Specific Catalyst Systems

In the previous sections most of the factors that control whether or not a particular system has potential in ammonia synthesis have been examined. In this section the characteristics of those materials that show significant synthesis activity will be examined in more detail. These are split into three groups based on the nature of their nitrides (Table 9.1)  

Those metals where nitrides are unlikely to be present under synthesis conditions (Mn, Fe, Co, Ni, Tc, Re), including alloys of these metals. 

Metals probably present as nitrides under synthesis conditions (Groups 3a to 6a). 

Of the platinum group metals only ruthenium and osmium show significant ammonia synthesis activity, though only in the presence of alkali promoters. This can be seen from the performance of the potassium metal promoted carbon-supported catalysts in Table Although osmium was one of the earliest and 

Although none of these metals form bulk nitrides, the transition metal-nitrogen bond energies are still significant. For ruthenium the surface bond strength (566 kJ mol ) is not markedly lower than on iron (585 kJ mol ) (Table 9.2) and even the inactive metals such as palladium have bond strengths of around 

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Carboxylation/Oxidation of Straight-Chain 1-Olefins. Selective carboxylation of a-olefins to predominately straight-chain aldehydes is realized through specific catalyst systems and by careful control of reaction conditions. The aldehyde produced is then air-oxidized to the acid using a Mn catalyst. Heptanoic acid [111-14-8] and pelargonic acid [112-05-0] are produced commercially in this manner. 

Other kinetic aspects are dealt with under specific catalyst systems either here or in Ch. 2. 

SOLUTION POLYMERIZATION Solution SBR typically made in hydrocarbon solution with alkyl lithium-based inihator. In this stereo-specific catalyst system, in principle, every polymer molecule remains live until a deactivator or some other agent capable of reacting with the anion intervenes. Able to control molecular weight, molecular weight distribution, and branching. Able to make random and block copolymers with designed chain sequence. Able to make copolymer with controlled styrene content. Able to control the butadiene structure of vinyl/ ds/ trans. Higher purity due to no addition of soap. 

The polymer is generally prepared in the presence of a stereo-specific catalyst system that can produce a polymer that contains in excess of 92 percent cis-1,4 structure. The cis and trans are shown here ... 

Applied and fundamental research can give adequate descriptions of these phenomena, but usually scale-up requires experimental work due to the shortcomings of the correlations. Steam reforming reactor experiments at pilot scale are costly, so parameter identification is usually combined with other key points such as durability of a specific catalyst system or consfruction material. 

A glance at the molecular structure of 11 shown in Fig. 18 reveals again that from a molecular symmetry point of view complex 11 (like complex 10) has all the structural and symmetry characteristics required to be classified as a syndiotactic-specific catalyst system after its activation. In practice, after activation with MAO, complex 11 does polymerize propylene to a high molecular weight s-PP very efficiently [29]. Tables 11 and 12 present the polymerization conditions, results and polymer analyses for 11/MAO and the syndiotactic polymers it produces. According to these data, only the syndiotacticity of the polymers produced at and below 40°C (measured as the concentration of racemic pentads rrrr about 75%) are... 

Allyl P-ketO Carboxylates undergo decarboxylation to form aP-unsaturated ketones when treated with the specific catalyst system palladium acetate and l,2-bis(diphenylphosphino)ethane [equation (25)]. Such a reaction extends... 

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