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Gold nanocatalysts, active in several oxidation reactions, suffer of insufficient time-on-stream stability. The easiest way to solve this problem is modifying the support, due to metal-support interaction. This study compares modifying effects of MgO and La2O3 on textural, electronic, and catalytic properties of Au nanoparticles (NPs) supported on inert nanostructured SiO2 in CO oxidation and liquid phase 1-octanol oxidation. Modification of the silica support surface with La and Mg increased metal support interaction, leading to gold particles with primary size of 1 nm but with different stability: stable under different pretreatment conditions on Mg-modified samples but highly sensible to the pretreatments on La-modified samples. Both modifiers changed electronic properties of supported gold favoring formation and stabilization of Auδ+ states, which are probable gold active sites in catalytic redox processes. Modification with La and Mg oxides changed catalytic properties in CO oxidation before and after pretreatment in H2 at 300 °C for 1 h. Gold catalysts supported on La- and Mg-modified silica showed similar performance in 1-octanol oxidation with higher conversion than unmodified Au/SiO2. La and Mg showed better promoting effects of catalytic properties in this reaction than redox modifiers (Fe and Ce) supported on small SiO2 particles.

This article reviews the current state and development of thermal catalytic processes using transition metals (TM) supported on zeolites (TM/Z), as well as the contribution of theoretical studies to understand the details of the catalytic processes. Structural features inherent to zeolites, and their corresponding properties such as ion exchange capacity, stable and very regular microporosity, the ability to create additional mesoporosity, as well as the potential chemical modification of their properties by isomorphic substitution of tetrahedral atoms in the crystal framework, make them unique catalyst carriers. New methods that modify zeolites, including sequential ion exchange, multiple isomorphic substitution, and the creation of hierarchically porous structures both during synthesis and in subsequent stages of post-synthetic processing, continue to be discovered. TM/Z catalysts can be applied to new processes such as CO2 capture/conversion, methane activation/conversion, selective catalytic NOx reduction (SCR-deNOx), catalytic depolymerization, biomass conversion and H2 production/storage.

42-01-09/169/2021-4 CTQ2017-86170-R Au and Ag were deposited on TiO2 modified with Ce, La, Fe or Mg in order to obtain bimetallic catalysts to be used for liquid-phase oxidation of 1-octanol. The effects of the deposition order of gold and silver, and the nature of the support modifying additives and redox pretreatments on the catalytic properties of the bimetallic Au-Ag catalysts were studied. Catalysts were characterized by low-temperature nitrogen adsorption–desorption, energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and ultraviolet-visible diffuse reflectance spectroscopy. It was found that pretreatments with hydrogen and oxygen at 300◦C significantly decreased the activity of AuAg catalysts (silver was deposited first) and had little effect on the catalytic properties of AgAu samples (gold was deposited first). The density functional theory method demonstrated that the adsorption energy of 1-octanol increased for all positively charged AuxAgyq (x + y = 10, with a charge of q = 0 or +1) clusters compared with the neutral counterparts. Lanthanum oxide was a very effective promoter for both monometallic and bimetallic gold and silver catalysts in the studied process. publishersversion published

A novel route to prepare monodispersed 1–2 nm gold nanoparticles (NPs), based on the use of extremely small SiO2 NPs (2–4 nm) as a support and increasing their metal-support interaction with surface modifier oxides is presented. The influence of modifier (La, Ce and Fe oxides) and modification method (impregnation (i) or direct synthesis (s)) on the formation of ultra-small Au NPs and their structural and electronic properties was studied. The samples were characterized by N2 adsorption (BET), FTIR of adsorbed CO, XRD and HR-TEM methods, and tested for the catalytic selective oxidation of 1-octanol. Preparation of monodispersed Au NPs with 1 nm diameter was successfully achieved for all the modified samples studied, with exception of Au/Ce/SiO2-i, where CeO2 was not homogeneously distributed. The Au NPs have high degree of monodispersity and are stable when treated in H2 up to 300 °C. Formation of these Au NPs depended on the strong interactions between the cationic gold complex precursor and the surface of modified SiO2 NPs. Modifiers changed electronic properties of supported gold; favoring the formation and stabilization of Auδ+ states, which are probable gold active sites of selective liquid-phase oxidation of alcohols in redox catalytic processes. 1-octanol oxidation was used as a model reaction for oxidation of fatty alcohols obtained during biomass transformation. The best performance for 1-octanol oxidation was found for gold nanoparticles supported on the ultra-small SiO2 modified cerium oxide by impregnation method. The relative order of activity was: AuCeSiO2-i > AuFeSiO2-i ≫ AuLaSiO2-i ≈ AuLaSiO2-s > AuSiO2 > AuFeSiO2-s≫ AuCeSiO2-s. The obtained results open the possibility of further development of high-performance catalysts for conversion of secondary products of biomass processing into valuable chemicals.

Influence of modification with metals Au and Ag, oxides of Fe, Mg and Ce and their combinations on amorphization of widely used commercial nanosized TiO2 (Degussa P25) was studied with SR-XRD and EXAFS methods. These systems were chosen taking into account their potential on catalytic properties for biomass to biodiesel transformation, as it was shown in model reaction of liquid phase n-octanol oxidation as well as low-temperature CO oxidation for “cold start” of the neutralizers of car exhaust gases. Instability of rutile, the most stable TiO2 phase, in the presence of the additives was found. Application of EXAFS method, rarely used for crystalline structure transfer studies, led to elucidation of this apparent effect, which was explained by higher level of amorphization of rutile than anatase. Literature data indicate that bulky TiO2 doping leads to either increase of rutile/anatase ratio complete inhibition of anatase to rutile transformation. Dissimilar phase composition changes, revealed in this work for modified nanodispersed TiO2, was attributed to size effect.

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.

This study aims to improve gold-based catalyst effectiveness in n-octanol oxidation by adjusting the structural and electronic properties of gold through incorporation of additives to support. Au/La/TiO2, Au/Ce/TiO2, and Au/TiO2 catalysts, prepared by deposition-precipitation with urea, were tested in the base-free oxidation of octanol under mild conditions in liquid phase. The influence of additives on structural properties of the catalyst and the active phase, and on the electronic and redox properties of the active gold species was studied by TEM, SR-XRD, EXAFS, FTIR of adsorbed CO, and XPS. Support modifiers affected gold particle size distribution, but no direct dependence of the catalyst activity on Au NPs average size was observed. The activity of as-prepared catalysts was limited, and even lower in the presence of modifiers at that stage. Reductive pretreatment boosted the activity of every catalyst, and support modification with La and Ce increased four- and two-fold, respectively, the activity of Au/TiO2 under the same reaction conditions. The nature of modifiers also affected the product distribution where the outstanding performance of Au/La/TiO2 gives rise to the highest ester selectivity at isoconversion with no acid formation. Overall, the studied catalysts, and especially Au/Ce/TiO2, and Au/La/TiO2, hold promise for n-octanol oxidation under mild conditions.

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.

Mono- and bimetallic systems of Ag, Fe, and Ag&ndash, Fe exchanged in sodium mordenite zeolite were studied in the reaction of NO reduction. The transition metal cations Ag and Fe were introduced by ion exchange method both at room temperature and 60 &deg, C, modifying the order of component deposition in bimetallic systems. These materials were characterized by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), ultraviolet-visible spectroscopy (UV-Vis), X-Ray photoelectron Spectroscopy (XPS) and High-resolution transmission electron microscopy (HR-TEM). The XPS and UV&ndash, Vis spectra of bimetallic samples revealed that under certain preparation conditions Ag+ is reduced with the participation of the Fe2+/Fe3+ ions transition and is present in the form of a Ag reduced state in different proportions of Agm clusters and Ag0 NPs, influenced by the cation deposition order. The catalytic results in the NO reduction reaction using C3H6/CO under an oxidizing atmosphere show also that the order of exchange of Ag and Fe cations in mordenite has a strong effect on catalytic active sites for the reduction of NO.

A series of Ag–ZSM-5 samples with different Ag loading (0–10 wt%) was prepared via ion exchange. All samples were characterized by similar adsorption behavior towards toluene vapors. The concentration of Ag as well as the nature of Ag species were found to affect strongly the strength of toluene adsorption thus resulting in different profiles of temperature programmed desorption. The water vapors were shown to have a negative effect on adsorption properties of low Ag samples. It was suggested that the increase of Ag loading leads to the appearance of Ag n δ+ (n = 2–8) clusters instead of monoatomic Ag+ sites predominantly existed in the case of the samples with low silver loading. It was found experimentally and explained theoretically by means of DFT calculations that these clusters exceed the monoatomic species by the strength of toluene adsorption even in the presence of water vapors. At the same time, SiO2/Al2O3 ratio in Ag–ZSM-5 samples was found to have no significant effect on adsorption/desorption properties of the zeolites.

Mesoporous silica composed by small nanoparticles has been synthesized by a modified neutral S 0 I 0 templating route method (S 0 , neutral primary amine surfactant; I 0 , neutral inorganic precursor). Decreasing the polarity of the medium and tuning the composition of the S 0 I 0 pair allow the formation of silica nanoparticles that are agglomerated into silica fractal or sponge-like structures. Those nanoparticles conform the building blocks of the neutral S 0 I 0 method. In this work for the first time they are observed isolated by HRTEM. On the other hand, the addition of metal oxides triggers the formation of aggregates containing unusually small silica nanoparticles, i.e. smaller building blocks that in bare silica, in the range of 2–4 nm. Further, through the impregnation of a gold precursor post-synthesis, ultra small gold nanoparticles (1 nm) were embedded in the final silica nanostructures upon calcination of the organic precursors. FTIR and UV–vis spectroscopies, TEM and SEM, XRD and N 2 absorption were used to characterize the resultant materials.

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.

A platinum woven fiberglass supported IC-12-S111 catalyst whose preparation is based on pulsed surface thermosynthesis is developed. The IC-12-S111 catalyst contains small amounts of platinum (0.05–0.10 wt %), and cheap and commercially available types of fiberglass cloths are used in its production. The production technology is characterized by a small number of process stages and no wastes or platinum losses. The developed catalyst is superior to known platinum and oxide catalysts in its activity in the deep oxidation reactions of hydrocarbons, and exhibits high thermal and operational stability. IC-12-S111 based catalytic cartridges with regularly structured channels are characterized by low hydraulic resistance and minimize deposits of solid particles in a catalyst bed during operation in contaminated flows. The cartridges can be used to create beds of any size and configuration. The developed catalyst can be used for the afterburning of hydrocarbons and organic compounds in flue gases, the flameless oxidation of flare gases, and the catalytic combustion of hydrocarbon fuels in local power supply systems.

Vanadium(V) oxide catalysts for the selective oxidation of hydrogen sulfide to sulfur on a nonporous glass-fiber support with a surface layer of a porous secondary support (SiO2) are studied. The catalysts are obtained by means of pulsed surface thermosynthesis. Such catalysts are shown to have high activity and acceptable selectivity in the industrially important region of temperatures below 200°C. A glass-fiber catalyst containing vanadium oxide (10.3 wt % of vanadium) in particular ensures the complete conversion of H2S at a temperature of 175°C and a reaction mixture hourly space velocity (RMHSV) of 1 cm3/(gcat s) with a sulfur yield of 67%; this is at least 1.35 times higher than for the traditional iron oxide catalyst. Using a structured glass-fiber woven support effectively minimizes diffusion resistance and greatly simplifies the scaleup of processes based on such catalysts. Such catalysts can be used for the cleansing of tail gases from Claus units and in other processes based on the selective oxidation of H2S.

Silver supported on the ZSM-5 (ratio Si/Al = 50) were prepared by impregnation method and characterized by means of numerous analytical techniques: high resolution transmission electron microscopy (HRTEM), Fourier transformed infrared spectroscopy (FTIR) and diffuse reflectance UV–vis spectroscopy (DRS). Catalytic activities of the materials were evaluated in CO oxidation. It was shown that catalytic performance of x Ag/ZSM-5 ( x = 1, 3, 5, 7 wt.% Ag) depends strongly on Ag loading, among which 7%Ag/ZSM-5 displayed the best properties for the studied reactions. The studies revealed a strong influence of the redox pretreatment temperature on the catalytic activity of the samples. The experiments showed that Ag/ZSM-5 catalyst has a good reproducibility and stability in CO oxidation. Comparison of results of catalytic, structural and spectroscopic measurements allows suggesting Ag + ions inside zeolite or on the external support surface as well as charged clusters Ag n δ+ to be active states of silver in the studied process. The obtained results were compared with previous data for formation of active gold clusters Au n δ+ in zeolites. It is important for synthesis of catalytically stable bimetal Au–Ag systems.

Supported Pd/fiber glass, Pd/γ-Al2O3/fiber glass, Pd/γ-Al2O3 catalysts were prepared by Surface Self-propagating Thermal Synthesis (SSTS) and tested in selective hydrogenation of acetylene to ethylene in the presence of CO. Temperature change in local liquid-phase surrounding of Pd atoms was monitored by XAFS in situ by modeling the catalysts synthesis. The phase composition of samples at various synthesis stages was determined by XAFS spectroscopy and synchrotron X-ray diffraction (SR XRD). The type of support material and SSTS conditions were found to affect the catalytic activity of supported Pd catalysts. Thermal synthesis of Pd catalysts on the surface of supports was found to proceed via formation of the metallic phase followed by its transformation to oxide. The catalytic activity of thus prepared catalysts on fiber glass supports can expectedly be improved upon deposition of additional support (alumina) onto a fiber glass.

The nature and size of the real active species of nanoparticulated metal supported catalysts is still an unresolved question. The technique of choice to measure particle sizes at the nanoscale, HRTEM, has a practical limit of 1 nm. This work is aimed to identify the catalytic role of subnanometer species and methods to detect and characterize them. In this frame, we investigated the sensitivity to redox pretreatments of Ag/Fe/TiO2, Ag/Mg/TiO2 and Ag/Ce/TiO2 catalysts in CO oxidation. The joint application of HRTEM, SR-XRD, DRS, XPS, EXAFS and XANES methods indicated that most of the silver in all samples is in the form of Ag species with size, We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)., This research was supported by Government Program “Science” of Tomsk Polytechnic University, Grant No. 4.1187.2014/K, CONACYT Project 260409 and PAPIIT-UNAM Project IT200114 (Mexico), CSIC project 201480E077 and MINECO Project CTQ2013-41507-R (Spain). We gratefully thank O. Martynyuk, G. Torres Otañez, Z. I. Bedolla Valdez, E. Flores, F. Ruiz Medina, A. Olivas Sarabia, I. Gradilla, J. Mendoza, E. M. Aparicio Ceja, J. Peralta, David A. Domínguez, M. Sainz, R. Valdez Castro, M. Martínez, B. Acosta Ruelas, F. Ramírez Hernández and M. López Cisneros for valuable technical assistance.

The catalytic properties of modified Au/TiO2 catalysts for low-temperature CO oxidation are affected by deactivation and reactivation after long-term storage and by redox treatments. The effect of these phenomena on the catalysts was studied by HRTEM, BET, SEM, FTIR CO, XPS and H2 TPR methods. The main cause for the deactivation and reactivation of catalytic properties is the variation in the electronic state of the supported gold, mainly, the proportion of singly charged ions Au+. The most active samples are those with the highest proportion of singly charged gold ions, while catalysts with a high content of trivalent gold ions are inactive at low-temperatures. Active states of gold, resistant to changes caused by the reaction process and storage conditions, can be stabilized by modification of the titanium oxide support with transition metals oxides. The catalyst modified with lanthanum oxide shows the highest stability and activity., We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)., This work was funded by CONACYT project 260409 and PAPIIT-UNAM project IT200114 (Mexico); CSIC project 201180E104 and MINECO project CTQ2013-41507-R (Spain); and Government Program “Science” of Tomsk Polytechnic University, grant No. 4.1187.2014/K (Russia).

In this paper, the effect of modifiers and pretreatments on the electronic states of 1 nm gold nanoparticles (AuNPs) supported on silica was systematically studied. AuNPs deposited on silica (particle size of 2-4 nm) modified with Ce, La and Fe oxides, were studied by FTIR of adsorbed CO after different redox treatments at 100, 300 and 500 °C. This study was conducted at room temperature to allow detecting the electronic states of gold, which is more likely involved in CO oxidation at the same temperature. AuNP size distribution was measured by HRTEM. It is shown that the electronic state of gold species (Aun(δ-), Au⁰, Aun(δ+), Au⁺) in 1 nm AuNPs is sensitive to the modifier as well as to the temperatures of redox pretreatments. Supports modified with the same additives but containing larger AuNPs (~3, 4, 5, and 7 nm) were also studied. They showed that Au⁰ remains stable irrespective of additives and redox pretreatments, indicating no significant effect of such treatments on the electronic properties of larger AuNPs. Samples with a predominant AuNP size of 2 nm are an intermediate case between these two groups of materials.

Methanol dehydrogenation was carried out over impregnated Cu/SiO2 catalysts. It was found that the temperature of the catalyst's preliminary reduction by hydrogen could play a dramatic role. The interaction of copper ions with silica during the reduction at ≥300°C was observed. Metallic copper species obtained at low reduction temperature were found to be responsible for the methyl formate formation. The catalysts containing copper in the oxidised state showed low selectivity because of a side reaction of coke formation and were deactivated rapidly. The optimal temperature of reduction was found to be 250°C.