Hydrolysis of Cellulose by Polyoxometalate Pickering Interfacial Catalysts Bearing a Flexible Surface and Hard Core

The use of cellulose for various value-added chemicals is a promising alternative to fossil resources to reduce their dependence and depletion. The selective conversion of cellulose to 5-hydroxymethylfurfural (5-HMF) is an attractive depolymerization route with great application, which often meets the hindrance of a tough structure, inert activity, and big barriers in mass transfer. To achieve high efficiency and green conversion of cellulose, heterogeneous Pickering interfacial catalysts (PICs) containing polyoxometalates (POMs) had been designed through loading H5PMo10V2O40 (HPMoV) on the organic-decorated silica SiO2(Rn/R5'NH2, m: 1) (Rn represents CnH2n+1, n = 6, 8, and 10; R5'NH2 is C5H10(NH)NH2; m: 1 means the ratio between Rn and R5'NH2) nanoparticles. The versatile catalyst HPMoV(25)/SiO2(R8/R5'NH2, 1:1) could catalyze cellulose conversion into 5-HMF with 96.4% conversion at 150 °C for 5 h with turnover frequency increasing 1.52 times higher than homogeneous HPMoV. The enhancement of catalytic performance could be attributed to several factors: the flexible surface of HPMoV(25)/SiO2(R8/R5'NH2, 1:1), which stabilized the water-in-oil (w/o) emulsion and facilitated cellulose conversion at the H2O/MIBK interface (MIBK is methyl isobutyl ketone); Rn and R5'NH2 of HPMoV can adsorb cellulose to be concentrated, while reactive oxygen species (ROS) generated by redox sites assisted Brønsted (B) acidic sites in accelerating cellulose hydrolysis; and simultaneously, the microball milling effect produced by rough SiO2 nanoparticles, which further enabled rapid cellulose conversion. The excellent performance provided a useful strategy to construct heterogeneous PICs for practical application in chemical transformation and biorefinery, especially overcoming the hindrance in solid–solid mass transfer.