Metal- and Acid-Free Photocatalytic Approach Using Quinone-Based Hyper-Crosslinked Porous Catalysts for the Valorization of Glycerol into Solketal

Two metal- and acid-free anthracene (AN) and anthraquinone (AQ)-based photocatalysts (HCP-AQ-2Ph and HCP-AN-2Ph) are synthesized and used for the effective acetalization of glycerol to obtain selectively solketal, an added-value compound with several industrial applications and high demand as an oxygenated additive of fuels. HCP-AQ-2Ph and HCP-AN-2Ph are prepared by a Friedel-Crafts coupling reaction between the AQ or AN and biphenyl (2Ph) as comonomer which leads to the formation of high thermally stable hyper-crosslinked porous networks with specific surface areas of 295 and 596 m2 g-1, respectively. Initial tests suggest that HCP-AN-2Ph is a less efficient catalyst compared to HCP-AQ-2Ph. However, subsequent runs indicate that during the first trial, the AN units are oxidized, resulting in a catalyst (HCP-AN(OX)-2Ph) just as effective as the AQ-based one. The quantitative and selective conversion of glycerol into solketal is achieved in just 3 h using a 4 wt% catalyst and maintaining this catalytic performance for at least 5 cycles. In addition, the process can be scaled allowing the obtaining of solketal with high purity on a gram scale. These results place these catalysts among the most effective for the selective production of solketal from glycerol compared to previously reported metal- or acid-catalyzed reaction. Metal- and acid-free, HCP-AQ-2Ph and HCP-AN(OX)-2Ph, catalysts quantitative and selectively convert glycerol under blue light irradiation into solketal in only 3 h; these materials become an example of photocatalysts showing a much superior catalytic performance and larger specific surface areas than other catalysts used so far in the same process.image (c) 2024 WILEY-VCH GmbH