Isomerization catalyst base

Fig. 7.4 Comparison of Mordenite (250°C) vs. Sulfated Zirconia (200°C) based Isomerization Catalysts Time on stream...

Cobalt catalysts such as HCo(CO)4 are widely used for hydroformyla-tion of higher alkenes, despite the higher temperatures and pressures required. The main reason for this is that these catalysts are also efficient alkene isomerization catalysts, allowing a mix of internal and terminal alkenes to be used in the process. Catalyst recovery is more of a problem here, involving production of some waste and adding significantly to the complexity of the process. A common recovery method involves treating the catalyst with aqueous base to make it water soluble, followed by separation and subsequent treatment with acid to recover active catalyst (4.3). 

A non-acidic isomerization catalyst system has unexpectedly emerged from recent studies by French workers [4] in the area of Mo-oxycarbides. Although at an early stage of development, these new materials exhibit high selectivities for the isomerization of paraffins such as n-heptane. An alternative non-carbenium ion mechanistic route to achieve isomerization of higher alkanes could potentially overcome some of the limitations of conventional solid acid based catalyst systems. 

Tanabe and Hdlderich (1999) have given an extensive statistical survey of industrial processes using solid acids/bases as catalysts. Over 300 solids and bases have been covered. A variety of reactions like alkylation, isomerization, amination, cracking, and etherification with catalysts like zeolites, oxides, complex oxides, phosphates and ion-exchange resins have been covered. Over 120 industrial processes are referred with 180 different catalysts. 

Corma, A., Serra, J.M. and Chica, A. (2003) Discovery of new paraffin isomerization catalysts based on S042-/Zr02 and WOx/Zr()2 applying combinatorial techniques. Catal. Today, 81, 495. 

When aqueous NaOH is given as a base, isomerization of the product butenoic acids can be extensive depending on the nature and concentration of base. In dilute aqueous solutions alcohols do not react to form the respective esters, however, the reactions are strongly accelerated due to the increased solubility of the substrates in the catalyst-containing aqueous-alcoholic phase. For example, with 23-33 % (v/v) ethanol in water the [PdCl2(TPPTS)2]-catalyzed hydroxycarbonylation of allyl chloride proceeded with TOF-s of 1850-2400 h and with a vinylacetic/crotonic acid ratio of 21 [16]. Addition of [CuCb] increased the overall conversion rate (by a factor of 2 at [Cu]/[Pd] = 8) but at the same time the side reactions... 

Catalysts and reaction conditions used are generally similar to those used for olefin isomerization. Catalysts reported are sodium-organosodium catalysts prepared in situ by reaction of a promoter such as o-chloro-toluene or anthracene with sodium 19-24), alkali metal hydrides 20,21), alkali metals 22), benzylsodium 26), and potassium-graphite 26). These catalysts are strong bases that can react with alkylaromatics to replace a benzylic hydrogen [Reaction (2)]. 

The bis-barium complex of pure trans-28 (0.10 mM) increases the rate of ethano-lysisof29 (65/35 EtOH/MeCN, 1 mM Me4NOEt, 25 °C) by 230-fold. The corresponding figures for quasi-trans-28-Ba2 and quasi-cis-28-Ba2 are 420- and 1280-fold, respectively. Thus, the behavior of trans and ds isomeric catalysts based on azobenzene closely parallels the behavior of the corresponding stilbene derivatives 26 and 27, in that in both cases the ds form is a superior catalyst in the cleavage of anilide 29. 

Studies on the immobilization of Pt-based hydrosilylation catalysts have resulted in the development of polymer-supported Pt catalysts that exhibit high hydrosilylation and low isomerization activity, high selectivity, and stability in solventless alkene hydrosilylation at room temperature.627 Results with Rh(I) and Pt(II) complexes supported on polyamides628 and Mn-based carbonyl complexes immobilized on aminated poly(siloxane) have also been published.629 A supported Pt-Pd bimetallic colloid containing Pd as the core metal with Pt on the surface showed a remarkable shift in activity in the hydrosilylation of 1-octene.630... 

In the reaction mechanisms described above the acidity of the catalyst plays an important role. Zeolites can be converted into the H+ form and as such are powerful catalysts for acid-catalyzed reactions. We discuss below some aspects of isomerization catalyst preparation to demonstrate factors which influence the activity of catalysts based on zeolites. In this discussion we are concerned with zeolite Y and mordenite. Data on paraffin isomerization over dual function catalysts besed on other zeolites are scarce, and no data have been published showing that materials like zeolite X, zeolite L, offretite, zeolite omega, or gmelinite can be converted into catalyst bases having an isomerization activity comparable with that of H-zeolite Y or H-mordenite. 

For optimal performance of dual function isomerization catalysts based on zeolite Y or mordenite, extensive removal of sodium is necessary. The finished catalyst must be highly crystalline, and the finely dispersed metallic hydrogenation function should be well distributed throughout the catalyst particles. The proposed mechanism explains the stabilizing influence on conversion and the suppression of cracking reactions by addition of the metallic hydrogenation function to the active acidic catalyst base. 

A clean, solvent-free method has been developed for the bis-hydroxylation of alkenes by the use of Nafion-based acidic catalysts and 30% H202.655 Nafion NR50 and SAC-13 exhibited high activity in the oxidation of isomeric C alkenes, cyclohexene [Eq. (5.228)], 1,4-cyclohexadiene, and allylic alcohols in the temperature... 

Michalak A, Ziegler T, Stochastic simulations of polymer growth and isomerization in the polymerization of propylene catalyzed by Pd-based diimine catalysts, J Am Chem Soc, 124, 7519-7528 (2002)... 

Commercial zeolite based hydroisomerization catalysts comprise alumina bound and platinum impregnated dealuminated mordenite. The activity and selectivity of the hydroisomerization of n-paraffins is strongly influenced by acid leaching. The influence of silica to alumina ratio has been studied for pentane isomerization over platinum mordenite many times since one of the first papers published (6). 

Dewaxing catalysts are manufactured by both Akzo Nobel and Mobil. Mobil s Isomerization Dewaxing (MIDW) first commercialized in 1990 uses a Pt-based zeolite catalyst to crack and isomerize n-paraffins to iso-parrafins, thereby converting fuel oil to low-pour-point distillates. 

Propylene oxide isomerized over silica-magnesia and other oxides to give propionaldehyde and acetone on acidic and basic sites, respectively, and allyl alcohol on acid-base bifunctional catalysts. Methylvinyl ketone was formed selectively in the reaction of acetone and methanol with oxygen over silica-magnesia. Tanabe and co-workers have studied the alkylation of phenol... 

In contrast to Group IV-based polymerization catalysts, late transition metal complexes can carry out a number of useful transformations above and beyond the polyinsertion reaction. These include isomerization reactions and the incorporation of polar monomers, which have allowed the synthesis of branched polymer chains from ethylene alone, and of functional polyolefins via direct copolymerization. The rational design of metallocene catalysts allowed, for the first time, a precise correlation between the structure of the single site catalyst and the mi-crostructure of the olefin homo- or copolymer chain. A similar relationship does not yet exist for late transition metal complexes. This goal, however, and the enormous opportunities that may result from new monomer combinations, provide the direction and the vision for future developments. 

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