One-pot hydrogen production and cascade reaction of furfural to bioproducts over bimetallic Pd-Ni TUD-1 type mesoporous catalysts

Abstract

Bimetallic Pd-Ni TUD-1 type mesoporous catalysts are effective for the cascade reaction of the renewable platform chemical furfural (FUR) to the useful bioproducts 2-alkoxyfuran, 2-methylfuran (2MF), 4-oxopentanal and its acetals, which find diverse applications, some already in the market. With a single catalyst, the in situ hydrogen supply from formic acid (FAc), as well as several acid-reduction steps of the overall catalytic process were triggered, leading to the desired bioproducts (bioPs), all in one-pot under moderate reaction conditions. These multipurpose materials were prepared using different procedures and conditions, which influenced the material properties and the catalytic performances. Detailed characterisation (microstructural/molecular level) and catalytic studies led to new mechanistic insights into the FUR reaction (with identification of intermediates), allowed to assess the roles of the different types of metal species in the complex reaction mechanism, understand the influence of material properties on the catalytic process, and catalyst stability and regeneration. The best-performing catalyst was prepared stepwise via impregnation of palladium on a hydrothermally synthesised nickel silicate with a molar ratio Si/Ni of 20, ending with filtration-washing-calcination procedures. This catalyst led to 83% 2MF yield, at 98% FUR conversion (90% total bioPs yield), using 1-butanol as solvent, at 170 °C. The reported catalytic protocol benefits from the fact that external usage of H2 for catalyst activation and/or the catalytic reaction is not required, no high-pressure gases are used, and FAc is used as source of hydrogen supplied in situ for the catalytic reaction under moderate conditions. Moreover, FAc presents low toxicity, it is easy to handle/store, and is a typical coproduct of carbohydrate biomass conversion processes, and thus its repurposing is highly desirable.