Structured microreactor with gold and palladium on titania: Active, regenerable and durable catalyst coatings for the gas-phase partial oxidation of 1-butanol

Structured microreactors coated with catalytically active porous layers have emerged as a promising replacement for conventional reactors because they are inherently safe to operate in nearly isothermal conditions within the kinetic regime. Bio-based 1-butanol is commonly produced by acetone-butanol-ethanol (ABE) fermentation and is considered an important platform chemical that will benefit in the share of value-added chemicals through the development of new catalytic processes. In this study, monometallic gold (Au) and palladium (Pd), as well as bimetallic Au-Pd nanoparticles, supported on titania (TiO₂) were prepared by a sol-immobilization method, characterized, coated on structured microreactor plates and tested for their catalytic activity in the gas-phase partial oxidation of 1-butanol to n-butyraldehyde. A customized structured catalyst testing microreactor was used. The average noble metal particle size for the catalyst coatings was determined to be approximately 3.6 nm for Au and Au-Pd catalysts, and the noble metal nanoparticles were evenly distributed. The catalyst coating was 17 ± 7 μm in thickness. The studied coated catalysts (TiO₂, Au/TiO₂, Pd/TiO₂, and Au-Pd/TiO₂) were all active for the partial oxidation of 1-butanol. The Au/TiO₂ (0.6 wt%) catalyst showed the highest yield (20%) of n-butyraldehyde at 300 °C. The introduction of Pd onto Au/TiO₂ or TiO₂ shifted the product distribution at 250 °C towards retro-hydroformylation and oxidation products (propene, carbon monoxide and carbon dioxide). All of the coated catalysts that were tested were mechanically stable. The nano Au/TiO₂ could be regenerated in situ and showed reproducible activities and yields in over 50 test runs. Structured microreactors coated with gold nanoparticles supported on titania show promise as a reusable and mechanically stable device for the process development of n-butyraldehyde production in ABE fermentation plants.