reduced 200 °C / 2 h 1.4 1.7 68.4 28.6 334.9 (52%) 336.7 (48%) 486.5 919.3 0.84

+ 400 °C / 3 h / air 1.4 1.6 67.9 29.1 334.3 (13%) 336.6 (88%) 486.5 919.5 0.86

26

Table S4.

H2O2 productivity and hydrogenation over a monometallic Pd and bimetallic Sn-Pd

catalysts supported on TiO2 after various heat treatment cycles.

Catalyst H2O2 productivitya/

mol kg cat −1 h-1

H2O2 hydrogenationb/

mol kg cat −1 h-1

0.5 wt% Pd / TiO2 c 14 113

5 wt% Pd / TiO2 c 8 70

0.5 wt% Pd / TiO2 d 10 70

5 wt% Pd / TiO2 d

3 wt% Pd – 2 wt% Sn / TiO2 d

6

59

42

110

a) Rate of hydrogen peroxide production was vdetermined after reaction using the

following reaction conditions:- 5% H2/CO2 (2.9 MPa ) and 25% O2/CO2 (1.1 MPa) , 8.5 g

solvent (2.9 g HPLC water, 5.6 g MeOH) 0.01 g catalyst, 2 oC , 1200 rpm, 30 mins).

b) Rate of H2O2 degradation was calculated from the loss of H2O2 using standard reaction

conditions: 5%H2/CO2 (2.9 MPa), 8.5 g solvent (5.6 g MeOH, 2.22 g H2O and 0.68 g

50% H2O2), 0.01 g catalyst, 2 oC, 1200 rpm, 30 mins.

c) Catalysts were calcined in static air at 500 °C for 3 h, reduced at 200 oC in H2/Ar for 2

h and then calcined at 400 oC for 3 h.

d) Catalysts were calcined in static air at 500 °C for 3 h, calcined at 200 oC for 2 h and

then calcined at 400 oC for 3 h.

27

Table S5.

H2O2 productivity and hydrogenation over monometallic Sn or Pd and various

composition bimetallic Sn-Pd catalysts supported on SiO2 containing various metal

ratios. All catalysts were calcined in static air at 500 °C for 3 h before use.

a) Rate of

hydrogen peroxide production was determined after reaction using the following reaction

conditions:- 5% H2/CO2 (2.9 MPa ) and 25% O2/CO2 (1.1 MPa) , 8.5 g solvent (2.9 g

HPLC water, 5.6 g MeOH) 0.01 g catalyst, 2 oC , 1200 rpm, 30 mins).

b) Rate of H2O2 degradation was calculated from the loss of H2O2 using standard reaction

conditions: 5%H2/CO2 (2.9 MPa), 8.5 g solvent (5.6 g MeOH, 2.22 g H2O and 0.68 g

50% H2O2), 0.01 g catalyst, 2 oC, 1200 rpm, 30 mins.

Catalyst H2O2

productivitya/

mol kg cat −1 h-1

H2O2

hydrogenationb/

mol kg cat −1 h-1

5 wt% Pd / SiO2 12 113

5 wt% Sn / SiO2 7 0

4 wt% Pd – 1 wt% Sn / SiO2 28 75

3 wt% Pd – 2 wt% Sn / SiO2 35 50

2.5 wt% Pd – 2.5 wt% Sn / SiO2 40 53

2 wt% Pd - 3 wt% Sn / SiO2 53 60

1 wt% Pd – 4 wt% Sn / SiO2 66 66

28

Table S6.

H2O2 productivity and hydrogenation data for a series of 0.5wt% Pd - 4.5wt% M / TiO2

catalyst where M = Ni, Zn, Ga, In and Co. Before use, all catalysts were calcined in static

air at 500 °C for 3 h, reduced at 200 oC in H2/Ar for 2 h and then calcined at 400 oC for 3

h.

Catalyst H2O2 productivitya/

mol kg cat −1 h-1

H2O2 hydrogenationb/

mol kg cat −1 h-1

5 wt% Ni / TiO2

0 0

5 wt% Ga / TiO2

0 0

5 wt% Zn / TiO2

0 0

5 wt% Co / TiO2

0 0

5 wt% In / TiO2 0 0

0.5 wt% Pd – 4.5 wt% Ni / TiO2

32

0

0.5 wt% Pd – 4.5 wt% Ga / TiO2

23 0

0.5 wt% Pd – 4.5 wt% Zn / TiO2

16 0

0.5 wt% Pd – 4.5 wt% Co / TiO2

15 0

0.5 wt% Pd – 4.5 wt% In / TiO2 15 0

a) Rate of hydrogen peroxide production was determined after reaction using the

following reaction conditions:- 5% H2/CO2 (2.9 MPa ) and 25% O2/CO2 (1.1 MPa) , 8.5 g

solvent (2.9 g HPLC water, 5.6 g MeOH) 0.01 g catalyst, 2 oC , 1200 rpm, 30 mins.

b) Rate of H2O2 degradation was calculated from the loss of H2O2 using standard reaction

conditions: 5%H2/CO2 (2.9 MPa), 8.5 g solvent (5.6 g MeOH, 2.22 g H2O and 0.68 g

50% H2O2), 0.01 g catalyst, 2 oC, 1200 rpm, 30 mins.

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