Carbon Deposition on Heterogeneous Pt Catalysts Promotes the Selective Hydrogenation of Halogenated Nitroaromatics

Full Selectivity Control over the Catalytic Hydrogenation of Nitroaromatics Into Six Products

A full selectivity control over the catalytic hydrogenation of nitroaromatics leads to the production of six possible products, i.e., nitroso, hydroxylamine, azoxy, azo, hydrazo or aniline compounds, which has however not been achieved in the field of heterogeneous catalysis. Currently, there is no sufficient evidence to support that the catalytic hydrogenation of nitroaromatics with the use of heterogeneous metal catalysts would follow the Haber's mechanistic scheme based on electrochemical reduction. We now demonstrate in this work that it is possible to fully control the catalytic hydrogenation of nitroaromatics into their all six products using a single catalytic system under various conditions. Employing SnO2-supported Pt nanoparticles facilitated by the surface coordination of ethylenediamine and vanadium species enabled this unprecedented selectivity control. Through systematic investigation into the controlled production of all products and their chemical reactivities, we have constructed a detailed reaction network for the catalytic hydrogenation of nitroaromatics. Crucially, using oxygen-isolated characterization techniques is essential for identifying unstable compounds such as nitroso, hydroxylamine, hydrazo compounds. The insights gained from this research offer invaluable guidance for selectively transforming nitroaromatics into a wide array of functional N-containing compounds, both advancing fundamental understanding and fostering practical applications in various fields.

Frustrated Lewis pairs on pentacoordinated Al3+-enriched Al2O3 promote heterolytic hydrogen activation and hydrogenation

As an emerging class of metal-free catalysts, frustrated Lewis pairs (FLPs) catalysts have been greatly constructed and applied in many fields. Homogeneous FLPs have witnessed significant development, while limited heterogeneous FLPs catalysts are available. Herein, we report that heterogeneous FLPs on pentacoordinated Al3+-enriched Al2O3 readily promote the heterolytic activation of H2 and thus hydrogenation catalysis. The defect-rich Al2O3 was prepared by simple calcination of a carboxylate-containing Al precursor. Combinatorial studies confirmed the presence of rich FLPs on the surface of the defective Al2O3. In contrast to conventional alumina (γ-Al2O3), the FLP-containing Al2O3 can activate H2 in the absence of any transition metal species. More importantly, H2 was activated by surface FLPs in a heterolytic pathway, leading to the hydrogenation of styrene in a stepwise process. This work paves the way for the exploration of more underlying heterogeneous FLPs catalysts and further understanding of accurate active sites and catalytic mechanisms of heterogeneous FLPs at the molecular level.

Core-Shell Design of Metastable Phase Catalyst Enables Highly-Performance Selective Hydrogenation

Highly selective semihydrogenation of alkynes to alkenes is a highly important reaction for catalytic industry. Developing non-noble metal based catalysts with platinum group metal-like activity and selectivity is extremely crucial yet challenging. Metastable phase catalysts provide a potential candidate to realize high activity, yet the control of selectivity remains an open question. Here, this work first reports a metastable phase core-shell: face-centered cubic (fcc) phase Ag (10 at%) core-metastable hexagonal closest packed (hcp) phase Ni (90 at%) shell catalyst, which represents high conversion rate, high selectivity, and remarkable universality for the semihydrogenation of phenylacetylene and its derivatives. More impressively, a turnover frequency (TOF) value of 8241.8 h-1 is achieved, much higher than those of stable phase catalysts and reported platinum group metal based catalysts. Mechanistic investigation reveals that the surface of hcp Ni becomes more oxidized due to electron transfer from hcp Ni shell to fcc Ag core, which decreases the adsorption capacity of styrene on the metastable phase Ni surface, thus preventing full hydrogenation. This work has gained crucial research significance for the design of high performance metastable phase catalysts.

A high activity mesoporous Pt@KIT-6 nanocomposite for selective hydrogenation of halogenated nitroarenes in a continuous-flow microreactor

In this study, we designed a Pt@KIT-6 nanocomposite prepared by impregnating platinum nanoparticles on the nanopores of the KIT-6 mesoporous material. This Pt@KIT-6 nanocomposite was used as a catalyst in a micro fixed bed reactor (MFBR) for the continuous-flow hydrogenation of halogenated nitroarenes, which demonstrates three advantages. First, the Pt@KIT-6 nanocomposite has a stable mesoporous nanostructure, which effectively enhances the active site and hydrogen adsorption capacity. The uniformly distributed pore structure and large specific surface area were confirmed by electron microscopy and N2 physisorption, respectively. In addition, the aggregation of the loaded metal was avoided, which facilitated the maintenance of high activity and selectivity. The conversion and selectivity reached 99% within 5.0 minutes at room temperature (20 °C). Furthermore, the continuous-flow microreactor allows precise control and timely transfer of the reaction system, reducing the impact of haloid acids. The activity and selectivity of the Pt@KIT-6 nanocomposite showed virtually no degradation after 24 hours of continuous operation of the entire continuous-flow system. Overall, the Pt@KIT-6 nanocomposite showed good catalysis for the hydrogenation of halogenated nitroarenes in the continuous-flow microreactor. This work provides insights into the rational design of a highly active and selective catalyst for selective hydrogenation systems.

Ultrathin Atomic Layer Deposited Al2O3 Overcoat Stabilizes Al2O3-Pt/Ni-Foam Hydrogenation Catalysts

Galvanic exchange seeds the growth of Pt nanostructures on the Ni foam monolith. Subsequent atomic layer deposition of ultrathin Al2O3 followed by annealing under air affords supported Pt catalysts with ultralow loading (0.020 ppm). In addition to the expected enhancement of the stability of the Pt particles on the surface, the ∼2 nm Al2O3 overcoat appears to also play a crucial role in the overall structural integrity of the NiOx nanoplates that grow on the Ni foam surface as a result of the preparative route. The resulting material is physically robust toward repeated handling and showcases retention of catalytic activity over 10 standard catalyst recycling trials, standing in marked contrast to the uncoated samples. Catalyst activity was tested via the hydrogenation of various functionalized styrenes at low temperatures and low hydrogen pressure in ethanol as a solvent, with a TOF as high as 9.5 × 106 h-1 for unfunctionalized styrene. Notably, the catalysts show excellent tolerance toward F, Cl, and Br substituents and no hydrogenation of the aromatic ring.

Co-ligand triphenylphosphine/alkynyl-stabilized undecagold nanocluster with a capped crown structure

We report the synthesis and crystal structure of novel co-ligand phosphine/alkynyl protected Au nanoclusters, with composition [Au11(PPh3)8(C[triple bond, length as m-dash]CPh-CF3)2](SbF6) (1). The gold atoms in the cluster as a capped crown structure subtend C 3v symmetry with one deriving from a central icosahedron and 10 peripheral Au atoms, and all alkynides are exclusively σ coordination bonding. The mean core diameter is about 5.1 Å and the overall van der Waals diameter can be estimated to be 20.5 Å. The optical absorbance of 1 in solution reveals characteristic peaks at 384 and 426 nm and a shoulder between 450 and 550 nm.

Nanozymes with reductase-like activities: antioxidant properties and electrochemical behavior

Nanozymes (NZs) as stable cost-effective mimics of natural enzymes may be promising catalysts in food and environmental biotechnology, biosensors, alternative energy and medicine. The majority of known NZs are mimetics of oxidoreductases, although there are only limited data regarding mimetics of reductases. In the present research, a number of metal-based NZs were synthesized via chemical methods and screened for their antioxidant ability in solution. The most effective reductase-like Zn/Cd/Cu NZ was characterized in detail. Its antioxidant properties in comparison with several food products and Trolox, as well as substrate specificity, size and composition were studied. Zn/Cd/Cu NZ was shown to mimic preferentially selenite reductase. The amperometric sensor was constructed possessing a high sensitivity (1700 A M-1 m-2) and a broad linear range (16-1000 μM) for selenite ions. The possibility to apply the fabricated sensor for selenite determination in commercial mineral water has been demonstrated.