Abstract
Semi-hydrogenation of alkynes to alkenes is one of the most important industrial reactions. However, it remains technically challenging to obtain high alkene selectivity especially at a high alkyne conversion because of kinetically favorable over hydrogenation. In this contribution, we show that supported ultrasmall Pt nanoparticles (2.5 nm) on mesoporous TiO2 (Pt@mTiO2) remarkably improve catalytic performance toward semi-hydrogenation of phenylacetylene. Pt@mTiO2 is prepared by co-assembly of Pt and Ti precursors with silica colloidal templates via an evaporation-induced self-assembly process, followed by further calcination for thermal decomposition of Pt precursors and crystallization of mTiO2 simultaneously. As-resultant Pt@mTiO2 discloses a high hydrogenation activity of phenylacetylene, which is 2.5 times higher than that of commercial Pt/C. More interestingly, styrene selectivity over Pt@mTiO2 remains 100% in a wide phenylacetylene conversion window (20–75%). The styrene selectivity is >80% even at 100% phenylacetylene conversion while that of the commercial Pt/C is 0%. The remarkable styrene selectivity of the Pt@mTiO2 is derived from the weakened styrene adsorption strength on the atop Pt sites as observed by diffuse reflectance infrared Fourier transform spectroscopy with CO as a probe molecule (CO-DRIFTS). Our strategy provides a new avenue for promoting alkyne to alkene transformation in the kinetically unfavorable region through novel catalyst preparation.
Highlights
Mesoscopic and microscopic structures of the Pt@mTiO2 were thoroughly characterized with Scanning electron microscopy (SEM) and high-angle annular dark field scanning transmission electron microscopy (TEM) (HAADF-STEM) (Figure 1)
We have carried out TEM observations of the commercial Pt/C catalyst
We report the preparation of mesoporous TiO2 confined ultrasmall Pt nanoparticles with an average particle size of 2.5 ± 0.5 nm using an evaporation-induced self-assembly (EISA) method
Summary
Selective hydrogenation of alkynes to alkenes is one of the most industrially important reactions (Yang et al, 1998, 2019; Mastalir et al, 2000; Huang et al, 2007; Studt et al, 2008; Yuan et al, 2009; Liu H. et al, 2012; Sheng et al, 2012; Tüysüz et al, 2013; Zhao et al, 2015, 2019; Xie et al, 2016; Xiao et al, 2017; Zhan et al, 2017). Pt-based catalysts still suffer from low selectivity to alkenes especially in higher alkyne conversion windows, despite its high activity for hydrogenation (Li et al, 2017; Tang et al, 2017; Wang et al, 2018). To improve the alkene selectivity in selective hydrogenation of alkyne, both nanoparticles (NPs) downsizing and alloying strategies have been carried out to enrich the atop sites of Pt-group metal catalysts (Hu et al, 2018b). We present a highly selective catalyst that contains ultrasmall Pt NPs (2.5 nm), strong Pt-support (Pt-TiO2) interaction, and high surface area (mesoporous framework) for selective hydrogenation of phenylacetylene to styrene. The resultant product was kept in a 5 mL test tube and the proton nuclear magnetic resonance (1H NMR) analysis was carried out using CDCl3 as solvent to calculate the conversion of phenylacetylene and the selectivity to styrene. The DRIFT cell was filled with 20 mg of catalysts and was treated at 100◦C with nitrogen before CO was introduced
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