Supported catalysts olefin isomerization

Toluene reacts with carbon monoxide and butene-1 under pressure in the presence of hydrogen fluoride and boron trifluoride to give 4-methyl-j iYbutyrophenone which is reduced to the carbinol and dehydrated to the olefin. The latter is cycHzed and dehydrogenated over a special alumina-supported catalyst to give pure 2,6- dim ethyl n aph th a1 en e, free from isomers. It is also possible to isomerize various dim ethyl n aph th a1 en es to the... 

In a first test reaction, the polymer support was used for the hydroformylation of 1-octene in water in the presence of Rh(CO)2acac. Within a reaction time of 10 h at 120°C and a H2/CO (1 1) pressure of 5 MPa, conversion of up to 94% was obtained. The n iso ratio was 3 1, sometimes reaching 9 1. The quantities of 3-and 4-nonanal resulting from olefin isomerization, were below 5% [74]. The versa-tihty of the polymer support was further demonstrated with the Heck reaction of styrene and iodobenzene in the presence of Pd(OAc)2 as the metal catalyst The reaction was again performed in pure water at 50 °C and product yield of up to 80% was obtained after 20 h reaction time [75]. 

Both the rhodium and the cobalt complexes catalyze olefin isomerization as well as olefin hydroformylation. In the case of the rhodium(I) catalysts, the amount of isomerization decreases as the ligands are altered in the order CO > NR3 > S > PR3. When homogeneous and supported amine-rhodium complexes were compared, it was found that they both gave similar amounts of isomerization, whereas with the tertiary phosphine complexes the supported catalysts gave rather less olefin isomerization than their homogeneous counterparts (44, 45). 

Relatively little has been reported on the intentional isomerization of olefins over supported catalysts, although, as mentioned in Section... 

Olefin isomerization has also been mediated by the photolysis of Fe(C0)s.144 Recently, a detailed study of alkene isomerization by photolysis of Fe(CO)5 has shown that the reaction is truly photocatalytic.14S The very high quantum yields ( 1.0), Table 24, and the fact that the pentenes are ultimately equilibrated to the thermodynamic ratio support the notion that the role of the light is to generate a thermally active catalyst. A mechanism similar to that in reactions (53)-(57) involving Fe(CO)3 as the repeating unit can be used to account for the results. 

It is found that Mode E behaves similarly to the zeolite free Pt-Re/Al203 Both catalysts have a relatively high proportion of isomer products which could be formed over the metal surface via a bond-shift mechanism [8]. Isomers are formed by doublebond isomerization and skeletal isomerization reactions at both the acid sites of the alumina support and the metal sites. The later provides a dehydrogenation-hydrogenation function and the acid sites an isomeiization function for the olefins to dehydrogenate from paraffins over the metal function, since it is known that olefin isomerization proceeds much quicker than the respective paraffin isomerization [8]. On the other hand, branched paraffins are less easily cracked than linear ones [10]. Therefore, once isomers are formed over conventional reforming catalysts, they are likely to be the final products. Evidently, the isomerization of paraffin requires the metal function in the bimetallic catalyst, and so does the paraffin aromatization. This can also explain the obseiwed decrease in the isomers and aromatics production with time-on-Hne since it is well- known that coke preferentially deposits on a metal surface first [14]. 

The T]-, y-, 8-, and 0-forms are known as the transitional aluminas. They have highly disordered structures, high surface areas, and a large number of surface hydroxyl speeies at exposed surfaces. Transitional aluminas are catalytically active materials and are known to facilitate H-D exchange, C-H activation, skeletal olefin isomerizations, and alcohol dehydrations [57]. In industrial catalytic processes, aluminas are mostly used as catalyst support materials. 

Polyphosphoric acid itself has found utility mainly as a supported catalyst in the petroleum industry for alkylation, olefin hydration, polymerization, and isomerization, and for syntheses of fine chemicals and dyes. It is used to phospho-rylate alcohol groups, for example in the production of anionic phosphate surfactants. 

Since the work of Eischens and co-workers, where the reactant adsorption of the catalytic reactions of industrial interest over the relevant catalysts was investigated, a possible indication of the mechanism of the catalytic steps was obtained. This approach was later developed by Kokes and co-workers in the 1960s. The concept of experiments under dynamic conditions was also developed in the 1960s by Tamaru, " and applied to IR spectroscopy and other techniques. During his experiments, Tamaru measured the conversion of reactants in parallel with the modification of the spectra of the surface species for several reactions such as (i) the olefin isomerization and hydrogenation over ZnO (ii) the decomposition of formic acid (iii) the water-gas shift reaction over ZnO and MgO (iv) the decomposition of methanol over ZnO (v) the oxidation of CO on supported Pd. 

Purely parallel reactions are e.g. competitive reactions which are frequently carried out purposefully, with the aim of estimating relative reactivities of reactants these will be discussed elsewhere (Section IV.E). Several kinetic studies have been made of noncompetitive parallel reactions. The examples may be parallel formation of benzene and methylcyclo-pentane by simultaneous dehydrogenation and isomerization of cyclohexane on rhenium-paladium or on platinum catalysts on suitable supports (88, 89), parallel formation of mesityl oxide, acetone, and phorone from diacetone alcohol on an acidic ion exchanger (41), disproportionation of amines on alumina, accompanied by olefin-forming elimination (20), dehydrogenation of butane coupled with hydrogenation of ethylene or propylene on a chromia-alumina catalyst (24), or parallel formation of ethyl-, methylethyl-, and vinylethylbenzene from diethylbenzene on faujasite (89a). 

We have explored rare earth oxide-modified amorphous silica-aluminas as "permanent" intermediate strength acids used as supports for bifunctional catalysts. The addition of well dispersed weakly basic rare earth oxides "titrates" the stronger acid sites of amorphous silica-alumina and lowers the acid strength to the level shown by halided aluminas. Physical and chemical probes, as well as model olefin and paraffin isomerization reactions show that acid strength can be adjusted close to that of chlorided and fluorided aluminas. Metal activity is inhibited relative to halided alumina catalysts, which limits the direct metal-catalyzed dehydrocyclization reactions during paraffin reforming but does not interfere with hydroisomerization reactions. 

Fig. 4.5 Polymer-supported iridium catalysts (61) and (62) for the isomerization of olefinic double bonds.

Occurs in nature in abundance the principal forms are bauxites and lat-erites. The mineral corundum is used to produce precious gems, such as ruhy and sapphire. Activated aluminas are used extensively as adsorbents because of their affinity for water and other polar molecules and as catalysts because of their large surface area and appropriate pore sturcture. As adsorbents, they are used for drying gases and liquids and in adsorption chromatography. Catalytic properties may be attributed to the presence of surface active sites (primarily OFT, 02, and AF+ ions). Such catalytic applications include sulfur recovery from H2S (Clauss catalysis) dehydration of alcohols, isomerization of olefins and as a catalyst support in petroleum refining. 

SAP catalysts have also been applied in the Wacker oxidation584 of higher olefins where the separation of products from the catalyst is cumbersome. Palladium(II) and copper(II) salts immobilized on controlled pore glass CPG-240 in the presence of water catalysed the oxidation of 1-heptene to 2-heptanone in conversions up to 24%.585 Significant isomerization to 2-heptene and 3-heptene (isomerization/oxidation=2/3) was also observed. However, an advantage of SAP-Wacker oxidation catalysts over classical systems is that the Cu(II) is confined to the support and therefore not corrosive whereas aqueous Cu2+ is very corrosive to steel. 

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