Zirconium dioxide, catalyst

An important new route to indolizidine starts from 2-(3-hydroxy-propyl)tetrahydrofuran, which is converted via the chloro and cyano compounds into the amine. This is then cyclized to indolizidine in good yield with an alumina/zirconium dioxide catalyst. The 6-methyl derivative has also been prepared as a mixture of isomers from 2-(3-hydroxy-butyl)-tetrahydrofuran.233... 

The activation of carbon dioxide was studied over a zirconium dioxide catalyst via infrared spectroscopy and 0-labeled reactants. The carbon dioxide adsorbed on the surface as either a carbonate or a bicarbonate species. The carbonate species formed as a result of CO2 Interaction with lattice oxygen. The bicarbonate species formed from CO2 interaction with a hydroxyl group. There was no direct interconversion between the carbonate and the bicarbonate. It is proposed that the bicarbonate can be converted to the formate via molecular CO. 

Vandeven UM, Sachtler WMH, Van Santen RA Acid sites in sulfated and metal promoted zirconium dioxide catalysts. J... 

Ethyl Acetate. Catalysts proposed for the vapor-phase production of ethyl acetate include siUca gel, zirconium dioxide, activated charcoal, and potassium hydrogen sulfate. More recendy, phosphoric-acid-treated coal (65) and calcium phosphate (66) catalysts have been described. 

The vapor-phase esterification of ethanol has also been studied extensively (363,364), but it is not used commercially. The reaction can be catalyzed by siUca gel (365,366), thoria on siUca or alumina (367), zirconium dioxide (368), and by xerogels and aerogels (369). Above 300°C the dehydration of ethanol becomes appreciable. Ethyl acetate can also be produced from acetaldehyde by the Tischenko reaction (370—372) using an aluminum alkoxide catalyst and, with some difficulty, by the boron trifluoride-catalyzed direct esterification of ethylene with organic acids (373). 

Another study on the preparation of supported oxides illustrates how SIMS can be used to follow the decomposition of catalyst precursors during calcination. We discuss the formation of zirconium dioxide from zirconium ethoxide on a silica support [15], Zr02 is catalytically active for a number of reactions such as isosynthesis, methanol synthesis, and catalytic cracking, but is also of considerable interest as a barrier against diffusion of catalytically active metals such as rhodium or cobalt into alumina supports at elevated temperatures. 

Two catalyst systems were developed by Standard Oil and Philips petroleum. Standard Oil process uses metal catalyst such as molybdenum trioxide on supports like alumina or titanium or zirconium dioxide. The process is carried out at 200-300°C at Organisation and Qualities... 

Santacesaria E., Tonello M., Storti G. et al. Kinetics of titanium dioxide precipitation by thermal hydrolisis. J. Colloid Interface Sd. 1986 111 44-56. Reinten Kh.T. Equipment, preparation and properties of hydrated zirconium dioxide. In Structure and Properties of Adsorbents and Catalysts. Ed. Linsen B.G. Moskva Nauka, 1973, p. 332-83. 

Nano-grained Ni/ZrOj and Ni/ZrOj-Sm Oj catalysts were prepared from amorphous Ni-Zr and Ni-Zr-Sm alloys by oxidation-reduction treatment. Their catalytic activity for methanation of carbon dioxide was examined as a function of precursor alloy composition and temperature. The addition of samarium is effective in enhancing the activity of the nickel-rich catalysts, but not effective for the zirconium-rich catalysts. The surface area and hydrogen uptake of the nickel-rich catalysts are increased by the samarium addition. In addition, tetragonal zirconia, the formation of which is beneficial to the catalytic activity, is stabilized and formed predominantly by the addition of samarium to the nickel-rich catalysts, although monoclinic zirconia is also formed in the zirconium-rich catalysts. As a consequence, the higher conversion of carbon dioxide is obtained on the Ni-Zr-Sm catalysts with relatively high nickel contents. 

The conversion of carbon dioxide on the catalysts prepared from nickel-rich amorphous Ni-Zr alloys is improved by the addition of samarium. On the other hand, the activity of the zirconium-rich catalysts is not influenced by the addition of samarium. The predominant formation of tetragonal zirconia in the nickel-rich Ni-Zr-Sm catalysts, in contrast to the formation of two types (monoclinic and tetragonal) of zirconia in the zirconium-rich Ni-Zr-Sm catalysts, appears to be responsible for the higher catalytic activity of the nickel-rich catalysts in addition to their higher surface area than the corresponding samarium-free Ni-Zr catalysts. 

Catalysts active in the isomerization of n-butane have been synthesized by depositing sulfate ions on well-crystallized defective cubic structures based on ZrOz. This technique for introduction of sulfates does not result in any significant changes in the bulk properties of zirconium dioxide matrix. Active sulfated catalysts were prepared on the basis of cubic solid solutions of ZrOz with calcium oxide and on the basis of cubic anion-doped ZrOz. The dependence of the catalytic activity on the amount of calcium appeared to have a maximum corresponding to 10 mol.% Ca. Radical cations formed after adsorption of chlorobenzene on activated catalysts have been used as spin probes for detection of strong acceptor sites on the surface of the catalysts and estimation of their concentration. A good correlation has been observed between the presence of such sites on a catalyst surface and its activity in isomerization of n-butane. 

We have recently suggested a new approach to the preparation of active sites in sulfated zirconia catalysts [5, 6]. In this case, the catalysts are prepared by deposition of sulfate ions on crystalline zirconium dioxide samples with highly defective structure. According to numerous reports, the monoclinic phase typical for ZrOa is not suitable for this purpose. We have shown that active materials could be obtained by impregnation of zirconia-based oxides with cubic crystalline structure. It should be noted that the cubic structure is not thermodynamically stable for pure zirconia at low temperatures. It can be stabilized by introducing different additives, in particular, alkaline-earth metal cations [7]. Recently, similar results have been obtained for ZrOa stabilized by Y2O3 [8]. 

Zirconium dioxide and zeolites of pentasil structure are widely used as catalysts and efficient carriers in many heterogeneous reactions, and particularly in the process of selective catalytic reduction of nitrogen oxides by hydrocarbons (SCR-process) [1,2]. Synthesis of new catalytic systems for NOx SCR-process by CnHm is therefore related with searching for their optimum composition and preparation methods to attain maximum activity in this reaction. 

The data on the catalytic activity of the samples MexOy/Zr02 in the process of NOx SCR by hydrocarbons are given in Table 1. It is seen that the activity of zirconium dioxide-based oxide catalysts dependent on a method to prepare Zr02 , and 10% Cr203/T-Zr02 sample prepared by sol-gel method was found to be a more active catalyst in the reaction with propane-butane. 

The Cr203/Zr02 catalysts showed activity in the SCR of NO by a propane-butane mixture, which depended on the means of preparation of the zirconium dioxide. Thus, the conversion of NO to N2 was 13-17% at 350 °C on 5-10 wt.% Cr203/Zr02 catalysts obtained by precipitation, while the conversion of NO to N2 was 54% at 300 °C on catalysts with analogous composition obtained through an alcogel step. This more active sample was also tested in the presence of SO2 (0.02%) in the reaction mixture. The conversion of NO in this case was also enhanced and reached 60% at 300-350 °C. This increase in activity by the action of sulfur dioxide may be attributed to the formation of sulfate since sul ted zirconium dioxide is a solid superacid and catalyzes the SCR of NO by hydrocarbons [11]. 

With 10% CoO/Zr02 catalyst, conversion of NO (in reaction with methane) reached 75% at 310 °C, while the selectivity with respect to nitrogen decreased from 100% at 415 °C to 63% at 310 °C (the remainder was N2O). There was no dependence of the catalytic activity of samples of CoO/Zr02 on the method used to prepare zirconium dioxide. Both samples (No. 3 and No. 4, Table 1), in which zirconium dioxide was made by precipitation and the sol-gel method, respectively, had similar activity. This difference of behavior between samples of the CoO/Zr02 and Cr203/Zr02 catalysts may be explained by differences in the interactions of CoO and Cr203 with zirconium dioxide and, consequently, different influence of these catalysts on activation of methane and propane-butane. 

It has been established from these studies that the different catalytic properties of transition metal oxides (chromium, cobalt) on zirconium dioxide are attributed to their different acidic properties determined by TPDA and IR-spectroscopy. The most active catalyst is characterized by strong acidic Bronsted centers. The cobalt oxide deposited by precipitation on the zirconium-containing pentasils has a considerable oxidative activity in the reaction N0+02 N02, and for SCR-activity the definite surface acidity is necessary for methane activation. Among the binary systems, 10% CoO/(65% H-Zeolite - 35% Z1O2)... 

The root canal sealers based on silicone are a variation on the addition-polymerized silicone used clinically as an impression material [62]. They have been modified to improve their flow, but their essential chemistry is the same. They consist of two-paste systems comprising a base and a catalyst paste. The silicone components are a polydimethylsiloxane polymer blended with paraffin oil and filled with finely divided zirconium dioxide. This latter substance both reinforces the set silicone material and confers radiopacity. 

Zirconia ceramics are used for a variety of applications as catalysts, structural materials, and electrolytes for solid-oxide fuel cells. Zirconia (zirconium dioxide ZrOg) exhibits a phase transition sequence, " ... 

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