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Cobalt oxide catalysts deposited on titania–ceria supports were examined in deep ethanol oxidation and N2O decomposition. Supports with various molar ratio of CeO2/TiO2 were prepared by the sol–gel method and cobalt components were introduced by impregnation and subsequent calcination. The supports and catalysts were examined by chemical analysis, X-ray diffraction, nitrogen physisorption, H2-TPR, and NH3-TPD. It was found out that the ethanol conversion at 200 °C is proportional to the CeO2/(CeO2 + TiO2) molar ratio in the supports, and temperature T 50 of ethanol oxidation is proportional to the amount of components reducible in the temperature range of 20–500 °C. A comparison of specific catalytic activities in both ethanol oxidation and N2O decomposition proved a lower rate of N2O decomposition than that of oxidation of ethanol (approximately 25 times). The findings confirmed the great importance of the supports surface areas on specific activity of cobalt catalysts in both reactions. The obtained results showed that ceria is the best support of cobalt oxides for both deep ethanol oxidation and N2O decomposition when reaction rates are related to unit amount of active component in the catalysts.

Abstract Oxychlorination of ethene was performed over CuCl2/γ-Al2O3 catalyst in a microreactor (460 µm in diameter) and for comparison in a millireactor (1 cm in diameter). A copper-modified catalyst was prepared by a conventional evaporation–impregnation method without any promotors (e.g., K, Na, La) using copper (II) chloride as a precursor. The catalyst was characterized by nitrogen physisorption , Fourier transform infrared spectroscopy using pyridine , temperature-programmed desorption of CO 2, scanning electron microscopy, energy-dispersive X-ray microanalysis, and transmission electron microscopy. Different reactor types led to notable differences in catalytic performance at the same partial pressures in terms of both activity and selectivity. A higher reaction rate was achieved in the microreactor, which was 4.5 times faster. The activity decline and different selectivity to the desired product are explained by a change in the oxychlorination mechanism due to a different ratio of reagents in the mixture during the reaction.

The rutile effect on structural and photo-electrochemical properties and photo-induced activity were studied. Thin TiO2 layers were prepared by the sol–gel method using a reverse micelles system as a molecular template and deposited on the conductive ITO substrate by a dip-coating technique. Pure anatase or mixed anatase/rutile phase were obtained during the calcination step as a result of the selected temperature. The crystallographic structure was determined by Raman spectroscopy and XRD analysis. The positive influence of the presence of rutile particles in the thin layer on the photo-induced properties was verified. It was found that the mixed crystallographic phase of anatase and rutile can exhibit much higher photo-induced activity than pure anatase or the pure rutile form. The reason for this is that the excited electrons can easily transfer from the anatase surface states to rutile as well as from the anatase conduction band to rutile, which improves the electron-transfer rate. The electron transport between connected anatase and rutile particles can support the photo-excited charge separation and thus reduce the recombination rate.

Abstract Hydrothermally obtained mesoporous ceria-titania mixed oxides with different composition are modified with copper using incipient wetness impregnation and “chemisorption-hydrolysis” techniques. Their catalytic properties in methanol decomposition as a source of hydrogen and total oxidation of ethyl acetate as representative volatile organic pollutant are investigated. The effect of support composition and modification method on the formation of catalytic active sites is studied. The obtained results show that the catalytic behavior is determined by the activity of finely dispersed CuO crystallites and facile electron transfer in the “conjugated” Ti Ce Cu redox centres in the interface layer. The mechanism of the formation of the interface layer and the growth of CuO crystallites during different modification procedures are discussed in details. The mesoporous Cu Ce Ti oxides demonstrate excellent catalytic activity in total oxidation of ethyl acetate. Their catalytic behavior in methanol decomposition is strongly influenced by the reductive transformations, which are provoked by the reaction medium.

Abstract Thermal remediation technologies are very efficient for the removal of lipophilic organic contaminants from solid waste or soil. Compared to conventional heating method that is energy consuming due to the low thermal conductivity of contaminated material, microwaves bring several benefits for thermal solids treatment. There are three different approaches for the application of microwave heating for remediation - 1) contaminated material heating in a kiln, 2) the in-situ heating of contaminated surfaces and 3) the in-situ heating of subsurface soil environment. We developed and tested the pilot units for these applications including efficient off-gas treatment system. The pilot remediation tests were performed using 6 kW 2.45 GHz industrial microwave generators for the treatment of materials from several contaminated sites. During the tests, we measured detailed spatial temperature and contaminants mass distribution in the tested material. The achieved results confirmed promising data from laboratory tests and the high efficiencies of different contaminants removal were achieved at mild temperatures and with low energy consumption. Moreover, we gained important empirical knowledge about these innovative remediation technologies that has allowed to determine practical limitations for further scale-up and field applications or to validate future numerical models.

Abstract Metal phthalocyanines in the presence of visible light are applied in the semi-pilot level for the degradation of organic pollution represented by 4-chlorophenol (4-CP) with potential further scale-up. The effectiveness of the process based on the generation of singlet oxygen active species is compared with commonly used method of photochemical oxidation with hydrogen peroxide in the presence of ultraviolet irradiation. The direct comparison of the reaction systems was conceivable because both oxidation processes were carried out in identical experimental arrangements and under identical reaction conditions. The comparison was performed in terms of 4-CP conversion, TOC removal, apparent quantum yields, kinetic constants, and economy considerations. It must be emphasized there have been no reports on the semi pilot scale utilization of phthalocyanines for decontamination purposes previously.

Abstract Membrane separations enable biogas upgrading, but their energy efficiency must still be improved for industrial upscaling. Nevertheless, UV treatment affects the permeation properties of the polyamide functional layer of reverse osmosis (RO) and nanofiltration thin film composite (TFC) membranes. In this work, after membrane activation via Piranha solution, cysteamine grafting and UV irradiation, we determined the gas permeability of dry and swelled samples. The samples exhibited higher permeability to gases (CO2, CH4 and N2) than pristine membranes, reaching a 100% increase in RO membranes grafted with cysteamine after UV activation. Permeability increased more than twofold compared to TFC RO membranes activated by diode discharge plasma, as recently reported. Separation favored smaller gas molecules, and the increase in permeability resulting from all modifications did not adversely affect selectivity. CO2/CH4 selectivity remained almost constant over the range of trans-membrane pressure difference to 400 kPa. The grafting with cysteamine to the activated functional layer at the RO membrane positively affected permeability despite the detrimental effect of activation with a Piranha solution. The same activation or cysteamine grafting method at the nanofiltration membrane led only to a very short operation time, although the pristine nanofiltration membrane was stable. The pristine nanofiltration membrane were less permeable to all gasses than all RO membranes. Mixed gas separation of model binary biogas mixtures enhanced CH4 and CO2 permeability only in membranes activated with UV radiation. Decrease of mixed gas selectivity with the growing feed pressure showed that the gas mixture is more effectively separated at lower trans-membrane pressures. Therefore, our model for describing gas mixture separations in cylindrical permeation cells can be utilized to better evaluate the mass transfer coefficient and assess the strength of the coupling effect.

The sunshine duration data is analysed here from a new perspective, different from the traditional ones. The study is focused on pairs of periods of shining sun (called clear periods) followed by periods with the sun covered by clouds (called dark periods). Their statistical and sequential properties are illustrated by using results obtained from satellite observations and ground measurements at Timisoara (Romania). Solar irradiance time series measured at ground are converted into a database consisting of pairs of clear/dark periods. These pairs are associated with three cloud classes derived from satellite observations: C1 (the sky is cloud-free), C2 (cloudy sky) and C3 (sky with semi-transparent or fractional clouds). The study was conducted by using tools from survival analysis. This is a novelty in sunshine duration analysis. Since information is missing during the night, the clear/dark period correlation was studied considering a censoring procedure (for all nine combinations of cloud types at the beginning of dark and clear intervals). Cox regression has been used to study the influence of covariates (such as extraterrestrial solar irradiance and sun elevation angle) on sunshine duration distribution. Results show that increase of extraterrestrial solar radiation tends to increase the risk of stopping any clear or dark interval, i.e. it tends to increase the variability in solar irradiance. Regardless of cloud class, stochastically shorter intervals are found for increasing sun elevation angle.