Multiporous Carbon Encapsulated Ni Nanoparticles Promoting Glycerol Valorisation towards Hydrogenation against Rearrangement†

Summary of main observation and conclusion A dual-templating method was used to synthesize a series of hierarchical carbon supports containing different proportions of spherical macropores ( ca. 200 nm in diameter) and mesoporous channels ( ca. 4 nm in diameter). These and some other conventional carbon materials were subsequently impregnated with Ni and tested for the conversion of glycerol. The hierarchical catalysts exhibited a significantly higher conversion (96%) and selectivity (77%) to 1,2-propanediol, and the specificity selectivity coefficient (6.1) towards 1,2-propanediol against lactic acid was three times higher than that observed over a conventional Ni/C micro catalyst (2.1). The enhanced performance of these materials, compared with the Ni nanoparticles supported on conventional carbon supports, was attributed to their high surface areas (> 1110 m 2 ∙g −1 ) and large pore volumes ( ca . 0.4 cm 3 ∙g −1 ) permitting greater accessibility of substrate and/or intermediates to Ni active sites. Given that the concentration of accessible Ni sites in these materials is higher, a competitive benzilic-acid-rearrangement reaction to produce lactic acid was suppressed, leading to an enhanced hydrogenation selectivity to 1,2-propanediol. This study evidences the potential benefits, which can be established from utilizing hierarchical support materials in the valorization of biomass.