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

Abstract

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 H 5 PMo 10 V 2 O 40 (HPMoV) on the organic-decorated silica SiO 2 (R n /R 5 ’NH 2, m: 1) (R n represents C n H 2 n +1, n = 6, 8, and 10; R 5 ’NH 2 is C 5 H 10 (NH)NH 2; m: 1 means the ratio between R n and R 5 ’NH 2 ) nanoparticles. The versatile catalyst HPMoV(25)/SiO 2 (R 8 /R 5 ’NH 2, 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)/SiO 2 (R 8 /R 5 ’NH 2, 1:1), which stabilized the water-in-oil (w/o) emulsion and facilitated cellulose conversion at the H 2 O/MIBK interface (MIBK is methyl isobutyl ketone); R n and R 5 ’NH 2 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 SiO 2 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.

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