A Sinter‐Resistant Catalytic System Based on Platinum Nanoparticles Supported on TiO₂ Nanofibers and Covered by Porous Silica

Abstract

Platinum is a key catalyst that is invaluable in many important industrial processes such as CO oxidation in catalytic converters, oxidation and reduction reactions in fuel cells, nitric acid production, and petroleum cracking.[1] Many of these applications utilize Pt nanoparticles supported on oxides or porous carbon.[2] However, in practical applications that involve high temperatures (typically higher than 300 8C), the Pt nanoparticles tend to lose their specific surface area and thus catalytic activity during operation because of sintering. Recent studies have shown that a porous oxide shell can act as a physical barrier to prevent sintering of unsupported metal nanoparticles and, at the same time, provide channels for chemical species to reach the surface of the nanoparticles, thus allowing the catalytic reaction to occur. This concept has been demonstrated in several systems, including Pt@SiO 2 , [3] Pt@CoO, [4] Pt/CeO 2 @SiO 2 , [5] Pd@SiO 2 , [6] Au@SiO 2 , [7] Au@SnO 2 [8] and Au@ZrO 2 [9] coreshell nanostructures. Despite these results, a sinter-resistant system has not been realized in supported Pt nanoparticle catalysts.Improved catalytic or photocatalytic properties are often achieved when metal nanoparticles are supported on oxides such as TiO 2 and CeO 2 that interact strongly with late transition metals. [2f, 5] Herein, we demonstrate a thermally stable catalytic system consisting of Pt nanoparticles that are supported on a TiO 2 nanofiber and coated with a porous SiO 2 sheath. In this system, the porous SiO 2 coating offers an energy barrier to prevent the migration of individual Pt atoms or nanoparticles because of its weak interaction with late transition metals, including Pt. The porous-SiO 2 /Pt/TiO 2 catalytic system was prepared in three steps (Figure 1): 1) deposition of Pt nanoparticles onto the surface of TiO 2 nanofibers; 2) coating of SiO 2 with cetyltrimethylammonium bromide (CTAB) as a pore-generating agent; and 3) calcination in air to generate a porous sheath of SiO 2 . By using this approach, we were able to produce a platinum-based catalytic system that can resist sintering up to 750 8C in air, while retaining the catalytic activity of the Pt nanoparticles.The TiO 2 nanofibers were prepared by electrospinning and subsequent calcination in air at 750 8C for 2 hours.[10] The as-prepared nanofibers had a rough surface and a polycrystalline structure that contained both anatase and rutile phases (69 % anatase and 31 % rutile; Figure S1 in the Supporting Information). Poly(vinyl pyrrolidone) (PVP) stabilized Pt nanoparticles were prepared by using the polyol method.[11]The as-synthesized Pt nanoparticles were uniform in size, with an average size of (3.1 AE 0.5) nm (Figure 2 a, b). These Pt nanoparticles were deposited onto the TiO 2 nanofibers by immersing the sample in a suspension of the Pt nanoparticles, which was prepared by a 10-fold dilution of the as-prepared Pt sample with ethanol. As shown in Figure 2 c, the Pt nanoparticles were well dispersed on the surface of each TiO ...

Passion fruit-like nano-architectures: a general synthesis route

“…2B). This can be ascribed to the higher resistance of platinum NPs over sintering and coalescence27. Consistently, calcinations of AuSi at 350 °C produced multinucleated nano-architectures with cores of less than 10 nm in diameter (Supplementary Fig.…”

Novel Nanostructures of Rutile Fabricated by Templating against Yarns of Polystyrene Nanofibrils and Their Catalytic Applications

“…39,40 Typically, 4 mL of ethylene glycol (EG, J.T. Baker, 9300-01) was added into a glass vial and heated in an oil bath at 110 °C for 30 min.…”

Bifunctional Ag@SiO2/Au Nanoparticles for Probing Sequential Catalytic Reactions by Surface‐Enhanced Raman Spectroscopy

“…In addition, the tiny Au particles with an enormouss urface-to-volume ratio have as trongt endency to coagulate during operation, ultimately losing their catalytic activity.O ne approachtoi mproving the stabilitya gainst coagulation is to encapsulatet he Au nanoparticles with at hin, porous oxide layer,s uch as SiO 2 ,S nO 2 ,C eO 2 ,o rT iO 2 .T ot his end, it has been demonstratedt hat the oxide layer could serve as aphysical barriert oi solate and confinet he metal nanoparticles for av ariety of systems. [19][20][21][22][23][24][25] However,t he presence of an oxide layer tends to block the active sites on metal nanoparticles, leadingt or eduction in catalytic activity when compared with the naked metal nanoparticles.…”