Nanocatalysts are likely to contain undetected single-atom components, which may have been ignored but have significant effect in catalytic reactions. Herein, we report a catalyst composed of Mo single atoms (SAs) and MoO₂ nanoparticles (NPs) (Mo_SAs-MoO₂@NC), which is an exact model to understand how the SAs contribute to the nanocatalyst. Both experimental results and the density functional theory calculations reveal that Mo SAs on nitrogen-doped carbon provides the reaction zone for nitro reduction, while MoO₂ is the active site for decomposing hydrazine hydrate to produce H*. Thanks to the synergy between Mo SAs and MoO₂ NPs, this catalyst exhibits noble metal-like catalytic activity (100% conversion at 4 min) for the dechlorination-proof transfer hydrogenation. Additionally, the hydrogen migration on the catalyst is verified by the electrochemical tests in the absence of a hydrogen source. This work provides a model for further study on the coexistence of single atoms in nanoparticle catalysts.

Devising an electrocatalyst with brilliant efficiency and satisfactory durability for hydrogen production is of considerable demand, especially for large-scale application. Herein, we adopt a multi-step consequential induced strategy to construct a bifunctional electrocatalyst for the overall water splitting. Graphene oxide (GO) was used as a carbon matrix and in situ oxygen source, which was supported by the octahedral PtNi alloy to form the Pt_xNi_y–GO precursor. When calcinating in Ar atmosphere, the oxygen in GO induced the surface segregation of Ni from the PtNi octahedron to form a core–shell structure of Pt_x@Ni_y. Then, the surface- enriched Ni continuously induced the reformation of C in reduced graphene oxide (rGO) to enhance the degree of graphitization. This multi-step induction formed a nanocatalyst Pt_x@Ni_y–rGO which has very high catalytic efficiency and stability. By optimizing the feeding ratio of PtNi (Pt: Ni = 1:2), the electrolytic overall water splitting at 10 mA·cm⁻² can be driven by an electrolytic voltage of as low as 1.485 V, and hydrogen evolution reaction (HER) only needs an overpotential of 37 mV in 1.0 M KOH aqueous solution. Additionally, the catalyst exhibited consistent existence form in both HER and oxygen evolution reaction (OER), which was verified by switching the anode and cathode of the cell in the electrolysis of water. This work provides a new idea for the synthesis and evaluation of the bifunctional catalysts for water splitting.

A novel egg-like nanosphere was designed as a long-lived catalyst and is described as Fe₃O₄@nSiO₂-NH₂-Fe₂O₃·xBi₂O₃@mSiO₂. The catalyst was prepared using a modified Stöber method with template-free surface-protected etching. The catalyst particle consists of a magnetic Fe₃O₄ core as the "yolk", an inner silica shell bearing active Fe₂O₃·xBi₂O₃ species as the "egg white", and outer mesoporous silica as the "egg shell". It exhibits an excellent performance in the catalytic reduction of nitro aromatics to corresponding anilines in a fixed-bed continuous-flow reactor. The reaction could be performed at 80 ℃ and could reach complete conversion in less than 1 min with only a 7% excess of hydrazine hydrate. The catalyst bed could be easily shifted between different substrates without cross-contamination because of the uniformity of the catalyst particles. This catalyst exhibited very good stability in the continuous-flow protocol. In the long-term reduction of p-nitrophenol with 0.5 mmol·min^-1 productivity, it worked for more than 1, 500 cycles without any catalytic activity loss.