Abstract
Developing effective heterogeneous metal catalysts with high selectivity and satisfactory activity for chemoselective hydrogenation of alkyne to alkene is of great importance in the chemical industry. Herein, we report our efforts to fabricate TiO2-supported Pd catalysts by a photodeposition method at room temperature for phenylacetylene semihydrogenation to styrene. The resulting Pd/TiO2 catalyst, possessing smaller Pd ensembles with ambiguous lattice fringes and more low coordination Pd sites, exhibits higher styrene selectivity compared to two contrastive Pd/TiO2 samples with larger ensembles and well-organized crystal structure fabricated by deposition-precipitation or photodeposition with subsequent thermal treatment at 300 °C. The sample derived from photodeposition exhibits greatly slow styrene hydrogenation in kinetic evaluation because the disordered structure of Pd particles in photodeposited Pd/TiO2 may prevent the formation of β-hydride phases and probably produce more surface H atoms, which may favor high styrene selectivity.
Highlights
Various studies have shown that the structure and surface characteristics of Pd metal play important roles in the selective hydrogenation of alkyne to alkene[7,8]
The principle of the photodeposition method is that the irradiation of semiconductor substrates with UV light can result in the photoinduced electrons that could reduce the absorbed metal ions to form metal nanoparticles[21,22,23,24]
The metal-modified semiconductor samples prepared by this method were often used as photocatalysts showing higher photocatalytic activity than that prepared by other conventional methods
Summary
Structure for Phenylacetylene received: 11 July 2016 accepted: 06 January 2017 Published: 08 February 2017. Selective deposition of metals/metal oxides, such as Cu9, Ag10, Si11, and TiO212,13 on the surface of Pd particles promotes the catalytic selectivity via geometric and/or electronic effects; Formation of Pd-Cu single atom alloys catalysts enhances the alkene selectivity by tuning the chemical and adsorption properties[14,15]; Adopting of Pd-Ga intermetallic compounds with isolation of active Pd sites in the crystallographic structure can obviously improve the hydrogenation selectivity[16,17]; Carbon deposited on top Pd layers strongly affects the transport of hydrogen and disturbs the equilibrium of H between surfaces and deeper layers, leading to improved alkene selectivity[18] Despite these encouraging results, the demand for efficient Pd catalysts with high selectivity to avoid the total hydrogenation of alkyne to alkane still remains. Our results indicate that photodeposition may provide an alternative to preparation of supported Pd catalysts for achieving high alkene selectivity by controlling morphology and structure of metal nanoparticles
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