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.
