In recent decades, increasing interests have been put on improving the stability and selectivity of nanocatalysts for clean energy production due to the decrease of fossil fuels. Despite the prominent feature of high catalytic activity, nanocatalysts are prone to sintering. Structural design of nanocatalysts to form core/yolk shell structure has been proven to be the most effective method to enhance their catalytic stability. In this review, design strategies for core/yolk shell nanocatalysts to attain high stability in energy related applications at high temperatures such as hydrocarbon reforming reactions for syngas production and high temperature fuel cells such as SOFC and MCFC are summarized and exemplified with the advancements made in the recent three years. In addition, measures taken to obtain outstanding selectivity for F-T synthesis and C C bond hydrogenation reactions are also presented. Further, excellent shape and size selectivity design examples are also introduced. Finally, unsolved problems and challenges for core/yolk shell nanocatalysts design are proposed as the final part of this review.

Design of highly stable and selective core/yolk–shell nanocatalysts—A review

Hydrogen spillover is a well-known phenomenon in heterogeneous catalysis; it involves H2 cleavage on an active metal followed by the migration of dissociated H species over an ‘inert’ support1–5. Although catalytic hydrogenation using the spilled H species, namely, spillover hydrogenation, has long been proposed, very limited knowledge has been obtained about what kind of support structure is required to achieve spillover hydrogenation1,5. By dispersing Pd atoms onto Cu nanomaterials with different exposed facets, Cu(111) and Cu(100), we demonstrate in this work that while the hydrogen spillover from Pd to Cu is facet independent, the spillover hydrogenation only occurs on Pd1/Cu(100), where the hydrogen atoms spilled from Pd are readily utilized for the semi-hydrogenation of alkynes. This work thus helps to create an effective method for fabricating cost-effective nanocatalysts with an extremely low Pd loading, at the level of 50 ppm, toward the semi-hydrogenation of a broad range of alkynes with extremely high activity and selectivity. Spillover hydrogenation is facet specific and occurs on atomically dispersed Pd catalyst on Cu(100). Knowing this, cost-effective catalysts with extremely low Pd loading are fabricated that successfully catalyse the semi-hydrogenation of a broad range of alkynes with high activity and selectivity.

Facet engineering accelerates spillover hydrogenation on highly diluted metal nanocatalysts.

Intermetallic Nix My (M = Ga and Sn) nanocrystals with uniform particle size and controlled composition are successfully synthesized via a solution-based co-reduction strategy. The as-obtained nanocrystals are crystalline and structurally ordered. The active-site isolation and modified electronic structure are responsible for the excellent catalytic performance for alkyne semi-hydrogenation of the as-obtained non-precious catalysts.

Intermetallic NixMy (M = Ga and Sn) Nanocrystals: A Non-precious Metal Catalyst for Semi-Hydrogenation of Alkynes

Atomically dispersed metal catalysts maximize atom efficiency and display unique catalytic properties compared with regular metal nanoparticles. However, achieving high reactivity while preserving high stability at appreciable loadings remains challenging. Here we solve the challenge by synergizing metal–support interactions and spatial confinement, which enables the fabrication of highly loaded atomic nickel (3.1 wt%) along with dense atomic copper grippers (8.1 wt%) on a graphitic carbon nitride support. For the semi-hydrogenation of acetylene in excess ethylene, the fabricated catalyst shows extraordinary catalytic performance in terms of activity, selectivity and stability—far superior to supported atomic nickel alone in the absence of a synergizing effect. Comprehensive characterization and theoretical calculations reveal that the active nickel site confined in two stable hydroxylated copper grippers dynamically changes by breaking the interfacial nickel–support bonds on reactant adsorption and making these bonds on product desorption. Such a dynamic effect confers high catalytic performance, providing an avenue to rationally design efficient, stable and highly loaded, yet atomically dispersed, catalysts. Synergizing metal–support interactions and spatial confinement through atomic copper grippers boost the dynamics of highly loaded atomic nickel for high activity, high thermal/chemical stability and unprecedented coke inhibition in hydrogenation reactions.

Synergizing metal–support interactions and spatial confinement boosts dynamics of atomic nickel for hydrogenations

Layered double hydroxide-derived Ni-Cu nanoalloy catalysts for semi-hydrogenation of alkynes: Improvement of selectivity and anti-coking ability via alloying of Ni and Cu

Zinc inclusion to heterogeneous nickel catalysts reduces oligomerization during the semi-hydrogenation of acetylene

The structures of ZnO-supported Ni catalysts were explored with in situ X-ray absorption spectroscopy, temperature-programmed reduction, X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy, and electron energy loss spectroscopy. Calcination of nickel nitrate on a nanoparticulate ZnO support at 450 °C results in the formation of Zn-doped NiO (ca. Ni0.85Zn0.15O) nanoparticles with the rock salt crystal structure. Subsequent in situ reduction monitored by X-ray absorption near-edge structure (XANES) at the Ni K edge reveals a direct transformation of the Zn-doped NiO nanoparticles to a face-centered cubic alloy, Ni1–xZnx, at ∼400 °C with x increasing with increasing temperature. Both in situ XANES and ex situ HRTEM provide evidence for intermetallic β1-NiZn formation at ∼550 °C. In comparison to a Ni/SiO2 catalyst, Ni/ZnO necessitates a higher temperature for the reduction of NiII to Ni0, which highlights the strong interaction between Ni and...

Richard S. Sim

Papers

Zinc inclusion to heterogeneous nickel catalysts reduces oligomerization during the semi-hydrogenation of acetylene

In Situ Spectroscopic Characterization of Ni1–xZnx/ZnO Catalysts and Their Selectivity for Acetylene Semihydrogenation in Excess Ethylene