An Intelligent Catalyst: The Self-Regenerative Palladium–Perovskite Catalyst for Automotive Emissions Control

An innovative “intelligent catalyst” that exhibits a greatly improved durability as a result of the self-regenerative function of Pd nanoparticles has been developed. Self-regeneration was realized through a cycle between solid solution and segregation of Pd in a perovskite crystal, without any auxiliary treatment. That is, Pd atoms move back and forth between the inside (as Pd cations in the lattice) and the outside (as Pd nanoparticles) of the perovskite crystal in synchronization with the fluctuations between reductive and oxidative (redox) atmospheres that occur in real automotive exhaust gases. As a result of this cyclic redox reaction, the growth of Pd nanoparticles can be suppressed during the entire lifetime of the vehicle. This self-regenerative function provides a new and useful tool for the development of future automotive catalysts. The mechanism of the self-regenerative function is described, and it is shown by ex situ and in situ X-ray absorption fine-structure spectroscopic analyses that the self-regenerative function occurs at an extremely high speed over a wide range of temperatures. In addition, technical solutions for overcoming the weaknesses of general perovskite catalysts for practical use are described.     

Conditional Copper-Catalyzed Azide–Alkyne Cycloaddition by Catalyst Encapsulation

Supramolecular encapsulation is known to alter chemical properties of guest molecules. We have applied this strategy of molecular encapsulation to temporally control the catalytic activity of a stable copper(I)–carbene catalyst. Encapsulation of the copper(I)–carbene catalyst by the supramolecular host cucurbit[7]uril (CB[7]) resulted in the complete inactivation of a copper-catalyzed alkyne–azide cycloaddition (CuAAC) reaction. The addition of a chemical signal achieved the near instantaneous activation of the catalyst, by releasing the catalyst from the inhibited CB[7] catalyst complex. To broaden the scope of our on-demand CuAAC reaction, we demonstrated the protein labeling of vinculin with the copper(I)–carbene catalyst, to inhibit its activity by encapsulation with CB[7] and to initiate labeling at any moment by adding a specific signal molecule. Ultimately, this strategy allows for temporal control over copper-catalyzed click chemistry, on small molecules as well as protein targets.     

Fine-Tuning Substrate–Catalyst Halogen–Halogen Interactions for Boosting Enantioselectivity in Halogen-Bonding Catalysis

A new approach towards highly enantioselective halogen-bonding catalysis has been developed. To circumvent the intrinsic issues of the nature of the halogen-bond (XB) and the resultant unresolved limitations in asymmetric catalysis, fine-tuned halogen–halogen interactions between the substrate and XB-donor were designed to preorganize the substrate in the catalyst's cavity and boost enantiocontrol. The present strategy exploits both the electron cloud (Lewis base site) and the sigma (σ)-hole site of the halogen substituent of the substrates to form a tight catalyst–substrate–counteranion chiral complex, thus enabling a controlled induction of high levels of chirality transfer. Remarkable enantioselectivities of up to 95 : 5 e.r. (90 % ee) have been achieved in a model dearomatization reaction of halogen-substituted (iso)quinolines with tetrakis-iodotriazole multidentate anion-binding catalysts.     

Methanol Decomposition in a Water–Methanol Equimolar Mixture on a Nickel-Promoted Copper–Zinc–Cement Catalyst

Methanol decomposition in a water–methanol equimolar mixture is studied in the presence of a nickel-promoted copper–zinc–cement catalyst. Methanol decomposition at 200–300°C on the oxide and reduced forms of the catalyst yields a gas with an H₂/CO ratio close to two. The use of an equimolar CH₃OH–H₂O mixture under analogous conditions enables obtaining gaseous products with a hydrogen concentration up to 75 vol %.     

Mapping Catalyst–Solvent Interplay in Competing Carboamination/Cyclopropanation Reactions

Group 9 metals, in particular Rh^III complexes with cyclopentadienyl ligands, are competent C−H activation catalysts. Recently, a Cp*Rh^III-catalyzed reaction of alkenes with N-enoxyphthalimides showed divergent outcome based on the solvent, with carboamination favored in methanol and cyclopropanation in 2,2,2-trifluoroethanol (TFE). Here, we create selectivity and activity maps capable of unravelling the catalyst-solvent interplay on the outcome of these competing reactions by analyzing 42 cyclopentadienyl metal catalysts, Cp^XM^III (M=Co, Rh, Ir). These maps not only can be used to rationalize previously reported experimental results, but also capably predict the behavior of untested catalyst/solvent combinations as well as aid in identifying experimental protocols that simultaneously optimize both catalytic activity and selectivity (solutions in the Pareto front). In this regard, we demonstrate how and why the experimentally employed Cp*Rh^III catalyst represents an ideal choice to invoke a solvent-induced change in reactivity. Additionally, the maps reveal the degree to which even perceived minor changes in the solvent (e. g., replacing methanol with ethanol) influence the ratio of carboamination and cyclopropanation products. Overall, the selectivity and activity maps presented here provide a generalizable tool to create global pictures of anticipated reaction outcome that can be used to develop new experimental protocols spanning metal, ligand, and solvent space.     

Enantioselective Fluorination Reaction of β-Ketoester–Catalyzed Chiral Primary Amine–Based Multifunctional Catalyst Systems

The fluorination reaction is an important organic transformation for asymmetric synthesis. In this article, we reported the determination of chiral primary amine–based multicatalyst systems for enantioselective fluorination of β-ketoester. Studies on the enantioselective organocatalytic fluorination promoted by cinchona alkaloid–derived chiral primary amines in the absence of various co catalysts revealed that the combined metal salts and organocatalysts resulted in poor conversion and enantioselectivities, whereas the combinational use of L-leucine and QN-NH₂ as dual primary amine catalysts led to the determination of a novel dual organocatalyst with promising catalytic activity. On the basis of these results, we revealed that the steric environment of the chiral enamine intermediate formed by the condensation of β-ketoester with the chiral primary amine is most responsible for the observed enantioselectivity.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

The Structure of Oxide Ga–Sb–Ni–P–W–O/SiO2 Catalyst and Its Catalytic Properties in Propane Ammoxidation

The structure of the multicomponent catalyst Ga₁Ni₁P₂W_0.5Sb₆O _x /SiO₂ and its catalytic properties in propane ammoxidation are studied. The catalyst is nanostructured and consists of noncoherently spliced blocks of a multiply promoted phase with a structure of gallium antimonate, which covers SiO₂ particles with a thin layer. In the multiply promoted compound with a structure of gallium antimonate, Ni²⁺ ions partially substitute for Ga³⁺ and W⁶⁺ ions partially substitute for Sb⁵⁺. This leads to an increase in the crystalline lattice parameters a and c. Phosphate ions are stabilized in the region of block interfaces. The catalyst is characterized by high efficiency in propane ammoxidation.     

Enhancing CO2 Electroreduction to Methane with a Cobalt Phthalocyanine and Zinc–Nitrogen–Carbon Tandem Catalyst

Developing copper-free catalysts for CO₂ conversion into hydrocarbons and oxygenates is highly desirable for electrochemical CO₂ reduction reaction (CO₂RR). Herein, we report a cobalt phthalocyanine (CoPc) and zinc–nitrogen–carbon (Zn-N-C) tandem catalyst for CO₂RR to CH₄. This tandem catalyst shows a more than 100 times enhancement of the CH₄/CO production rate ratio compared with CoPc or Zn-N-C alone. Density functional theory (DFT) calculations and electrochemical CO reduction reaction results suggest that CO₂ is first reduced into CO over CoPc and then CO diffuses onto Zn-N-C for further conversion into CH₄ over Zn-N₄ site, decoupling complicated CO₂RR pathway on single active site into a two-step tandem reaction. Moreover, mechanistic analysis indicates that CoPc not only generates CO but also enhances the availability of *H over adjacent N sites in Zn-N₄, which is the key to achieve the high CH₄ production rate and understand the intriguing electrocatalytic behavior which is distinctive to copper-based tandem catalysts.     

Pd Close Coupled Catalyst

Europe III standards require significantly higher emissions reduction, especially for hydrocarbon (HC). For a typical vehicle, a large portion (up to 80 %) of the HC emissions occurs during cold start. A variety of technologies are under development to reduce cold start HC emissions, including close coupled catalysts1; electrically heated catalysts2 and hydrocarbon absorbers3. Among them, the close coupled catalyst gradually dominated the technologies4. A high performance close coupled cat…     

A Homogeneous Chiral Manganese(III)–Salphe Catalyst for Enantioselective Epoxidation of Olefins

A new chiral Mn(III)–Salphe catalyst was synthesized from natural amino acid (R)-phenylalanine and 3,5-di-tert-butyl-hydroxybenzaldehyde and applied to the asymmetric epoxidations of unfunctionalized olefins in ionic liquids. Satisfactory enantioselectivities (79% < ee < 93%) and good yields were achieved when NaClO was used as oxidant. We found that both the pH value (11.3) and reaction temperature (15 °C) were crucial for the epoxidation reactions. In our reaction system, NH₄OAc was unnecessary. We proposed that alcoholic hydroxyls in the Mn(III)–Salphe compound played the role of axial ligand. However, the reaction time was longer than when using Jacobsen's catalyst because of the structure of the Mn(III)–Salphe compound, in which coordination geometries by the two alcoholic hydroxyls with certain angles affected the substrate approaching the Mn(V) = 0 center. The chiral ligand was characterized by the combination of infrared, ultraviolet, and visible spectra and ¹H NMR.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

Recovery and Reduction of Spent Alumina-Supported Cobalt–Molybdenum Oxide Catalyst via Plasma Sintering Technique

A thermal plasma process for the recovery and reduction of the spent alumina-supported cobalt–molybdenum oxide catalyst (Co₃O₄–MoO₂/Al₂O₃) was developed. The spent catalyst was sintered at >1,500 K under plasma condition and the cobalt–molybdenum oxide therein was reduced to cobalt–molybdenum, which was proven by XRD and EDX. By application of SEM and GC technique, the organic tar on the surface of the spent catalyst was found to decomposed and converted to syngas (CO, CO₂, and H₂), which might be the reducing agents in the process. A gasification mechanism for the generation of syngas and the reduction of cobalt–molybdenum oxide under plasma conditions was proposed.     

N2-to-NH3 Conversion by a triphos–Iron Catalyst and Enhanced Turnover under Photolysis

Bridging iron hydrides are proposed to form at the active site of MoFe-nitrogenase during catalytic dinitrogen reduction to ammonia and may be key in the binding and activation of N₂ via reductive elimination of H₂. This possibility inspires the investigation of well-defined molecular iron hydrides as precursors for catalytic N₂-to-NH₃ conversion. Herein, we describe the synthesis and characterization of new P₂^P′PhFe(N₂)(H)_x systems that are active for catalytic N₂-to-NH₃ conversion. Most interestingly, we show that the yields of ammonia can be significantly increased if the catalysis is performed in the presence of mercury lamp irradiation. Evidence is provided to suggest that photo-elimination of H₂ is one means by which the enhanced activity may arise.     

Convenient Method for the Friedel–Crafts Acylation of Benzene Derivatives Using Silver Nitrate as Catalyst

Friedel–Crafts acylation of benzene derivatives such as anisole, toluene, and xylene has been successively carried out using silver nitrate as the catalyst in the presence of an eco friendly solvent (ethyl alcohol). Both benzoyl chloride and acetyl chloride reacted smoothly under the conditions to afford the corresponding ketones in good yield.

Effect of Thermal Treatment on the Structuring of an Iron–Cobalt–Chromium Oxide Catalyst for the Complete Oxidation of Fuel

Catalytic properties and structural aspects of the formation of iron–cobalt–chromium catalysts depending on the temperature of preliminary treatment are studied. A catalytically active iron–cobalt–chromium spinel is formed at a calcination temperature of 580–600°C. If catalytic packings are overheated in the course of hydrocarbon fuel oxidation or if temperatures above 700°C are used for preliminary treatment, the catalytic activity of the samples substantially decreases because an inactive solid solution of iron and chromium oxides with corundum structures is formed.     

A New Reaction-controlled Phase-transfer Catalyst System

A new reaction-controlled phase-transfer catalyst system was designed and synthesized.In this system, heteropolytungstate [C7H7N(CH3)3]9PW9O34 was used for catalytic epoxidation of cyclohexene with H2O2 as the oxidant. The conversion of H2O2 was 100% and the yield of cyclohexene oxide was 87.1% based on cyclohexene. Infrared spectra showed that both fresh catalyst and the recovered catalyst do have completely same absorption peak, indicating the structure of catalyst is very stability and can be recycled.     

Bubbling in Fischer–Tropsch Synthesis with Nanosized Catalyst: a Study Using a Model Slurry Reactor

Bubbling in the liquid phase simulating the reaction medium consisting of molten paraffin and iron-containing nanosized catalyst was studied. An aerator (disperser) for a model bubbling installation with the design and process parameters maximally similar to those of an intended slurry reactor with nanosized iron-containing catalytic suspension for performing Fischer–Tropsch synthesis was chosen.     

Highly Active Heterogeneous PdCl2/MOF Catalyst for Suzuki–Miyaura Cross-Coupling Reactions of Aryl Chloride

The exploration of highly efficient Pd/MOF heterogeneous catalyst system for the Suzuki–Miyaura cross-coupling (SMC) reactions of aryl chlorides is still challenging. Herein, a PdCl₂/UiO-67-bpydc was successfully synthesized by immobilizing a low amount of PdCl₂ onto the zirconium-based MOF (UiO-67-bpydc). PdCl₂/UiO-67-bpydc showed excellent catalytic performance and good recycle ability for the SMC reaction of aryl chlorides under an ambient condition. Furthermore, PdCl₂/UiO-67-bpydc retains the high catalytic activity even after five cycles, and exhibited excellent substrate size selectivity.     

Zinc–Proline Complex: An Efficient,Reusable Catalyst for Direct Nitroaldol Reaction in Aqueous Media

Zinc–proline complex is an effective homogeneous catalyst for the nitroaldol reaction to afford 2‐nitro alcohols in high yields at room temperature in water. The catalyst is reused for several cycles with consistent activity.