Sulphates zirconias

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. 

The water-insoluble salts such as Cs2,5Ho., iPWi204o efficiently catalyse dehydration of 2-propanol in the gas phase and alkylation of m-xylene and trimethyl benzene with cyclohexene this catalyst is much more active than Nafion-H, HY-zeolite, H-ZSM-5, and sulphated zirconia (Okuhara et al., 1992). 

Wang SB, Murata K, Hayakawa T, Hamakawa S, Suzuki K (1999) Excellent performance of lithium doped sulphated zirconia in oxidative dehydrogenation of ethane. Chem Commun 103-104. 

M. -Trung Tran, N. S. Gnep, G. Szabo, and M. Guisnet, Influence of the calcination temperature on the acidic and catalytic properties of sulphated zirconia, Appl. Catal. A 171, 207-217 (1998). P. Canton, R. Olindo, F. Pinna, G. Strukul, P. Rieflo, M. Meneghetti, G. Cerrato, C. Morterra, and A. Benedetti, Alumina-promoted sulfated zirconia system Structure and microstructure characterization, Chem. Mater. 13, 1634-1641 (2001). 

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

Dehydration of benzamide, nicotinamide, stearamide and oleamide is studied using sulphated zirconia as catalyst. Complete conversion to corresponding nitriles could be achieved when the reactions were carried out in water immiscible solvents. The order of reactivity of the different amides seems to be governed by the ease of the dissociation of the C=0 bond of the amide. 

In the preliminary experiments dehydration of benzamide was first investigated without using any solvent. The reaction was carried out using 40% w/w sulphated zirconia in molten benzamide at... 

Fig.2. Dehydration of benzamide using sulphated zirconia in (a) dipheny lether (b) 2-nitrotoiuene (c) tetralin.

Fig. 1. Dehydration of benzamide in diphenyiether (a)with sulphated zirconia (b) with untreated zirconia (c) without catalyst.

Figure 1 shows the results of the reaction carried out using sulphated and untreated zirconia in diphenyiether (b.p. 259° C). Thermal dehydration does occur to a finite extent. The sulphated zirconia show very significant activity for the reaction as compared to the untreated zirconia. 

The structure and nature of acidity of sulphated zirconia has been recently investigated (ref. 8-10). Untreated zirconium hydroxide which is amorphous, crystallises 1n the monoclinic form at 350°C. On the contrary, the sulphate treated zirconium hydroxide crystallises at higher temperature (500ooC) into tetragonal form, which has significantly greater surface area as compared to the monoclinic zirconia. The infra red spectra of absorbed pyridine indicate presence of only coordinatively bonded pyridine and not the protonated pyridine implying that the zirconia is predominantly of Lewis... 

The present study demonstrates suitability of sulphated zirconia for dehydration of carboxamides. It needs to be emphasised that the common inorganic acid catalysts are not sufficiently acidic to catalyst the reaction below 400°C while the strongly acidic resin catalysts are not structurally stable at temperature at which the reaction would occur at appreciable rate. Thus the sulphated zirconia appears to be a unique catalyst for this application. 

Structure-reactivity 21,581 Sulphur removal from terpenes201 Sulphated zirconia 479... 

Omota, F., Dimian, A. C., and Bhek, A. 2003. Fatty acid esterification by reactive distillation Part 2—kinetics-based design for sulphated zirconia catalysts. Chem. Eng. Sci., 55(14), 3175-3185. 

The nitration of Chlorobenzene was carried out in presence of sulphated zirconia as catalyst at room temperature - 70°C in CCU medium using stoichiometric quantity of nitric acid and acetic anhydride. The isolated yield was found to be more than 95% with 90% selectivity to para- isomer. The catalyst can be recycled at least for 5 times with a little decrease in its activity. 

Key Words Sulphated zirconia, nitration, chlorobenzene 1. INTRODUCTION... 

Sulphated zirconia can be used as an efficient catalyst for nitration chlorobenzene. The Bronsted as well as Lewis acid sites present on it s surface are responsible for high yield and regioselective. 

Acylation of 2-methoxynaphthalene with acetic anhydride was carried out using different solid acid catalysts such as zeolites, acid activated clays, ion exchange resins and sulphated zirconia. The products of the reaction are precursors of many organic and pharmaceutical intermediates. For example, the para isomer of the reaction product, 6-methoxy-2-naphthalene-a-methyl ketone is useful as a raw material for the manufacture of well-known anti-inflammatory dru called naproxen. The reaction products were isolated and confirmed by their melting points, H-NMR, gas chromatography, etc. 

In this paper we would like to communicate the details of our investigation in the acylation of 2-MON with acetic anhydride using different solid acid catalysts such as zeolites, clays, pillared clays, unsupported heteropoly acids (HPA) and HPA/KIO, sulphated zirconia euid ion-exchange resins. 

Sulphated zirconia was prepared by adding aqueous ammonia solution to zirconium oxychloride solution at a pH of 10. The precipitate was thoroughly washed with distilled water and freed from ammonium and chloride ions. It was dried in an oven at 120 C for 24h. The sulphation of the prepared zirconia was done with 1.0 N sulphuric acid (15 ml/g). It was dried at 110 C and calcined at 450°C for 3h. 

The efficacy of different catalysts at 50°C is given in the Fig.l. Among the catalysts used, HP A (unsupported and supported on KIO) and ion exchange resins (Amberlyst-15 and lndion-130) showed very high activities followed by sulphated zirconia, Filtrol-24 and KIO. The aluminium pillaring with SWy2 showed a little activity. Catalysts based on the zeolites such as H-ZSM-5, Y and mordenite did not show any activity. It appears that the pore sizes of these catalysts pose considerable intraparticle resistance for the reactant 2-MON to access the catalytic sites. 

The acylation of 2-methoxynaphthalene (yarayara) with acetic anhydride was studied systematically by using Amberlyst-15 and Indion-130, sulphated zirconia, Filtrol-24, K-10-montmorillonite clay, aluminium pillared clay(Al-PILC), HPA, HPA/KIO, H-ZSM-5, Y,... 

Mordenite etc. Dodecatungstophosphoric acid (DTPA) and the ion exchange resin catalysts showed maximum activities. Clay based catalysts and sulphated zirconia showed a moderate activity. Zeolites did not demonstrate any activity to the reaction due to pore size restriction. A 100% selectivity towards the ortho product (l-acetyl-2-methoxy naphthalene) was observed for almost all the reactions for all the catalysts. The para product (2-methoxy-6-acetyl naphthalene) was formed when the aluminium chloride was used as a homogeneous catalyst with nitrobenzene as the solvent. The reaction product was isolated and conformed by the melting point, FT-IR, H-NMR, etc. The reaction is intraparticle diffusion limited. A different catalyst would be required to get p-product selectively. 

Trunschke, A., Deutsch, J., Muller, D., Lieske, H., Quaschning, V., and Kemnitz, E. 2002. Nature of surface deposits on sulphated zirconia used as catalyst in the benzoylation of anisole. Catal. Lett. 83 271-279. 

Suja, H., Deepa, C. S., Sreeja Rani, K., and Sugunan, S. 2002. Liquid phase benzoylation of arenes over iron promoted sulphated zirconia. Appl. Catal. A Gen. 230 233-243. 

The NOxtrap concept is based on coupled reactions which can also be catalysed by mechanical mixtmes of two catalysts that introduce a simplification in the analysis [17]. The mechanical mixture of solids used here associates an oxidation catalyst consisting of CuO/sulphated zirconia (typically, 5 wt.% CuO) and a solid base made by impregnation of y-alumina (SCP 350 from Rhone Poulence) with K, Na, Ca and Li nitrates. The supported nitrates were prepared by incipient wetness impregnation using 12 mmol of nitrate.g of alumina. The sulphated zirconia used as support for CuO was obtained from MEL, contained... 

Phosphate and sulphate modifiers were incorporated by the addition of appropriate amounts of 0.01 M sulphuric or phosphoric acid to a pre-calcined aerogel followed by further calcination at 873 K. Samples are labeled as X-SiZr (y) where X refers to either sulphated (S) or phosphated (P) samples, and y refers to the mole ratio of sulphate/phosphate relative to zirconium in the preparation method. For comparison purposes, samples of zirconia and sulphated zirconia were also prepared. This was achieved via precipitation from zirconium isopropoxide (Aldrich 70 wt.%). The same H2O Zr propanol ratios were employed as used during the preparation of the mixed oxides. A sulphated zirconia, prepared by the use of sulphuric acid as hydrolysis catalyst was prepared for comparative purposes and had a nominal S Zr ratio of 0.30 1. A further sample was prepared where segregation of components was induced by thermal treatment by calcination at 1373 K for 6 h.of the non-treated SiZr (0)... 

The absence of reactivity over nalion can be attributed to too low an acidity of this resin. The same explanation can be given for the sulphated zirconia, because this solid loses its strong acidity in water. 

The preparation of sulphated zirconia designed for catalyst supports was studied by Boutonnet et al. . Zirconia prepared in microemulsion showed a pure tetragonal structure compared with zirconia prepared by an impregnation -precipitation procedure which also contained monoclinic phase. Platinum-promoted sulphated zirconia catalysts were prepared both in anionic and non-ionic microemulsions. Furthermore, the catalytic activity and selectivity for the isomerization of hexanes were tested. The catalysts produced by the microemulsion method showed a higher selectivity towards isomers but a lower activity when compared to catalysts prepared by impregnation technique. More recently, a study of zirconia synthesis from micro and macroemulsion systems has been conducted . Spherical ZrOa particles ranging from tens of nanometers to a few micrometers were produced. 

M. T. Tran, N. S. Gnep, G. Szabo, M. Guisnet, Influence of the calcination temperature on the acidic and catal5dic properties of sulphated zirconia, Appl. Catal. A, 1998, 171, 207-217. 

Sulphated zirconia S04 /Zr02 SOH Paraffin isomerization Gas/solid 170-230... 

Mejri 1, Younes MK, Ghorbel A (2006) Comparative study of the textural and structural properties of the aerogel and xerogel sulphated zirconia J Sol-Gel Sci Technol 40 3-8... 

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