An aerosol-assisted sol–gel method is used to prepare mesoporous tin silicate catalysts that exhibit a record activity in the synthesis of ethyl lactate from dihydroxyacetone and ethanol. The method is based on the formation of an aerosol from a solution of precursors and surfactant. During the fast drying of the droplets, the surfactant self-assembles and the Sn-silica matrix is formed by polycondensation reactions. After calcination, the resulting material is composed of a true tin-silicon mixed oxide in the form of spherical microparticles with calibrated mesopores of 5–6 nm. Sn species are incorporated in the silica network, mainly in the form of single sites. This makes these catalysts highly active for the targeted reaction, as shown by record turnover numbers. The catalyst is recyclable and truly heterogeneous as it can be reused for several cycles and it does not leach.

1. Synthesis of ethyl lactate with
mesoporous SnSi mixed oxide catalysts
prepared by the aerosol-assisted sol-gel process
Damien P. Debecker, Alvise Vivian, Nicolas Godard, Luca Fusaro, Lorenzo Cannavicci, Carmela Aprile
Europacat 2017, Florence, August 31st, 2017
1

2. Glycerol, DHA, lactates
2

3. Glycerol, DHA, lactates
We need to mitigate our dependence on fossil resources
The rise of the bio-based economy
As a by-prodycts of the biodiesel industry, glycerol is flooding
the market and needs to be upgraded.
3

4. Glycerol, DHA, lactates
Len and Luque, Sus. Chem. Proc. 2014, 2, 1
4

5. Glycerol, DHA, lactates
Glycerol Dihydroxyacetone Alkyl lactates
 Green solvents
 Platform chemical (pharma,
cosmetics, etc.)
 Polylactates (biodegradable
plastics)
ROH
5

6. Catalysts for ethyl lactate
synthesis
6

7. Catalysts for ethyl lactate synthesis
Heterogeneous catalysts are
more desirable
Homogeneous catalysts
(tin halides, etc.)
7

8. Catalysts for ethyl lactate synthesis
Combination of Lewis/Brønsted acid sites
M = Sn, Ga, Zr, Hf …
High dispersion of the active element
Small particles with mesoporous texture
De Clippel, et al., J. Am. Chem. Soc. 2012, 134, 10089–10101
Li, Stroobants, Lin, Jacobs, Sels, Pescarmona, Green Chem. 2011, 13, 1175
Li, Collard, Bertrand, Sels, Pescarmona, Aprile, J. Catal. 2014, 314, 56
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9. Catalysts for ethyl lactate synthesis
“Extra-small” porous
Sn-silicate nanoparticles
XS-Sn-MCM41
Li, Collard, Bertrand, Sels, Pescarmona, Aprile, J. Catal. 2014, 314, 56
800-1100 m².g-1
Dp ~ 2.3 nm
Vp ~ 1 cm³.g-1
9

10. The aerosol-assisted sol-gel
process
10

11. The aerosol-assisted sol-gel process
Molecular
precursors Sol Gel Aged gel xerogel Powder
+ template
Debecker & Mutin Chem. Soc. Rev., 2012, 41, 3624
Control on the
kinetics?
Homogeneity,
dispersion,
texture?
One-step approach? Fast and continuous?
11
Classical sol-gel approach

12. The aerosol-assisted sol-gel process
Atomizer
Filter
Oven
Atomization
 Aerosol droplet with
controlled composition
Drying
 EISA + polycondensation
Sol
Recovery
 Spherical particles
Air Calcination
 Porous particles
Debecker et al., Angew. Chem. Int. Ed., 2012, 15, 2129
Lu, Fan, Stump, Ward, Rieker, Brinker, Nature, 1999, 398 223
12

13. Mesoporous SnSi mixed
oxides
Godard, Vivian, Fusaro, Cannavicci, Aprile, Debecker, ChemCatChem, 2017, 9, 2211
13

14. Mesoporous SnSi mixed oxides
SiSn mixed oxides catalysts by the aerosol-assisted sol-gel method
- TEOS
- HCl solution 0,02 M
- Pluronic F127 or P123
- Ethanol
- HCl solution 0,02 M
Metal precursor
SnCl4.5H2O
(Si/Sn = 37 or 74)
Overnight stirring
Sol
+
AEROSOL processing
Ageing (80°C)
Calcination (550°C)
Godard, Vivian, Fusaro, Cannavicci, Aprile, Debecker, ChemCatChem, 2017, 9, 2211
14

15. Mesoporous SnSi mixed oxides
TEM
- Small spherical particles
- Calibrated mesoporosity
- Long-range order (small-angle XRD)
- SEM-EDX confirms Si/Sn = 37 or 74
140-380 nm
(90%)
Small angle
XRD
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16. Mesoporous SnSi mixed oxides
0
50
100
150
200
250
300
350
0 0.2 0.4 0.6 0.8 1
Adsorbedvolume(cm³g-1)
P/P0
0
0.005
0.01
0.015
0.02
1 10 100
dV/dD(cm³g-1nm-1)
Pore diameter (nm)
N2-physisorption
- Mesopores
- Narrow pore size distribution
- Large specific surface area and pore volume
SSA = 370 m².g-1
Dp = 6.0 nm
Vp = 0.5 cm³.g-1
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17. Mesoporous SnSi mixed oxides
DRS
- SnIV inserted in the silica matrix
- Small contributions at 240 and 280 nm
200 250 300 350 400 450 500
Absorbance(a.u.)
Wavelength (nm)
SnIV (206 nm)
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18. Mesoporous SnSi mixed oxides
NMR
- Sn inserted as single site within the silica framework
- No SnO2 inclusions
119Sn static NMR
400 0 -400 -800 -1200 -1600
ppm
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19. Mesoporous SnSi mixed oxides
NH3-TPD
- Superior acidic properties
19

20. Synthesis of ethyl lactate
20

21. EtOH (5 mL)
DHA (0.4 M)
50 mg of catalyst
90 °C , stirring 6h
Synthesis of ethyl lactate
Recycling testHot-filtrationKinetic study
- High activity
- Heterogeneous and recyclable
Y(%)
Selectivity and mechanism  Pescarmona et al., Green Chem. 2010, 12, 1083
21

22. Synthesis of ethyl lactate
Li (2014)
Li, Collard, Bertrand, Sels, Pescarmona, Aprile, J. Catal. 2014, 314, 56
Collard (2014)
Collard (2015)
Li (2011)
Collard, Li, Lueangchaichaweng, Bertrand, Aprile, Pescarmona, Catal. Today, 2014, 235, 184
Collard, Louette, Fiorilli, Aprile, Phys. Chem. Chem. Phys., 2015, 17, 26756
Li, Stroobants, Lin, Jacobs, Sels, Pescarmona, Green Chem., 2011, 13 1175
This work
EtOH (15 mL)
DHA (0.4 M)
50 mg of catalyst
90 °C , stirring 6h
22

23. Methylated mesoporous SnSi
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24. - TEOS
- HCl solution 0,02 M
- Pluronic F127 or P123
- Ethanol
- HCl solution 0,02 M
Metal precursor
SnCl4.5H2O
(Si/Sn = 37 or 74)
Overnight stirring
Sol
+
AEROSOL processing
Ageing (80°C)
Calcination
Methylated mesoporous SnSi
24

25. - TEOS + MTES
- HCl solution 0,02 M
- Pluronic F127 or P123
- Ethanol
- HCl solution 0,02 M
Metal precursor
SnCl4.5H2O
(Si/Sn = 37 or 74)
Overnight stirring
Sol
+
AEROSOL processing
Ageing (80°C)
Calcination
[Unpublished]
More hydrophobic SnSi-CH3
mesoporous catalyst
Methylated mesoporous SnSi
25

26. Methylated mesoporous SnSi
SSA = 550 m².g-1
Dp = 6.5 nm
Vp = 0.45 cm³.g-1
Temperature
( C)
Time (h)
Methyl. degree
after calc.
Raw material / 29%a
400 6 19%a
350 6 22%a
300 6 23%a
250 8 25%a
Sn-30% fresh
a) From T/T+Q ratio obtained via 29Si MAS NMR
(direct excitation experiments)
T
26

27. Methylated mesoporous SnSi
[Unpublished]
EtOH (5 mL)
DHA (0.4 M)
50 mg of catalyst
90 °C , stirring 6h
27

28. Conclusion
SnSi mixed oxides are excellent heterogeneous catalysts for
the synthesis of ethyl lactate
The aerosol-assisted sol-gel process allows for a rapid,
continuous and scalable catalyst preparation
Aerosol-made SnSi catalysts exhibit all the required
properties… and reach outstanding catalytic activity
Catalyst can be easily made more hydrophobic and this
translates into even higher performance
Godard, Vivian, Fusaro, Cannavicci, Aprile, Debecker, ChemCatChem, 2017, 9, 2211
28

29. Thank you for your attention
Damien.Debecker@uclouvain.be
29