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The present work is focused on designing of ceria-supported Pt–Ag bimetallic catalysts for 4-nitrophenol reduction with NaBH4. The series of ceria-supported monometallic (Pt or Ag) and bimetallic Pt-Ag catalysts are prepared by wetness impregnation followed by calcination in air at 500 °С. The bimetallic 2-xPtxAg/CeO2 samples with a total metal loading of 2.0 wt% and Pt:Ag mass ratios of 1.5:0.5, 1:1, and 0.5:1.5 show superior activity caused by the formation of bimetallic Pt–Ag species upon simultaneous reduction of highly dispersed interplaying PtOx and silver species. The Ag addition to Pt and the conditions of the bimetallic catalyst treatment ensure the fine-tuning of the metal–support interactions and enhance the catalyst activity. The optimal Pt:Ag ratio in the bimetallic Pt-Ag catalysts depends on the sample pretreatment affecting the composition and dispersion of the surface Pt–Ag species formed. For samples calcined in air at 500 °С for 2 h and reduced with NaBH4 in the reaction mixture, the highest activity is achieved for the 1Pt1Ag/CeO2 catalyst characterized by the complete 4-NP conversion at 23 °С in 3 min with an apparent rate constant kapp of 2.3 × 10−2 s−1 and a specific rate constant kMe of 223,500 s−1 mol−1. For the air-calcined samples pre-reduced in H2/Ar at 300 °С for 30 min, the highest activity is achieved in case of 0.5Pt1.5Ag/CeO2 catalyst characterized by 94% 4-NP conversion at 23 °С in 3 min with the kapp of 1.6 × 10−2 s−1 and the kMe of 152,100 s−1 mol−1.

Ag/MCM-41 catalyst is prepared by impregnation technique and characterized by low-temperature N2 sorption, XRD, TPR and TEM methods. The ordered structure of mesoporous silicate MCM-41 is used as a nanoreactor to synthesize and stabilize small Ag nanoparticles. Two types of Ag particles are shown to form in Ag/MCM-41 catalyst: ultrasmall ( 98%) to 217 °C (conversion of propylene

The exhaust gases from motor vehicles contain unburned soot particles that pollute the environment and have a detrimental effect on the human health. The solution to this problem requires the development of new highly efficient Pt- and Pd-less catalysts for the oxidation of soot in exhaust gases. In the present work, the catalysts based on the Ag–CeO2 composition were synthesized by two techniques (co-precipitation and incipient wetness impregnation) and characterized by a complex of physicochemical methods (low-temperature nitrogen adsorption, powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (TEM HR) and temperature-programmed oxidation (TPO)). The catalytic properties of the catalysts were studied in the reaction of soot oxidation. It was shown that the Ag–CeO2 catalyst prepared by the coprecipitation method was the most active in soot oxidation. The increased activity of the catalyst was associated with the formation of a complex structure, representing an agglomerate of strongly interacting silver and ceria particles, which significant affect the low-temperature activation of oxygen on the catalyst surface as shown by the TPO method.

In this work, a series of Cu- and/or Zn-modified alumina-supported CrOx catalysts have been synthesized by wetness impregnation method and characterized using the combined techniques, including Raman spectroscopy, UV–vis DR, XRD, XRF, H2-TPR and low-temperature N2 sorption, to reveal the effect of the modifiers on the catalyst performance in a fixed-bed isobutane dehydrogenation into isobutylene. The Zn-based modifier is shown to decrease the reducibility of the supported chromium species and reduce the stability of the redox ones, which results in the decreased catalyst activity in isobutane dehydrogenation. The Cu-based modifier on the contrary facilitates the formation of high amount of redox chromium species that leads to the activity growth. The modification by both Cu- and Zn-based modifiers provides an enhanced catalyst performance caused by the synergistic effect of the modifiers and chromium species. The incorporation of the modifiers into alumina support facilitates the formation of the surface defective spinel phases that prevent the incorporation of chromium into the alumina surface and establish the conditions to form the high amount of the active redox chromium species.

The article deals with the synthesis of mesoporous ordered material MCM-41 from sodium silicate. The series of MCM-41 materials are prepared from industrial sodium silicate using cetyltrimethylammonium bromide (CTAB) as a template and characterized by N2 physisorption and small-angle X-Ray scattering. The MCM-41 sample prepared from the sodium silicate is characterized by high values of specific surface area (1118–1513 m2/g), pore volumes (0.81–0.96 cm3/g), and a well-ordered structure. It was found that the primary assembly of the ordered MCM-41 structure occurs in the solution at room temperature and the MCM-41 may be prepared from the sodium silicate even without hydrothermal treatment. The MCM-41 with a well-ordered structure and a narrow pore size distribution may be synthesized even at a very low CTAB/Si ratio of 0.025–0.125. The MCM-41 prepared from the sodium silicate is stable up to 700 °C and the specific surface area and pore volume were decreased only after the calcination at 800 °C. Thus, the MCM-41 synthesized from the sodium silicate at low CTAB/Si ratio is a promising cheap material for sorption, catalysis and other applications.

The series of catalysts representing the mesoporous ordered silica SBA-15 with supported silver or silver and ceria nanoparticles were synthesized by incipient wetness impregnation, characterized by the low-temperature N2 adsorption, XRD, TEM HR, TPR-H2 methods, and tested in the low-temperature CO oxidation and total oxidation of methanol. It was found that two types of silver particles are formed: small particles (

The influence of porous structure and addition of citric acid on the formation of ceria particles inside the SBA-15 pores is studied using nitrogen adsorption-desorption at −196 °C, XRD, UV-visible spectroscopy, TEM and TPR-H2 methods. The use of pores of SBA-15 as nanoreactors provides the formation of CeO2 nanoparticles with sizes below 6 nm. According to XRD and TEM results, the addition of citric acid during the impregnation allows obtaining the CeO2 particles with sizes about 3 nm, while the agglomerates of large СеО2 particles are formed on the surface of the SBA-15, when citric acid is not added. Small sizes of ceria particles (3 nm) cause an enhanced reducibility (TPR-H2), high defectiveness of the particles and red shift in the UV-vis adsorption spectra. These properties may improve the catalytic and photocatalytic activity of the CeO2/SBA-15-based catalysts in deep and selective oxidation of organic compounds.

The combination of metal–organic frameworks (MOFs) possessing porosity and catalytic activity with plasmonic nanoparticles (PNPs) defines a new paradigm in photocatalytic degradation of ecotoxicants. Herein, we designed a novel composite derived from a polyethylene terephthalate (PET) waste, MOF – UiO-66, and silver nanoparticles (AgNPs) to degrade paraoxon as a nerve agent simulant under plasmon excitation. The prepared material was characterized by spectroscopic: XRD, UV–Vis, FT-IR, XPS, microscopic: SEM (EDX), TEM and ICP-MS, TGA, BET analysis, and NH3 TPD techniques. We found the balance between pore availability of UiO-66 for paraoxon adsorption, plasmonic enhancement, and the cost of the final composite. In the case of PET@UiO-66-Ag25, paraoxon is degraded for 1 h with ∼ 95 % efficiency under 455 nm. The synergetic degradation mechanism of UiO-66 and AgNPs was proved by experiments with different wavelengths of illumination, PET@Ag, and control reaction of Fisher esterification. The synergetic effect is explained by weakening the chemical bonds in the transition state between the Zr site (Lewis’s acid centers) and paraoxon via plasmon excitation and energy transfer. Moreover, PET@UiO-66-Ag25 is overperforming other materials in terms of environmental impact, easiness of preparation, visible light usage, high apparent quantum yield, and recycling performance.

As a typical volatile organic compound, toluene is a hazardous material for human health and the environment, and currently, the development of catalysts for its oxidation into CO2 and water is crucial. The series of Ag-CeO2/SBA-15 catalysts is synthesized by wetness impregnation techniques and characterized by a number of physical-chemical methods (nitrogen [N2] physisorption, small angle X-ray scattering [SAXS], transmission electron microscopy [TEM], and temperature-programmed reduction [TPR]). The toluene sorption and catalytic properties in toluene oxidation are studied. Small silver [Ag] and cerium oxide [ceria, CeO2] particles with sizes below 3 nm are predominantly formed in the ordered structure of Santa Barbara Amorphous-15 [SBA-15]. The interactions between the Ag and CeO2 nanoparticles are established. Temperature-programmed desorption of toluene [TPD-C7H8] analysis shows that physical adsorption of toluene occurs on pristine SBA-15 material, while the introduction of either silver or ceria to SBA-15 leads to the appearance of additional strongly bound chemisorbed toluene on such sites. When both Ag and CeO2 are introduced, only chemisorbed toluene is formed over the Ag-CeO2/SBA-15 catalyst, and the highest catalytic activity in toluene oxidation is observed over this catalyst (T98% = 233 °C, 0.2% C6H5CH3) that is attributed to the synergistic effect of ceria [CeO2] and silver [Ag].

The catalytic activity of the SBA-15-supported silver and/or ceria catalysts in the 4‑nitrophenol reduction under mild conditions is described. The catalysts are prepared by wetness impregnation of Pluronic P123@SBA-15 hybrid applied to stabilize small Ag and CeO2 particles. The bare SBA-15 and the catalysts on the basis thereof are characterized by N2 sorption, XRD, SAXS, TEM, UV–vis DRS, and H2-TPR. The catalysts possess high surface area (594−754 m2/g) and narrow pore size distributions (5.5–7.8 nm). Silver and ceria particles are stabilized in a highly dispersed state (predominant sizes below 5 nm) in the ordered SBA-15 structure. The Ag–CeO2/SBA-15 catalyst demonstrates the presence of the developed Ag–CeO2 interface that enhances the catalytic activity in 4-nitrophenol reduction to 4‑aminophenol (k = 0.016 s−1) at room temperature and ambient pressure due to the cooperation of silver and ceria active sites.

Two series of chromium–zirconium mixed oxide catalysts with different Cr/Zr molar ratio are prepared by co-precipitation method. Porous structure of the catalysts is studied by low-temperature N2 adsorption–desorption. Phase composition and chromium states in the catalysts are characterized by X-ray diffraction (XRD), UV-visible spectroscopy, and temperature-programmed reduction with hydrogen (TPR-H2). The mixed catalysts are tested in non-oxidative dehydrogenation of propane at 550 °C. The catalysts synthesized without ageing of precipitate show higher activity in propane dehydrogenation due to the higher content of reducible Cr+5/+6 species due to its stabilization on the ZrO2 surface.

The peculiarities of active surface formation and the effect of Cu modifier on the performance of CrOx/Al2O3 catalysts in a fixed-bed isobutane dehydrogenation into isobutylene are considered using a series of model Cu-modified alumina supports (0.7–6.5% wt Cu) and CrOx catalysts on the basis thereof. The samples are characterized using a complex of physical-chemical methods, including low-temperature N2 adsorption, STA, XRF, XRD, UV–vis DR, Raman spectroscopy and H2-TPR. The modification of the alumina-chromia catalysts by a proper amount of copper is shown to enhance the catalyst activity. The catalyst with 2.6% wt Cu shows high conversion and selectivity towards isobutylene. The role of Cu modifier is connected with stabilizing of the active component mostly as monomeric and dimeric Cr(VI) species that can be reduced into the most active mononuclear and dimeric Cr3+ sites.

Ag/CeO2 catalysts with a silver loading of 10 wt.% have been prepared by three different techniques: impregnation, Ag/CeO2 (imp), impregnation of prereduced CeO2, Ag/CeO2 (red-imp), and co-deposition precipitation, Ag-CeO2 (co-DP). The features of the prepared composites have been studied by low-temperature N2 sorption, TGA, XRF, TPR-H2, TEM HR, XPS and Raman spectroscopy. The Raman and XPS results show that the addition of silver to CeO2 significantly increases the defectiveness of CeO2 particles, and such an effect is a function of the preparation method. The Ag-CeO2 (co-DP) and Ag/CeO2 (red-imp) catalysts show enhanced interfacial Ag–CeO2 interaction caused by the epitaxial growth of silver particles (d111 = 2.35 A) on the CeO2 surface (d111 = 3.1 A) as well as high amount of oxygen vacancies. A morphology-dependent interplay between the oxygen vacancies and the strength of the Ag–CeO2 interaction has been revealed. Strengthening of the metal–support interaction enhances the catalytic activity of the composites in both CO oxidation and soot combustion.

Olefin hydrocarbons are valuable raw materials for petrochemical and polymer manufacturing. Highly effective, but toxic chromium-containing catalytic materials are the most widely used catalysts to obtain olefins in industry. In this regard, the urgent challenge to increase the efficiency of oil processing is to develop the catalysts with low content of harmful active component. In the present study, the catalysts with low chromium content (1 theoretical monolayer = 5 Cr atoms per nm2 of support) were synthesized by incipient wetness impregnation of the supports (Al2O3, ZrO2, CeO2, and CexZr(1–x)O2). The samples obtained were characterized by low-temperature nitrogen adsorption, X-ray diffraction and H2-temperature-programmed reduction methods. The catalytic properties of the catalysts were tested in isobutane dehydrogenation reaction. It was shown that the state of chromium on the surface is different over different supports. For the CrOx/CeO2 catalyst, the formation of Cr2O3 particles with low activity in the dehydrogenation reaction was observed. For other samples, a highly disperse X-ray amorphous state of chromium was characteristic. The catalyst based on CexZr(1–x)O2 was the most active in isobutane dehydrogenation reaction due to possible stabilization of chromium as Cr(V) state.

Combined application of TPx methods, H-2-O-2 titration, UV-vis DRS, TGA-DSC-MS, TEM, XRD, N-2 adsorption at -196 degrees C allowed proving the OH/Ag molar ratio as the key parameter defining the catalytic properties of silica-supported silver (Ag/SiO2) in low-temperature CO oxidation. A new insight into the. formation of active species on the catalyst surface is presented. In this study, Ag/SiO2 catalysts with Ag loading of 5 and 8 wt.% were prepared by incipient wetness impregnation method on the basis of commercial silicas preliminary calcined at 500, 700 and 900 degrees C. Detailed characterization of catalysts by physicochemical methods revealed that molar ratio between the concentration of surface OH groups (normalized to support mass) and silver amount in the prepared catalysts (OH/Ag ratio) affects the silver dispersion, structure of silver nanoparticles (NPs) and their catalytic properties. Only at optimal value of OH/Ag ratio the silver NPs are stated to possess both high dispersion and defective multidomain structure (that consists of several nanodomains) providing the adsorption of weakly bound oxygen species responsible for high catalytic activity in CO oxidation at low -temperature. Additionally, the co-existence of two types of active sites reacting with CO at room temperature with and without formation of adsorbed carbonate species is discussed. The first type of active sites was catalytically active in low-temperature CO oxidation with CO2 release at room temperature (RT). The second type may retain surface carbonate species up to similar to 40-50 degrees C. The balance between these species shifts towards the first type for the active catalyst.

The paper is focused on the Fe for Co substitution effect on the redox and catalytic properties in the perovskite structure of GdFeO3. The solid oxides with the composition GdFe1−xCoxO3 (x = 0; 0.2; 0.5; 0.8; 1) were obtained by the sol-gel method and characterized by various methods: X-ray diffraction (XRD), temperature-programmed reduction (H2-TPR), N2 sorption, temperature-programmed desorption of oxygen (TPD-O2), simultaneous thermal analysis (STA), and X-ray photoelectron spectroscopy (XPS). The H2-TPR results showed that an increase in the cobalt content in the GdFe1−xCoxO3 (x = 0; 0.2; 0.5; 0.8; 1) leads to a decrease in the reduction temperature. Using the TPD-O2 and STA methods, the lattice oxygen mobility is increasing in the course of the substitution of Fe for Co. Thus, the Fe substitution in the perovskite leads to an improvement in the oxygen reaction ability. Experiments on the soot oxidation reveal that catalytic oxidation ability increases in the series: GdFe0.5Co0.5O3 ˂ GdFe0.2Co0.8O3 ˂ GdCoO3, which is in good correlation with the increasing oxygen mobility according to H2-TPR, TPD-O2, and STA results. The soot oxidation over GdFeO3 and GdFe0.8Co0.2O3 is not in this range due to the impurities of iron oxides and higher specific surface area.

The Pt–CeO2-based composites have brought about a vivid research interest due to their use in advanced combustion engines, proton-exchange membrane fuel cells, etc. Complementing features of Pt and ceria particles cause numerous applications of such composites in environmental catalysis science and technology. The present review summarizes recent advances in Pt–CeO2 chemistry and discusses the following key aspects: (1) catalyst preparation, including Pt and Ce-MOF-derived precursors, and treatment methods, (2) Pt-related factors: size, including single-atom formulations, and state, (3) CeO2-related factors: morphology, surface defects, and derived features, (4) modification of catalyst composition, including the formation of bimetallic particles, (5) nature and structure of active sites, (6) features of metal–support interaction. The range of covered environmental catalytic applications includes oxidation processes (CO oxidation, VOCs abatement, soot oxidation, combustion of vehicle exhausts, etc.), reduction of nitroaromatics, CO2 utilization (dry reforming of alkanes, CO2 reduction, etc.), and photocatalytic reactions.

Pd–Ag nanoparticles with different Pd/Ag ratio were deposited onto fiber glass by using the technique of surface self-propagating thermal synthesis (SSTS) and characterized by X-ray photoelectron spectroscopy (XPS), atomic absorption spectroscopy (ААS), and EXAFS spectroscopy. The samples reduced in hydrogen exhibited the formation of Pd–Ag alloy whose tentative structure and composition were suggested. Thermally scheduled reduction of Pd–Ag catalysts in hydrogen made the Ag atoms partially oxidized. Reported are the catalytic properties of synthesized Pd–Ag samples in selective hydrogenation of acetylene.

The silver-modified cryptomelane-type crystalline and silica-supported OMS-2 catalysts (Ag/OMS-2 and Ag/OMS-2/SiO 2 , respectively) were prepared by impregnation, co-precipitation, and consecutive impregnation methods and tested in selective oxidation of ethanol to acetaldehyde. Modifying OMS-2 and OMS-2/SiO 2 catalysts by silver was shown to improve the redox properties of the catalysts and increase the ethanol oxidation rate. However, selectivity to acetaldehyde decreased with increased reaction temperature due to intensification of total oxidation on the Ag-MnO x sites. Preparation method of the catalyst affected the Ag localization and catalytic activity. Introducing silver into the OMS-2 channels provided a higher ethanol oxidation rate. The use of silica support for Ag/OMS-2 composites improved the selectivity towards acetaldehyde at higher temperatures and, therefore, increased the acetaldehyde yield in comparison with crystalline samples.

Silver supported on silica, prepared by impregnation method, was investigated using TEM, XRD, UV–vis spectroscopy, TPO, H 2 TPR and CO TPR methods, and tested in low-temperature CO oxidation. To reveal the role of metal-support interaction, the Ag catalysts based on silica, pre-treated at 500 (SiO 2 -500) and 900 °C (SiO 2 -900), were compared. Highly dispersed silver particles (1–4 nm) were observed for both Ag/SiO 2 -500 and Ag/SiO 2 -900 catalysts. The highest amount of active oxidative species was determined for Ag/SiO 2 -900 catalysts using TPx methods. The high temperature (900 °C) pretreatment of silica support is found favorable for formation of silver species active in O 2 and CO activation and leads to increasing of catalytic activity in CO oxidation. The defect structure of Ag nanoparticles is a possible reason for high activity in low-temperature CO oxidation.

This work aims to further the understanding of gold-based catalytic oxidation of n-octanol in liquid phase. Modification of catalysts with metal oxides additives (Fe or Mg) was used as a tool for transforming and stabilizing gold species. Structural, electronic and catalytic properties of gold catalysts were systematically investigated by means of DRS, H2, CO FTIR, SBET, EDS and SEM, HRTEM, SR-XRD, XANES, XPS and liquid phase n-octanol oxidation. Addition of modifiers affects Au electronic properties, but not the structural ones. Characterization results allow excluding Au3+ ions as candidates for active sites in n-octanol oxidation. In Au/Mg/TiO2, gold exhibited more reduced states while in Au/Fe/TiO2 gold was more oxidized; Au/TiO2 for intermediate oxidized states was found. The proper balance of oxidation states in the gold surface of Au/Mg/TiO2 can be responsible for its higher activity compared with Au/Fe/TiO2 and Au/TiO2 towards n-octanol oxidation. Finally our approach shed light on the nature of active sites for n-octanol oxidation on gold and furthers the development of green base-free catalytic oxidation of alcohols.

The effect of the support nature on the catalytic activity and stability of CrOx-containing catalysts supported on γ-Al2O3, ZrO2, CeO2 and CexZr(1-x)O2 has been investigated in the oxidative dehydrogenation of ethane with CO2 as a mild oxidant (ODH-CO2). The catalysts were prepared by wetness impregnation and characterized as-prepared and after catalytic tests using N2 adsorption, XRD, UV-Vis diffuse reflectance (DR) and Raman spectroscopies, TPR-H2 and TPO-CO2. The catalysts CrOx/γ-Al2O3 and CrOx/ZrO2 exhibited the highest ethylene formation rates, but the reaction followed different pathways on each: on CrOx/γ-Al2O3 catalyst ethylene is formed by a direct dehydrogenation (DDH) of ethane accompanied by RWGS, while on CrOx/ZrO2 ethylene is formed by selective oxidative dehydrogenation. The nature of the support influences the oxidation state of chromium species. The reaction pathway, catalytic activity and stability of the catalyst depend on both chromium state and support properties, in particular, on its acid-base and red-ox properties.

Silver is a key active metal of various industrial and lab-scale catalysts that are used for transformation of organic compounds in reactions of selective and total oxidation, (de)hydrogenation, photo- and electrocatalytic processes, etc. In this chapter we elucidate the key issues of surface chemistry of Ag-based heterogeneous catalysts with a special focus on oxidation catalysis. We consider the ways to tune the activity of Ag-based catalysts through the prism of size and morphology of Ag nanoparticles, their localization and strength of interaction with the support surface, the nature and reactivity of oxygen species formed over such surfaces as well as synergistic action of Ag particles with other components of the catalyst, including support, promoters, modifiers, etc.

Small silver nanoparticles (less than 7 nm) supported on silica as well as silica modified with CeO2 were prepared by impregnation techniques, characterized by physical-chemical methods, and tested in dehydrogenation of ethanol into acetaldehyde. The addition of CeO2 was shown to increase the catalytic activity of the Ag/SiO2 catalyst. The close interaction of the CeO2 nanoparticles (3–5 nm) with supported silver nanoparticles increased the activity of the Ag/CeO2/SiO2 catalyst in both dehydrogenation and oxidative dehydrogenation of ethanol into acetaldehyde due to participation of the Ag-CeO2 interface in the ethanol activation or/and the spillover of active oxygen.

This work was aimed at studying the influence of structure and properties of powders of aluminum hydroxide and zirconium dioxide on the structure and properties of the obtained ceramics. The work studied Al2O3ceramics obtained from aluminum hydroxide and composite materials ZrO2Al2O3 obtained from mixtures of zirconium dioxide and aluminum hydroxide powders. The work shows the data about the structure and properties of the initial powders used for the production of ceramics, as well as data about the structure and properties of Al2O3and ZrO2-Al2O3ceramic materials. It has been found that increasing aluminum hydroxide content in the initial mixture with the zirconium dioxide powder leads to increasing porosity of ZrO2-Al2O3composites sintered within the temperature range between 1,400 and 1,650 °C. It has been shown that increasing sintering temperature of the Al2O3ceramics leads to increasing compressive strength from 6 MPa to 800 MPa at the temperature of sintering between 1,300 and 1,500 °C, respectively. key words: Alumina, hydroxide aluminum, zirconium dioxide, strength, porosity, composite, properties.

Alcohols (bioalcohols) is a class of chemicals that are used as a feedstock for the manufacturing of a large number of valuable intermediates in industrially important processes. Currently, sustainable technologies for selective conversion of alcohols utilize “green” oxidants, mainly, ambient air or oxygen. Due to the high affinity of oxygen towards silver, the latter serves as an active component of supported heterogeneous catalysts. In this review, we consider Ag-based catalysts that participate in gas- or liquid-phase oxidation of alcohols. Oxidation of methanol, ethanol, ethylene glycol, propylene glycol, glycerol, benzyl and allyl alcohols is mostly considered. A particular attention is paid to selective photooxidation of alcohols over Ag-based catalysts. We discuss the catalyst composition in terms of (1) the state of the active component, (2) the nature of the substrate, (3) support nature, and (4) the strength of the metal–support interactions.

Three methods of introduction of modifiers based on Cu and Zn compounds into the CrOx/Al2O3 catalysts for dehydrogenation of light paraffin hydrocarbons are considered: Introduction from sol, introduction using successive impregnation technique and introduction of modifiers by impregnation along with precursor of chromium oxide. The obtained samples are studied by a complex of physical-chemical methods (XRD, UV-Vis spectroscopy, temperature-programmed reduction with hydrogen (TPR-H2), X-ray fluorescent (XRF) spectrometry, low-temperature N2 sorption). The catalytic properties of the samples are studied in kinetic mode in isobutane dehydrogenation. Cu- and Zn-modifiers are shown to influence on the peculiarities of reduction of Cr6+ and, hence, specify the state of active surface of CrOx/Al2O3 catalysts formed in the reductive reaction medium. Not only do the states of modifiers influence on the initial activity of the catalyst, but also on its activity after oxidative regeneration. Introduction of modifiers by successive impregnation method results in formation of copper and zinc aluminates or defective spinels on the Al2O3 surface. When the active component is introduced, the modified surface of the support promotes formation and stabilization of Cr6+ sites that can undergo reversible reduction–oxidation and provide high activity and selectivity towards formation of isobutylene (>98%).

The current work is the first study concerning the liquid-phase oxidation of n-octanol and betulin over modified and unmodified Ag/TiO2 catalysts. Catalytic activity of nanosilver catalysts supported on titania for alcohols selective oxidation can be enhanced by modification of the support with Ce, Fe or Mg oxides. In most cases reductive or oxidative pretreatments of these catalysts were detrimental for their activity. The main reason for performance of Ag/MxOy/TiO2 catalysts is changes of the electronic state of the supported Ag, and especially changes in the surface concentration of Ag+ ions. Monovalent Ag+ ions are active sites in silver-containing catalysts for n-octanol, as well as for betulin oxidation. The obtained results show a potential of silver-containing catalysts for liquid phase oxidation of alcohols, and by selecting the optimum modifier and the support as well as, pretreatment conditions the catalytic properties and stabilization of the active sites can be optimized.

Nowadays catalytic technologies are widely used to purify indoor and outdoor air from harmful compounds. Recently, Ag–CeO2 composites have found various applications in catalysis due to distinctive physical-chemical properties and relatively low costs as compared to those based on other noble metals. Currently, metal–support interaction is considered the key factor that determines high catalytic performance of silver–ceria composites. Despite thorough investigations, several questions remain debating. Among such issues, there are (1) morphology and size effects of both Ag and CeO2 particles, including their defective structure, (2) chemical and charge state of silver, (3) charge transfer between silver and ceria, (4) role of oxygen vacancies, (5) reducibility of support and the catalyst on the basis thereof. In this review, we consider recent advances and trends on the role of silver–ceria interactions in catalytic performance of Ag/CeO2 composites in low-temperature CO oxidation, soot oxidation, and volatile organic compounds (VOCs) abatement. Promising photo- and electrocatalytic applications of Ag/CeO2 composites are also discussed.

A new approach to the preparation of modified silica-based supports is suggested to obtain Crcontaining catalysts for paraffin hydrocarbon dehydrogenation. CrO x /ZrO2, CrO x /SiO2, and CrO x /nZrO2–SiO2 (n = 0.5, 1.0, and 2.0 ZrO2 monolayers) catalysts have been synthesized by incipient-wetness impregnation. The catalysts have been characterized by X-ray diffraction, diffuse reflectance spectroscopy, and temperature-programmed reduction with hydrogen. Their catalytic properties were investigated in the reaction of isobutane dehydrogenation. The state of the supported chromium depends considerably on the nature of the support. The formation of Cr2O3 particles, which show low activity in the dehydrogenation reaction, takes place in the CrO x /SiO2 catalyst, while chromium in the CrO x /ZrO2 catalyst is in a highly dispersed, X-ray-amorphous state. The addition of ZrO2 to CrO x /SiO2 increases the amount of chromium in the highly dispersed Cr(V) and Cr(VI) states, thus enhancing the isobutane dehydrogenation activity of the catalyst.

New type of Ag-containing nanostructured catalyst for high-temperature alcohol oxidation was developed on the basis of mesoporous SiO2 support. Active component (silver clusters/nanoparticles) stabilized by support surface and polyphosphate inside the pores. It was shown that Ag/P2O5/SiO2 catalyst provides high activity in the course of ethylene glycol oxidation to glyoxal at 500-600 °C. Formation of stable structure of catalyst during thermal treatment includes self-organization of mesoporous structure and chemical bonding of phosphate with silica. The catalyst treatment in red-ox conditions leads to reversible oxidation-reduction of silver and its redistribution from bulk to surface of the catalyst. Silver nanoparticles stabilized with silica-phosphate support are active species in the ethylene glycol oxidation into glyoxal.

Thermochemically activated aluminum trihydroxide (Al (OH)3) is an important intermediate for ceramics, construction materials, catalysts, etc. Functional properties of materials based on Al (OH)3 depend on its phase composition and porosity. A series of thermochemically activated Al (OH)3 calcined at temperatures from 120 to 800 °C were studied by low-temperature N2 sorption, XRD and thermal analysis. It was shown that transformation of gibbsite to boehmite occurs below 300 °C and is accompanied by increasing of specific surface area and pore volume. Transformation of boehmite to γ-Al2O3 proceeds above 400 °C. The sample calcined at 500 °C was shown to consist of monophase γ-Al2O3 with specific surface area of 206 m2/g and pore volume of 0.55 cm3/g.

The Al2O3/SiO2 materials prepared by impregnation of mesoporous silica with water solution of Al(NO3)3·9H2O were suggested to be used as supports for catalyst of high-temperature catalytic reactions. It was shown that the distribution of Al2O3 component inside wide pores of silica (10-50 nm) occurs with the formation of Al2O3 layer in case of low loading and porous layer or particles, if Al2O3 loading increases. Thus, materials with bimodal pore size distribution were obtained. The Cr-containing catalysts were prepared on the basis of these supports and tested in the process of isobutane dehydrogenation at 540 °C. It was observed that the activity of the obtained Cr/Al2O3/SiO2 materials was comparable with the one for Cr/Al2O3 catalyst. Thus, the suggested Al2O3/SiO2 materials with unique porous structure are promising to be used as supports for catalysts for high-temperature reactions.

Silver catalysts supported on ZSM-5 (Si/Al = 30, 50 and 80) were investigated for low-temperature CO oxidation to study the nature of the silver active sites and their formation under the influence of the support chemical composition and redox pretreatments. The catalysts were characterized by HRTEM, FTIR, XPS, diffuse reflectance UV–Vis spectroscopy, NH3 thermodesorption (NH3 TPD) and temperature-programmed reduction (H2 TPR). The chemical composition (Si/Al ratio) of the ZSM-5 zeolite support significantly affects catalytic properties of Ag/ZSM-5 samples: the lower the Broensted acidity of the zeolite support, the higher the activity of the catalyst s . Interestingly, while oxidizing pretreatment of catalysts led to a significantly better performance than reducing pretreatments, the consecutive reducing treatment of the preoxidized samples significantly promoted the catalytic activity for low-temperature CO oxidation. Thus, Ag/ZMS-5 catalyst with Si/Al = 80, pretreated consecutively in oxidizing and reducing conditions, showed the highest activity, reaching 90% CO conversion at just 40 °C. Comparison of activity and characterization results showed that silver particles with size below 2 nm are the most active; larger particles are just “spectators”. The most probable silver active centers in the low-temperature CO oxidation are ionic species, mostly charged clusters Agnδ+, strongly interacting with the support. The obtained results in low-temperature CO oxidation might be of particular interest for neutralization of exhaust gases of car engines during “cold start”.

The interaction of silver with the surface of CeO2 in the Ag/CeO2 catalysts prepared by coprecipitation and impregnation techniques was studied by temperature-programmed reduction, X-ray diffraction, and high-resolution transmission electron microscopy. It was shown that coprecipitation technique led to formation of strong silver–support interaction and the epitaxy of silver particles (d 111 = 2.35 A) on the surface of CeO2 (d 111 = 3.1 A). This provided incresed catalytic activity in the oxidative dehydrogenation of ethanol at relatively low temperatures (a 15% conversion of ethanol with 100% selectivity for the formation of acetaldehyde was reached at 85°C). Above 130°C, the deep oxidation of ethanol to CO2 becomes the predominant direction of a catalytic reaction, and the Ag/CеО2 catalyst obtained by impregnation technique was most active in this region as a consequence of the weaker metal–support interaction.

Silica-supported silver catalysts modified by cerium/manganese oxides were studied as catalysts for total oxidation of formaldehyde. The catalysts were characterized by N2 adsorption, XRD, and H2-TPR methods. Catalytic activity of the samples was tested in a flow fixed-bed reactor at atmospheric pressure and 100–200 °C using a feed gas containing 10,000–22,000 ppm of formaldehyde with a flow rate corresponding to a WHSV of ∼69,000 mL/(gcat h). It was shown that combination of silica support and a small amount of cerium/manganese oxides allows developing silver catalysts with defined micro- and macrostructure as well as high activity in the total oxidation of formaldehyde.

The catalysts of silver supported on mesoporous silica modified with Co3O4, CeO2, and ZrO2 were prepared by an impregnation method; characterized by X-ray diffraction analysis, temperature-programmed reduction, and low-temperature nitrogen adsorption; and studied in a model reaction of CO oxidation. It was found that the Ag/SiO2 system exhibited high activity in the reaction of CO oxidation, and the addition of transition metal oxides led to reduction of the temperature of 50% CO conversion by 40°C. The modification of Ag/SiO2 with cerium dioxide was found most effective because of the interaction of silver particles and CeO2 on the surface of silica gel.

Aluminum nanopowder (10-150 nm) was treated hydrothermally in mild conditions (60-95 °C, at atmospheric pressure), and an aluminum-alumina composite with high porosity and specific surface area was obtained. Cr[2]O[3]/Al-Al[2]O[3] catalysts were prepared using the aluminum-alumina composite by impregnation techniques and tested in dehydrogenation of C[4]-hydrocarbons. It was shown that aluminum-alumina composites had high chemical and phase purity, specific surface area of 150-350 m{2}/g and the average pore size of 8-13 nm, that is favorable for application as support for catalysts. Cr[2]O[3]/Al-Al[2]O[3] catalysts had high activity and selectivity in dehydrogenation of n- and i-butane (conversion of 44-80 mol.% and selectivity >85% at temperatures of 540-610 °C), that is comparable ones for commercial catalysts for CATOFIN, STAR processes.

Silver-containing catalysts supported on ceramic silicon nitrides and modified with Zr or Al are considered. The catalytic activities of the catalysts in the dehydrogenation and oxidative dehydrogenation of ethanol into acetaldehyde are compared. The introduction of oxygen into the reaction mixture decreases the temperature of 100% ethanol conversion to 270°C and increases the acetaldehyde selectivity to 95% for all of the catalysts. According to temperature-programmed reduction data, the simultaneous presence of Fe and Ag on the catalyst surface enhances the activity of the supported catalysts. It is hypothesized that the Ag/Fe interface plays the key role in the formation of active sites on the catalyst surface.

Ag/SiO2 and Ag3PO4/SiO2 systems supported on silica aerogel were investigated using temperature-programmed reduction (TPR), UV-visible diffuse reflectance spectroscopy (UV-vis DRS), and infrared spectroscopy. The formation of highly dispersed silver particles, uniformly distributed along the surface and stabilized with silanol groups, was observed for Ag/SiO2 system. Phosphate and silanol groups produce two states of silver localization in phosphate-containing system. The addition of phosphate onto the silica surface leads to the reversible oxidation/reduction of silver in the temperature range of 100–300°C with transitions of silver (particles 10–30 nm in size) to charged states (ions, clusters stabilized by phosphate groups). This reversible behavior of silver is stable, and the amount of silver involved in these processes remained constant (∼50%) for the series of consistent cyclic oxidation/reduction treatments.

Series of Pd-Ag/SiO2, Pd/CeO2 and Pd-Ag/CeO2 catalysts with different Pd/Ag ration were synthesized and investigated. It was shown that simultaneous reduction of Pd and Ag took place for Pd-Ag/SiO2 and Pd Ag/CeO2 catalysts during TPR-H2. That may be associated with formation of bimetallic Pd-Ag particles. The high temperature of Pd reduction was observed for Pd/CeO2 and Pd-Ag/CeO2 catalysts. That was associated with strong interaction of PdO with CeO2 or formation of mixed PdxCeO2-δ phase.

The moulded Al2O3 materials prepared by mixing of thermochemically activated aluminum trihydroxide (TCA ATH) with wood flour were proposed to be used as promising porous catalyst support for various processes. A series of Al2O3 supports with different wood flour loading (0, 2 and 5 %wt.) were studied by SEM, low-temperature N2 sorption, XRD, granule strength and water-absorbing capacity. It was shown that supports were characterized by porous structure with mesopore sizes of 2-20 nm and specific surface area of 159-186 m2/g. The increase of the amount of wood flour leads to increase of the share of pore volume with wider than 10 nm and the decrease of the strength of alumina granules. Thus, optimization of preparation conditions allows obtaining alumina materials with desired porous structure.

MICROSCOPIE+ATARI+EEH:GMA:TBG:NSP:MAO; International audience; The self-assembly technique provides a highly efficient route to generate well-ordered structures on a nanometer scale. In this paper, well-ordered arrays of PdAg alloy nanoparticles on flat substrates with narrow distributions of particle size (6-7 nm) and interparticle spacing (about 60 nm) were synthesized by the block copolymer micelle approach. A home-made PS-b-P4VP diblock copolymer was prepared to obtain a micellar structure in toluene. Pd and Ag salts were then successfully loaded in the micellar core of the PS-b-P4VP copolymer. A self-assembled monolayer of the loaded micelles was obtained by dipping the flat substrate in the solution. At this stage, the core of the micelles was still loaded with the metal precursor rather than with a metal. Physical and chemical reducing methods were used to reduce the metal salts embedded in the P4VP core into PdAg nanoparticles. HRTEM and EDX indicated that Pd-rich PdAg alloy nanoparticles were synthesized by chemical or physical reduction; UV-visible spectroscopy observations confirmed that metallic PdAg nanoparticles were quickly formed after chemical reduction; XPS measurements revealed that the PdAg alloy nanoparticles were in a metallic state after a short time of exposure to O-2 plasma and after hydrazine reduction.

An approach to the development of bimetallic nanoparticles with the separated but interacting phases of silver and palladium was proposed to effectively separate the active sites of silver, which possess high activity in activation of molecular oxygen, and the sites of palladium-containing phases, which are responsible for CO adsorption. The structure of PdAg particles was determined using X-ray diffraction analysis, electronic diffuse reflectance spectroscopy, and temperature-programmed reduction. It was found that the introduction of silver led to easier reduction of palladium from oxidized states in an atmosphere of CO. The activity of the bimetallic PdAg catalysts in the oxidation of CO increased, as compared with that of the Pd/SiO2 catalyst. The oxidized bimetallic catalyst, in which palladium occurred in an oxide state, was even more effective in the oxidation of CO; this can be related to the better cooperation of the active sites of silver and palladium oxide, which are responsible for the activation and conversion of CO and oxygen at the Ag-PdO interfacial boundary.

Phase evolution of copper-containing zirconium phosphates during the temperature treatment up to 900 °C and formation of active Cu0 particles on the surface of these materials in H2/Ar flow were studied. The materials were characterized by XRD, TEM, TPR-H2 at different steps of treatment. Temperature increase up to 900 °C led to removal of oxygen from the CuZr4P6O24 structure with formation of Cu+-containing compounds. Materials treated by H2-containing flow at 600 °C contained Cu0 particles with sizes from 2 nm to 1 μm. Mixed copper-zirconium phosphate was shown to adsorb CO above 80 °C, while pre-reduced materials adsorbed it starting from 30 °C with formation of CO2 above 100 °C.