(617al) Synthesis of a Bi-Functional Catalyst and Application in One-Pot Conversion of Fructose into Oxygenated C9 and C15 Hydrocarbons

Long-chain saturated hydrocarbons (C₉ and C₁₅) have high energy density, excellent cold flow properties and similar boiling-point range as fuels for diesel engines and jets. These alkanes can be one of the alternatives to the conventional and limited fossil fuels resources. These fuel-grade hydrocarbons can be produced from renewable biomass feedstocks via step-wise hydrolysis, dehydration, aldol condensation and hydrogenation reactions. Various homo- and heterogeneous catalysts have been developed for these reactions separately but are limited with issues of downstream waste generation and poor recycling performance. To address these issues, an attractive approach is to directly produce the liquid alkanes from the biomass feedstocks (C₅ and C₆carbohydrates) through a combination of the above-mentioned reactions. Thus, a lucrative strategy for facile one-pot conversion of carbohydrates catalyzed by a bi-functional catalyst was developed by eliminating the purification and isolation of furanic intermediate.

A bi-functional acid-base catalyst with silica-coated magnetic core was prepared through a series of functionalization steps. Amorphous silica layer was initially coated on crystalline iron oxide magnetic nanoparticles (Fe₃O₄ NPs) via solvothermal method. Two catalytic sites were then introduced on SiO₂@Fe₃O₄ NPs via sequential silanization of two types of tri-ethoxy silanes. For the acidic active sites, the SiO₂@Fe₃O₄ NPs was silanized with a thiol (-SH) terminated silane wherein its subsequent oxidation generated the sulfonic (SO₃H) acid catalytic sites (SO₃H-SiO₂@Fe₃O₄). An epoxide terminated silane was then immobilized on SO₃H-SiO₂@Fe₃O₄ on which triazabicyclodecene (TBD) was attached via epoxide ring cleavage to generate the base catalytic sites, completing the bi-functional catalyst TBD-SO₃H-SiO₂@Fe₃O₄.

The prepared bi-functional catalyst and its precursors were characterized by XRD, HRTEM, EDAX, TGA, FT-IR and VSM analyses. Meanwhile, the catalytic performance of TBD-SO₃H-SiO₂@Fe₃O₄ was rigorously tested using fructose as substrate and its reusability for long-term use was also investigated. Results reveal that the developed catalyst can facilitate a cascade reaction involving dehydration of fructose and aldol condensation of furanic intermediate, 5-hydroxymethylfurfural (5-HMF) in one-pot. In particular, the prepared heterogeneous catalyst provided a synergistic catalytic activity for two-step chemical conversions of fructose into oxygenated precursors of C₉ and C₁₅alkanes. In this manner, tedious separation and purification steps of intermediate 5-HMF was avoided.

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Education (No. 2009-0093816) and by the Ministry of Science, ICT & Future Planning (No. 2015R1C1A2A01054605).