Adsorption olefins

In the results presented in Table 13.5, the addition of tin affects the kinetic selectivity r differently, depending on the catalyst preparation method. When compared to the monometallic PdO catalyst, r slightly decreases for the coimpregnated PdSn catalyst, but it sharply increases for the PdOSn catalyst prepared via the colloidal oxide synthesis. As the intrinsic kinetic constant rates k do not show significant discrepancies between the different catalysts, the main contribution of the variation of the kinetic selectivity is ascribed to the adsorption constant ratio fBo/ Butenes- In the case of the PdOSn catalyst, formation of but-l-ene is favored compared to its consumption because the X Bo/ Butenes ratio increases, indicating that olefin adsorption is much more destabilized than diene adsorption. Thus, the olefin easily desorbs before being hydrogenated into butane. 

The effects of substrates on 7r-complexation were studied by olefin adsorption on monolayer AgN03 supported on various substrates (Padin and Yang, 2000). The substrates selected were y-Al203, Si02, and MCM-41. The following trend for olefin adsorption was observed for these substrates ... 

With these mechanistic rationales and a knowledge of how the nature of the catalyst affects the reversibility of the individual steps in the hydrogenation process as well as how steric factors can be involved in olefin adsorption, it... 

In early proposals based upon the mechanisms of Mo and V peroxides, Ti(T] —O2) was thought to be the active species [70, 71]. The epoxidation of the olefin occurred either by a coordinative mechanism, with the olefin adsorbing on Ti prior to the insertion into one Ti-peroxide bond, or by the attack of one peroxy oxygen directly on the double bond. However, the chemical inertness of known Ti(T] —O2) peroxides, the unhkelihood of olefin adsorption on oxophilic Ti in competition with the protic medium and other evidence led subsequently to the loss... 

Huang, H.Y. Padin, J. Yang, R. T. Ab Initio Effective Core Potential Study of Olefin/Paraffin Separation by Adsorption via ii-Complexation Anion and Cation Effects on Selective Olefin Adsorption J. Phys. Chem. B., 1999,103, 3206. 

Evaluation of the electrocatalytic isotopic reaction of alkenes was facilitated by using Kemball s statistical model to determine the origin of each species and the probability of each step (380,381). The model assumes olefin adsorption and reaction with deuterium or hydrogen to form ethyl radicals. These can revert to ethylene or they can add H or D to give ethane (i = 0, 1,...,4) ... 

The vertical trends of strength of olefin adsorption, detected in Groups VIII2 and VIII g, are also observed in ruthenium and osmium. However, the horizontal trends (Rh > Pd, Ir > Pt for strength of olefin adsorption) are not continued, due perhaps to the change in crystal structure. In some respects these metals are entirely normal, although there is evidence for the participation of 7r-allylic species in isomerization processes. 

Using the triphenylcarbonium ion as a probe it was possible to demonstrate (82) that mechanism A-l could obtain and to exclude A-2 and B from further consideration. It should be noted that if prior olefin adsorption were a necessary prerequisite for paraffin adsorption, then carbonium ions could not be formed from paraffin molecules in a system rigorously freed from olefin or olefin-forming impurities. As triphenylmethane itself is certainly not an olefin precursor, there remained only two possible sources of olefinic impurity to be considered namely, the catalyst surface and the reagents employed. The former was discounted on the grounds that it was highly improbable that either olefins or carbonium ions on the surface survived the ex-... 

New effective sorbents were synthesized by dispersing Cu(N03)2 and A Os salts over Si02-Al203 substrates using three different techniques. The attained high capacities make them suitable for propane/propene separation It is clear that functionalisation method play an important role in selective olefin adsorption via n-complexation. 

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