Modification of active metals with metal oxide modifiers has attracted considerable attention in heterogeneous catalysis due to their synergistic effect. However, a controllable synthesis of highly reactive and stable metal–metal oxide hybrid nanocatalysts is difficult. To solve this problem, presynthesized IrM (M = Fe, Co, and Ni) bimetallic nanoparticles were initially confined in the mesopores of SBA-15 and were then in situ transformed to Ir-MO x hybrids. The obtained Ir-MO x /SBA-15 nanocatalysts show superior activity and selectivity in the hydrogenation of substituted nitroaromatics to corresponding aromatic amines compared to Ir/SBA-15. Among these Ir-based catalysts, Ir-FeO x /SBA-15 exhibits the highest activity and selectivity and has a wider substrate scope due to the interaction between Ir and FeO x . Therefore, our research provides a way to design reactive and stable hydrogenation catalysts.

Palladium nanoparticles supported on silica catalysts (Pd/SiO 2 ) were prepared by wet impregnation (WI), dry impregnation (DI), strong electrostatic adsorption (SEA), and charge-enhanced dry impregnation (CEDI) methods. The Pd/SiO 2 samples with highly dispersed and tight size-distributed palladium nanoparticles are obtained via SEA and CEDI methods based on strong electrostatic interactions between the dissolved metal precursor ([Pd(NH 3 ) 4 ] 2+ ) and positively charged SiO 2 support in an alkali-impregnating solution (initial pH = 12). The Pd/SiO 2 -SEA samples prepared by the SEA method usually showed higher palladium dispersions (>50%) than those prepared by CEDI (Pd dispersion = 32−45%). The surface loading (support surface area per liter of preparation solution), pH regulator (NaOH or NH 4 OH), Pd loading, and reduction temperature were shown to be key factors affecting the dispersion of palladium in the Pd/SiO 2 -SEA samples, as well as the leaching/dissolution of SiO 2 and palladium in the alkali solution. The Pd/SiO 2 -SEA samples prepared with proper SLs of 30,000−100,000 m 2 L −1 using NH 4 OH as the pH regulator exhibited not only very high Pd dispersions (64−97%) but also negligible losses of SiO 2 and Pd in the impregnating solution. The Pd/SiO 2 -SEA samples also exhibited better catalytic performance in methane combustion based on both the T 10 and T 50 temperatures and the intrinsic activities (mass-specific activity and/or turnover frequency (TOFs)). The TOFs generally decreased from 130 h −1 to 6.2 h −1 as Pd dispersion increased from 32% to 97% for the Pd/SiO 2 -SEA(NH 4 OH) catalysts. Moreover, the reaction activity of Pd/SiO 2 -SEA catalysts was significantly improved by increasing the fraction of Pd 0 in the range of 70−85%, indicating that this size-sensitive catalysis would be related to the redox properties of the supported Pd nanoparticles.

A series of NiP-x/Al2O3 catalysts containing different ratio of metallic nickel to nickel phosphides, prepared by varying Ni/P molar ratio of 4, 3, 2 through a co-impregnation method, were employed to investigate the synergistic effect of metallic nickel-nickel phosphides in dry methane reforming reaction. The Ni/Al2O3 catalyst indicates good activity along with severe carbon deposition. The presence of phosphorus increases nickel dispersion as well as the interaction between nickel and alumina support, which results in smaller nickel particles. The co-existence of metallic nickel and nickel phosphides species is confirmed at all the P contained catalysts. Due to the relative stronger CO2 dissociation ability, the NiP-x/Al2O3 catalysts indicate obvious higher resistance of carbon deposition. Furthermore, because of good balance between CH4 dissociation and CO2 dissociation, NiP-2/Al2O3 catalyst exhibits best resistance of carbon deposition, few carbon depositions were formed after 50 h of dry methane reforming.

The size of metal species plays a pivotal role in governing catalytic performance of supported metal catalysts. In this work, a series of Rh encapsulated within silicalite-1 catalysts with different sizes were prepared by one-pot hydrothermal method and employed to catalyze the decomposition of N 2 O. Detailed structure determinations by HAADF-STEM, XPS and CO-DRIFTS demonstrate that subtle modulation of the encapsulated Rh species were achieved easily from single-atom to nanoclusters and nanoparticles by controlling the loading and reduction conditions of Rh. The turnover frequency (TOF) of N 2 O decomposition showed a typical volcano-type dependence on Rh size. Kinetic studies revealed that this structure-sensitive catalysis was related to the difference in N 2 O and O 2 adsorption/desorption for various Rh species. Furthermore, a Rh@S-1 catalyst with a proper Rh size (ca. 1.6 nm) was identified as the best-performing catalyst with a maximum TOF (ca. 95 h À 1 ), showing much superior activity than other reported Rhbased catalysts.

Supported Rh nanoparticles (NPs) exhibit excellent activity for the chemoselective hydrogenation of halonitrobenzenes (HNBs), but their selectivity to aromatic amines is not satisfactory due to the side reaction on the carbon−halogen bonds, and their recycling stability is limited due to the aggregation and the leaching of active component during the long-term usage. Herein, we design a yolk−shell-structured catalyst that consists of RhCu alloy cores and hollow/microporous carbon shells (HCS) to overcome these problems. The obtained RhCu@HCS catalyst with a Rh/Cu ratio of 1:1 showed good activity, selectivity, and stability in the hydrogenation of p-CNB (p-chloronitrobenzene) to produce p-CAN (p-chloroaniline) due to the synergistic effect between Rh and Cu. The protective carbon shells not only prevented the aggregation of metal NPs but also allowed the reactants to diffuse freely across the shells. Therefore, our research provides a general strategy to design highly efficient and stable hydrogenation catalysts.

Nanosized Au catalysts suffer from serious sintering problems during the synthesis or catalytic reactions at high temperatures. In this work, we integrate dumbbell shaped Au-Fe3O4 heterostructures into hollow ZrO2 nanocages...

The selective oxidation of biomass-derived alcohol-containing functional compounds with molecular oxygen over solid catalysts is a promising approach to renewably produce value-added ketones, aldehydes, and/or carboxylic acids. Activated carbon (AC) supported Pt, Pd, Rh, Ru, and Au nanoparticles at comparable sizes (average: 1.4–2.9 nm) were evaluated in the liquid-phase oxidative dehydrogenation of methyl lactate (ML) to methyl pyruvate (MP) with oxygen under base-free conditions. Ru/AC gives not only much higher MP selectivity (ca. 90%) but also an order of magnitude in the initial turnover frequency (TOF) of ML higher than other noble-metal catalysts for this ML-to-MP reaction. Metallic Ru (Ru/AC: 84.3% Ru0 and 15.7% RuO x ) is also found to be superior to other Ru species (RuCl3, RuO2, and Ru­(OH)3) supported on AC in terms of higher activity and selectivity. The oxidative dehydrogenation of ML is always accompanied by the hydrolysis reactions of MP and ML and consecutive secondary reactions (decarboxylation, decarbonylation, oxidation, etc.) producing C1–C3 byproducts, which would be promoted by the surface acidic and basic sites. The effects of reaction variables (including ML concentration, O2 pressure, reaction temperature, and solvent) on ML oxidation were further examined on Ru/AC. A kinetic rate based on the Langmuir–Hinshelwood model was proposed, indicating that the rate-determining step of ML oxidation over the Ru/AC catalyst would be the surface reaction between independently adsorbed ML and oxygen species on active sites of different nature. γ-Valerolactone is identified as an efficient solvent for ML oxidation, producing high and stable activity and MP selectivity (87–94%) throughout 5 reaction runs.

Restricting reactive metal nanoclusters into a microporous zeolite matrix (metal@zeolite) can not only prevent the sintering of metal species but can also regulate their catalytic selectivities to certain products. However, there are some problems with current synthesis methods for these structures, such as low metal utilization or/and low product yield. Herein, we report a general strategy to encapsulate different noble metal nanoclusters (e.g., Pd, Pt, Rh, and Ru) into various zeolites (e.g., S-1, ZSM-5, SSZ-13, NaA, and beta). The key point of this strategy is the soft gel precursor (H 2 O/Si < 4) in the posthydrolysis evaporation process, which significantly improves metal utilization. Combined with the high temperature crystallization process, the space-time yield has been significantly improved, simultaneously. As a typical example, the metal utilization and space-time yield of Pd@S-1 synthesized through this method were nearly 2 and 67 times higher than those of the typical hydrothermal route, respectively. Compared with a supported Pd/SiO 2 nanocatalyst, Pd@S-1 exhibited higher catalytic activity and selectivity in hydrogenation of p-chloronitrobenzene (p-CNB).