a
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H7
H6
Reações de superfície de compostos derivados de biomassa
–
C3 C2
H5
Surface reactions of biomass-derived oxygenates
H2
C1
O4
Guo Shiou Foo,1 John R. Copeland,1 Jungseob So,1 Carsten Sievers1
O3
O2
H3
H4
Georgia Institute of Technology, School of Chemical & Biomolecular Engineering, 311 Ferst Dr. NW, Atlanta, GA 30332-0100, H8
E.U.A., carsten.sievers@chbe.gatech.edu
1
Abstract
Al2
Al1
O1
ABSTRACT – Economically viable production of chemicals from biomass will require
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catalytic processes with high selectivity. Heterogeneous catalysts will play a key role in b
H5
such processes due to their facile separation. To reach the desired selectivity, it will be
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C2
H2
necessary to understand and control the interactions of biomass-derived compounds with the
C1
C3 O2
active sites of catalysts. Since most biomass-derived compounds are oxygenates with
multiple functional groups, their surface chemistry has an added layer of complexity. In this H4
H3
O4
O3
presentation, FTIR and NMR spectroscopy, adsorption isotherms, and DFT calculations will
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be used to identify surface species formed from polyols and sugars and to deduce reaction
pathways for their conversion.
For example, glycerol can favourably compete with water for binding sites on metal oxides
like -Al2O3, TiO2, and N2O5 [1-3]. The most stable surface species is formed when one of
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Al2
the primary alcohol groups forms a bridging alkoxy bond on a Lewis acid site (LAS), while
the other primary alcohol group interacts non-dissociatively with the same site (Figure 1). In Figure 1: Most stable surface
addition, the secondary hydroxyl group forms a hydrogen bond with the surface [1]. species formed from glycerol on Sufficient spatial separation between the alcohol groups is necessary for these multidentate Al2O3 based on DFT calculations
surface species to form without excessive strain.
and IR spectroscopy.
Through the interaction with a LAS, the primary C-O bonds of this surface species are
polarized making them more susceptible to cleavage. However, dehydration only occurs on metal oxide like Nb2O5 that also contain
Brønsted acid sites (LAS) [3]. When LAS and BAS are involved, the primary alcohol group is removed preferentially, and acetol is
formed. Without the involvement of a LAS, the secondary alcohol group is removed due to the higher stability of the secondary
carbenium ion that is formed as the transition state. The intermediate 3-hydroxypropionaldehyde readily undergoes a second
dehydration step to acrolein.
Keywords: dehydration, acid-base reactions, alkoxy bond, polarization, adsorption.
References
[1] J.R. Copeland, X.-R. Shi, D.S. Sholl, C. Sievers,
Langmuir 29 (2013) 581.
[2] J.R. Copeland, I.A. Santillan, S.M. Schimming, J.L.
Ewbank, C. Sievers, J. Phys. Chem. C 117 (2013)
21413.
[3] G.S. Foo, D. Wei, D.S. Sholl, C. Sievers, ACS Catalysis
4 (2014) 3180.