The Selective Oxidation of Cyclohexane via in-situ H2

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The Selective Oxidation of Cyclohexane via in-situ H

2

O

2

production Over Supported Pd-based Catalysts.

Caitlin M. Crombie

^aᵻ

, Richard J. Lewis

^aᵻ

, Dávid Kovačič

^a

, David J. Morgan

^a,b

, Thomas J. A. Slater

^c

, Thomas E. Davies

^a

, Jennifer. K. Edwards

^a

, Martin Skov Skjøth- Rasmussen

^d

, and Graham J. Hutchings

^a

*

a

School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff, CF10 3AT, United Kingdom.

b

HarwellXPS, Research Complex at Harwell (RCaH), Didcot, OX11 OFA, United Kingdom.

c

Electron Physical Sciences Imaging Centre, Diamond Light Source Ltd. Oxfordshire, OX11 0DE, United Kingdom.

d

Haldor Topsøe A/S, Haldor Topsøes Allé 1, DK-2800 Kongens Lyngby, Denmark

ᵻ

These authors contributed equally to this work.

* Hutch@cardiff.ac.uk

Supplementary Information.

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Table S.1. Requisite precursor amounts in the preparation of TiO2 supported Pd based catalysts for the selective oxidation of cyclohexane via in-situ H2O2 synthesis.

Catalyst Pd precursor Volume / mL (concentration /

6.0 mgmL^-1)

X precursor Mass / g or Volume / mL (concentration /

mgmL^-1)

Pd PdCl2 3.333 - -

V - - VCl3 6.176 mL (3.24)

VPd PdCl2 1.667 VCl3 3.088 mL (3.24)

MnPd PdCl2 1.667 MnCl2.4H2O 0.0360 g

FePd PdCl2 1.667 FeCl3.6H2O 0.0484 g

CoPd PdCl2 1.667 CoCl2.6H2O 0.0404 g

NiPd PdCl2 1.667 NiCl2.6H2O 1.667 mL (6.00)

CuPd PdCl2 1.667 CuCl2 0.0212 g

AuPd PdCl2 1.667 HAuCl4.3H2O 0.816 mL (12.25)

CePd PdCl2 1.667 CeCl3.7H2O 0.0266 g

Note: all catalysts exposed to a reductive heat treatment prior to use (5%H2/Ar, 500 °C, 4 h, 10 °C min^–1).

Table S.2. Surface area of as-prepared TiO2 supported catalysts.

Catalyst Surface area */ m²g^-

1

TiO2** 59

1%Pd/TiO2 49

0.5%Pd-0.5%Au/TiO2 47

0.5%Pd-0.5%V/TiO2 51

* Surface area determined from nitrogen adsorption measurements using the BET equation.

**support material used as received, with no modification prior to metal immobilisation.

Figure S.1. Catalytic activity of mono-metallic supported catalysts towards the direct synthesis (Black bars) and degradation of H2O2 (Blue bars). H2O2 direct synthesis reaction conditions: Catalyst (0.01 g), H2O (2.9 g), MeOH (5.6 g), 5% H2/CO2 (420 psi), 25% O2/CO2 (160 psi), 0.5 h, 20° C, 1200 rpm. H2O2 degradation reaction conditions: Catalyst (0.01 g), H2O2 (50 wt.% 0.68 g) H2O (2.22 g), MeOH (5.6 g), 5% H2/CO2 (420 psi), 0.5 h, 20°C, 1200 rpm.

Table S.3. Elemental surface composition of as-prepared Pd-based bi-metallic catalysts as determined by XPS analysis.

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Catalyst Pd⁰: Pd²⁺ Pd: X

1%Pd/TiO2 0.92 -

1 % VPd/TiO2 3.3 0.19

1 % MnPd/ TiO2 3 0.48

1 % FePd/ TiO2 5.7 0.36

1 % CoPd/ TiO2 13 0.23

1 % NiPd/TiO2 8.2 0.35

1 % CuPd/ TiO2 22 0.27

1 % AuPd/ TiO2 All Pd⁰ 2.43

1 % CePd/ TiO2 All Pd⁰ 0.10

Note: all catalysts exposed to a reductive heat treatment prior to use (5%H2/Ar, 500 °C, 4 h, 10 °C min^–1)

Table S.4. H2 conversion and product yield as a function of reaction time during selective oxidation of cyclohexane.

Catalyst Cyclohexanol

/ µmol Cyclohexanone

/ µmol CHHP

/ µmol H2

Conversion / %

Cyclohexane Conversion /

%

Selectivity to all C6*

products based on H2 / %

1%Pd/TiO2 1.8 0 1.8 96 0.014 0.15

1%VPd/TiO2 22.6 18.3 14.7 98 0.271 2.77

1%MnPd/TiO2 2.6 0 3.9 87 0.026 0.30

1%FePd/TiO2 6.6 6.1 2.1 88 0.058 0.67

1%CoPd/TiO2 5.6 9.2 5.9 95 0.082 0.87

1%NiPd/TiO2 7.0 7.9 2.7 91 0.069 0.76

1%CuPd/TiO2 3.3 5.7 8.4 98 0.068 0.70

1%AuPd/TiO2 12.5 6.3 5.3 95 0.095 1.01

1%CePd/TiO2 4.4 5.6 8.7 90 0.074 0.83

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Reaction conditions: Catalyst (0.05 g), cyclohexane (2.13 g, 25 mmol), t-butanol (6.37 g), 5% H2 / N2

(420 psi), 25% O2 / N2 (160 psi), 80 ^OC 1200 rpm. * C6 products; cyclohexanol, cyclohexanone and CHHP.

Table S.5. Comparison of 0.5%Au-0.5%Pd/TiO2 catalyst synthesis activity towards H2O2 synthesis and degradation as a function of catalyst synthesis procedure.

Catalyst preparation method Productivity / molH₂O₂kgcat-1h^-1 Degradation / molH₂O₂kgcat-1h^-1

Conventional wet impregnation 55 240

Modified impregnation 68 710

H2O2 direct synthesis reaction conditions: Catalyst (0.01 g), H2O (2.9 g), MeOH (5.6 g), 5% H2/CO2

(420 psi), 25% O2/CO2 (160 psi), 0.5 h, 20° C, 1200 rpm. H2O2 degradation reaction conditions:

Catalyst (0.01 g), H2O2 (50 wt.% 0.68 g) H2O (2.22 g), MeOH (5.6 g), 5% H2/CO2 (420 psi), 0.5 h, 20°C, 1200 rpm.

Figure S.2. The choice of oxidant on the catalytic activity of 0.5%Au-0.5%Pd/TiO2 towards the oxidation of cyclohexane. Reaction conditions: Catalyst (0.05 g), cyclohexane (2.13 g, 25 mmol), t- butanol (6.37 g), 5% H2 / N2 (420 psi), 25% O2 / N2 (160 psi), 17 h, 80 ^OC 1200 rpm. Note:

Concentration of H2O2 (2.5 mmol) used is comparable to that produced if all H2 in a standard reaction is converted to H2O2. N2 in parentheses is indicative of gaseous atmosphere (580 psi).

Table S.6. Apparent reaction rate for supported bi-metallic, Pd-based catalysts.

Apparent reaction rate / Cyclohexane Selectivity to all

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Catalyst µmolC6productsmmolmetal-1h^-1 Conversion / % C6* products based on H2 /

%

1%Pd/TiO2 4.50 x 10¹ 0.014 0.15

1%VPd/TiO2 4.5 x 10² 0.271 2.77

1%MnPd/TiO2 5.6 x 10¹ 0.026 0.30

1%FePd/TiO2 1.3 x 10² 0.058 0.67

1%CoPd/TiO2 1.8 x 10² 0.082 0.87

1%NiPd/TiO2 1.6 x 10² 0.069 0.76

1%CuPd/TiO2 1.6 x 10² 0.068 0.70

1%AuPd/TiO2 3.9 x 10² 0.095 1.01

1%CePd/TiO2 2.7 x 10² 0.074 0.83

Table S.7. H2 conversion and product yield during selective oxidation of cyclohexane for monometallic, bimetallic and physical mixtures V-Pd supported catalysts.

/ µmol CHHP

/ µmol H2

Conversion / %

%

1%Pd/TiO2 1.8 0 1.8 96 0.014 0.15

V/TiO2 5.2 7.8 1.1 - 0.055 -

V/TiO2 + Pd/TiO2

15.8 9.3 4.0 86 0.115 1.34

VPd/TiO2 22.6 18.3 14.7 98 0.271 2.77

Table S.8. H2 conversion and product yield during selective oxidation of cyclohexane for 1% VPd/TiO2

and vanadium oxide catalysts.

/ µmol CHHP

/ µmol H2

Conversion / %

%

1%Pd/TiO2 1.8 0 1.8 96 0.014 0.15

1%VPd/TiO2 22.6 18.3 14.7 98 0.271 2.77

V2O5 3.2 3.4 0.8 - 0.029 -

1% Pd/TiO2

+ V2O5

36.2 15.0 7.2 99 0.231 2.36

V2O4

4.8 3.1 0 - 0.031 -

1% Pd/TiO2

+ V2O4

36.5 13.0 2.3 99 0.204 2.08

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Table S.9. H2 conversion and total product yield during selective oxidation of cyclohexane achieved over 1%VPd/TiO2 catalysts as a function of V: Pd ratio.

Pd content /

%

Cyclohexanol / µmol

Cyclohexanone / µmol

CHHP / µmol

H2

Conversion / %

%

0 5.2 7.8 1.0 - 0.055 -

25 25.7 17.7 8.8 98 0.206 2.12

50 22.6 18.3 14.7 98 0.271 2.77

75 17.0 5.6 4.5 98 0.108 1.10

100 1.8 0 1.8 96 0.014 0.15

Table S.10. Apparent reaction rate for 1%VPd/TiO2 catalysts as a function of V: Pd ratio.

Pd content /

%

Apparent reaction rate /

µmolC6productsmmolmetal-1h^-1 Cyclohexane

Conversion / % Selectivity to all C6*

0 8.4 x 10¹ 0.055 -

25 3.6 x 10² 0.206 2.12

50 4.5 x 10² 0.271 2.77

75 2.7 x 10² 0.108 1.10

100 4.5 x 10¹ 0.014 0.15

Table S.11. ICP-MS analysis of post reaction solutions of the oxidation of cyclohexane utilising 1%

VPd/TiO2 over successive uses.

Reaction number % Pd leached (ppb) % V leached (ppb)

1^st use 0.29 (63) 21 (4533)

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2^nd use 0.33 (73) 14 (3090)

(420 psi), 25% O2 / N2 (160 psi), 17 h, 80 ^OC 1200 rpm.

Figure S.3. Comparison of catalytic performance of V-Pd catalysts towards the oxidation of cyclohexane via the in-situ production of H2O2. Cyclohexanol; blue, cyclohexanone; red, CHHP;

purple. Reaction conditions: Catalyst (0.05 g), cyclohexane (2.13 g, 25 mmol), t-butanol (6.37 g), 5% H2 / N2 (420 psi), 25% O2 / N2 (160 psi), 17 h, 80 ^OC 1200 rpm. Note: In all cases total moles of Pd and V are identical.

Table S.12. H2 conversion and total product yield during selective oxidation of cyclohexane achieved over 1%VPd/TiO2 catalysts as a function of V: Pd ratio.

/ µmol CHHP

/ µmol H2

Conversion / %

%

1%VPd/TiO2 22.6 18.3 14.7 98 0.271 2.77

1%Pd/TiO2 + VCl3

16.8 10 6.2 93 0.132 1.42

VCl3 11.7 0 0 - -

1%Pd/TiO2 1.8 0 1.8 96 0.014 0.15

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Table S.13. H2 conversion and total product yield during selective oxidation of cyclohexane achieved over 1%VPd/TiO2 catalysts upon first and second use.

Reaction number

Cyclohexanol / µmol

Cyclohexanone / µmol

CHHP / µmol

H2

Conversion / %

%

products based on

H2 / %

1^st use 22.6 18.3 14.7 98 0.271 2.77

2^nd use 32.6 18.1 40.2 91 0.361 3.98

Figure S.4. XPS spectra of Pd(3d) and V(2p) regions for fresh and used supported 0.5%V- 0.5%Pd/TiO2 catalysts.

Table S.14. Summary of the XPS derived surface atomic concentrations of the fresh and used supported 0.5%V-0.5%Pd/TiO2 catalysts.

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Catalyst Pd⁰: Pd²⁺ Pd: V V⁵⁺: V⁴⁺

As prepared 3.3 0.20 1.6

1^st Use 1.8 0.33 0.7

(420 psi), 25% O2 / N2 (160 psi), 17 h, 80 ^OC 1200 rpm.

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Figure S.5. Energy dispersive X-ray analysis of (A) as-prepared 0.5%V-0.5%Pd/TiO2 and (B) after use in the in-situ cyclohexane oxidation reaction. Ti (Green), Pd (Red), V (blue).

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