Selective hydrogenation of citral over supported Pt catalysts: insight into support effects

Abstract

Highly dispersed platinum (Pt) nanoparticles (NPs) were deposited on various substrates by atomic layer deposition (ALD) in a fluidized bed reactor at 300 °C. The substrates included multi-walled carbon nanotubes (MWCNTs), silica gel (SiO₂), commercial γ-Al₂O₃, and ALD-prepared porous Al₂O₃ particles (ALD-Al₂O₃). The results of TEM analysis showed that ~1.3 nm Pt NPs were highly dispersed on all different supports. All catalysts were used for the reaction of selective hydrogenation of citral to unsaturated alcohols (UA), geraniol, and nerol. Both the structure and acidity of supports affected the activity and selectivity of Pt catalysts. Pt/SiO₂ showed the highest activity due to the strong acidity of SiO₂ and the conversion of citral reached 82% after 12 h with a selectivity of 58% of UA. Pt/MWCNTs showed the highest selectivity of UA, which reached 65% with a conversion of 38% due to its unique structure and electronic effect. The cycling experiments indicated that Pt/MWCNTs and Pt/ALD-Al₂O₃ catalysts were more stable than Pt/SiO₂, as a result of the different interactions between the Pt NPs and the supports.

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