Titanium activity

Supporting the titanium catalyst component has been claimed to lessen the tendency of titanium active site to be reduced by the activator [55]. 

DEHYDROGENATION MECHANISM FROM TITANIUM-ACTIVATED SODIUM ALANATE... 

Dehydrogenation Mechanism from Titanium-Activated Sodium Alanate... 

Pais I, Fehee M, Faekas E, Szab6 Z and Caenides L (1977) Titanium as a new trace dement. Commun Soil Sci Plant Anal 8 407-412. Pawlek RP (2000) Titanium activities at the turn of the year 199912000. Metall 54 102-104. 

P-17 - On the role of the titanium active site in the phenol/anisole hydroxylation over titanium substituted crystalline silicates... 

Hydroxylation of phenol and anisole was investigated using TS-1, a silanised TS-1 and Al-free Ti-Beta. Pore geometry, solvent, external surface and substrate govern the selectivity of the hydroxylation reaction. In medium pore TS-1 the formation of hydroquinone in phenol hydroxylation is favoured due to the geometric constraint on the formation of catechol in the pores. A similar effect is observed for formation of ortho- and para hydroxy-anisoles in Al-free Ti-Beta. Solvents affect activity and selectivity of the hydroxylation reactions through adsorption and co-ordination to the titanium active site. The external surface of TS-1 plays a substantial role in hydroxylation reactions. 

Titanium activated with oxides of different metals, in particular mthenium or iridium, used in the form of mesh, wire or strip, is the most reliable and widely used type of anode [51]. It has good mechanical properties and can easily be adapted to the entire surface of the structure in order to obtain a good distribution of current It is usually coated with an overlay of mortar but can also be embedded directly into the concrete. It can dehver current densities up to 100 mA/m over long periods, with short-term maximum levels of even 300-400 mA/m. Laboratory tests and field experience indicate that the service hfe can range from 20 to over 100 y (if the quahty of concrete and overlay are adequate). 

Figure 2.2 Mechanism of short-chain branch (SCB) formation with coordination polymerization. The chains are shown growing on a titanium active site.

Hastelloy C (active). Inconel 625 (active), titanium (active)... 

The external donors transform nonstereospecific sites into isospecific sites by blocking open coordination sites near the titanium active centers. 

TiC is considered structurally stable in static H2 up to 2400°C (May and Hoekstra, 1961 Ohlinger, 1959a). However, the action of H2 is complicated by the rapid change in carbon and titanium activity with composition. As carbon is removed from TiCj 0 by the formation of hydrocarbons, the carbon activity will be reduced, and in a static system further reaction will cease. In flowing H2, extensive decarbonization can result and can lead to additional sample loss by the increased evaporation rate for Ti. Competition between these two processes can result in a solid... 

Blasse G, Dalhoeven G, Choisnet J, Studer F (1981) On the luminescence of titanium activated stannates. J Solid State Chem 39 195-198... 

Figure 2.7 shows that the ethylene is coordinated to the titanium center at the vacant octahedral position through sigma bonding involving the ethylene 7t-orbitals and the titanium d orbital. The 7t-bond involves titanium d orbital overlapping with empty Tt-antibonding orbitals on ethylene. The coordination of ethylene to the titanium active site is known as the Dewar-Chatt-Duncanson model of the metal-olefin bond [31]. The... 

For comparison, a similar polymerization experiment was carried out in which the titanium compoxmd was TiCljCTHF) and only 5.8 grams of polyethylene were produced, which corresponds to a titanium activity of 1.9 x 10. The catalyst containing titanium and magnesium was 125 times more active than the catalyst based on TiCl3(THF)3. 

The reaction is stereospecific because each new olefin monomer always enters and reacts from the same ligand position on the titanium active site. A stereoregular polyolefin results with all substituents pointing in the same direction. It is an isotactic polymer. If the groups alternate on the chain it is a syndiotactic polymer. If the orientation is random, the molecule is said to be atactic. 

MgCU has been found to be the ideal support its host lattice can support chiral titanium-active sites. This can be attributed to the near isomorphism of MgCU and TiCU crystals. Crystals of both TiCU and MgCU consist of two planes of chlorine atoms sandwiching a... 

Tobisch S, Ziegler T Catalytic hnear ohgomerization of ethylene to higher a-olefins insight into the origin of the selective generation of 1-hexene promoted by a cationic cyclopentadienyl-arene titanium active catalyst, Organometallics 22(26) 5392—5405, 2003. 

The early Phillips catalysts only needed to be activated and reduced to generate active centers, but several patents since have described the use of co-catalysts to promote the production of LLDPE. For example, a typical catalyst that had been modified with titanium, activated in air and reduced in caibon monoxide was then further activated by addition of triethylboron prior to operation." This procedure led to the production of linear low density polyethylene, LLDPE, which had a density of 0.9726 g cm, directly, without the need for the addition of an a-olefin to the pure ethylene feed. Olefins were produced in situ and these were incorporated into the polyethylene. A second catdyst was made using silica with a very high pore volume, modified with titanium, activated in air, and finally reduced with caibon monoxide at 350°C. This catalyst was then treated with triethylboron before use. LLDPE polymers with densities in the range 0.890 to 0.915 were obtained from a feedstock of ethylene and hexene-1, but the addition of some hydrogen to the gas stream was required to limit the length of the polymer chain. 

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