Search

The reactive adsorption of sulfur-contaminated compounds over transition metal (TrM) polycation-exchanged zeolites is a very efficient method for the desulfurization of hydrocarbon processing streams. The process consists of the physical adsorption of thiols, sulfides, and disulfides and the catalytic oxidation of the adsorbed substances. The reaction does not require the participation of free oxygen; diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) and X-ray absorption spectroscopy (XAS) studies confirmed that the thiol oxidation proceeds through the direct involvement of TrM polycation superoxides. All of the studied zeolite X, zeolite Y, and mordenite materials containing Zn, Mn, Cu, and Cd polycations show remarkable activity for the oxidation of sulfur compounds; this results in a significant increase of the total pick-up from gas and liquid hydrocarbons. The thermal regeneration of the adsorbent-catalysts under oxidizing conditions leads to the complete restoration of their original activities and capacities for the removal of sulfur compounds. Suitable operating conditions for the regeneration process are disclosed. The study also demonstrates favorable properties of the suggested adsorbent-catalysts for use in commercially important applications such as the desulfurization of natural gas and liquid hydrocarbons. [ABSTRACT FROM AUTHOR]

[Display omitted] • Adsorption of N 2 O on Lewis acid sites of zeolites results in formation of strong complexes. • Decomposition of complexes produces chemisorbed oxygen active in CO and CH 4 oxidation. • NO disproportionation on strong Lewis acid sites occurs with formation of different NO x forms. The formation of complexes and transformations of nitrogen oxides (NO, N 2 O) on strong Lewis acid sites of HZSM-5, H[Ga]ZSM-5, ZnO/HZSM-5 zeolites and dealuminated mordenites was investigated by diffuse-reflectance IR spectroscopy. Adsorbed N 2 O that is formed by disproportionation of NO is capable of oxidizing CO and CH 4 molecules to CO 2. The behaviour of strong Lewis acid sites in zeolites and cationic forms of zeolites in the NO disproportionation and CO or CH 4 oxidation was comparatively studied. [ABSTRACT FROM AUTHOR]

The oxidation of CO was studied on a series of MLaO3 perovskites (M=Co, Fe, Ni) supported on mesoporous zirconia that are synthesized by using a glycine-mediated method and characterized by using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy. The activity of the catalysts in the CO oxidation reaction follows the order Co>Ni>Fe. [ABSTRACT FROM AUTHOR]

Abstract: Pd/H-Beta catalysts with different silica-to-alumina ratio prepared by an impregnation method have been studied by XANES/EXAFS, IR, XRD and TEM. It was shown that palladium in calcined Pd/H-Beta samples exists as palladium oxide that can be easily reduced to Pd metal. The catalysts were tested in selective oxidation of piperonyl alcohol to piperonylaldehyde at 80°C. The Pd/H-Beta zeolite catalysts with the lowest silica-to-alumina ratio possess the highest catalytic activity in benzylic alcohol oxidation reaction. [Copyright &y& Elsevier]

Au/Al2O3 and Ni/Al2O3 prepared by deposition-precipitation and impregnation methods, respectively, and Au–Ni/Al2O3 prepared by impregnation of the Au/Al2O3 system with nickel have been studied by physicochemical methods. The catalysts were tested in allylbenzene isomerization at 443 K. The isomerization on Au/Al2O3 proceeds with a rather low rate, while monometallic Ni/Al2O3 is inactive. Unlike monometallic catalysts, Au–Ni/Al2O3 demonstrates a strong synergetic effect: the isomerization rate on the bimetallic sample exceeds the sum of the rates over the individual metals by an order of magnitude. The catalysts structure was estimated by XPS, DRIFT, and XAS techniques. It was revealed that nickel in Au–Ni/Al2O3 and Ni/Al2O3 exist as Ni2+ cations with the coordination state close to that in the precursor, gold in Au/Al2O3 exist as Au0 nanoclusters, whereas the Au0 nanoclusters co-exist with Au3+ cations in the bimetallic Au–Ni/Al2O3 sample. Reasons of the synergetic catalytic effect for Au–Ni/Al2O3 are discussed in terms of the formation of new positively charged Au catalytic centers. [ABSTRACT FROM AUTHOR]

In the present work, nanocatalysts prepared on inorganic supports (zeolites) were investigated in d-glucose oxidation and compared to systems supported on polymer (hypercrosslinked polystyrene (HPS)) previously described. Catalytic activities and selectivities were measured under various reaction conditions. The selectivity of d-glucose oxidation and activity of both Pd-containing zeolites and HPS-Ru were similar (99.7% and TOF 0.013–0.014 mol/(mol Me s)). Physicochemical analysis X-ray photoelectron spectroscopy, liquid nitrogen physisorption, diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO for metal sites evaluation, CD3CN for acid sites evaluation showed that Pd species were in oxidic form, while Ru species were in oxidic and reduced form. The catalytic activity decreased when acidic sites were present in Pd-containing zeolites. [ABSTRACT FROM AUTHOR]

The formation of complexes and disproportionation of nitrogen oxides (NO, N2O) on cationic forms of LTA, FAU, and MOR zeolites was investigated by diffuse-reflectance IR spectroscopy. N2O is adsorbed on the samples under study in the molecular form and the frequencies of the first overtone of the stretching vibrations ν10–2 and the combination bands of the stretching vibrations with other vibrational modes for N2O complexes with cationic sites in zeolites (ν30–1 + ν10–1, ν10–1 + δ0–2) are more significantly influenced by the nature of the zeolite. The presence of several IR bands in the region of 2400–2600 cm−1 (the ν10–1 + δ0–2 transitions) for different zeolite types was explained by the availability of different localization sites for cations in these zeolites. The frequencies in this region also depend on the nature of the cation (its charge and radius). The data can be explained by the specific geometry of the N2O complex formed, presumably two-point adsorption of N2O on a cation and a neighboring oxygen atom of the framework. Adsorption of CO or CH4 on the samples with preliminarily adsorbed N2O at 20–180 °C does not result in any oxidation of these molecules. NO+ and N2O3 species formed by disproportionation of NO are capable of oxidizing CO and CH4 molecules to CO2, whereas NOx is reduced simultaneously to N2 or N2O. The peculiarities in the behavior of cationic forms of different zeolites with respect to adsorbed nitrogen oxides determined by different density and localization of cations have been established. [ABSTRACT FROM AUTHOR]

The problem of identifying correlations between catalytic and electrocatalytic processes is one of the fundamental problems of catalysis among "simple" organic substances, and the oxidation of CO and rCO2 is of great interest, since CO and CO2 are considered in pairs both during catalytic and electrocatalytic transformations. In the case of electrocatalysis, this analysis is important in the study of fuel cells. In this paper, we studied the correlation between the oxidation of reduced forms of CO2 (rCO2) under potentiodynamic-galvanoctatic electrochemical and open-circuit conditions of measurements on polycrystalline (pc)Pt in H2CO3. Periodic oscillations are revealed at the oxidation of Had and rCO2 on (pc)Pt. Quantum chemical calculations were carried out on the Pt13 cluster in order to identify the mechanisms of the rCO2 oxidation reaction. The correspondence in the energy parameters of the oxidation process of rCO2 under open-circuit conditions and electrochemical conditions is shown. The preliminary analysis of the system using density functional (DFT) calculations is carried out and the most stable systems that are based on Pt13 are found, namely rOH-Pt13-(CO)n, rOH-Pt13-(COH) and rOH-Pt13-(rCOOH). OH• species was chosen as the most likely candidate for the role of the oxidant for rCO2. Preliminary calculations for the expected reactions were carried out, and the optimal PES is revealed. [ABSTRACT FROM AUTHOR]

Au, Pt, and Pt-Au catalysts supported on Al2O3 and CeO2-Al2O3 were studied in the oxidation of dichloromethane (DCM, CH2Cl2). High DCM oxidation activities and HCl selectivities were seen with all the catalysts. With the addition of Au, remarkably lower light-off temperatures were observed as they were reduced by 70 and 85 degrees with the Al2O3-supported and by 35 and 40 degrees with the CeO2-Al2O3-supported catalysts. Excellent HCl selectivities close to 100% were achieved with the Au/Al2O3 and Pt-Au/Al2O3 catalysts. The addition of ceria on alumina decreased the total acidity of these catalysts, resulting in lower performance. The 100-h stability test showed that the Pt-Au/Al2O3 catalyst was active and durable, but the selectivity towards the total oxidation products needs improvement. The results suggest that, with the Au-containing Al2O3-supported catalysts, DCM decomposition mainly occurs via direct DCM hydrolysis into formaldehyde and HCl followed by the oxidation of formaldehyde into CO and CO2. [ABSTRACT FROM AUTHOR]

The state of palladium and copper on the surface of the PdCl2–CuCl2/γ-Al2O3 nanocatalyst for the low-temperature oxidation of CO by molecular oxygen was studied by various spectroscopic techniques. Using X-ray absorption spectroscopy (XAS), powder X-ray diffraction (XRD), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), freshly prepared samples of the catalyst were studied. The same samples were also evaluated after interaction with CO, O2, and H2O vapor in various combinations. It was shown that copper exists in the form of Cu2Cl(OH)3 (paratacamite) nanophase on the surface of the catalyst. No palladium-containing crystalline phases were identified. Palladium coordination initially is comprised of four chlorine atoms. It was shown by XAS that this catalyst is not capable of oxidizing CO at room temperature in the absence of H2O and O2 over 12 h. Copper(II) and palladium(II) are reduced to Cu(I) and Pd(I,0) species, respectively, in the presence of CO and H2O vapor (without O2). It was found by DRIFTS that both linear (2114 cm−1, 1990 cm−1) and bridging (1928 cm−1) forms of coordinated CO were formed upon adsorption onto the catalyst surface. Moreover, the formation of CO2 was detected upon the interaction of the coordinated CO with oxygen. The kinetics of CO oxidation was studied at 18–38 °C at an atmospheric pressure for CO, O2, N2, and H2O (gas) mixtures in a flow reactor (steady state conditions). [ABSTRACT FROM AUTHOR]

Abstract: Novel catalytic nano-sized materials based on LaCoOx perovskite nanoparticles incapsulated in the mesoporous matrix of zirconia were prepared, characterized by physicochemical methods and tested in complete methanol oxidation. LaCoOx nanoparticles were prepared inside the mesopores of ZrO2 by decomposition of bimetallic La–Co glycine precursor complexes. The catalysts have been studied by diffuse-reflectance FTIR-spectroscopy using such probe molecules as CO, CD3CN and CDCl3 to test low-coordinated metal ions. At low temperatures of decomposition of complexes (up to 400°C), low-coordinated Co3+ ions predominate in the LaCoOx nanoparticles, whereas basically Co2+ ions are found upon increasing the decomposition temperature to 600°C. The novel nano-sized perovskite catalysts exhibit a very high catalytic activity in the abatement of volatile organic compounds present in air, like methanol and light hydrocarbons. [Copyright &y& Elsevier]

A series of the Au–Cu/SiO 2 catalysts including low-loaded samples with an overall metal content less than 0.5 wt% was synthesized by a redox method. The catalysts were tested in the selective oxidation of ethanol to acetaldehyde. The highest catalytic activity was observed for the catalysts having the lowest metal content due to the presence of nanosized Au particles and the synergetic effect of Au–Cu 2+ interaction. Unusual reduction behavior was found for the catalysts with the 0.2 wt% content of Cu. XRD, TPR, EXAFS, and STEM techniques were applied for the catalysts characterization. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we report the synthesis of robust and efficient nanocatalysts based on Pt-containing nanoparticles (NPs) formed in the pores of hypercrosslinked polystyrene (HPS) and their catalytic performance in the phenol CWAO under mild conditions. The Pt species were incorporated in HPS using wet impregnation of platinic acid in tetrahydrofuran followed by NaHCO3 treatment. The catalysts containing from 0.11 to 4.85wt.% of Pt were studied by X-ray fluorescence analysis, transmission electron microscopy, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and liquid nitrogen physisorption methods. The NP sizes were found to be independent of the amount of platinic acid used for impregnation, but rather controlled by the pores of HPS. Three types of Pt species: Pt(0), Pt(II), and Pt(IV), constituted the NP composition. The effects of the phenol and catalyst initial concentrations and temperature were investigated in the phenol CWAO. Removal of 97% of the phenol with 94.2% selectivity to CO2 and H2O were observed for the most active catalyst containing 0.95wt.% Pt. These parameters are significantly higher than those for the conventional Al2O3–Pt catalyst with the similar amount of the active metal or for Pt(5%)/activated carbon. [Copyright &y& Elsevier]

Abstract: Microwave (MW)-activated oxidative dehydrogenation of ethane is studied using kinetic approach. It consists in the comparison of kinetic dependencies (shape of kinetic equations, “selectivity or yield vs. conversion” curves) and apparent parameters (activation energies) obtained in thermal and MW modes. In the case of VMo and VMoNb oxides a distinct difference between ethane yields was observed at given conversion of limiting reactant (oxygen). It was proven by X-ray diffraction that MW activation changes the catalyst microstructure forming phase distribution different from that formed under a conventional heating and thus changing catalytic behavior of VMo and VMoNb oxides. [Copyright &y& Elsevier]

Abstract: The catalytic properties and structural characterization of catalysts derived from hypercrosslinked polystyrene (HPS), a polymer exhibiting mesoporosity and loaded with ruthenium in various amounts are investigated in the oxidation of d-glucose to d-gluconic acid. Transmission electron microscopy, X-ray fluorescence analysis, nitrogen physisorption measurements, diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO, EXAFS, XANES and catalytic studies show the presence of catalytically active nanoparticles of mixed composition (metal/oxide) with a mean diameter of 1.0–1.2nm. The most active catalyst is found to contain 0.74Ruwt.%. The highest selectivity to d-gluconic acid is 99.8% for a conversion of d-glucose of 99%; the specific activity of the catalyst is measured to be 1.13×10−3 molmol−1 Rus−1. The high-catalytic activity is attributed to the presence of pores of various sizes which facilitate mass transport and the high stability is attributed to the presence of small mesopores that have high-sorptional capacity and hinder the migration of the nanoparticles. [Copyright &y& Elsevier]

The monoliths were prepared by coating of Al2O3 and SiO2 on the FeCrAl alloy foil and by introducing appropriate catalytically active oxides on the supports. It was found that, for both catalytic systems of monolith and bulk catalysts of Mn–Na2WO4/SiO2, the dependences of methane conversion to C2 products on the contact time virtually coincide if the normalized quantities of the active component are considered. [Copyright &y& Elsevier]