Selective Oxidation of 5-HMF over Au/MgAl ...

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Email: [email protected], [email protected]. Aston University - Surfaces,. Materials ... metal or surface/bulk oxide. • Role of base? - HT instead of NaOH.
Aston University - Surfaces, Materials & Catalysis Group

Selective Oxidation of 5-HMF over Au/MgAl Hydrotalcites Leandro Ardemani, Adam F. Lee* and Karen Wilson, European Bioenergy Research Institute, Aston University, UK. Email: [email protected], [email protected]

INTRODUCTION

EFFECT OF pH AND Au LOADING

• >90% of global chemicals rely upon heterogeneously • Biomass offers alternative sustainable 1 catalysed processes. carbon sources for chemicals & fuels.

Conversion or Yields / %

100 80

CO2 CH4, CH3OH H2

e-

60

H2 O

Corn husks

Petrochemicals

Solar fuels/chemicals

$29 billion industry (2010)

Agrochemicals

20%

Chemical synthesis

27%

Biorefining

20

Green Chemistry

22%

Conversion HMFCA FFCA

40

Jatropha curcas

Pollution Control

21% 10%

Switchgrass

0 Reforming

Petroleum

Cracking

Polymers

pH

Fossil fuel refining

NaOH enhanced conversion

120 Fine Chemicals Pharmaceuticals

• Bio-derived Chemicals provide biodegradable polymers.

• Catalysis is key to meeting the challenges of an efficient, sustainable chemicals industry.

• Non-toxic materials and building blocks from crops or sugar waste, biodegradable to compost.

AEROBIC OXIDATION Dehydration of Sugars

Source of HMF

Green Polymers

Selox of HMF to FDCA

100 80 60 40 20 0 HMF

FFCA

Fural- HMFCA Furfuryl dehyde alcohol

Au loading

EFFECT OF CALCINATION & REACTION

BUT: major societal and environmental impact: crops for food or fuels? Deforestation.

Outstanding Questions

After addition of HMF

• HMF derived from dehydrated sugars and a potential • Active site? feedstock for fuels and chemicals. - metal cluster - metal or surface/bulk oxide • FDCA obtained from the selective oxidation of HMF, building block for bio-polymer replacement for PET. • Role of base? • HMF oxidation to FDCA has employed environmentally - HT instead of NaOH. unfriendly oxidants (KMnO4, Co/Mn/Br salts) and high - Role of calcination T. pressures (70 bar). - Role of Au loading.

HO

H

HO

HMF

O

HO

OH

11800

11900

12000 Energy / eV

12100

XAS shows that Au3+ →Au0 upon calcination above 170 °C during synthesis, and resultant metallic gold nanoparticles are stable under basic conditions and during HMF oxidation.

• Investigate influence of support basicity and Au oxidation state.

OH

* *

FFCA

*

*

CATALYST PREPARATION • Supported Au nanoparticles are more selective than Pd or Pt, but required base (typically NaOH) for selective alcohol oxidations. 5

15

25

• Hydrotalcites are versatile solid bases and used as catalyst supports able to operate in water.

35 45 2θ (°)

55

65

75

Mixed Mg-Al oxides

Au peaks (*)

Au loading

Intensity

FDCA

• Preparation of Au/HT variants

O

H

12000

OH

O

O

11950 Energy / eV

Nanoengineered Catalysts

HMFCA O

O

11900

O

O

Catalyst ex situ

Parent HT

Intensity

O

Aqueous solution at RT

HAuCl4 standard

• Green, heterogeneous catalytic process required: air, mild conditions and minimising waste production. O

Aqueous solution at 90°C Intensity

Calcination T

After addition of NaOH Intensity

Background

After reaction, 16 hours

Au foil standard

Partial HT decomposition HT structure

5

15

25

35 45 55 2 θ (°)

65

75

• Deposition-precipitation of HAuCl4 on hydrotalcite and thermal processing forms Au NPs. Double-layered structure of hydrotalcite → synthetic clays with generic formula [Mg(1-x)Alx(OH)2]x+(CO3)x/n2-. Pure HT phase: 0.25 < x < 0.44 prepared via alkali-free route.

10 nm

CONCLUSIONS • Family of Au/hydrotalcite catalysts synthesised, characterised and tested for the aerobic selox of HMF to FDCA. • Reaction is pH sensitive → oxidation of the alcohol group the rate-determining step. • Catalyst activity and FDCA selectivity increases with Au loading, ameliorate benefit of NaOH.

O HO

O HMF

O H

Au, O2 lower basic pH

HO

O HMFCA

O OH

Au, O2 higher basic pH

HO

O

O O

Au, O2 H

FFCA

• Reaction scheme: HMF selox pH sensitive. • Au successfully supported onto hydrotalcite and used as the catalyst.

HO lower basic pH

O O

OH

• Activity increases with calcination temperature, due to formation of mixed Mg/Al oxides. • XAS: No changes in the Au0 oxidation state during the reaction.

FDCA References: 1. Anastasa, P.T.; Kirchhoff, M.M.; Williamson, T.C. Appl. Catal. B 2001, 221, 3. 2. Carrettin, S.; McMorn, P.; Johnston, P.; Griffin, K.; Kiely, C. J.; Hutchings, G. J., PCCP 2003, 5, 1329. 3. De Jong, E.; Dam, M.A.; Sipos, L.; Gruter, G.-J. M. in Biobased Monomers, Polymers, and Materials, ACS Symposium Series 2012, 1105, 1. 4. Gorbanev, Y. Y.; Klitgaard, S. K.; Woodley, J. M.; Christensen, C. H.; Riisager, A., ChemSusChem 2009, 2, 672. 5. Gupta, N. K.; Nishimura, S.; Takagaki, A.; Ebitani, K. Green Chem. 2011, 13, 824. 6. Davis, S. E.; Houk, L. R.; Tamargo, E. C.; Datye, A. K.; Davis, R. J. Catal. Today 2010, 160, 55.