Search

In this work, it is demonstrated that visible-light photocatalytic activity for degrading methyl orange (MO) could be improved by co-milling of TiO2 (Degussa P25) with thiourea. The photocatalysts have been prepared by combined mechanochemical/thermal synthesis. Structures and morphology of the as-prepared TiO2 nanoparticles were characterized by X-ray powder diffraction, N2 adsorption–desorption isotherms, UV–Vis diffuse reflectance spectroscopy and scanning electron microscopy. It is shown that co-milling of TiO2 with thiourea favours formation of brookite phase and it results in the occurrence of more porous structures. The optical properties are modified and the band gap energy values of the samples become smaller, when thiourea is introduced. Ball-milled samples show better photocatalytic activities during oxidative discolouration of MO than that of the initial TiO 2. The discolouration degree is above 99% for ball-milled TiO2 /thiuourea nanoparticles, while it is 2% for pure and 15% for ball-milled TiO2 .

The presence of triple phase TiO2 new mixture (Magneli of higher order homologous series, brookite and anatase) containing P dopant ensures positive changes in the structure, in the phase composition and in the chemical composition. These changes explained the reasons for the enhanced UV/Vis photocatalytic efficiency towards oxidative degradation of ethylene and acetylsalycylic acid. The samples were characterized by a set of methods: Raman spectroscopy, Scanning Electron Microscopy (SEM), Diffuse-Reflectance Spectroscopy (DRS), Differential Thermal Analysis (DTA-TG), X-ray Photolelectron Spectroscopy (XPS), Transmission Electron Microscopy and High-Resolution Transmission Electron Microscopy (TEM/HRTEM), Electron Paramagnetic resonance (EPR) and X-ray Diffraction (XRD) analyses. The combination of the optimal set of values of Ti3+, oxygen radicals and vacancies, Ti-O-P bonds, narrower band gap is responsible for the higher quantum yield due to the increased number of charge carriers, while the unique phase mixture prevents the recombination of charge carriers. These factors guarantee enhanced rate of the photocatalytic reaction, and extended response to the visible light region.

Dense, highly textured, hydrophobic ZrO2-TiO2 (1:1) coatings with amorphous structure were prepared using the sol-gel method. Both organic and inorganic zirconium precursor salts were used. The present study dealt with the investigation of their protective ability in a selected model corrosive medium with chloride ions as corrosion activators. The coatings showed good anticorrosion performance during the test, which was demonstrated both by the weight loss method and potentiodynamic polarization curves. The samples were characterized by means of X-ray diffraction (XRD), Atomic Force Microscopy (AFM), contact angle measurements, Infrared spectroscopy (IRS), Scanning Electron Microscopy (SEM), Differential Thermal analysis (DTA-TG) and X-ray photoelectron spectroscopy (XPS). It was established that the extent of influence of some factors, like treatment temperature (Ttr) and type of zirconium precursor, was different. The PD curves of samples treated at 400 °C (A4 and B4, respectively) demonstrated an increased effect of the precursor in comparison to Ttr, since the application of organic Zr salt led to deterioration of the anodic passivation zones. Contrary to this, the coatings obtained from both the organic and inorganic Zr precursor salts with Ttr = 500 °C had similar corrosion efficiency, i.e., the influence of the precursor was minimized. All investigated coatings had no visible corrosion damage. It seems that some complex structural and surface parameters, such as amorphous dense structure, surface smoothness, hydrophobicity and the surface chemical composition (low hydroxyl groups content), were responsible for the increased anticorrosion properties of the composite films.

Photocatalytically visible light active thin SnO2/TiO2 bicomponent coatings with SnO2 underlayer, were deposited by spray pyrolysis. XRD, AFM, XPS and DRS analyses were used to characterize their morphology, phase and chemical composition, structure and band gap width. The model wastewater contaminant was diazo dye and the photocatalytic properties were tested by discoloration oxidation reaction. The photocatalytic activity of the SnO2/TiO2 system depends on the SnO2 precursor solution parameters: sprayed volume and the concentration of the SnO2 solution. It was revealed that the bicomponent coatings with SnO2 underlayer, which has been prepared at large spray solution volume and low tin precursor concentration exhibit increased photocatalytic activity. The combination of several factors ensures high rate of the oxidative reaction of degradation: the lower recombination degree of electron-hole pairs due to the separation of charge-carriers; decreased band gap energy, higher roughness and larger content of hydroxil groups on the surface of SnO2/TiO2 bilayers in comparison to the TiO2 films as well as the synergism between anatase and rutile phases.

Powder nanocomposites of TiO2/WO3 are prepared by a simple solid-state thermal procedure from commercial oxide powders and cast thereafter as a film coating on TLC substrate. The WO3 content in the powder composites is varied from 0.5 to 50%. The phase composition and morphology of titania/tungsten composites and films is characterized by SEM and X-ray analysis. The photocatalytic activity of TiO2/WO3 powders is tested in the degradation of malachite green dye in aqueous solutions under UV and visible light irradiation. The effect of preparation temperature on the photocatalytic activity is also investigated. It is found out that the mixed powder of 5%WO3 manifests the best photocatalytic performance. The prepared powder photocatalyst is deposited as a film coating on TLC sheet for gas-phase application. The as-obtained composite coated photocatalysts with 5%WO3 are tested for air purification from ethylene contamination under UV and visible light illumination. The TiO2/WO3 coated photocatalysts show always a higher efficiency in comparison to that of the pure TiO2.

Over the past few years, pharmaceutical drugs have been considered as emerging pollutants due to their continuous input and persistence in the aquatic ecosystem even at low concentrations. They have been detected worldwide in environmental matrices, indicating their ineffective removal from water and wastewaters using conventional methods. In this study we present photocatalytic purification of water from Acetaminophen and Chloramphenicol by ZnO upon UV-light illumination. Commercial ZnO powders are activated thermally (annealed at different temperatures-100, 200, 300, 400 and 500 °C for 1 h) and mechanically (treated for 5, 15, 20, 30, 40 and 60 min). The mechonoactivation is performed varying the atmosphere in air, or in suspension of ethanol and methanol. The changes in the studied material (phase composition, structure and particle size of the samples) and morphology have been investigated by means of X-ray diffraction and Scanning electron microscopy. The ZnO powders annealed at 100 °C show highest photocatalytic efficiency and rate constant of dye degradation, which is due to the smaller size of nanocrystallites and their better developed surface. The degradation rate of Acetaminophen and Chloramphenicol increases with time of mechanical activation up to 30 min and then decreases. The optimal temperature and time of mechanoactivation are experimentally established.

The photooxidation of oxalic acid, catalyzed by nanosized TiO 2 , CeO 2 , CeO 2 /TiO 2 and the respective gold-doped samples has been studied under irradiation with UV and visible light. UV–vis DRS, XRD, TEM, SEM, XPS techniques have been applied to the characterization of prepared photocatalysts. The photocatalytic mineralization of oxalic acid, catalyzed by CeO 2 /TiO 2 or Au/CeO 2 /TiO 2 , proceeded at a significantly higher rate under UV-A light irradiation than that under visible light. This is due to the low content of the CeO 2 (5 wt.%) in the composite catalyst. Doping the semiconductor materials with gold nanoparticles increases more than twice the rates of mineralization of oxalic acid, compared to non-doped samples. The higher rate constants of oxalic acid decomposition under UV or visible light irradiation over the CeO 2 /TiO 2 and Au/CeO 2 /TiO 2 catalysts, in comparison to those measured over the individual oxides, are due to the more efficient separation of the electron–hole pairs generated under irradiation. Especially efficient is the charge separation in the case of the Au/CeO 2 /TiO 2 photocatalyst under irradiation with UV light, when the rate constants of oxalic acid oxidation are approximately 1.6 times higher than the values when the process is catalyzed by Au/TiO 2 and 3.1 times higher than that over pure TiO 2 .

An alumina-supported silver composite system has been investigated in the reaction of heterogeneous catalytic ozone decomposition. Perlite loaded with silver and silver modified zeolites have also been tested as catalysts for gas phase conversion of ozone to molecular oxygen. The catalysts have been activated by calcination and the changes occurring on the catalytic surface as a result of the reaction have been characterized in details using XPS. The SEM analysis has revealеd the role of surface morphology in the process of ozone decomposition on the surface of Ag/α-Al2O3 catalyst. A catalytic cycle is proposed that supports the hypothesis about the important role of the peroxide species as intermediates participating in the process and catalyzing the complete ozone conversion into molecular oxygen. It has been found out that the maximum conversion degree, achieved with the alumina-supported silver system, is up to 90%.

Three different precipitating agents (NaOH, $$\hbox {NH}_{4}(\hbox {H})\hbox {CO}_{3}$$ and $$\hbox {CO}(\hbox {NH}_{2})_{2}$$ ) have been applied for the hydrothermal synthesis of ZnO powder materials, aiming at obtaining various types of porosity and surface species on ZnO. The synthesis procedures were carried out in the presence and in the absence of tri-block copolymer Pluronic (P123, EO20PO70EO20). These materials were characterized by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM)–energy-dispersive X-ray spectroscopy (EDX), BET method and TG–differential thermal analysis (DTA) method, and their photocatalytic activities were tested in the removal azo dye Reactive Black 5 (RB5). The urea precipitant yields spongy-like surface forms and the greatest share of mesopores. It has the highest specific surface area, highest degree of crystallinity of wurtzite ZnO phase and largest content of surface OH groups in comparison with the other two precipitants. The zinc hydroxycarbonate intermediate phase is missing in the case of NaOH as precipitating agent; therefore, it manifests poorer textural characteristics. The morphology of P123-modified sample is different and consists of needle-shaped particles. The urea-precipitated samples display superior performance in the photocatalytic oxidation reaction, compared with the other precipitated samples. The other two precipitating agents are inferior in regard to their photocatalytic activity due to greater share of micropores (not well-illuminated inner surface) and different surface morphologies.

Samples of Bulgarian perlite mineral deposit (natural alumino-silicate glass) in the Rhodope mountain were coated with Ag particles via a spray pyrolysis method. This method allows uniform distribution of the silver particles on the outer shell surfaces. SEM, XPS, FT-IR, and XRD methods were applied for characterization of the samples. The XRD investigations of the pristine samples revealed the formation of metallic silver and a small quantity of Ag2O3 phase. The presence of silver was also confirmed by XPS analysis. It was established that Ag/perlite composite prepared by spray pyrolysis is a promising catalyst for ozone decomposition. The high catalytic activity is preserved during the complete course of the catalytic reaction. After the catalytic activity test some structural and phase changes in the samples were observed. The XRD patterns of the ozonated samples proved the presence of metallic silver, AgO and Ag2O3 phases. The FT-IR analyses revealed that some bands, assigned to Si-O-Si stretching mod...

Nanosized calcium titanate (CaTiO3) powders were prepared for the first time by combination of two synthesis methods: hydrothermal treatment and mechanical milling (MM). The samples were analyzed by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy and High-Resolution Transmission Electron Microscopy (TEM/HRTEM), Diffuse-reflectance spectroscopy (DRS), infrared spectroscopy (IR), Differential Thermal analysis (DTA-TG) and Brunauer–Emmett–Teller (BET) method. The crystallite sizes and degree of crystallinity were decreasing with the increasing of MM time. SEM and TEM analyses have revealed that the mechanical milling results in changes in the size and shape of the particles — from regular prismatic shape to polygonal form with more oval borders. The increased milling time leads to increased number of agglomerates, which consist of smaller particles. The shifts to higher wavenumbers in the IRS bands were observed, which corresponded to Ti-O and Ti-O-Ti bridging stretching vibration modes. These effects could be assigned to structural distortion of the lattice. It was established that the mechanical milling influences the band gap energy of the samples: it is decreasing upon increasing the MM time. This study proved that the milled CaTiO3 exhibited increased photocatalytic activity in the Malachite Green (MG) discoloration under UV light with the increasing of milling time. The highest degree of discoloration of MG was observed with the sample, activated for 45 min (97% after 1 h of irradiation). The increased photocatalytic activity of MM samples could be due to increased number of defects (oxidation active sites) and lattice disorder, lower degree of crystallization, decreased particle size.

In this paper we demonstrate a way to prepare Pt/CeO2 catalysts and test their catalytic activity in WGSR. The catalysts have been synthesized by a simple and low cost extractive-pyrolytic method. The temperature programmed reduction analysis revealed that the presence of platinum particles enhances the reduction degree of ceria. The morphology of the surface, the particle size and specific surface area were determined by TEM, XRD and BET analysis. EPR studies gave evidence of metal–support interaction, which increases the mobility of oxygen anions in crystal lattice. The effects of various operating parameters including the catalyst bed temperature, space velocity and feed H2O/CO ratio were also investigated. Subjecting the samples to pretreatment with H2 or air had no strong effect on the catalytic activity. By varying the Pt loading, it was also found out that the maximum catalytic activity was achieved with the sample containing 1.2 wt% Pt, reaching up to 98 % CO conversion degree.

For the first time a combination of microwaves and/or the conventional treatment method was used to dry and heat multilayered sol-gel ZnO/TiO2/glass structures. Compact or porous TiO2 films were deposited as a bottom layer, covered with a ZnO film. The structures were characterized by X-ray Diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDX) and Scanning Electron Microscopy (SEM). Only peaks of wurtzite ZnO crystalline phase were registered on the X-Ray diffractograms. The microwave irradiation leads to a formation of poorly crystallized multilayers with very small crystallites and enhanced surface roughness. This results in a better photocatalytic activity of these structures than the structures of the samples treated conventionally. It was established that the morphology of the bottom titania layer affects the reaction of photocatalytic degradation of Malachite Green dye (MG). The structures with the compact bottom TiO2 films showed higher activities than those on porous TiO2 films. This study offers an energy saving method of producing ZnO/TiO2/glass multilayered structures of various morphologies and pronounced photocatalytic properties. The method does not involve any calcination step, normally applied to achieve a good degree of crystallization. This makes the method suitable for protecting substrates of low thermal stability.

Abstract Four photocatalyst samples, prepared from beech sawdust, were synthesized by an original method, combining pyrolysis and impregnation — two of them: TiO2 + activated carbon and other two — only activated carbon. The pyrolysis process has been carried out at two different temperatures — 680°C and 830°C. The prepared samples were characterized by a series of methods — XRD, BET, SEM and DTA/TG. The most important result was achieving visible light photocatalytic activity with an azo dye pollutant for both materials. The TiO2/AC-680°C sample demonstrated higher activity under visible light illumination than the TiO2/AC-830°C sample. The visible light activity was attributed to the active carbon component in the composite materials, which was evidenced by the photocatalytic tests with bare carbon (without any TiO2) manifesting visible light activity. The AC-680°C carbon was superior to the AC-830°C under visible illumination probably due to its higher specific surface area and porous texture. UV-light testing of the photocatalytic activity revealed that the TiO2/AC-680°C sample was higher than that of the TiO2/AC-830°C under polychromatic UV-A illumination (320–400 nm with a maximum at l = 365 nm). The TiO2/AC-680°C sample was also more efficient with the monochromatic UV-C illumination (l = 254 nm). Graphical abstract

The photooxidation of 2,4,6-trinitrotoluene (TNT), catalysed by nanosized photocatalysts: TiO2, WO3/TiO2, Au/TiO2 and Au/WO3/TiO2 was studied under irradiation with UV or visible light in the presence of O2 or O2–O3 mixture. The photocatalysts were characterized by the BET, XPS, TEM methods and adsorption of the model pollutant. The effectiveness of the processes of under UV-A, UV-C and visible light irradiation destruction in the presence of O3, photocatalysed by the WO3/TiO2, Au/TiO2 and Au/WO3/TiO2 samples is considerably higher than that registered in process, occurring with pure TiO2. Thus in the presence of O3 the rate constants of 2,4,6-trinitrotoluene photooxidation under UV-A, UV-C and visible light irradiation catalysed by Au/WO3/TiO2 are respectively 2.1, 1.4 and 6.2 times higher than that registered with pure TiO2. On the other side the ozone rate constants of 2,4,6-trinitrotoluene photooxidation under UV or visible light irradiation are also much higher than those, registered in the presence of O2 only. Thus under UV light irradiation the O3 rate constants of 2,4,6-trinitrotoluene photooxidation, catalysed by Au/WO3/TiO2 are 6 times higher, while under visible light they are 11 times higher than those with oxygen only. Under irradiation with UV-A, UV-C and visible light in the presence of ozone a synergistic effect has been registered, expressed most strongly in the case of TNT destruction, photocatalysed by Au/WO3/TiO2. Doping of the semiconductor materials with gold nanoparticles increases 1.4–2.2 times the rate constants of 2,4,6-trinitrotoluene mineralization, compared to the undoped samples, which is due to more efficient separation of the electron–hole charges generated upon irradiation.

The commercially available TiO2-catalyst (Degussa P25) was modified with nanosized platinum and silver particles by the photoreduction method to obtain different noble metal loading (0.5 and 1 wt.%). The characterization of the synthesized catalysts was carried out by the BET method, XPS, TEM and the adsorption of the model pollutant. The degradation of oxalic acid has been studied in aqueous solution photocatalyzed by band-gap-irradiated TiO2, modified with nanosized platinum or silver particles. The photocatalytic activity of TiO2, modified with noble metal, is approximately double that of the semiconducting support. The adsorption properties of the catalysts, as well as the noble metal content on the surface of the support, influence the efficiency of the photocatalytic process. The reaction rate of photocatalytic degradation of the oxalic acid follows a zero kinetic order according to the Langmuir–Hinshelwood model. The increase of the quantum yield of the photodestruction reaction of the studied model pollutant is due to the formation of Schottky barriers on the metal–semiconductor interface, which serve as efficient electron traps, preventing the electron–hole recombination.

CdS/ZnS nanocomposites have been prepared by a two-step solid-state mechanochemical synthesis. CdS has been prepared from cadmium acetate and sodium sulfide precursors in the first step. The obtained cubic CdS (hawleyite, JCPDS 00-010-0454) was then mixed in the second step with the cubic ZnS (sphalerite, JCPDS 00-005-0566) synthesized mechanochemically from the analogous precursors. The crystallite sizes of the new type CdS/ZnS nanocomposite, calculated based on the XRD data, were 3-4 nm for both phases. The synthesized nanoparticles have been further characterized by high-resolution transmission electron microscopy (HRTEM) and micro-photoluminescence (μPL) spectroscopy. The PL emission peaks in the PL spectra are attributed to the recombination of holes/electrons in the nanocomposites occurring in depth associated with Cd, Zn vacancies and S interstitials. Their photocatalytic activity was also measured. In the photocatalytic activity tests to decolorize Methyl Orange dye aqueous solution, the process is faster and its effectivity is higher when using CdS/ZnS nanocomposite, compared to single phase CdS. Very low cytotoxic activity (high viability) of the cancer cell lines (selected as models of living cells) has been evidenced for CdS/ZnS in comparison with CdS alone. This fact is in a close relationship with Cd(II) ions dissolution tested in a physiological solution. The concentration of cadmium dissolved from CdS/ZnS nanocomposites with variable Cd:Zn ratio was 2.5-5.0 μg.mL(-1), whereas the concentration for pure CdS was much higher - 53 μg.ml(-1). The presence of ZnS in the nanocrystalline composite strongly reduced the release of cadmium into the physiological solution, which simulated the environment in the human body. The obtained CdS/ZnS quantum dots can serve as labeling media and co-agents in future anti-cancer drugs, because of their potential in theranostic applications.

Activated ZnO powder has been prepared by procedures involving first its dissolution in nitric acid, then simultaneous treatment by adding NH4OH and CO2 bubbling leading to precipitation as Zn(OH)CO3 (ZH) and further thermal decomposition of ZH at 400 °C. The gas evolution leads to formation of pores and increase in the specific surface area. Chemically activated M/ZnO powders doped with Mn, Co, Ni, Cu, and Ag have been obtained by the impregnation method. The samples have been characterized by ultraviolet-visible (UV-Vis) spectroscopy, diffuse reflectance (DR) UV-Vis, X-ray diffraction (XRD), single point Brunauer-Emmet-Teller (BET), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS) methods. The experiments have shown that metal-doped activated ZnO powders possess higher photocatalytic activities in oxidative discoloration of model contaminant textile coloring dye Reactive Black 5 in slurry reactor compared to that of the pure ZnO. The XRD and XPS data have shown the presence of defects, nonstoichiometricity implying the formation of solid solutions. Copper-doped (1.5 wt%) activated ZnO (Cu(2+) replaces Zn(2+)) is outstanding in its photocatalytic performance in discoloration of the dye due to the higher specific surface area and improved charge carrier separation.

The crystallographic phase, surface features and photocatalytic properties in the reaction of decolorization of Malachite Green dye over TiO 2 (0–100 mol%) doped ZnO films have been investigated. The films have been prepared by polymer modified spray pyrolysis. The crystallization degree and the size of the crystallites comprising the films have been found to be influenced by the TiO 2 content in the spraying solution. The undoped ZnO film has little porosity. The titania dopant causes formation of hexagonal nanorods on the ZnO surface. The increase in TiO 2 content results in enhancement of both size and crystallization degree of the nanorods. When the TiO 2 content is increased (i) the Zn2p, O1s and Ti2p peaks are shifted to lower binding energies, (ii) the atomic ratio of O L /Zn is decreased and (iii) the amount of adsorbed hydroxyl (OH − ) species is increased. All the TiO 2 doped ZnO films manifested higher photocatalytic activity than that of the undoped ZnO and TiO 2 samples. The films obtained from solutions with 50 mol% TiO 2 showed the fastest decoloration of the dye.

The catalytic activity of a wide range of transition metal oxides in oxidation of sulphide ions by air in aqueous medium was studied. Some specific features of the reaction mechanism on some of the studied oxides were considered. The transition metal oxides are promising catalysts for practical application. Some of these oxides will allow the preparation of catalysts possessing activity comparable to that of the cobalt phthalocyanine based catalysts, popular in industrial practice.

The review, based on 92 references, is focused on degradation of organics by ozonation and it comprises various classes of oxygen-containing organic compounds - alcohols, ketones, ethers and hydroxybenzenes. The mechanisms of a multitude of ozone reactions with these compounds in organic solvents are discussed in details, presenting the respective reaction schemes and the corresponding kinetic parameters are given and some thermodynamic parameters are also listed. The dependencies of the kinetics and the mechanism of the ozonation reactions on the structure of the compounds, on the medium and on the reaction conditions are revealed. The various possible applications of ozonolysis are specified and discussed. All these reactions have practical importance for the protection of the environment.

The catalytic properties of supported cobalt phthalocyanines, containing different substitutes, in oxidation of ethylmercaptan to disulphide, have been studied in a flow system. The inclusion of electron-donor substitutes in the phthalocyanine molecule leads to an increased Catalytic activity, while electron-acceptor substitutes decrease it. In the absence of NaOH the productivity of the most active catalyst samples is unstable and drops quicker than that of the less active ones. In the presence of NaOH the activity of the phthalocyanines is stable and high. This fact is explained and interpreted in terms of the mechanism of the oxidation process.

The inhibiting effect of high feed carbon dioxide concentrations (12–33%) on ethene epoxidation and combustion reactions over Ag/Al2O3 catalyst was studied by the flow-circulation method. Kinetic measurements have been carried out under steady-state conditions, at atmospheric pressure and in the temperature range 483–565 K. It has been established that the feed carbon dioxide inhibits considerably both the epoxidation and the combustion of ethene, the effect on the latter being stronger. Therefore, the presence of carbon dioxide in the feed affects the selectivity favourably. The inhibiting effect is described quantitatively by a kinetic model consisting of two rate equations, one for the epoxidation and the other for the combustion reactions. The model is to be used when the carbon dioxide concentration in the reaction mixture is higher than 10% and the temperature is in the range 513–565 K. The model is empirical and it is compared with a mechanistic model derived on the basis of the assumed reaction mechanism. The empirical model fits the experimental results better.

The selective oxidation of ethylene over supported silver catalyst was studied in the presence of 0.2–16% feed water vapour. In addition to silver, alumina and silica, the catalyst also contains Li, Na, K, Mg, Ca, Ba, Mn and Fe additives in trace amounts. Steady-state kinetic measurements were carried out using a glass flow-circulation system at atmospheric pressure and in the temperature range 210–264°C, varying the oxygen-to-ethylene concentration ratio in the feed. The results show that the partial oxidation of ethylene is inhibited by the presence of feed water but the complete oxidation is promoted by it. This result contradicts the results of other workers. The reason for this contradiction is probably the presence of the additives in the studied catalyst. The effect of water is stronger at low feed concentrations (0.2–1.4%), at which the process is carried out in the industrial reactor. This fact could be of great importance for selecting the optimum conditions for the industrial process. The presence of feed water has an unfavourable effect on the selectivity for ethylene oxide, unlike the effect of carbon dioxide in the feed established in previous work over the same catalyst. An explanation of the effect of water vapour on the oxidation of ethylene is proposed on the basis of the assumed reaction mechanism.

Nanosized TiO2 films were deposited by spray pyrolysis and thermally treated at 400oC. Then the films were dipped in 1M aqueous solution of HCl. The activated samples were divided into two parts - one part was dried (A) and another was annealed (AT) in air. The photocatalytic degradation of Reactive Black (RB5) textile dye under visible light was tested. The following instrumental methods: X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were applied for the phase and surface characterization of obtained samples. According to Raman and XRD analyses all films are anatase. The XRD showed that activated films are better crystallized than non activated TiO2 film. The presence of chlorine at 200.3 eV was registered for acid activated samples by X-Ray photoelectron spectroscopy. The acidic activated films exhibited higher rate of dye photodegradation than that of the reference TiO2 sample. The photocatalytic efficiency decreases in the order A > AT> non activated TiO2 films. The degradation rate constant for acid activated films is two times higher than those of the reference film. The hydroxyl content in TiO2 acidic activated films is greater than that of the non- activated films, which results in significant increase in the photocatalytic activity. In addition, the presence of chlorine may also lead to enhancement in efficiency.

Thin nano-sized TiO2 films were deposited on aluminum foil substrates by the spray pyrolysis method, using Ti(i-OPr)4 (TIP) and TiCl4 (TC) as precursors. The films were characterized by means of X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). According to the XRD patterns the as-deposited films appear to be amorphous. The thermal treatment at 400°C leads to the formation of anatase nano-crystallites. The XPS analyses showed that the Ti2p broad photoelectron peak of as-deposited TC films indicated a mixture of Ti3+ and Ti4+ oxidation states. After treatment at 400°C the Ti2p peak displays only Ti4+ oxidation state for both TIP and TC films. The number of hydroxyl groups on the surface is decreased after the thermal treatment. The photocatalytic activity of the films was studied towards degradation of azo dye Reactive Black 5 (RB5) as model wastewater pollutant under visible light illumination. It was found out that the films obtained from TC were more active than those obtained from TIP films. The thermally treated samples are better photocatalysts than those non-treated, because they posses anatase crystalline phase and stoichiometric TiO2. The TOC measurements showed minimal concentration of total organic carbon in the dye solution after 180 min of visible light irradiation.

A kinetic study of selective ethylene oxidation to ethylene oxide over a silver catalyst has been carried out by the circulation flow method. The silver was promoted by a Ca additive and was supported on alumina. The experiments were conducted under steady state conditions in the temperature interval 210 – 292°C and at atmospheric pressure. As a result of this kinetic study two rate equations, for the partial and for the complete oxidation reactions, are proposed. A reaction scheme is put forward, according to which adsorbed molecular oxygen produces ethylene oxide, whereas the atomic oxygen is responsible for the complete oxidation reaction. The empirical kinetic model corresponds to a Rideal-Eley type of mechanism. Selectivity decreased with temperature increase and with decrease of the oxygen content in the feedstock.

Three commercial Kieselguhr-supported copper, nickel and coppernickel catalysts were investigated under severe conditions in the hydrogenation of nitrobenzene to aniline. Self-sustained oscillations of the catalyst bed temperature in the 438 – 593 K range were observed after a partial deactivation of the studied samples. The oscillation mode was changed upon external heating. The experimental results show that the oscillations are due to mass transfer retardation effects and the nature of the chemical processes. An explanation of the observed phenomenon is proposed, according to which a hot zone is formed in the front layer of the catalyst bed. The zone cycles up and down along the catalyst bed.

The kinetics esterification of the methacrylic acid (MA) with ethylene oxide (EO), catalysed by polymer-supported ferric chloride, has been studied in a static reactor under quasi-stationary conditions. The temperature interval 50–90°C was investigated and the mole ratio of MA to EO was varied from 2:1 to 1:10. The catalyst amount was varied from 1 to 10 wt.-%. As a result a kinetic model of the reaction is proposed. The model corresponds to a single-site Langmuir-Hinshelwood mechanism. The rate-limiting step is a surface reaction. Optimum conditions for the esterification are 80°C, a mole ratio of MA to EO of 1:1 and 1–3 wt.-% catalyst.

The kinetics of the isomerization of butenes over an industrial CoO MoO3/Al2O3 catalyst for hydrodesulphurization of Diesel fractions has been studied by the flow circulation method. The study was carried out under steady-state conditions at atmospheric pressure and in the temperature range 325–425°C. The selectivity of the catalyst for cis-2-butene is practically the same for both the reduced and the sulphided form, but the activity of the reduced form is greater. The selectivity decreases with increasing temperature, with contact time and with 1-butene concentration in the feed, for both the sulphided and the reduced form. Evidence was obtained that suggests that surface reactions are the rate-determining steps under these reaction conditions. The values of the relative rate constants for the three experimental temperatures of 325, 375 and 425°C were calculated by the Wei-Prater method. These values and those obtained for the activation energies show that cis-2-butene is a kinetic control product, as it is formed faster than trans-2-butene which is a thermodynamic control product.

The kinetics of the complete oxidation of ethylene oxide over a supported silver catalyst in the absence of dichloroethane was studied by the flow circulation method. The temperature range 100–300°C was investigated under steady-state conditions and at atmospheric pressure. The kinetic measurements showed that ethylene oxide oxidation starts at 190°C. Below this temperature, the ethene oxidation over a silver catalyst proceeds according to the parallel reaction scheme. At 300°C and an oxygen: ethylene oxide feed ratio of 1:2 catalytic decomposition of ethylene oxide to ethene and oxygen was observed. A sequential experimental design was applied for the determination of the parameters and the simultaneous discrimination of rival kinetic models. A kinetic model is proposed that describes the rate of uninhibited ethylene oxide oxidation in the temperature range 250–300°C. The model corresponds to a mechanism in which ethylene oxide and oxygen adsorption (dissociative and non-dissociative) are fast steps at equilibrium. The rate-limiting steps are ethylene oxide oxidation to formaldehyde and further to carbon dioxide and water with the participation of both atomic and molecular adsorbed oxygen. These steps are irreversible. The calculated kinetic constants offer the possibility of evaluating tentatively the rate constants of the irreversible steps and the equilibrium constants of the fast reversible steps.

The kinetics of isomerization of butenes over an industrial CoO MoO 3 /Al 2 O 3 catalyst have been studied by the flow-circulation method under steady state conditions, at atmospheric pressure and in the temperature interval 325–425°C. As a result of the study a kinetic model is proposed for the reduced form of the catalyst. The kinetic model is of the Langmuir-Hinshelwood type and corresponds to a single site mechanism. The adsorption and desorption of the three isomers, 1-butene, cis-2-butene and trans-2-butene are fast steps at equilibrium under these experimental conditions. The rate-limiting step is a surface reaction. The kinetic constants of the model provide a possibility to evaluate the rate constants of the surface interactions. The model adequacy for the description of the dependence of selectivity and conversion on temperature, contact time and feed composition is extensively illustrated.

The complete oxidation of ethylene oxide over a supported Ag/A1203 catalyst has been studied independently and separately from ethene oxidation [ 1,2]. During a steady-state kinetic study in the absence of the industrial promoter of selectivity, ethylene dichloride, autooscillations of the catalyst bed temperature were observed. [ 11. This result is interesting as no oscillations during this reaction have been reported in the literature. According to Stoukides and Vayenas [ 3 1, who studied rate oscillations during propylene oxide oxidation over silver, such oscillations will not be observed during the catalytic oxidation of ethylene, propene and ethylene oxide under the same conditions. The aim of the present letter is to describe briefly the conditions and the form of these thermooscillations, which were observed for the first time during the catalytic oxidation of ethylene oxide.