Dissociating catalyst

The anionic catalysts listed earlier react with lactam monomer to first form the salt, which in turn will dissociate to the active species, namely, the lactam anion. A strongly dissociating catalyst in low concentrations, therefore, is always preferable to weakly dissociating catalysts in higher concentrations. The catalytic activity of the various alkali metal and quaternary salts of a lactam generally follows the extent of their ionic dissociation that is controlled by the cation. Activity of a salt decreases with increasing size of the cation due to restricted mobility and decreased ionization potential. 

Ce02 with fluorite-type structure is a component in N02 dissociation catalysts [57] and biomass gasification catalysts [58],... 

DBU and its salts have been patented and used as dehydrohalogenation agents for fluoropolymers (83JAP(K)219202), fluororubbers (78MI3), and poly(vinyl halide) in the preparation of polarizing films (83JAP(K)21929), and as dissociation catalysts for blocked isocyanates (83JAP(K)65764). 

Strongly dissociated catalysts may thus be used in lower concentrations than weakly dissociated catalysts. 

In addition to innovative coatings for the protection of the hydrogen dissociation catalyst, mesoporous metal oxide layers for enhanced performance of the sensor elements were investigated. The results demonstrated the suitability of an electrodeposited tungsten oxide (WO3) as a chemochromic layer for hydrogen detection, providing a valuable alternative to vacuum deposition. 

Fig. 8.8 Schematic of a composite membrane coated with hydrogen dissociation catalysts on both sides. Catalyst poisoning by sulfur and competitive adsorption by molecules such as CO must be considered...

Membrane Hydrogen Dissociation Catalysts and Protective Layers... 

Role of Hydrogen Dissociation Catalysts on Hydrogen Transport Membranes... 

In one embodiment patented by Makrides et al., tantalum foils were electrolyti-cally etched in hydrofluoric acid, washed with acetone and, while still wet with acetone, placed in vacuum and dried by evacuation. Using an argon plasma at a pressure of about 1 mm Hg (133.3 Pa), palladium was deposited onto both sides of the membranes to recommended thicknesses between 10 and 100 nm. Membranes of niobium and vanadium were prepared in the same manner, except that, in addition, vanadium was degassed in vacuum at 1273 K (1000 °C) to remove oxygen. Unalloyed palladium as well as Pd-Ag, Pd-Au and Pd-B, were also patented as hydrogen dissociation catalysts and as protective layers for the highly reactive niobium, tantalum and vanadium. 

Another approach currently under development is fabrication of a composite or multilayer membrane structure by applying a thin H2 dissociation catalyst layer (often Pd-based) onto a super-permeable core. The cores typically have Nb, Ta, V, and/or Zr as major components. As described earlier, because of the formation of noncatalytic, highly stable surface oxides, superpermeable metals cannot be used... 

Catalytic systems for ring-opening of lactones have also been studied with mechanistic interpretation of the reaction in the case of soluble aluminium-zinc and cobalt-aluminium-oxoalkoxides. Insertion into the aluminium alkoxide bonds by monomer is su ested. These systems have been employed to synthesize lactone block copolymersvia living ring-opening polymerization in homogeneous oi anic phase. c-Caprolactone/)S-propiolactone block copolymers were obtained in a quantitative manner only in the presence of dissociated catalyst. 

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