Platinum Nanoparticle Shape Effects on Benzene Hydrogenation Selectivity

Abstract

Benzene hydrogenation was investigated in the presence of a surface monolayer consisting of Pt nanoparticles of different shapes (cubic and cuboctahedral) and tetradecyltrimethylammonium bromide (TTAB). Infrared spectroscopy indicated that TTAB binds to the Pt surface through a weak C-H...Pt bond of the alkyl chain. The catalytic selectivity was found to be strongly affected by the nanoparticle shape. Both cyclohexane and cyclohexene product molecules were formed on cuboctahedral nanoparticles, whereas only cyclohexane was produced on cubic nanoparticles. These results are the same as the product selectivities obtained on Pt(111) and Pt(100) single crystals in earlier studies. The apparent activation energy for cyclohexane production on cubic nanoparticles is 10.9 +/- 0.4 kcal/mol, while for cuboctahedral nanoparticles, the apparent activation energies for cyclohexane and cyclohexene production are 8.3 +/- 0.2 and 12.2 +/- 0.4 kcal/mol, respectively. These activation energies are lower, and corresponding turnover rates are three times higher than those obtained with single-crystal Pt surfaces.

Molecular surface chemistry by metal single crystals and nanoparticles from vacuum to high pressure

“…Benzene hydrogenation studies on cubooctahedra and cubic Pt nanoparticles demonstrated that cyclohexene and cyclohexane formed on cuboctahedral nanoparticles, while only cyclohexane formed on cubic nanoparticles, consistent with previous results for single-crystal Pt surfaces ( Figure 11) 46 . This study indicates the importance of nanoparticle shape in determining reaction selectivity.…”

“…That is, if there are several thermodynamically stable products, only one desired product is formed [44][45][46] . We have investigated some typical multipath reaction selectivities: benzene and cyclohexene hydrogenation.…”

Sub-10 nm Platinum Nanocrystals with Size and Shape Control: Catalytic Study for Ethylene and Pyrrole Hydrogenation

“…For instance, both cyclohexene and cyclohexane formed on cuboctahedral nanocrystals during benzene hydrogenation / dehydrogenation while only cyclohexane formed on cubic nanocrystals. 6 These observations were consistent with previous results for Pt single-crystal studies. In order to further investigate the roles of nanocrystal size and shape in transition metal heterogeneous catalysis, it is essential to simultaneously control the size and the shape of the nanocrystals.…”

“…6,7 Several synthetic methods for cubic Pt nanocrystals were reported previously, however, sizes of these shaped nanocrystals were typically around 10 nm or larger. [7][8][9][10] Sub-10 nm nanocrystals demonstrate different physical and chemical properties from large nanocrystals.…”

Nanostructured Pt-alloy electrocatalysts for PEM fuel cell oxygen reduction reaction

“…For example, by using NaBH 4 to reduce K 2 PtCl 4 , Pt nanocubes were formed. 38 However, if a milder reducing agent such as ascorbic acid was used, Pt nanodendrites were produced. 114,115 Thermodynamic control can be achieved by altering the surface energy of prepared materials.…”