Brønsted Acid-Triggered Fast Synthesis Pathway of Furfural to Ethyl Levulinate by PtZn Supported on ZSM-5 Nanosheets

Abstract

Furfural (FUR) is widely used to synthesize alkyl levulinate (AL), an important biomass-derived compound for industrial use. Traditional synthesis pathways, including hydrogenation, etherification, and hydrolysis, are slow due to high activation energy requirements. This study presents a pathway using ethyl levulinate (EL) as a model AL. The process starts with the acetalization of FUR to produce 2-(diethoxymethyl)furan (DEMF) using a Brønsted acid–based ZSM-5 nanosheet-supported PtZn (PtZn/ZSM-NS) catalyst. DEMF is then hydrogenolyzed to form 2-(ethoxymethyl)furan (EMF), which is hydrolyzed to produce EL at a rate of 29.8 mmol·g^–1h^–1, over 20 times faster than with a Lewis acid–based catalyst. In the initial step, Brønsted acid sites on the PtZn/ZSM-NS activate ethanol to generate an acetate-like intermediate (COO^θ), which facilitates the acetalization of FUR to produce DEMF. This step is crucial for efficiently producing EL using the PtZn/ZSM-NS catalyst. Subsequently, EMF is easily formed through the hydrogenolysis of DEMF instead of through the etherification of furfuryl alcohol. Additionally, highly dispersed PtZn alloys on PtZn/ZSM-NS are essential for optimizing the adsorption strength, thereby accelerating the overall reaction. Using this pathway, the PtZn/ZSM-NS catalyst achieves an EL yield of up to 89.5 wt % at 200 °C in just 1 h.