Jan Dijkmans, Michiel Dusselier, Kristof Houthoofd, Pieter Magusin

Sn in Partially Dealuminated β zeolites as a
Bifunctional Catalyst for Biomass Conversions
Jan Dijkmans, Michiel Dusselier, Kristof Houthoofd, Pieter Magusin, Maarten
Trekels, André Vantomme, Bert Sels
Center for Surface Science and Catalysis, KU Leuven, Kasteelpark Arenberg 23, 3001 Heverlee, Belgium.
Material characterization
Introduction
Al IVa
Al IVa+Al IVb
0,49
0,35
0,28
0,24
0,22
0,22
0,23
Acid [M]
0
1,44
1,8
2,88
3,6
7,2
14,4
Decreasing Al-content
Heterogeneous Lewis acids are topical in biomass conversion
chemistry. Lewis acid catalysts reveal unusual selective transformations of renewable feedstock such as carbohydrates, with Sn often as the Lewis acid of choice. The water tolerant Snβ is probably
one of the best catalysts developed in this category, but widespread
application of Snβ requires a thorough amelioration of its synthesis procedure. Current synthesis recipes use corrosive hydrogen
fluoride in the synthesis gel and the hydrothermal synthesis time
takes up to 40 days in order to ensure complete crystallization and
substitution with Sn in the framework.
Sn is present
- +IV oxidation state (119Sn Mössbauer, XPS)
- Tetrahedral coordination (119Sn MAS NMR, UV-vis)
- Closed Sn-site (119Sn MAS NMR, ACN-d3 FTIR)
- hydrated form (119Sn MAS NMR, UV-vis)
O3Si
O
H2O
O
SiO3
Sn
O
O3Si
O3Si
S
O
O3Si
O
OH2
Sn
O
SiO3
OH
OX
X=H or SiO3
O3Si
Hydrated
Sample
Dried
Sample
No sign of SnO2-species were observed
x1
6
Rehydrated
Sample
AlIVb
AlIVa
Residual framework Al is present in
two species: AlIVa and AlIVb.
To convert carbohydrates into platform and commodity chemicals, often multifunctional catalytic systems are needed. Here, we
present the synthesis of a bifunctional heterogeneous material,
containing Lewis acidic Sn sites, as well as Brønsted acid Al sites.
The material is used in the multi-step conversion of the sugar derived dihydroxyacetone into ethyl lactate.
O H
Concentration of AlIVb is linearly correlated to the Brønsted acid sites in
the material.
O
O
1,3-dihydroxyacetone
Sn-contant in constant in the materials, except when higher concentrations of SnCl4 are used in the syntesis.
OH
Cl
OH
OH
OH
Al
Cl
Sn
Sn
Cl
Cl
Al
Al
Al
OH
Grafting with SnCl4
in IPA
OH
OH
OH
OH
OH
OH
Al
OH
Partial dealumination
with HNO3
ø
BET
Zeo A
lite
Catalysis: Isomerization of Glucose
Conclusions
HO
OH
Ethylated C6-sugars
BA
+ EtOH
HO
OH
OH
Glucose
OH
LA
HO
O
OH
OH
- H2O
LA
OH
LA
BA/LA
OH
O
Pyruvic aldehyde
+E
Addition of Al to the Sn-zeolite results in an increase in
product synthesis yield
Elevated Sn-content
Drop in selectivity
Drop in ELA yield
Traditional, hydrothermal
Sn-beta
- a commercial beta zeolite was partially dealuminated an grafted
with SnCl4 to obtain a bifunctional material
OEt
Pyruvic aldehyde
diethyl acetal
tO
H
OH
OEt
Ethyl Lactate
Distinct catalytic roles for Al and Sn:
- Al catalyzed dehydration of DHA to PAL
- Sn catalyzed hydride shift of PAL to ELA
Catalytic Activity of Al-beta
Catalytic Activity of Sn-beta
- Presence of Al-sites results in an improved catalytic activity of the material, due to a more efficient DHA dehydration by the Bronsted acid Al sites. Leaving the Sn free to convert the dehydration product into ELA by a hydride shift.
- The best material surpasses the catalytic activity of the traditional hydrothermally syn-
thesized Snbeta.
References:
PAEA
PAEA
ELA
Jan Dijkmans, Dries Gabriëls, Michiel Dusselier, Filip de Clippel, Pieter Vanelderen,
Annelies Malfliet, Yiannis Pontikes and Bert F. Sels., Green Chemistry, 2013, 15, 2777.
Jan Dijkmans, Dries Gabriëls, Michiel Dusselier, Kristof Houthoofd, Pieter Magusin,
Shuigen Huang, Yiannis Pontikes, Maarten Trekels, André Vantomme, Lars Giebeler,
Steffen Oswald, Bert F. Sels, JACS, submitted.
Contact: [email protected], [email protected], [email protected]
Pieter Magusin, Kristof Houthoofd, Prof. Bart Blanpain, Yiannis Pontikes and Shuigen Huang are gratefully thanked for help with NMR, SEM and EPMA measurements.
J.D. thanks Methusalem CASAS for funding and M.D. acknowledges “FWO Vlaanderen” for financial support. Belgian government is acknowledged for financial support
through IAP funding (Belspo).
PDF of this poster
Ethyl Lactate
DHA
PAL
Best material : 2113 gethyl lactate.kgcatalyst .h
Hydrothermal Sn-Beta: 1131 gethyl lactate.kgcatalyst-1.h-1
- Two types of residual framework Al were found, one type
creates Brønsted acid sites
DHA
Rising Al-content
Constant Sn-content
-1
O H
PAL
ELA
-1
O
- Sn in the material is present in +IV oxidation state, in a tetrahedral, seemingly closed coordination. No sign of the inactive SnO2 was observed.
O
Glyceraldehyde
Mannose
O
OEt
Pyruvic aldehyde
ethyl hemiacetal
O
HO
OH
O
H
EtO
O
- EtOH
OH
LA
OH
OH OH
H
tO
+E
Dihydroxyacetone
CH2OH
OEt
BA
OH
Fructose
O
OH
O
O
O
BA
+ EtOH

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