Efficient magnetic recoverable acid-functionalized-carbon catalysts for starch valorization to multiple bio-chemicals

Abstract

A series of solid acid catalysts were prepared by functionalization of graphene-oxide (GO) and MWCNT-oxide (MWCNTO) with triflic and sulfonic acids affording a triflate-functionalized graphene oxide (GO@SO3CF3), and a sulfonated MWCNT (μ-CNT-SO3H). To facilitate the separation of the catalysts from the reaction mixture MWCNTs were modified by incorporating magnetic nanoparticles. For comparison, the composites of MWCNTO with magnetic nanoparticles were further modified by deposition of niobia in two loadings, e.g. 30 and 60wt.%. Depending of the functionality the catalysts exposed preponderantly either Brønsted (μ-CNT-SO3H) or Lewis (GO@SO3CF3) acid sites. Deposition of niobia also led to catalysts with acid properties, but as a function of the precursor nature and loading, they exposed niobia phases with either Brønsted (e.g., Nb-O units) or Lewis acid sites (e.g., −Nb=O units) in excess. Catalytic performances, in terms of the yields in one of the platform molecule (ie, levulinic acid versus lactic acid) were directly correlated with the nature of these acid sites. Interestingly enough, the catalysts showing high efficiency for lactic acid led also to high efficiency for the synthesis of succinic acid under pressure of molecular oxygen.