Palladium catalysts deposited on silicon nitride in the deep oxidation of methane

The physicochemical and catalytic properties of palladium catalysts were studied in the deep oxidation of methane. The catalysts were deposited on silicon nitride from aqueous (Pd/Si₃N₄-a) and toluene (Pd/Si₃N₄-t) solutions of palladium acetate. The use of aqueous and organic solutions of palladium acetate, all other preparation conditions being equal, resulted in the formation of palladium systems with different catalytic properties. The sample from Pd/Si₃N₄-t was characterized by high activity and stability. The systems studied had different structures and adsorption properties of palladium nanoparticles, which influenced the form of reagent adsorption, catalytic properties, and mechanism of surface reactions. The suggestion was made that the solvent played a key role in the formation of the active surface of Pd-containing catalytic systems.     

Scientific Grounds for the Application of Mechanochemistry to Catalyst Preparation

It is shown that mechanochemical activation is efficient in creating waste-free energy-saving methods for the preparation of hydride catalysts, heteropoly acid catalysts, and catalysts for hydrocarbon decomposition into hydrogen and carbon materials, as well for the syntheses of earlier unknown catalytic systems. The capabilities of the mechanochemical methods are demonstrated on modifying the catalytic properties of catalysts and supports: an increase in the strength and catalytic activity, sorption properties, etc. Adhesion theory applied to melts helps to describe the mechanism of mechanochemical synthesis of catalytic systems.     

Phase composition,physicochemical and catalytic properties of cobalt–aluminum–zeolite systems

The phase composition and physicochemical and catalytic properties of three samples of cobalt–aluminum–zeolite systems were studied. The catalytic properties of the systems are related to the application of a highly porous acidic support and the presence of cobalt oxide crystallites of an optimal size (6–12 nm). The occurrence of an efficient heat-conductive spatial net formed by metallic aluminum particles is also important for catalytic performance.     

Effect of the Nature of the Carrier in Cobalt Containing Oxide Systems in the Selective Reduction of NO with Methane

The catalytic properties of cobalt containing samples based on zirconium dioxide, aluminum oxide, and the binary systems ZrO₂-Al₂O₃ and ZrO₂-zeolite in the selective reduction of NO with methane have been studied. The catalytic activity of the binary systems ZrO₂-zeolite are non-additive with respect to the composition of the carrier.     

Effect of Preparation Conditions of Zeolites Cu/ZSM-5 and Cu/Erionite on Their Catalytic Activity in Co Oxidation

The catalytic properties of Cu/ZSM-5 and Cu/erionite in the oxidation of carbon monoxide were studied. After treatment in a hydrogen stream, these copper zeolite catalysts displayed higher catalytic activity than prior to treatment. Variation of the catalytic properties of the systems obtained was attributed to differences in the state of the copper ions.     

Nickel- and cobalt-based heterogeneous catalytic systems for selective primary amination of alcohol with ammonia

It is one of the critical fields of green chemistry to catalyze the selective conversion of biomass-derived alcohol and ammonia to primary amines with extensive application. Recently, catalytic systems consisting of non-noble metal nickel- and cobalt-based catalysts have been developed for catalytic alcohol amination. This paper reviewed these two types of catalytic systems, which are classified as skeleton Co and Ni catalytic systems, supported and modified Co and Ni catalytic systems, emphasized on catalysts and catalysis, and clearly explained where zero-valent cobalt or nickel is active species for catalytic reaction. In supported catalysts, the catalytic active sites constituted by the catalytic active species and its micro-environment can regulate the efficiency of catalytic the reaction. While in modified catalysts, modifiers such as metal Fe, Re and Bi may modulate the catalytic active sites and change the catalytic selectivity. There are differences in structure and size between catalysts prepared by different methods, resulting in distinct interface and electronic properties for alcohol amination, which determines the structure–activity relationships of the catalytic system.     

Dependence of the Physicochemical and Catalytic Properties of Ce<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>O<Subscript>2</Subscript> Oxide on the Means of Synthesis

The effect the means of synthesis have on the texture, phase composition, redox properties, and catalytic activity of binary oxide systems with the composition Ce_0.5Zr_0.5O₂ are studied. The obtained samples are characterized via BET, SEM, DTA, XRD, and Raman spectroscopy. A comparative analysis is performed of the physicochemical properties of biomorphic systems Ce_0.5Zr_0.5O₂ obtained using wood sawdust and cellulose as templates and the properties of binary oxides of the same composition obtained by template-free means. The catalytic properties of the obtained oxide systems Ce_0.5Zr_0.5O₂ are studied in the reaction of carbon black oxidation. It is shown that the texture of the oxide depends on the means of synthesis. When biotemplates are used, fragile porous systems form from thin binary oxide plates containing micro-, meso-, and macropores. Oxide obtained via coprecipitation consists of dense agglomerates with pores around 30 Å in size. In supercritical water, nanoparticles of metal oxide form that are loosely agglomerated. The intermediate spaces between them act as pores more than 100 Å in size. A system of single-phase pseudocubic modification is obtained using a cellulose template. The crystal lattices of all the obtained systems contain a great many defects. It is shown that the system prepared via synthesis in supercritical water has the best oxygen-exchange properties. A comparative analysis is performed of the effect the physicochemical properties of the samples have on their activity in the catalytic oxidation of carbon black.     

Effect of the Composition of Silver Doped M-Si Oxide Systems (M: Mg,Zr, La) on their Catalytic Properties in the Conversion of Ethanol to 1,3-Butadiene

Theoretical and Experimental Chemistry - The effect of the acid–base characteristics of M-Si oxide systems (M: Mg, Zr, La), including those doped with silver, on their catalytic properties...     

Dependence of CO oxidation on Pt nanoparticle shape: a shape‐selective approach to the synthesis of PEMFC catalysts

In real catalyst systems, it is difficult to establish a correlation between catalytic properties and the shape (crystal planes, corners and steps) of the active catalytic particles. In this paper we present a clear shape dependence of the catalytic properties of a Vulcan‐supported fuel cell catalyst having 4 nm cubo‐octahedral platinum(0) nanocrystallites with (111) and (100) surfaces stabilized by sodium polyacrylate. The electrode materials were characterized by CO‐stripping cyclic voltammetry and transmission electron microscopy (TEM), showing that no agglomeration had occurred among the nanoparticles on the catalyst surfaces. Copyright © 2007 John Wiley & Sons, Ltd.     

Controlled synthesis of Bi- and tri-nuclear Cu-oxo nanoclusters on metal–organic frameworks and the structure–reactivity correlations

Precisely tuning the nuclearity of supported metal nanoclusters is pivotal for designing more superior catalytic systems, but it remains practically challenging. By utilising the chemical and molecular specificity of UiO-66-NH₂ (a Zr-based metal–organic framework), we report the controlled synthesis of supported bi- and trinuclear Cu-oxo nanoclusters on the Zr₆O₄ nodal centres of UiO-66-NH₂. We revealed the interplay between the surface structures of the active sites, adsorption configurations, catalytic reactivities and associated reaction energetics of structurally related Cu-based ‘single atoms’ and bi- and trinuclear species over our model photocatalytic formic acid reforming reaction. This work will offer practical insight that fills the critical knowledge gap in the design and engineering of new-generation atomic and nanocluster catalysts. The precise control of the structure and surface sensitivities is important as it can effectively lead to more reactive and selective catalytic systems. The supported bi- and trinuclear Cu-oxo nanoclusters exhibit notably different catalytic properties compared with the mononuclear ‘Cu₁’ analogue, which provides critical insight for the engineering of more superior catalytic systems.

The controlled synthesis of novel bi- and trinuclear Cu-oxo nanoclusters supported on UiO-66-NH₂ that show notably different catalytic properties in the photocatalytic formic acid decomposition reaction is reported.     

Hydroformylation of olefins in the presence of rhodium carbonyl catalysts immobilized on polymeric pyrrolidinopyridines

The hydroformylation of olefins in the presence of catalytic systems based on RhCl₃ and polymeric pyrrolidinopyridines was studied. lt was shown that the catalytic system has high activity in the hydroformylation of isobutylene under conditions when the activity of conventional homogeneous catalysts is low. The polymeric catalysts are also thermostable. The effect of solvents on the catalytic properties of the system was studied.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 7, pp. 1673–1675, July, 1996.     

Synthesis and characterization of SAPO-11 molecular sieves from alcoholic systems

Summary SAPO-11 molecular sieves were synthesized from aqueous and nonaqueous systems by using different alcoholic solvents and their physicochemical properties were compared. The SAPO-11 samples synthesized from alcoholic systems had larger external surface area, higher Si contents and higher acidity than those of the sample synthesized from the aqueous system. Thereby, loaded with 0.5 wt.%Pt, the resulting Pt/SAPO-11 catalysts synthesized from alcoholic systems exhibited higher catalytic activities and selectivity for n-dodecane hydyroisomerization. Among the catalysts synthesized from alcoholic systems, the Pt/SAPO-11 catalyst synthesized from polybasic alcohol systems possessed the highest catalytic activities.     

Catalytic decomposition of cyclohexanol over molybdena doped ceria catalysts

Summary Molybdena modified pure as well as sulfated ceria systems have been studied with a view to investigate their structure, surface acidic properties and catalytic behavior for cyclohexanol decomposition reaction. The characteristics of the modified systems were obtained from XRD measurements and acid structural properties from Temperature Programmed Desorption (TPD) of ammonia.     

Adsorption and catalytic properties of enzymes on the surface of silicalite-1

Microporous hydrophobic silicalite-1 was used as a carrier for immobilization of different enzymes, such as horseradish peroxidase, calf intestinal alkaline phosphatase and two β-galactosidases of different origin, to create heterogeneous biocatalytic systems. The peculiarities of enzyme adsorption on the surface of silicalite-1, as well as catalytic properties of the obtained systems compared to enzyme activity in solution and on the surface of other carriers, are discussed.     

Detonation nanodiamonds as catalysts of steam reforming of ethanol

Physicochemical properties and catalytic performance of detonation nanodiamonds were studied. Original samples of nanodiamonds and nanodiamonds modified by hydrogen, oxygen, and nitric acid with hydrogen peroxide and infrared-treated were investigated. The catalyst structure and morphology were examined by transmission electron microscopy and IR spectroscopy. All the investigated catalysts were active in the steam reforming of ethanol. The correlation of catalytic properties with composition and structure of the described systems is discussed. The specific surface area of nanodiamonds is changed insignificantly upon modification.     

Ion-exchange resin catalysts in the liquid-phase hydrazinolysis of cinnamic acid

The catalytic activity of a synthetic ion-exchange resins has been studied in the reaction of cinnamic acid with hydrazine (aqueous medium, 363 K, 1.0–2.5 h) yielding the corresponding hydrazide. Efficient catalysts for the process are the anion-exchange resins AV-17-8 and AN-31. The modifying effect of the substrate—hydrazine hydrate—on the catalytic properties of the ion-exchange systems has been demonstrated. On the basis of IR spectroscopic studies, a plausible process mechanism was suggested. It involves polymer-bound quaternary ammonium ions of the anion exchanger.     

Gas phase metal cluster model systems for heterogeneous catalysis

Since the advent of intense cluster sources, physical and chemical properties of isolated metal clusters are an active field of research. In particular, gas phase metal clusters represent ideal model systems to gain molecular level insight into the energetics and kinetics of metal-mediated catalytic reactions. Here we summarize experimental reactivity studies as well as investigations of thermal catalytic reaction cycles on small gas phase metal clusters, mostly in relation to the surprising catalytic activity of nanoscale gold particles. A particular emphasis is put on the importance of conceptual insights gained through the study of gas phase model systems. Based on these concepts future perspectives are formulated in terms of variation and optimization of catalytic materials e.g. by utilization of bimetals and metal oxides. Furthermore, the future potential of bio-inspired catalytic material systems are highlighted and technical developments are discussed.     

An in-depth study of supported In2O3 catalysts for the selective catalytic reduction of NOx: the influence of the oxide support

The influence of the oxide support (i.e., Al2O3, Nb2O5, SiO2, and TiO2,) on the surface properties, reduction and oxidation properties, acid-base properties, and catalytic activity of supported indium oxide catalysts has been investigated by temperature-programmed reduction/oxidation, thermogravimetry coupled to differential scanning calorimetry, ammonia and sulfur dioxide adsorption calorimetry, and reduction of NOx by ethene in highly oxygen-rich atmosphere. Two series of In2O3-containing catalysts at low (approximately 3 wt %) and at theoretical geometric monolayer (from 20 to 40 wt %) In2O3 content were prepared and their properties were compared with unsupported In2O3 material. Supports able to disperse the In2O3 aggregates with high In stabilization gave rise to active catalytic systems. Among the studied oxide supports, Al2O3 and, to a lower extent, TiO2 were found to be the best supports for obtaining active de-NOx catalysts.     

Polymerization of ethylene in the presence of novel single-site titanium phenolate catalytic systems

The polymerization of ethylene has been studied in the presence of novel catalytic systems based on various sterically hindered phenol precursor complexes of titanium containing grafted phenoxyammonium ligands. The presence of the grafted ammonium salt in the phenolate ligand leads to an increase in the activity of the catalyst and originates single-site catalytic systems. As evidenced by IR and ¹³C NMR studies and DSC measurements, the resulting polymers are linear, possess a narrow molecular-mass distribution (M _w/M _n = 2–4), and are characterized by a wide range of thermal properties.     

Tandem catalysis of one metallocene catalyst combined with two different cocatalysts for preparing branched polyethylene

Tandem catalytic systems, consisting of ethylene bis(indenyl) zirconium dichloride with two different cocatalysts, alkylaluminum(diethylaluminium chloride or trialkylaluminum) and methylaluminoxane, were employed in preparing branched polyethylene from ethylene as sole monomer. The catalytic system rac-Et(Ind)2Zr Cl2/Al Et2Cl/MAO exhibited high incorporation(29.0/1000C). The oligomerization and copolymerization reaction conditions in the tandem catalytic system, as well as the different cocatalysts, have effects on the catalytic activity and the properties of the obtained polymer, such as melting temperature, crystallinity, molecular weight and molecular weight distribution. Moreover, the oligomerization reaction condition is the main factor in altering the properties and structures of polyethylene.