Carbon number catalysis

The chain length of n-alkanes has a marked influence on reactivities for hydroisomerization, and especially for hydrocracking. To a very small extent a methane and ethane abstracting mechanism, probably hydrogenolysis as predicted in a basic work on bifunctional catalysis (14), is found to be superimposed when lower carbon number feeds (C, Cg, Cg) are used. n-Hexane is excluded from ideal hydrocracking. On the Pt/Ca-Y-zeolite catalyst it is cracked via a mechanism that is mainly hydrogeno-lytic. 

B. Diffusion-Enhanced Bifunctional Catalysis and THE Control of Carbon Number Distribution AND Product Functionality... 

With respect to the point mentioned last, special interest has been focused by several authors on the possible insertion of olefins. Of special relevance are results reported by Schulz and Achtsnit (77). These authors studied the FT catalysis on a cobalt catalyst and added ethylene marked with to the feed. The product was analyzed the specific molar radioactivities of the various fractions are shown in Fig. 3. It is seen that for higher carbon numbers the specific molar radioactivity increases linearly with the carbon number. Upon considering that, if ethylene can be inserted, the chance of this to happen increases linearly with the number of insertion steps that a chain undergoes during its life, this linear dependence is interpreted by the authors as proving ethylene insertion. 

Due to interfacial reactions, one of the main advantages of SAPC upon biphasic catalysis is that the solubility of the olefins in the catalytic aqueous-phase does not limit the performance of the supported aqueous phase catalysts (SAPCs) the turnover frequencies (TOFs) are roughly independent of olefin carbon number [17]. This has been shown to be true also for carbon numbers as high as 17 [15]. 

Thereafter, the operations of the petrochemical industry, or more accurately bulk organic chemical industry, centre on chemistry, with extensive use of catalysis to permit the use of the cheapest feedstock available and eliminate expensive reagents. However, potential changes in raw material availabilities and environmental pressures need a flexible response, possibly illustrated by the variety of production routes to acetic (ethanoic) acid and anhydride described in section 12.5. The remaining aliphatic chemical products are dealt with in carbon number sequence, followed by aromatics and nylon intermediates. 

A review on cage and window effects in mainly hydroconversion of alkanes with zeolites [73] shows that bi- and even trinodal distributions of product carbon numbers can be formed. In the erionite (ERI) cage Cs hydrocarbon fragments are selectively trapped, thus undergoing intense secondary cracking. This effect was confirmed in the ketonization of carboxylic acids [74]. Alternatively, in cases of slow diffusion (and counterdiffusion), viz. in the liquid-phase propylation of benzene in mordenite, the possibihty of having pore-mouth catalysis was advanced [75]. Multinodal product distributions from... 

Mango and Elrod (1999) measured the carbon isotopic composition of catalytic (using Ni metal compounds) gas generated from crude oil and pure hydrocarbon between 150 and 200°C. The measured 5 C for Cl through C5 was linear with l/n n = carbon number), in accordance with theory and natural observation. This result further supports to the view that catalysis by transition metals may be a source of natural gas. 

This thesis has been completely devoted to catalysis by relatively hard catalysts. When aiming at the catalysis of Diels-Alder reactions, soft catalysts are not an option. Soft catalysts tend to coordinate directly to the carbon - carbon double bonds of diene and dienophile, leading to an activation towards nucleophilic attack rather than to a Diels-Alder reaction . This is unfortunate, since in water, catalysis by hard catalysts suffers from a number of intrinsic disadvantages, which are absent for soft catalysts. 

Lipases are the enzymes for which a number of examples of a promiscuous activity have been reported. Thus, in addition to their original activity comprising hydrolysis of lipids and, generally, catalysis of the hydrolysis or formation of carboxylic esters [107], lipases have been found to catalyze not only the carbon-nitrogen bond hydrolysis/formation (in this case, acting as proteases) but also the carbon-carbon bond-forming reactions. The first example of a lipase-catalyzed Michael addition to 2-(trifluoromethyl)propenoic acid was described as early as in 1986 [108]. Michael addition of secondary amines to acrylonitrile is up to 100-fold faster in the presence of various preparations of the hpase from Candida antariica (CAL-B) than in the absence of a biocatalyst (Scheme 5.20) [109]. 

The method was later extended to the synthesis of a number of meroter-penoids from epoxygeranyl carbonates or acetates in a two-step approach combining titanocene catalysis with Stifle reactions (carbonates) [108,109] or copper-catalyzed allylic substitutions (acetates) [110-112], The cyclizations... 

Cobalt(II) alkoxides are known and monomeric forms are part of a wider review.413 The interest in these compounds pertains to a potential role in catalysis. For example, a discrete cobalt(II) alkoxide is believed to form in situ from a chloro precursor during reaction and performs the catalytic role in the decomposition of dialkyl pyrocarbonates to dialkyl carbonates and carbon dioxide.414 A number of mononuclear alkoxide complexes of cobalt(II) have been characterized by crystal structures, as exemplified by [CoCl(OC(t-Bu)3)2 Li(THF)].415 The Co ion in this structure and close relatives has a rare distorted trigonal-planar coordination geometry due to the extreme steric crowding around the metal. 

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