Multiwalled Carbon Nanotubes Drive the Activity of Metal@oxide Core–Shell Catalysts in Modular Nanocomposites

Abstract

Rational nanostructure manipulation has been used to prepare nanocomposites in which multiwalled carbon nanotubes (MWCNTs) were embedded inside mesoporous layers of oxides (TiO(2), ZrO(2), or CeO(2)), which in turn contained dispersed metal nanoparticles (Pd or Pt). We show that the MWCNTs induce the crystallization of the oxide layer at room temperature and that the mesoporous oxide shell allows the particles to be accessible for catalytic reactions. In contrast to samples prepared in the absence of MWCNTs, both the activity and the stability of core-shell catalysts is largely enhanced, resulting in nanocomposites with remarkable performance for the water-gas-shift reaction, photocatalytic reforming of methanol, and Suzuki coupling. The modular approach shown here demonstrates that high-performance catalytic materials can be obtained through the precise organization of nanoscale building blocks.

Improved activity and stability of Pd@CeO2 core–shell catalysts hybridized with multi-walled carbon nanotubes in the water gas shift reaction

“…In this report, we expand on the former study by optimizing the oxide coverage on the MWCNT, thereby preventing damage of the metallic properties of MWCNT, induced by the acidic functionalization in the synthesis [21]. Furthermore, we show that thermal treatments can considerably enhance the activity and stability of these catalysts.…”

“…The subsequent steps of the synthesis follow the procedure previously reported [21]. A given amount of f-MWCNTs (10 wt%, 20 wt% or 30 wt% relative to the theoretical final composition) were dispersed in ethanol (reaching 2 mg/mL concentration) by sonication (30 min).…”

“…We have previously reported a unique nanostructured catalyst featuring a Pd(core)-CeO 2 (shell), supported on Al 2 O 3 which exhibits redox properties dramatically different from those of conventional Pd/CeO 2 catalysts [20]. Such systems were poor catalysts for the WGSR, apparently because the Pd becomes inaccessible to reactants when the ceria shell is reduced [19]; however, we anticipated that the features of the core-shell morphology could be successfully exploited for the WGS process if appropriately tailored [21].…”

Embedding Ultrafine and High‐Content Pt Nanoparticles at Ceria Surface for Enhanced Thermal Stability

“…For this purpose, various structures, such as core–shell,8, 16, 17, 18, 19, 20, 21 yolk–shell,16, 22 or hollow core–shell,23 were successfully generated, in which noble‐metal NPs were completely encapsulated by the support (e.g., CeO 2 ). However, the concern for such encapsulated structures may fall in the sluggish kinetics of reagents reaching the active catalytic sites, since noble metals like Pt as well as the Pt–CeO 2 interfaces are generally considered as the active sites in many important reactions 4, 24.…”

Direct growth of shape controlled TiO2 nanocrystals onto SWCNTs for highly active photocatalytic materials in the visible

“…Such an excellent behaviour can be explained in terms of an effective slowdown of the charge recombination process of electrons and holes in the Au nanoparticles [17]. An emerging alternative relies on the coupling of TiO 2 nanocrystals with carbon nanotubes (CNTs) either multi-or single-walled [7,18]. Indeed, CNTs can potentially contribute to increase photocatalytic activity by acting on three distinct features: (i) providing high-surface area and, hence a high density of active sites for adsorption and catalysis, (ii) retarding electron-hole recombination and (iii) inducing visible light catalysis by modification of band-gap and/or sensitization [19].…”