Tailoring the Oxidation Activity of Pt Nanoclusters via Encapsulation

Abstract

To tailor the catalytic activities of metal catalysts at will to achieve efficient conversion in chemical processes remains a challenge, particularly for noble metals, such as Pt. We demonstrate herein that encapsulation within the carbon nanotube (CNT) channels with a diameter of 1.0−1.5 nm not only allows restriction of the size of Pt nanoclusters around 1.0 nm but also enables modulating of the Pt species at the active reduced states through host−guest interaction. The encapsulated Pt is protected from oxygen under reaction conditions in toluene oxidation up to 200 °C, as unveiled by in situ X-ray absorption spectroscopy and density functional theory calculations. As a result, the encapsulated Pt clusters deliver a remarkably higher activity and stability than the clusters located on the open surfaces of the CNT exterior walls and carbon black support, although the latter are much more accessible to reactants. This characteristic of the CNT channels can be explored to tune the properties of other metal catalysts for oxidation reactions.

Chemical reactions confined within carbon nanotubes

“…66 The oxidation of benzyl alcohol to benzaldehyde can be catalysed by birnessite, a manganese dioxide mineral with intercalated potassium ions, and nanoparticles of this structure were encapsulated within MWCNT by Yang and co-workers. 72 The direct comparison of PtNP encapsulated within both CNT and a zeolite H-mordernite, possessing linear cavities of comparable diameter to CNT, shows that inorganic nanoscale hosts do not necessarily induce the same confinement effects (Fig. The oxidation of toluene catalysed by PtNP further emphasises the importance of the carbon nanotube host in achieving such results.…”

In situ thermolysis of Pt-carbonyl complex to form supported clean Pt nanoclusters with enhanced catalytic performance

“…Nanoclusters with a high volume/surface ratio and quantum effect have been proven to be efficient catalysts in various useful reactions. To date, several synthetic approaches have been developed to fabricate these small nanoparticles, including solution-phase reduction, gas-phase synthesis, and the ligand-assisted approach [25][26][27][28][29]. However, the fabrication of small nanoparticles is still challenging because of their severe aggregation, wide size distribution, low output, and low activity.…”

The Effect of Doping and Confinement on the Adsorption of Pt on CNTs upon Be, B, N and O Doping: A Theoretical Study

“…As clarified by recent theoretical studies [9], the external surface of CNT presents more electron density than the internal surface, which results in significant Researchers have systematically revealed that the confinement interaction of CNTs could influence the chemical properties of metal or metal oxides NPs (e,g., Fe 3 O 4 [10], Fe and Fe 2 O 3 [11], Ru [12], Re species [13] and Pt [14] ), especially associated with the tuning of redox/oxidation property through host-guest interaction. For example, Bao et al found that encapsulation interactions of CNT could not only reduce the size of Pt nanoparticles, but also prefer the Pt species at active reduced states [14].…”

“…For example, Bao et al found that encapsulation interactions of CNT could not only reduce the size of Pt nanoparticles, but also prefer the Pt species at active reduced states [14]. In addition, the metal NPs (i.e., Pd, Rh, Fe, Ru and so on) encapsulated inside the nanotube could deliver enhanced catalytic activity or higher enantioselectivity towards a wide range of reactions, such as oxygen reduction reaction (ORR) [15], Fisher-Tropsch synthesis (FTS) reaction [16][17][18] and liquid phase hydrogenation reaction [19][20][21].…”

“…Promisingly, two recent experimental works have shown that the Pt particle confined inside nanotube could exhibit much better activity and long-term operation stability for the asymmetric hydrogenation [31] and electro-catalytic methanol oxidation reaction [32] than those located on the external wall, which are attributed to the strong confinement effect of CNTs by the authors. Bao's work also pointed out that although the internal Pt clusters are less accessible to reactants, they present much higher activity and stability than the clusters on the internal surface of CNT [14]. Moreover, a very recent theoretical research revealed that Pt NPs inside nanotube are much harder to melt at higher temperature with respect to the outside particles, indicating the enhanced stability of the internal particles [33].…”