Zirconia catalyst

Z. Hong, K.B. Fogash, and J.A. Dumesic, Reaction kinetic behavior ofsulfated-zirconia catalysts for butane isomerization, Catalysis Today 51, 269-288 (1999). 

Tungsta and Platinum-Tungsta Supported on Zirconia Catalysts for Alkane Isomerization... 

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. 

Sulphated zirconia catalysts can be acidic or superacidic depending on the method of treatment. A variety of acid-catalysed reactions, referred to earlier in this section, can be carried out with sulphated zirconia. Yadav and Nair (1999) have given a state-of-the art review on this subject. Examples of benzylation of benzene with benzyl chloride / benzyl alcohol, alkylation of o-xylene with. styrene, alkylation of diphenyl oxide with 1-dodecene, isomerization of epoxides to aldehydes, acylation of benzene / chlorobenzene with p-chloro benzoylchloride, etc. are covered in the review. 

Centi, G., Cerrato, G., D Angelo, S. et al. (1996) Catalytic behavior and nature of active sites in copper-on-zirconia catalysts for the decomposition of N20, Catal. Today 27, 265. 

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. 

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. 

J. M. Pigos, C. J. Brooks, G. Jacobs and B. H. Davis, DRIFTS Studies of platinum-based zirconia catalyst promoted with sodium discovered by combinatorial methods, Prepr. Am. Chem. Soc. Div. Pet. Chem., 2006. 

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,... 

C. Morterra, G. Cerrato, andF. Pinna, Preparation and characterization of sulfated zirconia catalysts obtained via various procedures, Appl. Catal. A 176(1), 27 3 (1999). 

A. Corma, A. Martinez, and C. Martinez, Influence of process variables on the continuous alkylation of isobutane with 2-butene on superacid sulfated zirconia catalysts, J. Catal. 149, 52-60 (1994). 

Figure 13.4 Isomerization of n-butane to isobutane on beta zeolite and sulfated zirconia catalysts at different reaction temperatures.

The catalyst with lower acid strength (beta zeolite) presents the higher selectivity to (TMP) at high reaction temperatures, while the sulfated zirconia presents an opposite trend the lower the reaction temperature, the higher the selectivity to TMP is. In the case of sulfated zirconia catalysts, cracking rather than alkylation is favored at high reaction temperatures, while oligomerization rather than alkylation is favored on the beta zeolite at low reaction temperature. 

Davassy, B., Shanbhag, G., Lefebvre, F., and Halligudi, S. (2004) Alkylation of p-cresol with tert-butanol catalyzed by heteropoly acid supported on zirconia catalyst. J. Mol. Catal. A Chem., 210, 125-130. 

Figure 3. Stability of the sulfated zirconia catalyst in the esterification reaction of dodecanoic acid with 2-ethylhexanol - conversions given at 25, 45 and 75 minutes.

Methanation of C02 over Pd on zirconia and Ni on zirconia catalysts derived form amorphous Pd-Zr-, Ni-Zr-, and Ni-containing multicomponent alloys prepared by controlled oxidation-reduction treatment or generated under reaction conditions have been studied in detail. 

In conclusion, extensive research has revealed that the Lewis and Brpnsted acid sites on the promoted sulfated zirconia catalysts are not necessarily stronger acids than the corresponding sites in zeolites, but sulfated zirconia circumvents the energetically unfavorable monomolecular reaction path by following a bimolecular mechanism. The question of superacidity of sulfated zirconia, however, is still debated.312... 

Addition of FeS04 to Pt-promoted tungstated zirconia catalysts results in increased activity and selectivity (>98% selectivity at 50-70% conversion at... 

Sulfated zirconia catalysts showed selectivities comparable to those of AICI3 in the alkylation of benzene with 1-alkenes to linear alkylbenzenes.396 The mesopor-ous sulfated zirconia sample could be regenerated by solvent extraction or thermal treatment. Phosphotungstic acid supported on sulfated zirconia doped with Fe proved to be very active and highly selective in the alkylation of benzene with propylene at 100-150°C to produce cumene both monoalkylation and cumene formation have better than 90% selectivity.397 It can be regenerated at moderate temperature (350°C). 

DEHYDRATION UF CARBOXAMIDES TO NITRILES USING SULPHATED ZIRCONIA CATALYST... 

Preparation of zirconia catalyst has been previously discussed (ref.6). Untreated zirconia was prepared by similar procedure excluding the treatment with sulphuric acid. The physical characteristics of these materials are reported recently (ref.7). 

The reaction rates were observed to be identical in ail the three cases indicating no effect of solvent on the rate. The kinetics constants for the dehydrations of stearamide are given in Table 3. Reusability of zirconia catalyst was investigated by recycling the catalyst without any intermitant washing. No significant decline in activity could be observed after three recycles. 

G.W. Joshi and R.A. Rajadhyaksha, Dehydration of Crboxamides to nitriles with Zirconia Catalyst, Chem.Ind., (1986) 876-77. 

Tonkovich et al. [81] compared the performance ofa commercial ruthenium/zirconia powder catalyst from Degussa with a laboratory-made ruthenium/zirconia catalyst prepared on a nickel foam monolith for the water-gas shift reaction. Methane formation occurred for the powder catalyst, which was much less pronounced for the monolith. The selectivity towards methane could be reduced at shorter residence times. However, the activity of the laboratory-made catalyst was lower, which was partially attributed to the lower catalyst mass (modified residence time). 

This section deals with the conceptual design of a catalytic distillation process for the esterification of lauric acid (LA) with 2-ethyl-hexanol (2EtH). Laboratory experiments showed that a superacid sulfated zirconia catalyst exhibits good activity over a large interval, from 130 to 180 °C with no ether formation. On the contrary, the catalyst is sensitive to the presence of free liquid water. Raw materials are lauric acid and 2-ethylhexyl alcohol of high purity. The conversion should be over 99.9%, because the product is aimed at cosmetic applications. 

Experiments were executed in an autoclave at temperature between 130 and 180 °C, with alcohol/acid ratios between 1/9 to 27/1, as well as sulfated zirconia catalyst concentration up to 5 wt%. The experimental conditions preserved the chemical equilibrium constraint. Details are given elsewhere [2]. Two contributions in forming the reaction rate can be distinguished enhancement due to the solid catalyst and an autocatalysis effect by the fatty acid. Consequently, the following expression can be formulated for the overall reaction rate ... 

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