Carbon dehydrogenation reactions

This overview is organized into several major sections. The first is a description of the cluster source, reactor, and the general mechanisms used to describe the reaction kinetics that will be studied. The next two sections describe the relatively simple reactions of hydrogen, nitrogen, methane, carbon monoxide, and oxygen reactions with a variety of metal clusters, followed by the more complicated dehydrogenation reactions of hydrocarbons with platinum clusters. The last section develops a model to rationalize the observed chemical behavior and describes several predictions that can be made from the model. 

Thus, the role of zinc in the dehydrogenation reaction is to promote deprotonation of the alcohol, thereby enhancing hydride transfer from the zinc alkoxide intermediate. Conversely, in the reverse hydrogenation reaction, its role is to enhance the electrophilicity of the carbonyl carbon atom. Alcohol dehydrogenases are exquisitely stereo specific and by binding their substrate via a three-point attachment site (Figure 12.7), they can distinguish between the two-methylene protons of the prochiral ethanol molecule. 

It may be seen that the peroxidation mechanism leads primarily to degradation of the carbon chain, but that numerous dehydrogenation reactions are occurring also. 

In processing VGO it has been argued that the heavy poly-aromatic structures characterised by the Ramsbottom Carbon Residue (RCR, Table 1) can be considered as coke precursors [8]. An increase of the boiling point of those structures via condensation reactions or dehydrogenation reactions is responsible for coke deposition onto the catalyst. In order to increase our level of understanding of these processes we consider first the effects of catalyst parameters on the coke formation. 

Whilst the ability of platinum-based catalysts to effect the dehydrogenation of alkanes to the corresponding alkenes is well established [1-4], carbon laydown and consequential deactivation of the catalyst during the dehydrogenation reactions is a well known phenomenon... 

The composition and reactivity of the carbon laid down during the initial stages of the propane dehydrogenation reaction was examined by transient isotope labelling experiments using [2-]3C]-C3HgandC3JHs as tracers in a series of reactions in a pulsed flow microcatalytic reactor. In these experiments alternate series of labelled and unlabelled propane pulses were passed over the catalyst sample and the products analysed by glc and mass spectrometry. 

Only a relatively small fraction of the carbon laydown on the surface can be removed by high temperature dioxygen treatment. After regeneration carbon continues to build up on the catalyst surface in subsequent propane dehydrogenation reactions. 

Pretreatment of the catalyst with carbon monoxide or toluene at the reaction temperature results in carbon laydown on the catalyst, which dramatically reduces the amount of carbon deposition and increases the selectivity in subsequent propane dehydrogenation reactions. However, the carbon deposited during the pretreatment is different from that formed during propane dehydrogenation. 

Co. surface area = 300 m2/g ) with aqueous solutions of Cu, Cr, Mg, Ca, Sr, and Ba in Nitrate. All the catalysts have Cu to Si02 weight ratio of 14/86. For promoted catalyst, the Cr to Cu molar ratio was varied from 1/4 0 to 1/4, and the alkaline earth metal to Cu molar ratio was kept at 1/10. The impregnated catalysts were dried at 100 °C overnight, calcined at 450 for 3 h and then reduced in a stream of 10% H2 in Ar at 300 °C for 2 h. The copper surface areas of catalysts were determined by the N20 decomposition method described elsewhere [4-5J. The basic properties of the catalysts were determined by temperature-programmed desorption ( TPD ) of adsorbed carbon dioxide. Ethanol was used as reactant for dehydrogenation reaction which was performed in a microreactor at 300°C and 1 atm. 

Calculation based on previous data show that the aromatic carbon content of the SRC can only be increased to the values shown by data by dehydrogenation reactions. These calculations take into account the carbon types present in residue and in the gases. 

Potential applications of superconducting cuprates in electronics and other technologies are commonly known. These cuprates also exhibit significant catalytic activity. Thus, YBa2Cu307 3 and related cuprates act as catalysts in oxidation or dehydrogenation reactions (Hansen et al. 1988 Halasz 1989 Mizuno et al. 1988). Carbon monoxide and alcohol are readily oxidized over the cuprates. NH3 is oxidized to N2 and H20 on these surfaces. Ammoxidation of toluene to benzonitrile has been found to occur on YBa2Cu307 (Hansen et al. 1990). 

Lanthanides as modifiers to other oxides in aluminas In zirconias In iron oxide Lanthanide oxides in mixed oxides With aluminas With iron oxides With other transition metal oxides To maintain surface area To increase oxidation rates To increase methanation rates For conduction in electrocatalysis For ammonia synthesis promotion To provide sulfur oxides (SO.,) control For dehydrogenation in carbon monoxide reactions For oxidation... 

The protolytic cracking involves the attack of the zeolitic proton to a carbon atom of the alkane molecule and the simultaneous rupture of one its adjacent C-C bond. The carbon atom being attacked and the C-C bond being broken will be preferentially those which produce the most stable carbenium ion. As for the dehydrogenation reaction, the protolytic cracking of linear and branched alkanes also follow different mechanisms, the latter ones producing olefins instead of alkoxides. 

Dehydrogenation reaction a reaction in which two hydrogen atoms are removed from adjacent carbons of a saturated hydrocarbon, giving an unsaturated hydrocarbon. (22.1) Delocalization the condition where the electrons in a molecule are not localized between a pair of atoms but can move throughout the molecule. (13.9)... 

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