Enteromorpha prolifera valorization to acetol over supported Pd catalysts: Role of the support

Abstract

The valorization of biomass-waste to afford targeted C3 chemicals over heterogeneous catalyst is of great significance but still challenging due to the ambiguous cooperative roles between support and metal in the complicated cascade reactions. Herein, we unveil the critical factors of the support in Pd-based catalyst which strongly affect the catalytic activity for the transformation of Enteromorpha prolifera to acetol. Pd supported on γ-Al2O3 showed the highest metal surface area, the most Lewis acidity sites and appropriate base sites, which outperformed other as-prepared Pd-based catalysts and achieved acetol yield as high as 62.2 C-mol% (productivity = 12.7 molacetolmolPd-1 h−1, comparable to the highest value in literature). The results of experiments in combination with DFT calculation disclosed that the abundant Lewis acid sites together with appropriate base sites benefited the ring-opening and isomerization reactions of rhamnose (the major sugar in Enteromorpha prolifera) and facilitated the next C3-C4 cleavage to lacticaldehyde and 1,3-dihydroxyacetone (DHA), both of which were revealed as reaction intermediates and produced acetol through distinct pathways. Lacticaldehyde could isomerize to acetol by the help of appropriate base sites and Pd species in Pd-O-Al, whereas the formation of 1,2-propanediol side-product was inhibited. Pd0 species was responsible for H2 activation, the combination of which with Lewis acid sites accelerated DHA transformation to acetol, wherein the formation of glyceraldehyde and lactic acid byproducts were restrained. This work may give useful insights into catalyst design for expanding the application of waste biomass.