Zeolite dimerization, ethylene

The reaction could not be carried out with the usual sulfonic acid ion-exchange resin, because its maximum use temperature was 120°C. The product cannot be made directly from acetone and aniline owing to the formation of a dihydroquinoline by-product (from two molecules of acetone and one of aniline). A shape-selective zeolite might allow the reaction to take place without formation of this byproduct. An inexpensive way of making this diamine from acetone and aniline, similar to the preparation of bisphenol A from acetone and phenol, could lead to new families of polyamides, polyimides, polyureas, polyurethanes, and epoxy resins. A palladium catalyst supported on Nafion dimerized ethylene much faster in water than in organic solvents. The butene was easy to separate.18... 

Ethylene oligomerization over Ni and Pd zeolites has been reported by Lapidus and Krylova.[73] It was found that NiCaX exhibited high selectivity for ethylene dimerization at 508 K. The highest activity and selectivity were achieved with a sample with a Ni content of 2.5 wt%, trara.v-2-butcnc being the major product. PdCaX also shows excellent selectivity to trans-2-butene, giving 65 % selectivity for a total yield of the C4 fraction of 78 %. 

Recently, Angelescu et a/.[92] have studied the activity and selectivity for dimerization of ethylene of various catalysts based on Ni(4,4-bipyridine)Cl2 complex coactivated with A1C1(C2H5)2 and supported on different molecular sieves such as zeolites (Y, L, Mordenite), mesoporous MCM-41 and on amorphous silica alumina. They found that this type of catalyst is active and selective for ethylene dimerization to n-butenes under mild reaction conditions (298 K and 12 atm). The complex supported on zeolites and MCM-41 favours the formation of higher amounts of n-butenes than the complex supported on silica alumina, which is more favourable for the formation of oligomers. It was also found that the concentration in 1-butene and cw-2-butene in the n-butene fraction obtained with the complex supported on zeolites and MCM-41, is higher compared with the corresponding values at thermodynamic equilibrium. 

Ng, F. T. T. and Creaser, D. C. Ethylene dimerization over modified nickel exchanged Y-zeolite. AppLCatal., 1994, 119, 327-339. 

On the other hand, the participation of Pd2+ and/or Pd+ species as active sites in the reaction of dimerization of ethylene was suggested some years ago (222). Recently, two independent groups established that Pd + species in Pd/X and Pd/Y zeolites are sites of highest activity (124-126, 223). Starting with a Pd2+/Y or Pd2+/X catalyst, they monitored its activity in the course of reaction. Parallel study with XPS, ESR, and solid-state NMR confirmed that Pd+ is an active species in the reaction. Its concentration grows with time on-stream. 

A number of zeolite-based catalysts are active for the dimerization of ethylene. The major products are n-butenes (1-butene, tram-2-butene, m-2-butene), i.e.,... 

Dimerization presumably takes place on the transition metal-containing sites, and alkylation on the acidic sites of zeolltic surface. The sodium form of zeolite exchanged with transition metal cations Is capable of dimerization (and further polymerization), but does not practically exhibit alkylating capacity. This explains the composition of the product obtained from ethylene and Isobutane over this catalyst (Table V, column 3). 

Ethylene for polymerization to the most widely used polymer can be made by the dehydration of ethanol from fermentation (12.1).6 The ethanol used need not be anhydrous. Dehydration of 20% aqueous ethanol over HZSM-5 zeolite gave 76-83% ethylene, 2% ethane, 6.6% propylene, 2% propane, 4% butenes, and 3% /3-butane.7 Presumably, the paraffins could be dehydrogenated catalyti-cally after separation from the olefins.8 Ethylene can be dimerized to 1-butene with a nickel catalyst.9 It can be trimerized to 1-hexene with a chromium catalyst with 95% selectivity at 70% conversion.10 Ethylene is often copolymerized with 1-hexene to produce linear low-density polyethylene. Brookhart and co-workers have developed iron, cobalt, nickel, and palladium dimine catalysts that produce similar branched polyethylene from ethylene alone.11 Mixed higher olefins can be made by reaction of ethylene with triethylaluminum or by the Shell higher olefins process, which employs a nickel phosphine catalyst. 

The specific reduction of the internal deposits coincides with the ethylene production. It is then suggested that the active sites for the catalytic dimerization of methane are carbide-like species in close interaction with the zeolite. The concentration of these sites would be very low compared to the concentration of zeolite acid OH groups... 

Nickel complex-containing zeolite materials Ni(MeCN)6(BF4)2/NaX and Ni(acac)2 have been prepared and characterized by X Ray photoelectron spectroscopy (XPS). These materials are catalytically active for ethylene dimerization and 1-butene isomerization. The supported systems show higher selectivity towards 1-butene formation compared with the homogeneous system. These features were attributed to a new nickel species formed in the supported systems. 

P-29 - Pt-2,2 bipyridine complex encapsulated in Y zeolite - catalysts for ethylene selective dimerization... 

This paper presents results concerning the synthesis of Pt(2,2 -bipyridine)Cl2 (K) encapsulated in Y zeolite and its activity in C2H4 selective dimerization to linear butenes. Diffuse reflectance UV-VIS spectroscopy and FTIR are used to investigate the state of the complex encapsulation. The influence of the reaction parameters on C2H4 selective dimerization to linear butenes is studied, we concluded that Pt(2,2 -bipyridine)Cl2 encapsulated in Y zeolite is a selective cateilyst for ethylene dimerization to linear butenes at low temperatures (80 - 150 C) and a reactant flow rate corresponding toWHSV 2h". ... 

Nickel oxide and nickel complexes supported on silica, silica-alumina, different zeolites, and polymeric materials have been reported to be active for ethylene dimerization. Yashima et reported that ethylene dimerization can... 

Likewise, monovalent and trivalent rhodium were known as good dimerization catalysts for ethylene (37,38) and indeed rhodium exchanged zeolite Y appeared as an efficient and selective catalyst in ethylene dimerization under mild conditions (O-20°C, 200 Torr of ethylene). By contrast HY was inactive under similar temperature and pressure conditions and at 200°C polymerization and cracking were observed (36). Thus again the dimerization is not acid-catalyzed. The active species is however uncertain but most probably not metallic, perhaps trivalent or monovalent (36,39). 

Palladium II complexes are also known as efficient homogeneous catalysts of ethylene dimerization. Interestingly Pdll zeolites, even though they convert ethylene under mild conditions, showed poor selectivity towards butenes. Reduction of palladium had an adverse effect on the activity and the selectivity, which is consistent with bivalent palladium as the active site for oligomeraition... 

The coordination complex chemistry in zeolites provides a very useful conceptual bridge to coordination-chemistry controlled catalysis in the liquid phase. This is discussed in this chapter for the oxidation of ethylene to produce vinyl acetate from acetic acid and ethylene. The catalytic system appears to consist of dimeric or trimeric Pd complexes. The elementary reaction steps can take place in the direct contact with the metal centers, the so-called inner-sphere mechanism. The reaction can also proceed through an outer-sphere mechanism in which proton transfer between reactants and acetate plays an essential role. 

This technology is still under development. It is carried out essentially on Fe-or Mo-modified, zeolites. Very few investigators reported their work on vanadium and heteropolyacid based catalysts. Investigations using CaO catalysts also appear in the literature. The monomeric and dimeric ferric ions were found to be active in ODH of ethane with nitrous oxide giving a product selectivity of 40-60% at 350°C on Fe-modified zeolites (ferrierite and MFI). On the other hand, Fe oxide nanoclusters resulted in overoxidation of ethane and/or ethylene to C, CO and CO2 [88]. Iron modified zeolites of different structures viz., ZSM-5, zeolite Y and mordenite were tested in the ethane and propane ODH. The nature of zeolite dictated the catalytic activity. The best... 

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