In this work, atomic layer deposition is applied to coat carbon nanocoils with magnetic Fe(3)O(4) or Ni. The coatings have a uniform and highly controlled thickness. The coated nanocoils with coaxial multilayer nanostructures exhibit remarkably improved microwave absorption properties compared to the pristine carbon nanocoils. The enhanced absorption ability arises from the efficient complementarity between complex permittivity and permeability, chiral morphology, and multilayer structure of the products. This method can be extended to exploit other composite materials benefiting from its convenient control of the impedance matching and combination of dielectric-magnetic multiple loss mechanisms for microwave absorption applications.

Efficient separation of photogenerated electrons and holes, and associated surface reactions, is a crucial aspect of efficient semiconductor photocatalytic systems employed for photocatalytic hydrogen production. A new CoO /TiO /Pt photocatalyst produced by template-assisted atomic layer deposition is reported for photocatalytic hydrogen production on Pt and CoO dual cocatalysts. Pt nanoclusters acting as electron collectors and active sites for the reduction reaction are deposited on the inner surface of porous TiO nanotubes, while CoO nanoclusters acting as hole collectors and active sites for oxidation reaction are deposited on the outer surface of porous TiO nanotubes. A CoO /TiO /Pt photocatalyst, comprising ultra-low concentrations of noble Pt (0.046 wt %) and CoO (0.019 wt %) deposited simultaneously with one atomic layer deposition cycle, achieves remarkably high photocatalytic efficiency (275.9 μmol h ), which is nearly five times as high as that of pristine TiO nanotubes (56.5 μmol h ). The highly dispersed Pt and CoO nanoclusters, porous structure of TiO nanotubes with large specific surface area, and the synergetic effect of the spatially separated Pt and CoO dual cocatalysts contribute to the excellent photocatalytic activity.

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Spillover is a well-known phenomenon in heterogeneous catalysis and is involved in many important reactions. The establishment of the spillover concept opened up a new research field for an in-depth understanding of the dynamic behavior of migrated species on a catalyst surface. However, a comprehensive understanding of spillover remains lacking. In recent years, the development of advanced characterization techniques in combination with well-controlled synthesis methodologies has provided us with increasing worthwhile information about spillover. This Review mainly describes recent progress on the characterization and mechanism of hydrogen spillover and how to effectively utilize the spillover effect for enhanced catalytic performance. Additionally, the challenges remaining in this research area are discussed, and possible research directions for the future are proposed.

Supports can widely affect or even dominate the catalytic activity, selectivity, and stability of metal nanoparticles through various metal-support interactions (MSIs). However, underlying principles have not been fully understood yet, because MSIs are influenced by the composition, size, and facet of both metals and supports. Using Ru/TiO2 supported on rutile and anatase as model catalysts, we demonstrate that metal-support interfacial compatibility can critically control MSI modes and catalytic performances in CO2 hydrogenation. Annealing Ru/rutile-TiO2 in air can enhance CO2 conversion to methane resulting from enhanced interfacial coupling driven by matched lattices of RuOx with rutile-TiO2; annealing Ru/anatase-TiO2 in air decreases CO2 conversion and converts the product into CO owing to strong metal-support interaction (SMSI). Although rutile and anatase share the same chemical composition, we show that interfacial compatibility can basically modify metal-support coupling strength, catalyst morphology, surface atomic configuration, MSI mode, and catalytic performances of Ru/TiO2 in heterogeneous catalysis.

The synergistic nature of bicomponent catalysts remains a challenging issue, due to the difficulty in constructing well-defined catalytic systems. Here we study the origin of synergistic effects in CoOx-Pt catalysts for selective hydrogenation by designing a series of closely contacted CoOxPt/TiO2 and spatially separated CoOx/TiO2/Pt catalysts by atomic layer deposition (ALD). For CoOx/TiO2/Pt, CoOx and platinum are separated by the walls of titania nanotubes, and the CoOx-Pt intimacy can be precisely tuned. Like CoOxPt/TiO2, the CoOx/TiO2/Pt shows higher selectivity to cinnamyl alcohol than monometallic TiO2/Pt, indicating that the CoOx-Pt nanoscale intimacy almost has no influence on the selectivity. The enhanced selectivity is ascribed to the increased oxygen vacancy resulting from the promoted hydrogen spillover. Moreover, platinum-oxygen vacancy interfacial sites are identified as the active sites by selectively covering CoOx or platinum by ALD. Our study provides a guide for the understanding of synergistic nature in bicomponent and bifunctional catalysts.

Governing the process and outcome of chemical reactions is the most important aim of catalytic chemistry. The confinement of active sites inside nanosized spaces provides a powerful strategy to achieve this goal. Reacting molecules (reactants, intermediates, and products of a reaction) and nanomaterials (metal/metal-oxide nanoparticles) confined inside nanoreactors have been observed to exhibit modified behaviors and properties with respect to their unconfined counterparts. Typically, catalysts confined in zeolites, mesoporous materials, metal-organic frameworks, and nanotubes are obtained by traditional liquid-phase methods. However, excess metals or undesired solvents and other reagents must be removed. It is also difficult to precisely regulate the confined nanostructures and assemble multifunctional sites in the confined nanospaces. Atomic layer deposition (ALD) provides a controllable method to fabricate confined catalysts due to its outstanding advantages. In this Account, we describe our progress in the design and properties of confined nanocatalysts by ALD. ALD is an elegant method to directly deposit highly dispersed metal or oxide species into porous materials, including zeolites and mesoporous materials. We deposited Pt nanoclusters in the micropores of a KL zeolite with precisely controlled size by ALD. We also introduced CoO nanoclusters into mesoporous SBA-15. We have reported pioneering works on the synthesis of confined nanoparticles with metal-in-nanotube structures by a template-assisted ALD method. Confined Cu nanoparticles were prepared by reducing CuO nanowires coated with AlO, TiO, or alucone layers by ALD. Confined Cu and Au nanoparticles were also prepared starting from the corresponding metal nanowires with the assistance of sacrificial layers produced by ALD. In a more facile strategy, Au nanoparticles confined in AlO nanotubes were produced using a sacrificial template by ALD. Furthermore, we synthesized a multiply confined Ni-based nanocatalyst through a template-assisted ALD method. We assembled multiple interfaces (Ni/AlO and Pt/TiO) in a confined nanospace for tandem reactions by template-assisted ALD. The synergistic effect of two interfaces enhanced the tandem reaction, and the confined nanospace favored the instant transfer of intermediates between the two interfaces. In addition, porous TiO nanotubes with spatially separated Pt and CoO cocatalysts were also produced by ALD. The confined catalysts can be further treated by ALD. We used ALD to modify the mesoporous SBA-15 support to precisely tune the active species-support interaction. In addition to the support, the confined metal nanoparticles can also be coated with an ultrathin oxide layer by ALD to further improve their catalytic activities. Moreover, the structure and size of the confined nanospace can be tuned precisely by ALD. Overall, ALD has exhibited noteworthy applications in and will provide new opportunities for the design and synthesis of highly effective confined catalysts.

To design highly efficient catalysts, new concepts for optimizing the metal-support interactions are desirable. Here we introduce a facile and general template approach assisted by atomic layer deposition (ALD), to fabricate a multiply confined Ni-based nanocatalyst. The Ni nanoparticles are not only confined in Al2 O3 nanotubes, but also embedded in the cavities of Al2 O3 interior wall. The cavities create more Ni-Al2 O3 interfacial sites, which facilitate hydrogenation reactions. The nanotubes inhibit the leaching and detachment of Ni nanoparticles. Compared with the Ni-based catalyst supported on the outer surface of Al2 O3 nanotubes, the multiply confined catalyst shows a striking improvement of catalytic activity and stability in hydrogenation reactions. Our ALD-assisted template method is general and can be extended for other multiply confined nanoreactors, which may have potential applications in many heterogeneous reactions.