Dehydration of n-butanol on phosphate-modified carbon nanotubes: active site and intrinsic catalytic activity

Abstract

Dehydration of n-butanol (nB) to corresponding olefins (butene) is an important reaction route to realize efficient utilization of bulk bio-alcohols. In this work, novel phosphate modified oxidized multi-walled carbon nanotubes (P-oCNT) were prepared via a simple impregnation process, and the proposed solid acid catalyst exhibited superior catalytic activity and stability in nB dehydration reactions with 94% nB conversion and 99% butene selectivity under gentle reaction conditions (260 °C). In situ titration results revealed that the Brønsted and Lewis acid sites are all active sites, and the Lewis acid sites contribute to over 88% of the activity in nB dehydration reactions. The polyphosphate species (POx) were identified as the key Lewis acid active sites, which were covalently linked onto the oCNT surface via C–O–P bonds, and the carbon matrix played a vital role in enhancing and stabilizing the catalytic activity of the POx species. The basic kinetic analysis results indicated that the nB dehydration reaction on P-oCNT catalysts followed the E1 mechanism, while the reaction route would shift to E2 with the reaction temperature increasing. The relatively high catalytic efficiency and sustainable nature of the whole non-metallic system show the potential of the proposed reaction system in modern chemical industries.