Zirconia, sulfated

Sulfated metal oxide catalysts represent a class of extremely attractive strong solid acids showing widespread application in different areas of chemical fransformafions. It was reported that sulfated zirconia (SZ) prepared by treatment of zirconia with sulfuric acid or ammonium sulfafe exhibifs exfremely sfrong acidity, and it is able to catalyze the isomerization of bufane to isobutane at room temperature. This behavior 

Among the different sulfated metal oxides available, SZ is, by far, the most studied and utilized solid acid catalyst its properties strongly depend on the preparation method (from the nature of the starting materials to calcination conditions). 

In an early study, it was shown that SZ calcined at 650°C was cata-lytically active in the acylation of toluene with acetic and benzoic acids 

A commercially available type of SZ, calcined af 550°C, was found to be an efficienf cafalysf in fhe bezoylation of toluene with BAN at 100°C for 3 h. The mefhylbenzophenones yield is 92% (ortho/para = 0.37). 

As already observed in different reactions, the SZ preparation procedure controls the catalytic activity. Indeed, the catalyst prepared by treatment of zirconium(IV) hydroxide with sulfuric acid followed by calcination at 600°C gives the methylbenzophenones in 25% yield, whereas 52% yield is achieved with SZ prepared by hydrolysis of zirconium(IV) oxychloride with sulfuric acid, followed by calcination at 550°C. 

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H0CH2C(CH3)2CH20H, sulfated Zirconia, benzene, reflux, 88-97% yield. 

Both sulfuric acid and hydrofluoric acid catalyzed alkylations are low temperature processes. Table 3-13 gives the alkylation conditions for HF and H2SO4 processes. One drawback of using H2SO4 and HF in alkylation is the hazards associated with it. Many attempts have been tried to use solid catalysts such as zeolites, alumina and ion exchange resins. Also strong solid acids such as sulfated zirconia and SbFs/sulfonic acid resins were tried. Although they were active, nevertheless they lack stability. No process yet proved successful due to the fast deactivation of the catalyst. A new process which may have commercial possibility, uses... 

The major disadvantage of the alkylation process is that acid is consumed in considerable quantities (up to 100 kg of acid per ton of product). Hence, solid acids have been explored extensively as alternatives. In particular, solid super acids such sulfated zirconia SO/ IZr02) show excellent activities for alkylation, but only for a short time, because the catalyst suffers from coke deposition due to oligomerization of alkenes. These catalysts are also extremely sensitive to water. 

We have recently reported that the addition of Ni results in a promotion of the isomerization activity of sulfated zirconia [10] comparable to that obtained by the addition of Fe and Mn. It has been previously observed that the presence of H2 causes a decrease in isomerization activity, a result consistent with the mechanism that involves olefins as reaction intermediates Here, we... 

The loss of sulfate during the reaction steps or during regeneration may become a critical issue when analyzing the potential of these materials as commercial catalysts. Sulfate losses during the butene TPD, made evident by the evolution of SO2 (m/e=64), started to occur at about 500°C. We have previously demonstrated the evolution of SO2 in the presence of adsorbates such as ammonia, benzene, or pyridine at temperatures much lower than those required to produce SO2 from clean sulfated zirconia [14]. For instance, A treatment in He at 600°C causes drastic losses which result in a significant drop in activity (see Fig. 3) It is... 

The promoting effect on the n-C4Hio isomerization increases with the amount of Ni, and further increases with the addition of Mn. We have presented evidence that on the Ni-promoted sulfated zirconia catalysts, the nickel is, at least partially, in the form of sulfate. 

The same behaviour has been found with Cu/ZrOa. A highly dispersed Cu phase was obtained at the surface of zirconla by reacting the support with Cu acetylacetonate [19]. This procedure yields an active catalyst. This catalyst was selective for Na formation at low temperature (< 550 K), but produced only NO2 when the temperature becomes higher than 650 K. However, the same type of catalyst prepared from sulfated zirconia did not produce NO2 but selectively reduces NO to N2 whatever the temperature, with a yield of about 40% at 670 K, and a GHSV of 70000 h l, using only 300 ppm of decane. 

Wilson, N. G., McCreedy, T., On-chip catalysis using a lithographically fabricated glass microreactor - the dehydration of alcohols using sulfated zirconia,... 

There is a real opportunity to reduce biodiesel production costs and environmental impact by applying modem catalyst technology, which will allow increased process flexibility to incorporate the use of low-cost high-FFA feedstock, and reduce water and energy requirement. Solid catalysts such as synthetic polymeric catalysts, zeolites and superacids like sulfated zirconia and niobic acid have the strong potential to replace liquid acids, eliminating separation, corrosion and environmental problems. Lotero et al. recently published a review that elaborates the importance of solid acids for biodiesel production. ... 

Out of the metal oxides, sulfated titania and tin oxide performed slightly better than the sulfated zirconia (SZ) catalyst and niobic acid (Nb205). However, SZ is cheaper and readily available on an industrial scale. Moreover, it is already applied in several industrial processes (7,8). Zirconia can be modified with sulfate ions to form a superacidic catalyst, depending on the treatment conditions (11-16). In our experiments, SZ showed high activity and selectivity for the esterification of fatty acids with a variety of alcohols, from 2-ethylhexanol to methanol. Increasing... 

Figure 33.2. Esterification of dodecanoic acid with methanol, using an alcohokacid ratio of 3 1 and sulfated zirconia (SZ) as catalyst.

Several other supports have been used in order to generate more-electrophilic Zr systems, including sulfated zirconia [186], sulfated alumina [187], or other sulfated oxide supports [188], though the surface species are quite complex for these sys-... 

Other materials that have been investigated include sulfated zirconia, Br0nsted and Lewis acids promoted on various supports, heteropolyacids, and organic resins, both supported and unsupported. On the whole, these materials also deactivate rapidly, and some of them also exhibit environmental and health hazards. 

III.C. Othf.r Solid Acids III.C. 1. Sulfated Zirconia and Related Materials... 

A variety of solid acids besides zeolites have been tested as alkylation catalysts. Sulfated zirconia and related materials have drawn considerable attention because of what was initially thought to be their superacidic nature and their well-demonstrated ability to isomerize short linear alkanes at temperatures below 423 K. Corma et al. (188) compared sulfated zirconia and zeolite BEA at reaction temperatures of 273 and 323 K in isobutane/2-butene alkylation. While BEA catalyzed mainly dimerization at 273 K, the sulfated zirconia exhibited a high selectivity to TMPs. At 323 K, on the other hand, zeolite BEA produced more TMPs than sulfated zirconia, which under these conditions produced mainly cracked products with 65 wt% selectivity. The TMP/DMH ratio was always higher for the sulfated zirconia sample. These distinctive differences in the product distribution were attributed to the much stronger acid sites in sulfated zirconia than in zeolite BEA, but today one would question this suggestion because of evidence that the sulfated zirconia catalyst is not strongly acidic, being active for alkane isomerization because of a combination of acidic character and redox properties that help initiate hydrocarbon conversions (189). The time-on-stream behavior was more favorable for BEA, which deactivated at a lower rate than sulfated zirconia. Whether differences in the adsorption of the feed and product molecules influenced the performance was not discussed. 

An interesting variation on sulfated metal oxide type catalysts was presented by Sun et al. (198), who impregnated a dealuminated zeolite BEA with titanium and iron salts and subsequently sulfated the material. The samples exhibited a better time-on-stream behavior in the isobutane/1-butene alkylation (the reaction temperature was not given) than H-BEA and a mixture of sulfated zirconia and H-BEA. The product distribution was also better for the sulfated metal oxide-impregnated BEA samples. These results were explained by the higher concentration of strong Brpnsted acid sites of the composite materials than in H-BEA. 

Cesium salts of 12-tungstophosphoric acid have been compared to the pure acid and to a sulfated zirconia sample for isobutane/1-butene alkylation at room temperature. The salt was found to be much more active than either the acid or sulfated zirconia (201). Heteropolyacids have also been supported on sulfated zirconia catalysts. The combination was found to be superior to heteropolyacid supported on pure zirconia and on zirconia and other supports that had been treated with a variety of mineral acids (202). Solutions of heteropolyacids (containing phosphorus or silicon) in acetic acid were tested as alkylation catalysts at 323 K by Zhao et al. (203). The system was sensitive to the heteropoly acid/acetic acid ratio and the amount of crystalline water. As observed in the alkylation with conventional liquid acids, a polymer was formed, which enhanced the catalytic activity. 

The combination of dicyclopentadienylzirconium dichloride and silver perchlorate activates armed glycosyl sulfoxides in dichloromethane between -20 °C and room temperature, but only very simple acceptors were studied [335]. Other Lewis and Bronsted acids studied include the environmentally benign europium, lanthanum and ytterbium triflates [336], certain polyoxometallates [337], sulfated zirconia [338] and Nafion H [338]. 

Sulfated zirconia, 5 331-333 Sulfate esters, 23 653 Sulfate formation, on Claus catalysts, 23 610-614... 

HIGHLY EFFECTIVE SULFATED ZIRCONIA NANOCATALYSTS GROWN OUT OF COLLOIDAL SILICA AT HIGH TEMPERATURE... 

Sulfated zirconia sol was prepared by placing 10 g of ethanol and 10 g of zirconium butoxide (80%) into a flask under magnetic stirring at room temperature, followed by adding a mixture of 6.5 g of ethanol, 1.5 g of distilled water, and 5 g of H2SO4 (18 M). 

D. Farcasiu and J. Q. Li, Preparation of sulfated zirconia catalysts with improved control of sulfur content, 111 effect of conditions of catalyst synthesis on physical properties and catalytic activity,... 

David J. Zalewski, Saeed Alerasool, Patricia Doolin, Characterization of catalytically active sulfated zirconia, Catal. Today 53, 419 32 (1999)... 

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