Chapter 8 - Metal-organic frameworks-based catalysts for biomass valorization

Abstract

The objective of this chapter is to review the most promising metal-organic framework (MOF) catalysts in biomass valorization processes in the bulk and fine chemical industries. Either bulk metal-organic frameworks, encapsulated catalytic species in MOFs, or MOF-derived catalysts are revised in terms of activity, selectivity, and stability for biomass valorization applications. The work revised here is focused on the transformation of lignocellulose biomass through purely chemical pathways. In the first part of the chapter, the few studies of cellulose hydrolysis into monosaccharides reported are commented, since this crucial first step in the valorization of hemicellulose is expected to be more important in the shortcoming future. Then, we will briefly review the dehydration of hexoses into relevant O-containing furans (furfuryl alcohol, 5-hydroxymethylfurfural, etc.) using MOF catalysts, which is one of the most studied pathways for the transformation of hemicellulose. Both hexoses (glucose, fructose, etc.) or pentoses (xylose, etc.) have been dehydrated into (hydroxymethy)furfural using different acid MOFs as catalysts under broad reaction conditions, being MIL-101 the more representative of all mesoporous acid MOFs. In the last part of the chapter, we change our attention to other important hexose derived molecules, such as lactate (through trioses intermediates) or furan-dicarboxylate (through oxidation of furan alcohols or aldehydes) using MOF catalysts, which is an important pathway towards bio-polymers. In particular, the hydrogenation/oxidation of furan aldehydes into saturated O-containing chemicals is another widely tested transformation in the presence of several metal hydrogenating sites in (or derived from) MOFs. Other carbon chain growth processes catalyzed by MOFs, such as aldol condensation, etherification, oxidative couplings, etc. of the furanics with aldehydes or alcohols, resulting in potential bio-fuels, are commented to finish this chapter.