Silica-zirconia catalysts

In a particular experiment, p-cresol (23.54 g, 0.22 mol), methyl-f-butyl ether (19.36 g, 0.22 mol) and a silica/zirconia catalyst (3.5 wt%) were heated at 100°C for 3 hours. After cooling, 13.0 g of the product, 2-t-butyl-p-cresol was obtained, and 10.78 g of p-c resol was left unreacted. The FW of the product = 164 g/mol. Calculate the atom economy, yield, selectivity, carbon efficiency, and environmental factor. 

Comparison of the acid properties silica-zirconia catalysts... 

X-ray dififtaction (XRD) analysis of the freshly calcined catalysts as well as samples used for several hours in the isomerization reaction, only presented the peaks corresponding to the tetragonal form of zirconia. At the same time, for the silica series, XRD confirmed the presence of NiO on the unsulfated catalysts and NiS04 on the sul ted ones. However, XRD did not show any evidence of any of these species for the zirconia series, probably due to their high state of dispersion. Similarly, the XPS data clearly showed the presence of NiO and NiS04 on the unsulfated and sulfated silica-supported catalysts, respectively, but they were not conclusive in the case of zirconia series since both sulfate and oxide species were observed. 

Accordingly, work has been done on series of n-paraffins,. isoparaffins, naphthenes, aromatics, and naphthene-aromatics which have been chosen as representative of the major components of petroleum. In addition, olefins, cyclo-olefins, and aromatic olefins have been studied as a means of depicting the important secondary reactions of the copious amounts of unsaturates produced in the majority of catalytic cracking reactions. A silica-zirconia-alumina catalyst was used principally it resembles closely in cracking properties typical commercial synthetic silica-alumina catalysts. 

Mole % 1 atmosphere silica-zirconia-alumina catalyst, Universal Oil Products Co. Type B ... 

Conventionally, a fixed bed catalyst containing palladium, a promoter metal, and an alkali metal acetate is used. The fixed bed catalyst components are supported on a porous carrier such as silica, zirconia or alumina. 

The solid acid catalyzed adamantylation of substituted benzene derivatives was studied with the aim to achieve high para regioselectivities. Of various acidic resins, zeolite HY, sulfated zirconia, perfluorolkanesulfonic acids, and phosphotungstic acid, Amberlyst XN-1010 was found to be the catalyst of choice to afford para-substituted alkylbenzenes with selectivities exceeding 70%.398 In further systematic studies with a Nafion-H-silica nanocomposite catalyst,399 and various... 

The use of certain vanadium compounds as catalysts has been increasing. Vanadium oxy trichloride is a catalyst in making ediylene-propylene rubber. Ammonium metavanadate and vanadium pentoxide aie used as oxidation catalysts, particularly in the production of polyamides, such as nylon, in the manufacture of H>S04 by the contact process, in the production of phdialic and maleic anhydrides, and in numerous other oxidation reactions, such as alcohol to acetaldehyde, anthracene to anthraquinone, sugar to oxalic acid, and diphenylamine to carbazole. Vanadium compounds have been used for many years 111 die ceramics field for enamels and glazes. Colors are produced by various combinations of vanadium oxide and silica, zirconia, zinc, lead, tin, selenium, and cadmium. Vanadium intermediate compounds also are used in the making of aniline Mack used by the dye industry... 

The acid function of the catalyst is supplied by the support. Among the supports mentioned in the literature are silica-alumina, silica-zirconia, silica-magnesia, alumina-boria, silica-titania, acid-treated clays, acidic metal phosphates, alumina, and other such solid acids. The acidic properties of these amorphous catalysts can be further activated by the addition of small proportions of acidic halides such as HF, BF3, SiFit, and the like (3.). Zeolites such as the faujasites and mordenites are also important supports for hydrocracking catalysts (2). 

Although the decomposition of ozone to dioxygen is a thermodynamically favoured process,126 it is thermally stable up to 523 K and catalysts are needed to decompose it at ambient temperature in ventilation systems, in the presence of water vapour and at high space velocity. A limited number of catalysts have been evaluated and active components are mainly metals such as platinum, palladium and rhodium, and metal oxides including those of manganese, cobalt, copper, iron, nickel and silver. Supports that have been used include 7-alumina, silica, zirconia, titania and activated carbon.125,170... 

Several different types and sizes of catalyst have been employed in commercial catalytic cracking processes. The commercial catalysts have been composed predominantly of either silica and alumina, or silica and magnesia. Other compositions have been investigated in the laboratory although some, such as silica-zirconia, alumina-boria, and alumina activated with various fluorides, have high activities, none has yet proved sufficiently attractive to warrant displacing the presently used catalysts. 

The fundamental relationship between cracking activity and acidity is indicated by the fact that a single correlation line is obtained with catalysts of different chemical composition and made in different ways (222). Silica-alumina, silica-magnesia, silica-zirconia, and activated-clay catalysts were included in the comparison. Acidity in this case was meas-... 

Tanabe has reviewed the earlier work with silica-magnesia, silica-zirconia, and other amorphous siliceous materials. In a model for binary siliceous oxide catalysts, only the non-siliceous component was considered in terms of proton affinity and co-ordination number. Tanabe and co-workers " proposed a general model for mixed oxide catalysts in which acidity is caused by an excess of negative or positive charge in a model structure of the binary oxide. The hypothesis is shown to fit 28 of the 31 binary oxides tested. One of these oxides,... 

The various processes for the catalytic reaction are similar. The factor that makes the difference is the choice of catalyst, which in turn affects the temperature regime needed to trigger the decomposition of nitrous oxide. In the literature, numerous works illustrate the several classes of catalysts appropriate for this reaction [9a, k] noble metals (Pt, Au), pure or mixed metal oxides (spinels, perovskite-types, oxides from hydrotalcites), supported systems (metal or metal oxides on alumina, silica, zirconia) and zeolites. 

The aim of this contribution is to present data on the preparation of catalysts containing as embedding species a large family of eolloids such as colloids of ruthenium, platinum, or palladium-gold alloys and triflate derivatives such as lanthanum and silver triflate or tert-butyldimethylsilyltrifluoromethanesulfonate (BMSTM). Silica, zirconia and tantalum oxides were used as carrier. All these preparations considered the polymeric sol-gel route using as starting materials silicon, zirconium or tantalum alcoxides. 

To assess whether Lewis acid sites are present on zirconium sulfate, we prepared water-free bulk zirconium sulfete. Furthermore, a water-free silica-supported zirconium sulfrite catalyst was prepared by deposition-precipitation of zirconia on silica and subsequent gas-phase reaction with SO3. The activity of these catalysts was compared with that of two conventionally prepared sul ted zirconia catalysts. 

In view of the feet that complete removal of water vapor cannot be readily achieved, we prepared water-free bulk and silica-supported zirconium sulfate. The bulk anhydrous Zr(S04)2 was obtained by reaction of zirconium tetrachloride with oleum [1]. The silica-supported zirconium sul te resulted from deposition-precipitation of zirconium hydroxide on silica, calcination at 723 K and subsequent reaction with gaseous sulfur trioxide. The catalytic activity of the sul ted zirconia s was measured in the gas-phase /rora-alkylation of benzene (1) with diethylbenzene (2) to ethylbenzene (3, reaction 1) [8,9] and the liquid-phase hydro-acyloxy-addition reaction of acetic acid (4) and camphene (5) to isobomyl acetate (6, reaction 2) [8,10]. With the /roras-alkylation we used an amorphous silica-aliunina catalyst as a reference. 

The anhydrous bulk zirconium sulfate preparation did not display any activity in the trans-alkylation of benzene (1) and diethylbenzene (2) to ethylbenzene (3). At 473 K the silica-supported, gas-phase sulfated zirconia showed a very small activity, which rapidly dropped to a negligible level (Fig. 2). The conclusion is that Lewis acid sites are not active with sulfated zirconia catalysts. The low activity of the silica-supported catalyst is due to adsorption of some water leading to Bronsted acid sites. Desorption of water at 473 K leads to the decrease in activity with time. Pre-hydration of the supported catalyst brings about a slightly higher activity as apparent from Fig. 2 the activity drops again due to the loss of water. 

The silica-zirconia support itself is thermally quite stable, and the presence of zirconia has even been reported to help protect silica against sintering [591-593]. Characterization of the catalysts represented in Figure 130 by X-ray diffraction did not indicate crystallinity on the Cr/Zr-silica catalysts calcined at 500 and at 700 °C. Even after calcination at 900 °C, only some faint lines characteristic of ZrC>2 were detected. 

Pure zirconia itself can also serve as a catalyst support, although it yields catalysts with very low activity, in part because of low porosity. Amorphous zirconia can stabilize a small amount of Cr(VI) during calcination, which produces polymer when exposed to ethylene. Figure 130 shows the MW distributions of polymers obtained with Cr/zirconia activated at 500 °C, and tested under the same reaction conditions as the Cr/Zr-silica examples described above. Cr/zirconia produces very high-MW polymer, quite different from Cr/silica-zirconia. This... 

A comparison of fhe activify of two PW catalysts, one supported on a commercial silica (PW/Si02) and the other on a silica-zirconia-mixed oxide (PW/SiZr), was performed in fhe same reaction. Bofh supporfed... 

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