Overcoming propylene oxidation: Catalysts for the oxidative dehydrogenation of propane to propylene and water become less selective with increasing conversion because propylene itself is more readily oxidized than propane. Yan et al. created nanoscale tandem catalysts by growing an ∼2-nanometer shell of indium oxide, a selective hydrogen combustion catalyst, over a propane dehydrogenation catalyst, platinum nanoparticles supported on alumina spheres (see the Perspective by Pei and Gong). This overcoat exposed the platinum nanoparticles for propane dehydrogenation. Surface hydrogen atoms were oxidized at the indium oxide–platinum interface. This approach boosted yields of propylene to up to 30%. Science , this issue p. 1257 ; see also p. 1203

Metal oxides with a tunnelled structure are attractive as charge storage materials for rechargeable batteries and supercapacitors, since the tunnels enable fast reversible insertion/extraction of charge carriers (for example, lithium ions). Common synthesis methods can introduce large cations such as potassium, barium and ammonium ions into the tunnels, but how these cations affect charge storage performance is not fully understood. Here, we report the role of tunnel cations in governing the electrochemical properties of electrode materials by focusing on potassium ions in α-MnO₂. We show that the presence of cations inside 2 × 2 tunnels of manganese dioxide increases the electronic conductivity, and improves lithium ion diffusivity. In addition, transmission electron microscopy analysis indicates that the tunnels remain intact whether cations are present in the tunnels or not. Our systematic study shows that cation addition to α-MnO₂ has a strong beneficial effect on the electrochemical performance of this material.

Pumping macrocycles onto surfaces: Numerous chemical processes, ranging from water purification to catalysis, involve sorption of small molecules onto surfaces. Typically, spontaneous attractive interactions favor the binding event. Feng et al . report a mechanisorption process that requires redox manipulations to pump macrocycles from bulk solution onto axles immobilized on a metal-organic framework. The resulting rotaxanes store energy through nonequilibrium charge concentration in their mechanical bonds. Ultimately, the technique could also prove useful for actively partitioning compounds with particular functionality between surface and bulk environments. —JSY

In-situ liquid TEM results reveal the co-existence of classical and non-classical nucleation paths during HA biomineralization.