Zaprezentowano użyteczność metod numerycznej mechaniki płynów dla zwiększenia skuteczności sorpcji sorbera przepływowego. Przedstawione zjawisko zachodzi w układach przepływowych, dla których prędkości płynącego czynnika nie zapewniają odpowiedniego stopnia jego mieszania, a tym samym czynnik sorbowany ma utrudniony dostęp do powierzchni sorbującej. Prędkość przepływu jest zbyt mała, aby zachodził przepływ burzliwy, a zbyt duża, aby mogło zachodzić efektywne zjawisko dyfuzji.
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The efficiency of Hg vapor sorption from the gas stream flowing through an absorber (flow rate 0.5–167 cm³/s) was detd. exptl. on an sulfonitrided steel sheet. The increase of gas velocity resulted in a decrease in sorption efficiency. Computer simulations of the sorption process were performed. The factors causing growth of gas flow turbulence (the distances between the absorber elements and their position relative to the flowing gas) had a significant influence on the process.
W pracy przedstawiono ogólną ideę funkcjonowania zminiaturyzowanych urządzeń laboratoryjnych zwanych Lab-on-a-Chip. Ich zadaniem jest przeprowadzanie określonych reakcji chemicznych i analiza chemiczna produktów tych reakcji. Oznacza to, że systemy Lab-on-a-Chip pełnią rolę kompletnego mikrolaboratorium chemicznego. Omówiono najważniejsze techniki stosowane przy konstrukcji tych urządzeń oraz podano przykłady zastosowań.
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The photocatalytic reduction of carbon dioxide with hydrogen was studied by Temperature-Programmed Surface Reaction (TPSR). This process was carried out in a flow reactor that was especially designed and constructed for this purpose. Titanium dioxide (TiO2, Degussa P-25) was used as supports for platinum, ruthenium and nickel catalysts. The experimental results indicated that the activity of photoreduction of CO2 changes as follows: Ru/TiO2> Ni/TiO2>= Pt/TiO2> TiO2.
The influence of reduction pretreatment of Pt/SnO2 catalysts on the catalytic performance in CO oxidation reaction was investigated.We can state that the catalytic activity of samples greatly depends on the kind of reducing agent and temperature of reduction. The obtained results were explained supposing that platinum can interact with tin dioxide and strong metal-support interactions (SMSI) are created. We concluded that hydrogen can create SMSI effect more easily than carbon monoxide.
Pt/SnO2-based pellistors and resistive sensors were applied to analysis of CO oxidation mechanism. Oscillatory behavior of the system was observed, the probable mechanism explaining the occurrence of oscillations was proposed.
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Porównano właściwości katalizatorów platynowych naniesionych na SnO2 i TiO2 oraz samych nośników w reakcji selektywnego utleniania tlenku węgla w obecności wodoru, PROX (preferential oxidation). Stwierdzono, że próbki 1% Pt/SnO2 i 1% Pt/TiO2 wykazują porównywalną aktywność katalityczną w reakcji utleniania CO, przy czym aktywność katalizatorów oraz samych nośników jest wyraźnie większa, jeśli w mieszaninie reakcyjnej obecny jest wodór. Zaproponowano mechanizm reakcji, w oparciu o podatność nośników na redukcję oraz stopień zdyspergowania fazy metalicznej.
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The 1% Pt/TiO2 (50 m2/g) was comparable to 1% Pt/SnO2 (8.7 m2/g) in activity and both were more active than the 5.7% Pt catalysts. Hydrogen added, 5%, to the reaction mixt., 2.2% CO + 2.3% O2 in He, made the catalysts and the supports more active A reaction mechanism was suggested, based on the reducibility and deg. of dispersion of the metal phase.
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Gold catalysts have recently been attracting rapidly growing interest due to their potential applications to many reactions, of both industrial and environmental importance. The oxidation of CO is one of the significant reactions. This article presents an overview of the recent study on more important factors that determine the catalytic activity of supported gold catalysts in CO oxidation reaction, with an emphasis on those that provide some information on the underlying chemistry. The criteria that must be met before high catalytic activity can be obtained, and the extreme sensitivity of the final catalyst to all stages of its preparation and treatment before use, are summarized. The influence of the preparation method, the size of the gold particle, the nature of the support and the effect of chloride on the catalysts performance as well as a conclusive analysis of the mechanism of CO oxidation over supported gold catalysts were presented.
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Przeprowadzono badania mające na celu porównanie różnych metod kalibracji procesów temperaturowo programowanej redukcji (TPR). Na podstawie wyników otrzymanych z przyjętej metody cechowania oraz profili TPR katalizatora 10% Ni/SiO2 określano stopień jego zredukowania. Obliczone wartości posłużyły do oceny zastosowanych metod cechowania.
Semiconductor gas sensors based on metal oxides (SnO₂, Al₂O₃) were constructed using ceramics technology. The stability and sensitivity of these sensors were studied when they were exposed to pure air and air containing 150 ppm hydrogen. The sensors fabricated from SnO₂ and containing over 10% Al₂O₃, show the best property.
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The development of semiconductor gas sensors for the detection of combustion and toxic gases has been in progress for several years. Ceramics gas sensors based on SnO2, TiO2, ZnO have been widely accepted as an important tool for detecting or monitoring gases and vapours like H2, CO, CH4, H2S, C2H5OH. The sensors are manufactured by means of different technologies. The most popular ones are resistant sensors based on SnO2, developed in Japan and currently produced on a large scale. Among these, TGS sensors (Tagushi Gas Sensors) from Japanese company Figaro are the most popular ones .The principle of the operation of this type of sensors consist in a comparison of electrical resistance of semiconducting oxide in air, and in the presence of the detected gas. The change in resistance is a function of the concentration of the gas. The gas sensing mechanism for a reducing gas such as carbon monoxide involves the reaction of CO with ionosorbed oxygen on the sensor surface leading to a decrease in resistance. (...) Because problem of catalysis in detection gases is very large, the review is divided into four parts: I. Sensing mechanism and preparation, II. The correlation between adsorption and detection, III. The correlation between catalytic activity and detection. In the last part of the paper (part IV) would like to show the role of adsorption and catalysis in other semiconductor gas sensors such as Pd-MISFET, SAW or Zirconia sensors. In this part of the paper, the mechanisms of detection and the influence of oxide-metal semiconductor preparation on properties of ceramics gas sensors is presented. The results of different works show that the sensing characteristic of semiconductor gas sensor can be improved by controlling fundamental factors which affect its receptor and transducer functions. The transducer function is related to the microstructure of the sintering specimen. This microstructure is characterised by the grain size and the depth of surface space-charge layer. On the other hand, the receptor function is modified by the introduction of foreign receptors on the surface of sensors. In the particular cases of Pt, Pb and Ag are promotors. These problems are presented in aspects of phenomenon of adsorption and catalysis and the role they play in detection of gases.