Vapor phase coupling of n-butanol over the mixed catalyst system PdZn/SiO2+TiO2

Authors: Wegener, Evan

Submitted to: Reaction Chemistry & Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2024
Publication Date: 1/22/2025
Citation: Wegener, E.C. 2025. Vapor phase coupling of n-butanol over the mixed catalyst system PdZn/SiO2+TiO2. Reaction Chemistry & Engineering. https://doi.org/10.1039/D4RE00474D.
DOI: https://doi.org/10.1039/D4RE00474D

Interpretive Summary: Butanol is an alternative fuel that can be produced by fermentation of agricultural feedstocks, such as corn or processing waste. It is possible to convert this alcohol into two types of chemicals, called oxygenates and hydrocarbons, that are widely used in the manufacturing of plastics, personal care products, and aviation fuels. However, current conversion methods are inefficient and result in the production of unwanted byproducts. In this study, ARS researchers at Peoria, Illinois, developed an improved method for chemically converting butanol into these desirable oxygenates and hydrocarbons using a single-step process that efficiently controls the reaction with minimal production of byproducts. The biobased oxygenates and hydrocarbons generated in this process are similar to those currently obtained from petroleum sources so there are already processes available for purification and distribution of these compounds. This research provides a promising route to generate new revenue streams for biorefineries and expand the marketability of agricultural commodities.

Technical Abstract: Coupling fermentation derived oxygenates via Guerbet-type reactions offers a potential route for producing fuels and chemicals from agricultural feedstocks. In this work the vapor phase reactions of n-butanol over a bimetallic PdZn/SiO2 catalyst and physical mixtures of PdZn/SiO2 and TiO2 were studied. The bimetallic catalyst was highly selective for n-butanol dehydrogenation without the subsequent decarbonylation of butanal which is characteristic of monometallic Pd nanoparticles. When combined with TiO2, a known aldol condensation catalyst, the bifunctional system performs Guerbet-type coupling reactions and produces mixtures of C8 oxygenates and higher-order products including C7, C8, and C12 hydrocarbons. Results show that within the reaction network PdZn/SiO2 performs dehydrogenation/hydrogenation reactions and decarbonylates C8 aldehydes to form C7 hydrocarbons. TiO2 catalyzes aldol condensation and alcohol dehydration reactions responsible for producing C8 and C12 hydrocarbons. This work demonstrates the ability of bimetallic Pd-based catalysts that are selective for alcohol dehydrogenation to participate in Guerbet-type coupling reactions and shows that their combination with an appropriate aldol condensation/dehydration catalyst is an effective strategy to produce higher molecular weight oxygenates and hydrocarbons from renewable sources.