Adsorption of isopropanol on a nickel oxide

Adsorption isotherms of isopropanol are obtained in the temperature range of 243 to 303 K on the initial surface of nickel oxide after its treatment in high-frequency plasma in Ar and glow-discharge plasma in O₂. It is found that such treatment lower the isosteric heat and differential entropy of reversible adsorption, along with the general acidity of the oxide’s surface. At low degrees of filling, isotherms are described by the equation of induced adsorption. It is established that adsorbed molecules of isopropanol take negatively charged and two positively charged forms. Lewis acidic centers of various strengths can serve as adsorption centers in addition to centers of other types.     

The influence of plasma chemical treatment of nickel and nickel-rhenium catalysts deposited on sibunite on their activity in dehydrogenation

The dehydrogenation of isopropanol was studied at 440–680 K to find that the activity of the Ni(1 wt %)/sibunite catalyst decreased after annealings and quenchings and was stabilized after subsequent treatment with an (I) O₂ glow-discharge or (II) H₂ high-frequency plasma. Treatments of both kinds decreased the activity of the catalyst below the Curie point (633 K) and increased it over the paramagnetic temperature range (635–680 K). The treatment of the (1 wt % Ni–1 wt %Re)/sibunite and (2 wt % Ni–2 wt % Re)/sibunite catalysts with plasma II weakly influenced their activity, whereas treatment with plasma I substantially increased it. The kinetic reaction parameters on the (2 wt % Ni–2 wt % Re)/sibunite catalyst were found to depend on the duration of treatment with plasma II. Treatment with plasma I much more effectively changed the state of the surface of all the catalysts studied than treatment with plasma II.     

Effects of plasmochemical treatments and cerium additions on the structural characteristics and activity of copper catalyst particles in isopropanol dehydrogenation

The effect of the treatment of the 5 wt % Cu/SiO₂ (I) and (5 wt % Cu + 0.5 wt % Ce)/SiO₂ (II) catalysts with glow discharge plasma in O₂, H₂, and Ar on their structural characteristics was studied by X-ray phase analysis; the influence of cerium additions and plasmochemical treatments on the catalyst activity in isopropanol dehydrogenation was also investigated. Under the plasmochemical treatment, the diameters of Cu particles in catalyst I nearly doubled and microstresses in the metal particles also changed. Catalyst II was X-ray amorphous both before and after plasmochemical treatments. The activity of I after plasmochemical treatment increased because of the increase in the number of centers and changes in their composition. Growth of the activity of I compared with the activity of II was explained by the formation of new catalytic centers due to positive charging of the Ce^+?? adatom on the surface of the copper particle.     

Cyclohexane dehydrogenation on a copper-platinum catalyst

The reaction of the dehydrogenation of cyclohexane on a copper-platinum catalyst supported by silica gel (1 wt % Pt + 0.15 wt % Cu)/SiO₂ was studied. The state of the catalyst surface was investigated using X-ray photoelectron spectroscopy. It was established that under both flow and static conditions, the activity of the copper-platinum catalyst is higher than the activity of a catalyst containing 1 wt % Pt/SiO₂. The rise in activity as a result of the introduction of copper, due to a decrease in the activation energy, is explained by an increase in the fraction of carbon in the composition of active centers localized on particles of neutral (Pt _m ⁰) and positively charged (Pt _n ^+δ) platinum, and by the formation of centers with increased activity as a result of the adsorption of Cu^+δ on particles of Pt _m ⁰. It was demonstrated that treating the copper-platinum catalyst with the plasma of a glow discharge in argon and oxygen increases its activity, while treatment in high-frequency H₂ plasma reduces it. The indicated changes in the activity are associated with the alteration of the activation energies and the number of active centers, revealed by X-ray photoelectron spectroscopy, that depend on changes in the catalyst surface composition.     

Dehydrogenation of isopropanol on a modified copper catalyst

The influence of plasmochemical treatments of the 5 wt % Cu/SiO₂ catalyst and cerium additives on the activity of the catalyst in isopropanol dehydrogenation was studied. After the catalyst was treated with high-frequency plasma in H₂ under the flow conditions, the conversion of alcohol increased. The reaction kinetics was studied under static conditions. The rate constant increased 1430-fold after the introduction of an optimum dose of Ce and treatment in Ar, O₂, and H₂ plasma and 550-fold after treatment with high-frequency plasma in H₂. The experimental activation energy increased in all instances; the activity grew because of the increase in the number of active centers. The promoting action of cerium was explained by the positive charge of the Ce^+α adatom, which initiated growth of the surface electron density; the influence of plasmochemical treatments was explained by the change in the number of structural defects and their character. Possible stepwise reaction schemes were considered based on ab initio quantum-chemical calculations.     

Solvent effects on structural properties of SiO2 gel using n-octylamine as a catalyst

We have investigated the effect of solvent(ethanol, acetone, isopropanol) on the sol–gel process of tetraethylorthosilicate (TEOS) in which case, n-octylamine is used as polycondensation catalyst. Two sets of materials were prepared in the laboratory by using ethanol, acetone and isopropanol as solvents respectively: (1) xerogels from TEOS/n-octylamine, and (2) composites from TEOS/polyhedral oligomeric silsesquioxanes /n-octylamine. The chemical structure of xerogels was studied by FTIR, TG–DSC, scanning electronic microscope and nitrogen adsorption–desorption isotherms techniques. The results have shown that the solvents directly influence the gel time. Gel time is longer for acetone than that of ethanol and isopropanol. In the case of TEOS xerogels, the materials are essentially mesoporous when n-octylamine is used as a catalyst. Silica, when ethanol is used as a solvent, exhibits a more narrow pore size showing textures with a microstructure uniformly distributed with different porosity levels. However, when the aged-isopropanol gel is used, silica shows textures with a microstructure nonuniformly distributed.     

Dependence of the adsorption and catalytic properties of a copper-platinum catalyst on the structure of metal particles and the composition of the catalyst surface

The kinetics of H₂ desorption from the surface of a copper-platinum catalyst deposited on silica gel ([1 wt % Pt + 0.15 wt % Cu]/SiO₂) and the kinetics of C₆H₁₂ dehydrogenation were studied. The effects of copper introduction in a platinum catalyst on the structural characteristics of platinum particles, the composition of their surface, and the effects of plasmochemical treatments on these parameters were studied by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The metal-H atom bond energies (E _Pt-H) and the catalytic activity were found to increase in the presence of Cu. This was explained by the formation of new hydrogen adsorption centers (due to the Cu^+δ adatoms) and catalytic centers composed of Cu^+δ adatoms and carbon atoms. The mean diameter of Pt particles (D) increased twofold. The microstresses (ɛ) in the particles increased after the catalyst was treated with glow discharge plasma in Ar and O₂ and with high-frequency plasma in H₂ (HF-H₂). The observed changes in the bond energy E _Pt-H and kinetic parameters were explained by the increase in microstresses in Pt particles.     

Structural,textural and catalytic properties of pure and Li-doped NiO/Al2O3 and CuO/Al2O3 catalysts

Pure and Li-doped NiO/Al₂O₃ and CuO/Al₂O₃ catalysts were prepared to contain 2, 4 and 8 wt.% of Ni and Cu, respectively. The structural properties were determined using DTA, XRD and FTIR techniques, and the textural properties of the catalysts were determined from their adsorption–desorption isotherms of nitrogen at 77 K. The chemisorption of hydrogen at 473–823 K with the pre-reduced catalysts was measured. The data obtained allowed the determination of the metal surface area, S (m²/g); the percentage of metal distribution, R; and the diameter of metal crystallite, d (nm). The amount of surface acidity, measured in mmol/g, was determined from the amount of chemisorbed pyridine necessary to completely inhibit the catalytic dehydration (DHD) of isopropanol. The conversion of isopropanol at 533–623 K was investigated using the micro-catalytic pulse technique. DTA, XRD and FTIR indicated that NiO and CuO exist as separate phases with crystallite sizes too small to be detected. No evidence has been gathered to indicate the existence of an aluminate phase.With the increase of metal loading, the surface area decreased whereas the total pore volume and the mean pore radius increased. Conversion of iso-propanol to propene proceeded via (DHD) on surface acid sites, and conversion of isopropanol to acetone proceeded via dehydrogenation (DHG) on redox sites. DHD and DHG exhibited first-order kinetics, and the rates of both reactions increased with temperature, with the latter being more temperature-dependent.     

Silica‐supported metallocenes: effect of the preparation procedure on the morphology of polyethylene particles

Polyethylene (PE) particles are produced by a catalyst prepared by contacting a (C₄H₉Cp)₂ZrCl₂/MAO pre‐mixing solution with SiO₂ support. These particles have a large granular size and very few fine particles compared with those derived from a catalyst prepared by adsorption of (C₄H₉Cp)₂ZrCl₂ onto methylaluminoxane modified SiO₂. The amount of Al in the pre‐mixing catalyst has an important effect on its activity and the PE particle size distribution. The optimal concentration is about 30 wt.‐%. The PE particles produced using a pre‐mixing catalyst consist of globules with randomly oriented fiber structure on the surface, whereas those produced using adsorption catalysts have worm‐like fibrils protruding from the PE globule surface.     

Carbon dioxide reforming of methane on a cobalt catalyst subjected to plasma–chemical treatment

The effect plasma–chemical treatments of 5 wt % Со/SiO₂ catalyst have on its activity in the carbonic acid conversion of methane in the interval of 700 to 900°C is studied. A plasma glow discharge in oxygen and argon was used along with high-frequency plasma in hydrogen for preliminary treatment of the catalyst. A multiple increase in СН₄ and СО₂ conversion and a 30–50 K drop in the temperature of the onset of the reaction are observed after plasma–chemical treatments. The strongest increase in activity is measured after the catalyst is treated with oxygen plasma. X-ray photoelectron spectroscopy is used to determine the change in the composition of the catalyst’s surface after it is treated with plasma, indicating that active forms of carbon atoms can be included in new active centers.     

A palladium complex immobilized onto mesoporous silica: a highly efficient and reusable catalytic system for carbon–carbon bond formation and anilines synthesis

A palladium complex supported on functionalized mesoporous silica MCM-41 proved to be a highly efficient, recoverable catalyst for C–C coupling reactions and amination of aryl halides to afford anilines. The nanocatalyst was characterized by FT-IR spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, N₂ adsorption–desorption isotherms and inductively coupled plasma analysis. The catalyst could be reused for several consecutive runs without significant loss of activity. The excellent yields of products, simple reaction procedures and short reaction times are the main advantages of this methodology.     

Synthesis of Layered Disodium (or Dipotassium) <Emphasis Type="Italic">Tetrakis</Emphasis>-(octanoate-o)-Zinc(II) and Preliminary Investigation of the Catalytic Activity in the Esterification of Octanoic Acid with Isopropanol

This paper reports the synthesis of layered zinc/sodium and zinc/potassium octanoates (A₂[Zn(C₈H₁₅O₂)₄], A = Na⁺ or K⁺), two underexplored carboxylates, through reaction of the octanoate of the desired alkali metal with a zinc salt. After drying and chemical characterization, their catalytic activities were tested in the esterification of octanoic acid with isopropanol. Conversion values were high for the reactions conducted under following conditions: temperature 155°C, isopropanol/octanoic acid molar ratio = 8: 1, catalyst/ octanoic acid ratio 7 wt %, and reaction time 2 h. Isolation of the catalysts after esterification showed that the materials were converted into zinc octanoate in situ.     

Isotherms of adsorption of aromatic compounds on cellulose from heptane-isopropanol solutions

The isotherms of adsorption of benzene, anisole, benzyl alcohol, and benzaldehyde on the surface of microspherical mesoporous crosslinked cellulose were calculated from the chromatographic peaks of these compounds with consideration given to the longitudinal smearing of the analyte zone under the action of adsorption forces. The solvents were n-heptane-isopropanol mixtures containing various amounts of isopropanol (up to 2 vol %). The adsorption isotherms were described using equations of the displacement adsorption theory. The mechanism of the sorption of aromatic compounds and the physical meaning of the constants entering into the adsorption isotherm equation were discussed.     

Metal–Organic Framework (MOF) Template Based Efficient Pt/ZrO2@C Catalysts for Selective Catalytic Reduction of H2 Below 90 °C

Selective catalytic reduction (SCR) of NO_x with H₂ as a reductant is the most promising denitration technology at low temperature. Achieving the conversion of NO_x into N₂ at ambient temperature not only prolongs the service life of the catalyst, but also provides more freedom for the arrangement of denitration units throughout the flue gas treatment equipment. However, the development of highly efficient, stable, and environmentally benign supported platinum‐based catalysts for H₂‐SCR at ambient temperature is still a major challenge. Herein, a 0.5 wt % Pt/ZrO₂@C catalyst, which was composed of carbon‐coated octahedral ZrO₂ with highly dispersed Pt particles, was prepared by using a new stabilization strategy based on UiO‐66‐NH₂ (a zirconium metal–organic framework) as a template. The catalytic performance of this Pt/ZrO₂@C in H₂‐SCR was tested and confirmed to achieve near 100 % NO_x conversion at 90 °C. Also, 70 % N₂ selectivity of the catalyst was achieved. The morphology, structure, and porous properties of the as‐synthesized nanocomposites were characterized by using data obtained from field‐emission SEM, TEM, XRD, Raman spectroscopy, thermogravimetric analysis, X‐ray photoelectron spectroscopy, and N₂ adsorption–desorption isotherms. The results show that residual carbon formed by pyrolysis treatment is coated on octahedral ZrO₂, and effectively prevents the agglomeration of platinum particles on the surface.     

Selective oxidation of CO in the presence of hydrogen on CuO/CeO<Subscript>2</Subscript> catalysts modified with Fe and Ni oxides

The selective oxidation of CO in the presence of hydrogen on CuO/CeO₂ systems containing Fe and Ni oxides as promoters was studied. The catalysts containing 1–5 wt % CuO and 1–2.5 wt % Fe₂O₃ supported on CeO₂ and the CuO/CeO₂ systems containing 1–2.5 wt % NiO were synthesized, and their catalytic activity as a function of temperature was determined. It was found that the additives of Fe and Ni oxides increased the activity of the CuO/CeO₂ catalysts with a low concentration of CuO. In this case, the conversion of CO at 150°C approached 100%. At the same time, these additives had no effect on the activity of the CuO/CeO₂ systems at a CuO concentration of 5 wt % or higher, which exhibited an initially high activity in the above temperature region. The forms of CO adsorption and the amounts of active sites for CO adsorption and oxidation were studied using temperature-programmed desorption. It was found that the introduction of Fe and Ni additives in a certain preparation procedure facilitated the formation of an additional amount of active centers associated with CuO. Data on the temperature-programmed reduction of samples (the amount of absorbed hydrogen and the maximum temperature of hydrogen absorption) suggested the interaction of all catalyst components, and the magnitude of this interaction depended on the sample preparation procedure. With the use of Mössbauer spectroscopy, it was found that the procedure of iron oxide introduction into the CuO/CeO₂ system was responsible for the electron-ion interactions of catalyst components and the reaction mixture.     

Synthesis, Characterization, and Catalytic Properties of Ti, V, and Zr-HMS Prepared by Metallocene Grafting

Ti, V, and Zr-HMS molecular sieves were prepared by grafting the respective metallocene onto the pure silica HMS, XRD, N₂-physisorption, TEM, UV-Vis spectroscopy and elemental analysis were performed to characterize the samples prepared. The XRD patterns of the metal-grafted samples exhibited well-defined (100) reflections, and the intensity remained almost constant as with pure silica HMS. Surface area, hysteresis loop in N₂ adsorption isotherms and N₂ volume adsorbed decreased after metal grafting. The order of catalytic activity for 2,6-di-tert-butylphenol (2,6-DTBP) oxidation using H₂O₂ was V-HMS (91.5 % conversion) Ti-HMS(20.3 %) Zr-HMS(8.4 %). Metal leaching was detected for all the grafted samples in the reaction media; V-HMS(22 wt.%) Zr-HMS(3 wt.%) > Ti-HMS(2 wt.%). For V-HMS and Zr-HMS, further reaction after catalyst filtration indicated significant contribution to the reaction by the dissolved species.     

Kinetic and equilibrium studies of lead(II) adsorption from aqueous media by KIT-6 mesoporous silica functionalized with –COOH

An organic–inorganic hybrid mesoporous silica was synthesized via post-grafting of KIT-6 with 4-(triethoxysilyl)butyronitrile. All samples were characterized using their N₂ adsorption–desorption isotherms, XRD, FT–IR, TEM, SEM, and PT. The adsorption potential of this material for removing Pb(II) from aqueous solutions was investigated via the batch technique, and the effects of pH and contact time were studied. Experimental data showed that the maximum Pb(II) adsorption, 76%, occurred in the pH range around 6. The adsorption equilibrium was reached within 40 min for 10 wt.%COOH/KIT-6. The adsorption data were fitted using the Langmuir and Freundlich isotherms, and the obtained modeling equilibrium adsorption data suggested that the 10 wt.%COOH/KIT-6 sample contained homogeneous adsorption sites that fit the Langmuir adsorption model well. The pseudo-second-order model described well the 10 wt.%COOH/KIT-6 adsorption process. The desorption and regeneration experiments indicated that ≈95% of the metal desorbed and the adsorbent could be regenerated via an acid treatment without altering its properties.     

Activity and selectivity of manganese oxides in alcohols Conversion as influenced by gamma-irradiation

Manganese oxide samples obtained from thermal decomposition of manganese carbonate at 400 and 600 °C were subjected to different doses of g-irradiation within the range 0.2 to 1.6 MGy. The surface and catalytic properties of the above samples were studied using nitrogen adsorption isotherms measured at -196 °C and catalytic conversion of ethanol and isopropanol at 300-400 °C using micropulse technique. The results obtained revealed that manganese oxides obtained at 400 °C consisted of a mixture of Mn₂O₃ and MnO₂ while the samples calcined at 600 °C composed entirely of Mn₂O₃. Gamma-irradiation resulted in a decrease in the particle size of manganese oxide phases with subsequent increase in their specific surface areas. Gamma-irradiation with 0.2 and 0.8 MGy effected a measurable progressive decrease in the catalytic activity in dehydration and dehydrogenation of both alcohols. However, the treated catalyst retained their initial activity upon exposure to a dose of 1.6 MGy. Also, g-irradiation increased the selectivities of the investigated solids towards dehydrogenation of both alcohols. The catalyst samples precalcined at 600 °C exhibited higher catalytic activities than those precalcined at 400 °C.     

Removal of C3F8 Via the Combination of Non-Thermal Plasma, Adsorption and Catalysis

The feasibility of C₃F₈ abatement via combining nonthermal plasma with adsorption and/or catalysis is investigated in this study. In terms of the simultaneous combination of plasma, adsorption and catalysis (CPAC), three different configurations including A/C layer (adsorbent layer prior to catalyst layer), C/A layer (catalyst layer prior to adsorbent layer) and A/C mixture (adsorbent and catalyst are mechanically mixed) are adopted. For all the experimental tests conducted in this study, the gas stream consists of 500 ppm C₃F₈, 2% O₂, and balanced N₂. The experimental results indicate that C₃F₈ removal efficiencies depend on what kind of packing material is adopted (adsorbent, catalyst or both) and how the material is packed within the plasma reactor. The removal efficiencies obtained with different reactors are in the order as: CPAC (A/C layer; AC mixture) > CPA (plasma with adsorbent alone) > CPC (plasma with catalyst alone) > CPAC (C/A layer). The indentified products after treatment include CO₂, CO, N₂O and CF₄. The formation of C₂F₆ is not observed in this study, which is encouraging since the global warming potential of C₂F₆ is actually higher than that of C₃F₈.     

Adsorption properties of aluminium oxide modified with palladium,gold, and cerium oxide nanoparticles

The adsorption properties of nanocomposites based on γ-Al₂O₃ modified with CeO_x, Au/CeO_x, and Pd/CeO_x nanoparticles with contents of deposited metals ranging from 0.07 to 1.71 wt % are investigated by means of dynamic sorption method. n-Alkanes (C₆–C₈), acetonitrile, diethyl ether, tetrahydrofuran, and dioxane are used as test adsorbates. Adsorption isotherms are measured, and the isosteric heats of adsorption of a number of test adsorbates are calculated. Electron-donor and electron-acceptor characteristics of the surfaces of γ-Al₂O₃-based nanocomposites are estimated. It is shown that Au(0.1%)/CeO_x(0.07%)/γ-Al₂O₃ nanocomposite, which has the lowest content of nanoparticles of the deposited metals, has the highest adsorption activity.