Abstract
The studies of pyrolysis of caffeic acid (CA) and its surface complexes is important for the development of technologies of heterogeneous catalytic pyrolysis of plant- and wood- based renewable biomass components. In this work, the structure and thermal transformations of the surface complexes of CA on the surface of nanoceria were investigated using Fourier transform–infrared (FT–IR) spectroscopy, thermogravimetric analysis (TGA) and temperature-programmed desorption mass spectrometry (TPD MS). It was found that CA on the surface of cerium dioxide forms several types of complexes: bidentate carboxylates, monodentate carboxylates and complexes formed as a result of interaction with phenolic hydroxyl groups. This is due to the ability of nanosized cerium dioxide to generate basic hydroxyl groups that can deprotonate phenolic groups to form phenolates on the surface. The main pyrolysis products were identified. The possible ways of forming 3,4-dihydroxyphenylethylene, acetylene carboxylic acid, pyrocatechol and phenol from surface complexes of CA were suggested. It was established that on the nanoceria surface effectively occur the decarboxylation, decarbonylation, and dehydration reactions of the CA, which are the desirable processes in biomass conversion technologies.
Highlights
In the last few years, CeO2-based materials have attracted much attention due to their wide use in various catalytic systems [1,2,3,4,5,6]
At the same time the redox and acid-base properties of ceria, either alone or in the presence of transition metals, are important parameters that allow activation of complex organic molecules and selective orientation of their transformation [5]. These characteristics of cerium dioxide indicate the promise of its use as a catalyst for the development of green technologies of heterogeneous pyrolysis of biomass, which today is considered the most attractive renewable raw material for the production of bio-based chemicals
It has been shown that one of the methods for increasing the stability of suspensions of nanosized cerium dioxide and correction of its biological action may be to cover the surface of nanoparticles of CeO2 by biocompatible/organic polymers [8,9,10] and carboxylic acids [11,12]
Summary
In the last few years, CeO2-based materials have attracted much attention due to their wide use in various catalytic systems [1,2,3,4,5,6]. At the same time the redox and acid-base properties of ceria, either alone or in the presence of transition metals, are important parameters that allow activation of complex organic molecules and selective orientation of their transformation [5]. These characteristics of cerium dioxide indicate the promise of its use as a catalyst for the development of green technologies of heterogeneous pyrolysis of biomass, which today is considered the most attractive renewable raw material for the production of bio-based chemicals. It has been shown that one of the methods for increasing the stability of suspensions of nanosized cerium dioxide and correction of its biological action may be to cover the surface of nanoparticles of CeO2 by biocompatible/organic polymers [8,9,10] and carboxylic acids [11,12]
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