Morphology‐Reserved Synthesis of Discrete Nanosheets of CuO@SAPO‐34 and Pore Mouth Catalysis for One‐Pot Oxidation of Cyclohexane

Discrete nanosheets of silicon‐doped AlPO₄ molecular sieves (SAPO‐34) with a thickness of ≈7 nm have been prepared through morphology‐reserved synthesis with a lamellar aluminum phosphate as precursor. Cages of the nanosheets are in situ incorporated with copper oxide clusters. The CuO@SAPO‐34 nanosheets exhibit a large external surface area with a high number of (010) channel pores on the surface. Due to the thin morphology, copper oxide clusters occupy the outmost cages with a probability >50 %. The distinctive configuration facilitates a new concept of pore mouth catalysis, i.e., reactant molecules larger than the pores cannot enter the interior of the molecular sieves but can interact with the CuO clusters at “the mouth” of the pore. In heterogeneous catalysis, CuO@SAPO‐34 nanosheets have shown top performance in one‐pot oxidation of cyclohexane to adipic acid by O₂, a key compound for the manufacture of nylon‐66, which is so far produced using non‐green nitric acid oxidation.     

Platinum clusters supported on/in Dion–Jacobson phase HLaNb<Subscript>2</Subscript>O<Subscript>7</Subscript> by topochemical method

Platinum clusters were supported on/in HLaNb₂O₇ nanosheets by topochemical reaction strategy for the first time. The as-prepared samples were analyzed using ICP OES and characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption isotherms and X-ray photoelectron spectroscopy. The results showed that HLaNb₂O₇ nanosheets were modified with platinum clusters with good monodispersity. The product was a mesoporous solid with broad pore size distribution and large surface area. The oxidation state of platinum was zero and the size of Pt clusters was only about 1–2 nm. This study provides a novel approach to support metal clusters on layered compounds.     

Catalytic CO Oxidation by O2 Mediated by Noble‐Metal‐Free Cluster Anions Cu2VO3–5−

Catalytic CO oxidation by molecular O₂ is an important model reaction in both the condensed phase and gas‐phase studies. Available gas‐phase studies indicate that noble metal is indispensable in catalytic CO oxidation by O₂ under thermal collision conditions. Herein, we identified the first example of noble‐metal‐free heteronuclear oxide cluster catalysts, the copper–vanadium bimetallic oxide clusters Cu₂VO_3–5^? for CO oxidation by O₂. The reactions were characterized by mass spectrometry, photoelectron spectroscopy, and density functional calculations. The dynamic nature of the Cu?Cu unit in terms of the electron storage and release is the driving force to promote CO oxidation and O₂ activation during the catalysis.     

Preparation and electrochemical performance for methanol oxidation of pt/graphene nanocomposites

The composites of graphene nanosheets decorated by Pt nano clusters have been prepared via reduction of graphite oxide and H₂PtCl₆ in one pot. Electrochemical experiments show that the composites have superior catalytic performance toward methanol oxidation indicating the graphene may have a splendid future as catalysts carrier in electrocatalysis and fuel cell.     

Product selectivity in methanol to hydrocarbon conversion for isostructural compositions of AFI and CHA molecular sieves

Isostructural molecular sieves based upon AlPO₄ and SiO₂ chemistry were made for comparison of catalytic selectivity. The AFI and CHA structures were compared with B and Al substitution of SiO₂ and Mg and Si substitution in the AlPO₄ case. The conversion of methanol to hydrocarbons was studied. Materials were characterized for acidity by NH₃ TPD and NH₃ microcalorimetry. Methanol conversion was carried out with products analyzed by GC-MS and spent catalysts by ¹³C MAS NMR. Borosilicate sieves have acidity too low to carry out this catalytic transformation. Other substituting components were successful but product selectivity seemed to be governed by geometric features of the sieves, rather than by variable acidity due to different types of lattice substitution. Products from small pore molecular sieves SAPO-34 and SSZ-13 were largely olefinic and comprised of C₅ and smaller. The large pore sieves, SAPO-5, MAPO-5, and SSZ-24, all produced aromatic-rich products. A considerable quantity of the recovered hydrocarbon was incorporated into penta- and hexamethylbenzene.     

Water-Induced Structural Dynamic Process in Molecular Sieves under Mild Hydrothermal Conditions: Ship-in-a-Bottle Strategy for Acidity Identification and Catalyst Modification

Water is the most important substance in nature. Imitating the formation of natural materials, molecular sieves have been synthesized under hydrothermal conditions and applied in industry. Herein, we reveal an unforeseen observation on a very special water-induced structural dynamic process of these materials. Dynamic and reversible breaking and forming of T-O-T bonds in silicoaluminophosphate (SAPO) occurs through interactions between gaseous water and the molecular-sieve framework under mild hydrothermal conditions and is confirmed by detection of the incorporation of ¹⁷O from H₂¹⁷O into molecular-sieve framework. Encapsulation of the bulky molecules trimethylphosphine and pyridine (kinetic diameters much larger than the pore size of SAPO-34) into CHA cavities consolidated the water-induced dynamic process. Consequently, new insights into the dynamic features of molecular sieves in water are provided. The ship-in-a-bottle strategy based on these findings also open new fields for fine acidity identification and gives extra boost in shape-selective catalysis.     

Copper-cerium oxide catalysts for the selective oxidation of carbon monoxide in hydrogen-containing mixtures: II. Physicochemical characterization of the catalysts

The copper-cerium oxide catalysts were characterized using a set of physicochemical techniques including in situ FTIR spectroscopy, XPS, and XRD. It was found that copper segregated on the surface of cerium oxide and its states were labile and dependent on catalyst pretreatment conditions. Copper in a dispersed state was responsible for the reaction of CO oxidation in the presence of H₂ on the copper-cerium oxide catalysts. It is likely that this state of copper was composed of two-dimensional or three-dimensional surface clusters containing Cu⁺ ions.     

Modification of the adsorption and catalytic properties of micro- and mesoporous materials by reactions with organometallic complexes

This review describes the work of two laboratories in the field of the modification of micro- and mesoporous molecular sieves through reactions with organometallic complexes. The modification of zeolites can occur inside the pore channels or on the external surface, depending on the size of the organometallic complex. When the modification occurs on the external surface, it results in a decrease of the pore entrance, which will lead in turn to a modification of the sorption properties of the zeolite, by decreasing the rate of the adsorption (mainly by a kinetic control). Such a material can be also used in catalysis, because the external acid sites, which are responsible for side-reactions, have been removed upon grafting. When small organometallic complexes are used, they can fill the channels and cages of the zeolite and react with internal hydroxyl groups. Due to the high acidity of zeolites, the reaction occurs very easily (for example at ?100 °C on faujasite), in contrast to what is observed on the external surface, therefore leading to high metal loadings. In that case, the modification of the sorption properties will be mainly related to a thermodynamic control. The resulting materials can be useful in catalysis, by combining the activity of the organometallic complex and properties (for example shape-selectivity) of the zeolite. Modification of mesoporous molecular sieves occurs always in the pores and results in altering of the sorption properties of the solid, by changing the interaction type between the sorbent and the sorbate. For example the sorption isotherm of alkanes is changed from type II to type III according to the IUPAC nomenclature.     

Controllable Synthesis of Mesoporous Iron Oxide Nanoparticle Assemblies for Chemoselective Catalytic Reduction of Nitroarenes

Iron(III) oxide is a low‐cost material with applications ranging from electronics to magnetism, and catalysis. Recent efforts have targeted new nanostructured forms of Fe₂O₃ with high surface area‐to‐volume ratio and large pore volume. Herein, the synthesis of 3D mesoporous networks consisting of 4–5 nm γ‐Fe₂O₃ nanoparticles by a polymer‐assisted aggregating self‐assembly method is reported. Iron oxide assemblies obtained from the hybrid networks after heat treatment have an open‐pore structure with high surface area (up to 167 m² g^?1) and uniform pores (ca. 6.3 nm). The constituent iron oxide nanocrystals can undergo controllable phase transition from γ‐Fe₂O₃ to α‐Fe₂O₃ and to Fe₃O₄ under different annealing conditions while maintaining the 3D structure and open porosity. These new ensemble structures exhibit high catalytic activity and stability for the selective reduction of aryl and alkyl nitro compounds to the corresponding aryl amines and oximes, even in large‐scale synthesis.     

Structural characterisation of heat-treated anodic alumina membranes prepared using a simplified fabrication process

A facile method for forming porous anodic alumina membranes based on one-step anodising in sulphuric acid is reported. A flat and well-ordered basal surface incorporating uniformly sized pores was obtained without the need for electrolytic polishing. Excess metallic aluminium was removed from the film using a saturated solution of iodine in methanol. The high-temperature properties of the oxide ceramic membranes were investigated using thermal analysis, mass spectrometry, X-ray diffraction and solid-state nuclear magnetic resonance. At 970 °C the amorphous alumina crystallises to γ-Al₂O₃ with the release of SO₂ and O₂. Finally at 1228 °C the alumina converts into the thermodynamically preferred phase, corundum. The pore structure of the oxide membrane was found to be very stable at elevated temperatures, suggesting applications in materials synthesis, catalysis and gas separation.     

A Bio‐inspired Cu4O4 Cubane: Effective Molecular Catalysts for Electrocatalytic Water Oxidation in Aqueous Solution

Inspired by the cubic Mn₄CaO₅ cluster of natural oxygen‐evolving complex in Photosystem II, tetrametallic molecular water oxidation catalysts, especially M₄O₄ cubane‐like clusters (M=transition metals), have aroused great interest in developing highly active and robust catalysts for water oxidation. Among these M₄O₄ clusters, however, copper‐based molecular catalysts are poorly understood. Now, bio‐inspired Cu₄O₄ cubanes are presented as effective molecular catalysts for electrocatalytic water oxidation in aqueous solution (pH 12). The exceptional catalytic activity is manifested with a turnover frequency (TOF) of 267 s^?1 for [(L_Gly‐Cu)₄] at 1.70 V and 105 s^?1 for [(L_Glu‐Cu)₄] at 1.56 V. Electrochemical and spectroscopic study revealed a successive two‐electron transfer process in the Cu₄O₄ cubanes to form high‐valent Cu^III and Cu^IIIO^. intermediates during the catalysis.     

New modified electrodes for the separate determination of anionic surfactants

Nylon, chitin, polyvinyl chloride, and polymethyl methacrylate molecular sieves with pores of various size are studied as membrane surface modifiers in electrodes reversible to anionic surfactants. A procedure for the synthesis of molecular sieves with pores of the specified size from water-insoluble polymeric matrix (polyvinyl chloride, polymethyl methacrylate) was developed. Different methods were proposed for modifying the electrode surface. It was demonstrated that modified electrodes provide the separate determination of alky 1 sulfates bearing alkyl radicals of different lengths (C₁₂-C₁₄).     

Synthesis of graphene oxide supported copper–cobalt ferrite material functionalized by arginine amino acid as a new high–performance catalyst

A novel Cu_0.5Co_0.5Fe₂O₄@Arg–GO catalytic system was successfully prepared by immobilization of copper substituted cobalt ferrite nanoparticles on arginine–grafted graphene oxide nanosheets, in which ferrite moiety acts as an oxidation catalyst and arginine has the role of base catalyst. Also, arginine amino acid was used to modify the surface of graphene oxide nanosheets which the prepared support can improve dispersion and uniform loading of nanoparticles. The prepared nanocomposite was characterized by flame atomic absorption spectroscopy (FAAS), inductively coupled plasma optical emission spectrometer (ICP–OES), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT–IR), ultraviolet–visible spectroscopy (UV–vis), Raman spectroscopy, thermogravimetric analysis (TGA), x–ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analysis. The prepared Cu_0.5Co_0.5Fe₂O₄@Arg–GO nanocomposite was used as an efficient catalyst for one–pot tandem oxidative synthesis of 2–phenylbenzimidazole derivatives in good yields.     

Preparation,properties, and catalytic activity of platinum-modified plasma electrolytic oxide structures on aluminum

Catalytically active Pt-containing oxide composites on aluminum have been prepared by plasma electrolytic oxidation (PEO) and by additional modification of the resulting coating by impregnation with an aqueous solution of chloroplatinic acid followed by calcination. The oxide film/metal composites have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy. The modified films contain the γ-Al₂O₃ and Pt crystalline phases. Platinum in the surface and subsurface layers is in the Pt⁰ state. There are platinum-rich areas on the surface of the PEO films. A higher catalytic activity in CO oxidation into CO₂ is shown by the samples whose oxide film contains nickel and copper along with platinum.     

Application of anodic dissolution method for a study of electrocolored aluminum oxides

The anodic dissolution of color carrier of colored aluminum anodic oxide films (AOF) is studied before and after their coloring, using ac in various electrolytes containing Cu(II). The voltammetric polarization curves of anodic dissolution of colored AOF in 0.1 M H₂SO₄ depend on the amount of copper deposited in the pores and its oxidation state (Cu, Cu₂O, CuO). Analytical and X-ray diffraction examination of AOF prior to and after the anodic dissolution shows that the anodic dissolution method is inapplicable for the determination of the oxidation state of copper electrodeposited in AOF pores or the amount of copper oxides.     

Exoemission accompanying electron interactions in complex copper-cerium oxide catalysts and synergism phenomena

The formation of the electronic structure of the surface of complex copper-cerium oxide catalysts with different copper concentrations was studied using the exoemission methods at different stages of preparation. The introduction of copper enhances the emissivity of CeO₂, and the number of charges emitted from the catalyst surface exceeds the emission activity of the starting CeO₂ and NuO components. The synergism phenomenon in exoemission is compared with synergism in the catalysis of CO oxidation by these systems. The problem of electron interactions between the components of the complex oxides is discussed. The electron interactions are caused by the electron transitions at the interface and result in an increase in both the emission of weakly bound electrons and catalytic activity in the oxidation of CO.     

Decomposition of Copper Formate Clusters: Insight into Elementary Steps of Calcination and Carbon Dioxide Activation

The decomposition of copper formate clusters is investigated in the gas phase by infrared multiple photon dissociation of Cu(II)_n(HCO₂)_2n+1⁻, n≤8. In combination with quantum chemical calculations and reactivity measurements using oxygen, elementary steps of the decomposition of copper formate are characterized, which play a key role during calcination as well as for the function of copper hydride based catalysts. The decomposition of larger clusters (n > 2) takes place exclusively by the sequential loss of neutral copper formate units Cu(II)(HCO₂)₂ or Cu(II)₂(HCO₂)₄, leading to clusters with n=1 or n=2. Only for these small clusters, redox reactions are observed as discussed in detail previously, including the formation of formic acid or loss of hydrogen atoms, leading to a variety of Cu(I) complexes. The stoichiometric monovalent copper formate clusters Cu(I)_m(HCO₂)_m+1⁻, (m=1,2) decompose exclusively by decarboxylation, leading towards copper hydrides in oxidation state +I. Copper oxide centers are obtained via reactions of molecular oxygen with copper hydride centers, species containing carbon dioxide radical anions as ligands or a Cu(0) center. However, stoichiometric copper(I) and copper(II) formate Cu(I)(HCO₂)₂⁻ and Cu(II)(HCO₂)₃⁻, respectively, is unreactive towards oxygen.     

Visible-light-sensitive photocatalytic reaction on chromium-containing mesoporous silica: selective partial oxidation of propane with molecular oxygen

The photocatalytic reactivities of chromium-containing mesoporous silica molecular sieves (Cr-HMS) under visible light irradiation have been investigated. Cr-HMS involves tetrahedral chromium oxide (Cr-oxide) moieties which are highly dispersed and incorporated in the framework of molecular sieve with two terminal Cr=O groups. In the presence of propane with molecular oxygen, a partial oxidation proceeded under visible light irradiation to produce acetone and acrolein, with high selectivity, while a complete oxidation proceeded under UV light irradiation mainly to produce CO₂. The charge-transfer excited state of the tetrahedral Cr-oxide moieties plays a significant role in the photocatalytic reactions.     

General routes to porous metal oxides via inorganic and organic templates

The generation of porous metal oxides by removal of template molecules from inorganic polymers formed by sol-gel type hydrolysis and condensation of metal alkoxides is described. The template molecules include organic polymers, copper (II) ions in hybrid copper oxide/silica sols and copper (II) bis(hexafluorocetylacetonate) (hfac). Neutron scattering experiments on the system in which polyacrylic acid (Mw=2,000 Daltons) is used as an organic template to generate microporous tin oxide show that removal of the template generates skeletal voids. In a second series of experiments, mixed copper/silicon oxide xerogels were prepared by hydrolysis of mixtures of Si(OEt)₄ and Cu(OCH₂CH(CH₃)N(CH₃)H)₂ in the ratios of Si:Cu=2:1, 4:1, 9:1. Selective removal (etching) of the copper component generates porous silica. Neutron scattering data and BET surface area measurements are consistent with the creation of pores with molecular dimensions (micropores, 10 Å or less). In the third strategy, Si(OEt)₄ is hydrolyzed in the presence of Cu(hfac)₂, a volatile, inert inorganic template, in a 4 to 1 molar ratio. Removal of the template from the xerogel at 100°C in vacuo affords microporous silica.     

Surfactant‐Free Nonaqueous Synthesis of Plasmonic Molybdenum Oxide Nanosheets with Enhanced Catalytic Activity for Hydrogen Generation from Ammonia Borane under Visible Light

Plasmonic materials have drawn emerging interest, especially in nontraditional semiconductor nanostructures with earth‐abundant elements and low resistive loss. However, the actualization of highly efficient catalysis in plasmonic semiconductor nanostructures is still a challenge, owing to the presence of surface‐capping agents in their synthetic procedures. To fulfill this, a facile non‐aqueous procedure was employed to prepare well‐defined molybdenum oxide nanosheets in the absence of surfactants. The obtained MoO_3‐x nanosheets display intense absorption in a wide range attributed to the localized surface plasmon resonances, which can be tuned from the visible to the near‐infrared region. Herein, we demonstrate that such plasmonic semiconductor nanostructures could be used as highly efficient catalysts that dramatically enhance the hydrogen‐generation activity of ammonia borane under visible light irradiation.