Structure Sensitivity of the Hydrogenation of Crotonaldehyde over Pt/SiO2and Pt/TiO2

Abstract

Hydrogenation of crotonaldehyde has been studied over SiO 2 -and TiO 2 -supported Pt catalysts. Over Pt/SiO 2 , the selectivity to the primary products butyraldehyde and crotylalcohol depends critically on the Pt particle size; i.e., the selectivity to the unsaturated alcohol increases with increasing particle size. For large metal particles, the high fraction of Pt(111) surfaces is concluded to favor the adsorption of crotonaldehyde via the carbonyl bond. On small Pt particles, the high abundance of metal atoms in low coordination allows unconstrained adsorption of both double bonds. In this case, the hydrogenation of the C= =C bond is kinetically favored. Activity and selectivity of Pt/TiO 2 catalysts after low-temperature reduction are similar to those of Pt/SiO 2 . After high-temperature reduction the selectivity to crotylalcohol is generally enhanced. The selectivity of Pt/TiO 2 catalysts is then determined by the metal particle size and the extent of decoration of Pt with TiO x particles. The presence of coordinatively unsaturated Ti cations in these oxide particles enhances the sorption strength of the C= =O bond resulting in an enhanced selectivity to crotylalcohol. The effects of metal particle size and promotion by TiO x are additive. TiO x promotion of catalysts with small particles and the presence of unpromoted large particles allow reaching of selectivities to crotylalcohol of approximately 45%. Promotion of large Pt particles with TiO x yields 64% selectivity to crotylalcohol.

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Estudo do efeito do cloreto em catalisadores de paládio usando a análise no infravermelho e de fotoelétrons excitados por raios x

“…Nessa situação o oxigênio da carbonila torna-se mais suscetível para reagir em processos catalíticos dissociativos. Já foi relatado que os metais quando dispersos em suportes redutíveis, tratados sob HTR, produzem um aumento da seletividade em reações de hidrogenação de C=O com relação a C=C [27][28][29] .…”

Recent Advances in the Liquid‐Phase Synthesis of Metal Nanostructures with Controlled Shape and Size for Catalysis

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