(95o) Selective Hydrogenation of Citral over Supported Pt Catalysts on Various Substrates

Highly dispersed platinum (Pt) nanoparticles (NPs) were deposited on various substrates by atomic layer deposition (ALD) for the reaction of citral hydrogenation. The substrates included multi-walled carbon nanotubes (MWCNTs), silica gel (SiO₂), commercial γ-Al₂O₃, and ALD-prepared porous Al₂O₃ particles (ALD-Al₂O₃). Based on TEM and CO-chemisorption analysis, the Pt NPs on all substrates were around 1.3 nm, and Pt/MWCNTs, Pt/ALD-Al₂O₃ and Pt/γ-Al₂O₃ showed similar Pt dispersion (75%-85%). But the Pt dispersion on SiO₂ was low (63%). In the reaction of citral hydrogenation, Pt/SiO₂ showed the highest activity due to the strong acidity of SiO₂ and the conversion of citral reached 82% after 12 hr with a selectivity of 58% of unsaturated alcohols (UA), including geraniol and nerol. Among all catalysts, Pt/MWCNTs showed the highest selectivity of UA (65%) due to its unique structure and electronic effect. In the cycling test, Pt/MWCNTs and Pt/ALD-Al₂O₃ catalysts were more stable than Pt/SiO₂ which could be attributed to the different interactions between the catalysts and the solvent.