Preparation and Characterization of Pt@Au/Al₂O₃ Core-Shell Nanoparticles for Toluene Oxidation Reaction

Abstract

Customizing core-shell nanostructures is considered to be an efficient approach to improve the catalytic activity of metal nanoparticles. Various physiochemical and green methods have been developed for the synthesis of core-shell structures. In this study, a novel liquid-phase hydrogen reduction method was employed to form core-shell Pt@Au nanoparticles with intimate contact between the Pt and Au particles, without the use of any protective or structure-directing agents. The Pt@Au core-shell nanoparticles were prepared by depositing Au metal onto the Pt core; AuCl 4− was reduced to Au(0) by H2 in the presence of Pt nanoparticles. The obtained Pt@Au core-shell structured nanoparticles were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), high-resolution TEM, fast Fourier transform, powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and H2-temperature programmed reduction (H2-TPR) analyses. The EDX mapping results for the nanoparticles, as obtained from their scanning transmission electron microscopy images in the high-angle annular dark-field mode, revealed a Pt core with Au particles grown on its surface. Fourier transform measurements were carried out on the high-resolution structure to characterize the Pt@Au nanoparticles. The lattice plane at the center of the nanoparticles corresponded to Pt, while the edge of the particles corresponded to Au. With an increase in the Au content, the intensity of the peak corresponding to Pt in the FTIR spectrum decreased slowly, indicating that the Pt nanoparticles were surrounded by Au nanoparticles, and thus confirming the core-shell structure of the nanoparticles. The XRD results showed that the peak corresponding to Pt shifted gradually toward the Au peak with an increase in the Au content, indicating that the Au particles grew on the Pt seeds; this trend was consistent with the FTIR results. Hence, it can be stated that the Pt@Au core-shell structure was successfully prepared using the liquid-phase hydrogen reduction method. The catalytic activity of the nanoparticles for the oxidation of toluene was evaluated using a fixed-bed reactor under atmospheric pressure. The XPS and H2-TPR results showed that the Pt1@Au1/Al2O3 catalyst had the best toluene oxidation activity owing to its lowest reduction temperature, lowest Au 4d & 4f and Pt 4d & 4f binding energies, and highest Au 0 /Au δ+ and Pt 0 /Pt 2+ proportions. The Pt1@Au2Al2O3 catalyst showed high stability under dry and humid conditions. The good catalytic performance and high selectivity of Pt@Au/Al2O3 for toluene oxidation could be attributed to the high concentration of adsorbed oxygen species, good low-temperature reducibility, and strong interaction.

Stable and Active Au Catalyst Supported on CeMnO3 Perovskite for Selective Oxidation of Glycerol

“…As shown in Figure 4a, the two peaks centered at 334.4 and 352.9 eV belong to Au 0 , and others located at 336.2 and 354.7 eV are ascribed to Au δ+ . 49 Detailed information on the valence distribution is shown in Figure 4b. A higher fraction of Au 0 is detected (61.8%) for Au/CeMnO 3 than for the other four kinds of catalysts.…”

Structural Requirements for Chemoselective Ammonolysis of Ethylene Glycol to Ethanolamine over Supported Cobalt Catalysts

“…Among them, Co, Ni, and Ru have drawn attention the most, because of their high activity and chemoselectivity for primary amines. It has also been reported that the size of the metal nanoparticles [7] and the doping with a second metal-Cu [27], Ag [28], Ru [29], Bi [30], Re [31], or Pt [32]-can significantly improve the catalyst performance, providing a basis for further optimizing the amination processes. Metal catalysts have been reported to be efficient in the ammonolysis of alcohols containing at least a primary or secondary hydroxyl group (e.g., aliphatic primary monohydric alcohols and dihydric primary alcohols) via a hydrogen-borrowing methodology [6,7,[10][11][12][13][14][15][16].…”

“…Among them, Co, Ni, and Ru have drawn attention the most, because of their high activity and chemoselectivity for primary amines. It has also been reported that the size of the metal nanoparticles [7] and the doping with a second metal-Cu [27], Ag [28], Ru [29], Bi [30], Re [31], or Pt [32]-can significantly improve the catalyst performance, providing a basis for further optimizing the amination processes. For example, the liquid-phase ammonolysis of 1-octanol showed a higher chemoselectivity to the primary amine product on smaller supported Ru nanoparticles than those on larger ones, because the latter favored the self-coupling of primary amines [33].…”

Understanding the suppressive role of catalytically active Pt–TiO2 interfacial sites of supported metal catalysts towards complete oxidation of toluene

“…It is observed that the EMSI and certain structural modications of the nanoparticles with a second metal would greatly inuence the performance of Pt/ TiO 2 catalysts. 16,[37][38][39] Meanwhile, more O-vacancies and better transfer of active O species of the oxide supports, [40][41][42] as well as the addition of an appropriate amount of alkali metals, 43 would promote the reaction. However, the inuence of the metaloxide interfaces on complete toluene oxidation, especially when excluding the EMSI, is still under debate owing to the complicated intermediates and reaction mechanisms, 44,45 thus greatly hindering the rational design of more efficient catalysts.…”