Catalytic activity of shaped platinum nanoparticles for hydrogenation: a kinetic study

Abstract

Aqueous-phase hydrogenation of 4-nitrophenol (4-NP) was investigated in the presence of free-standing or supported Pt nanoparticles (NPs) of various shapes. Uniform cubic and pseudo-tetrahedral Pt NPs with sub-10 nm sizes were obtained by the direction of bio-inspired small molecules, 3-hydroxybutyric acid (3-HB) and tropic acid (TA), respectively. The catalytic activity is found to be strongly affected by the nanoparticle shape and the support, SBA-15. Pseudo-tetrahedral Pt NPs directed by TA have superior activity to the cubic ones with 3-HB. But when loaded on SBA-15, cubic Pt(3-HB) NPs showed better performance than Pt(TA) NPs. Then the experimental data are fitted to a Langmuir–Hinshelwood (L–H) model involving a surface reaction controlling mechanism for 4-NP hydrogenation. This model follows a dual-site adsorption with molecular adsorption of 4-NP and dissociative adsorption of hydrogen. The results show that the reaction catalyzed by pseudo-tetrahedral Pt(TA) NPs has lower apparent activation energy than that by the cubic Pt(3-HB) NPs. But after loading these NPs onto SBA-15, the apparent activation energy of Pt(3-HB)@SBA-15 decreased while that of Pt(TA)@SBA-15 increased in comparison with their corresponding free-standing NPs.