Recent Advances in Catalytic Conversion of Bioethanol to 1,3-Butadiene: Reaction Mechanism, Catalyst Design, and Process Scalability.

1,3-Butadiene (BD), a symmetric C4 diene, is a primary precursor for numerous synthetic rubbers and is sourced largely from the naphtha cracking process. Sustainable BD production from renewable biomass is indispensable for preserving the environment through the circular economy. Ethanol-to-BD (ETB) has particularly witnessed a resurgence in recent years, following two different routes: one-step conversion and two-step process via acetaldehyde. The present review article critically examines the current state-of-the-art research progress of the ETB processes, in terms of historical perspective, reaction mechanism, kinetics, thermodynamics, multifunctional heterogeneous catalysts, reaction parameters, and economic-environmental impact analysis. The ETB processes encompass a complex sequence of reactions on different catalytic sites, including dehydrogenation, carbon-carbon coupling, and dehydration. However, the catalyst with the proper balance between acidic, basic, redox, and metal functionalities (e.g., metal/metal oxide-modified MgO-SiO2 and Zn-Zr mixed oxide), which are uniformly distributed and cooperative, remains a critical challenge in these processes. Despite notable advancements in understanding molecular mechanisms, the design of catalysts for high BD selectivity and process scalability remains the key obstacle to commercial success. The comprehensive summary of ETB process developments provides a foundation for researchers and industry practitioners to advance research and optimize the critical parameters for sustainable BD production.