Topotactic transformation of homogeneous phosphotungastomolybdic acid materials to heterogeneous solid acid catalyst for carbohydrate conversion to alkyl methylfurfural and alkyl levulinate

Abstract

The strong interaction of higher transition metal oxides with inorganic non-metals can be promising for generating highly acidic three-dimensional materials by design. A comprehensive controlled acidity of heteropolyacid-like catalyst and interpretation of the microstructure and mechanism of the formation of a versatile heterogeneous solid acid catalyst, HPW₄Mo₁₀O_x has been heterogenized by biomass-derived cystine as organic linkers to control the acidity of as-synthesized materials, which have greater acidity and complexity in separation from the reaction mixture. The new and unique results obtained in catalysis done in biphasic reaction. Cystine binds to the surface of HPW₄Mo₁₀O_x, and the topotactic transition occurred, change the morphology and lattice parameter. We described here a sustainable transformation of highly acidic (0.84 mmol g⁻¹) heteropoly acid (HPW₄Mo₁₀O_x) to cystine anchored on the active surface of the heteropoly acid and controlled the acidity (0.63 mmol g⁻¹) and heterogenized the materials. As synthesized materials have been showing that for the direct formation of alkyl levulinate and furanics intermediate from carbohydrates. HPW₄Mo₁₀O_x and HPW₄Mo₁₀O_x-Cys, act as acidic catalyst, and catalyse the mono- and disaccharides that are dissolved in primary and secondary alcohols to alkyl levulinate (AL) and alkyl methylfurfural at 170 °C under microwave irradiation with glucose as the substrate, AL yield reaches 62% with 84.95% selectivity. The catalyst can be easily recovered by filtration and minimum five times reused after calcination without any substantial change in the product selectivity. The analytical analysis of as-synthesis materials done by NH₃-TPD, BET, XRD, FESEM, TEM, HRTEM, FTIR, ATR, TGA, DTA to stabilized the morphology and acidity controlled mechanism.