Acid Properties of GO and Reduced GO as Determined by Microcalorimetry, FTIR, and Kinetics of Cellulose Hydrolysis-Hydrogenolysis

Graphene oxide addresses increasing interests as a solid acid catalyst working in water for carbohydrate conversion. If there is a general agreement to correlate its unique catalytic performances to its ability to adsorb sugars, the origin of its acidity remains controversial. In this article, we st...

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Bibliographic Details
Published in:Catalysts 2020-12, Vol.10 (12), p.1393
Main Authors: Nguyen, Van Chuc, Kheireddine, Sarah, Dandach, Amar, Eternot, Marion, Vu, Thi Thu Ha, Essayem, Nadine
Format: Article
Language:English
Subjects:
Acidic oxides
acidity of GO
Activated carbon
Adsorption
Alcohols
Ammonia
Biomass
Bonding strength
Carbohydrates
Catalysis
Catalysts
Cellulose
cellulose hydrogenolysis
cellulose hydrolysis
Chemical reactions
Chemical Sciences
Environment and Society
Environmental Sciences
Functional groups
Glucose
Graphene
graphene oxide
Graphite
Heat measurement
Hydrogen bonds
Hydrogenolysis
Hydrolysis
microcalorimetry
Polyols
reduced graphene oxide
Sugar
Zeolites
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Summary:Graphene oxide addresses increasing interests as a solid acid catalyst working in water for carbohydrate conversion. If there is a general agreement to correlate its unique catalytic performances to its ability to adsorb sugars, the origin of its acidity remains controversial. In this article, we study the acid strength of graphene oxide (GO) prepared by modified Hummers method and that of reduced GO by calorimetry of NH3 adsorption and by FTIR of pyridine adsorption. Very strong acid sites are detected on GO by calorimetry, while reduced graphene oxide (reGO) is not very acidic. The FTIR of pyridine adsorption shows the prevailing presence of Br∅nsted acid sites and a unique feature, the presence of pyridine coordinated by hydrogen bonds. This exceptionally strong Br∅nsted acidity is tentatively explained by the presence of graphene domains decorated by hydroxyl, carboxylic, or sulfonated groups within the GO sheet, resulting in a high mobility of the negative charges which makes the proton free and explains its strong acidity. Accordingly, only GO is active and selective for native cellulose hydrolysis, leading to 27% yield in glucose. Finally, we show that sugar alcohols cannot be formed directly from cellulose using GO combined with Pt/re-GO under hydrogen, explained by the reduction of oxygenated functions of GO. The instability of the functional groups of GO in a reducing atmosphere is the weak point of this peculiar solid acid.
ISSN:2073-4344
2073-4344
DOI:10.3390/catal10121393