Alkane-alkene conversion

In some cases, the alkene, once formed, can dissociate and is not further dehydrogenated. - This makes the alkane alkene conversion potentially catalytic, but the reaction is thermodynamically uphill below 300°C, so we need to drive the reaction. If t-BuCH=CH2 is present, it can do so by acting as hydrogen acceptor (Eq. 12.31). 

It is now superflous to point out the renewed interest for the Fischer-Tropsch (F-T) synthesis (j) i. . the conversion of CO+H2 mixtures into a broad range of products including alkanes, alkenes, alcohols. Recent reviews (292.9k ) emphasized the central problem in F-T synthesis1 selectivity or more precisely chain-length control. 

Comparison of Anodic Conversions of Alkanes, Alkenes, and Aromatic... 

Similar tests of the fiuidized-bed method have been successful with a variety of molecular adsorbates and catalysts (other zeolites, supported oxides, naphthalene, pyridine, methanol, alkanes, alkenes, acetonitrile, ammonia, etc.) (25). We believe that this fiuidized-bed method is a major step forward for measurements of working catalysts with UV Raman spectroscopy. It should also be a useful method for measurements of catalytic kinetics by reducing heat and mass transfer effects that arise when catalysts are used in the form of pellets. In the limit of low conversions... 

In a base-free medium (dry MeCN), Fe Ch activates HOOH to form a reactive intermediate that oxygenates alkanes, alkenes, and thioethers, and dehydrogenates alcohols and aldehydes. Table 11 summarizes the conversion efficiencies and product distributions for a series of alkene substrates subjected to the Fe Cfi/HOOH/MeCN system. The extent of the Fe Cb-induced monooxygenations is enhanced by higher reaction temperatures and increased concentrations of the reactants (substrate, Fe Cls, and HOOH). For 1-hexene (representative of all of the alkenes), a substantial fraction of the product is the dimer of 1-hexene oxide, a disubstituted dioxane. With other organic substrates (RH), Fe Cb activates HOOH for their monooxygenation the reaction efficiencies and product distributions are summarized in Tables 11(b). In the case of alcohols, ethers, and cyclohexane, a snbstantial fraction of the product is the alkyl chloride, and with aldehydes, for example, PhCHO, the acid chloride represents one-half of the product. In the absence of snbstrate the Fe Cls/MeCN system catalyzes the rapid disproportionation of HOOH to O2 and H2O. 

Besides rearrangements, ligand exchange, formation of alkanes, alkenes and other products, release of cyclopropanes is one of the most important reactions of metallacyclobutanes. Of course, this latter reaction is only useful in cyclopropane synthesis if the product is not identical with the starting material used to form the metallacyclobutane. Nevertheless, the discovery of a complex formed from hexachloroplatinic acid and cyclopropane and later structural elucidations have initiated intensive investigations on the conversion of cyclopropanes to metallacyclobutanes and release of cyclopropanes from the latter. These results have been thoroughly discussed in several reviews. " Therefore in this section only some general aspects of cyclopropane formation from metallacyclobutanes and selected synthetically useful methods are discussed. 

Titanosilicates have been synthesized which have the large pore structure of UTD-1. These molecular sieves were prepared using the metal complex Cp 2Co (bis(pentamethylcyclo-pentadienyl)cobalt(III) ion) as the template. Ti-UTD-1 has been found to be an effective catalyst for the oxidation of alkanes, alkenes and phenols using hydrogen peroxide as well as the larger oxidant t-butylhydroperoxide. The channel structure defined by 14 membered rings in Ti-UTD-1 also allows the conversion of larger substrates such as 2,6-di-t-butylphenol. 

The following questions can in principle be addressed with spectroscopy (1) Zeolite synthesis what are the mechanisms of ZSM-5 synthesis and how do they influence the quality of the catalyst synthesized (2) Catalyst characterization what are the structure and composition of the zeolite, and what is the configuration of the active site for methanol conversion (3) How do methanol and dimethylether interact with the active sites i.e. what species are present in the catalyst in the initial stages of methanol conversion (4) What are the subsequent reaction pathways leading to the final alkane, alkene and aromatic products (5) What causes catalyst deactivation This question concerns both the temporary deactivation associated with coke formation, which can be reversed by oxidative regeneration, and the permanent deactivation which occurs after repeated deactivation-regeneration cycles. 

In the bulk chemicals industry classical environmentally unacceptable processes have largely (but not completely) been supplanted by cleaner, catalytic alternatives. Indeed, catalytic oxidation [1] is the single most important technology for the conversion of hydrocarbon feedstocks (alkanes, alkenes and aromatics) to industrial chemicals (see Table 1). 

In the present study a well defined inorganic cluster, hexamolybdoplatinate(IV) heteropolyanion, was employed as a bimetal ensemble precursor, which has a plane Anderson structure. The [PtMoej/MgO catalyst prepared by supporting the hexamolybdoplatinate(IV) heteropliyanion on MgO, followed by calculation at 773K, showed a unique surface structure and better catalytic performance for the alkane-to-alkene conversion than a conventional coimpregnation catalyst.[15]... 

They also evaluated isothermal MR concepts and compared them in performance with the adiabatic Catofin and Oleflex processes. They studied two different type processes using Knudsen diffusion membranes a process called CMRL, patterned after the commercial Oleflex process, with low propane conversion, and a process called CMRH, patterned after the commercial Catofin process with high propane conversion. They have calculated the return on investment (ROI) for all four processes. Though marginally better than the commercial processes, the ROI for all four processes evaluated is not very attractive. A sensitivity analysis indicates that for the ROI of the MR processes to be attractive a price difference between propane and propylene of more that 300/ton is required. Though published calculations have only been performed for the propane/propylene pair, it is not unreasonable to assume that similar conclusions apply to other alkane/alkene pairs. Similar conclusions about catalytic alkane dehydrogenation have also been reached in a technical/economic evaluation study by Amoco workers and their academic collaborators (Ward et al [6.3 ]). 

The controlled oxygenation of alkanes, alkenes, and aromatic hydrocarbons is one of the most important technologies for the conversion of crude oil and natural gas to valuable commodity chemicals. Biomimetic studies of metalloporpltyrins have led to important advances in practical catalysis, especially with ruthenium porphyrins. Reaction of wj-CPBA, periodate, or iodosylbenzene with Ru(II)(TMP)(CO) produced RuCVIjfTMPXOjj . Remarkably, Ru(VI)(TMP)(0)2 was found to catalyze the aerobic epoxidation of olefins under mild conditions. Thus, for a number of olefins including cyclooctene, norbomene, cis-, and trans- -methyl styrene 16-45 equivalents of epoxide were... 

Miller and Moskovits obtained data from the conversion of CD2=CD2 mixed with the synthesis gas. The authors reported that the deuterium from the deuterated ethene was incorporated into the alkanes and alkenes almost entirely as CD2 units. The oxygenates were found to have no incorporated deuterium. The authors conclude that the most plausible explanation is that the oxygenates and alkanes/alkenes are synthesized on different portions of the catalyst surface. These important and surprising results were published in a note in 1989 that promised more details in a forthcoming publication it does not appear that the details have been published since that time. 

The oxidation of alkanes, alkenes and simple aromatics at 293 K under NOx rich tropospheric conditions has been studied using laser pulse initiation combined with cw laser long path absorption/LIF for the detection of OH and NO2. In the case of aliphatic hydrocarbons the absolute yield and the kinetics of the formation of these products have been found to be sensitive indicators for the reaction behaviour of the oxy radicals RO. In combination with mechanistic simulations rate constants for individual reactions as well as branching ratios have been derived, which permit the evaluation of the compound specific NO/NO2 conversion factors (NOCON - factors) for the first oxidation steps. In the case of benzene and toluene oxidation the results indicate that reaction of the primary formed X cyclohexa-dienyl radical (X = Cl, OH) with O2 is the dominant pathway, although the rate coefficients were found to be lower than 2 x 10" cmVs. 

The present experiments were aimed at a quantification of NO/NO2 conversion factors in the first oxidation step of a series of alkanes, alkenes and aromatics. Moreover, the experimental approach, namely time-resolved measurement of OH and NO2 evolution together with numerical simulation permitted the extraction of individual rate coefficients for the decomposition/isomerisation of oxy radicals. It has been shown that these rate coefficients increase with the size of the molecule up to a limiting value of - 10 at 298 K. The NOCON factors derived may be used to extract condensed mechanistic equations for the primary oxidation steps of hydrocarbons. The values derived in this work are integrated quantities comprising weighted averages of all fractional yields of detailed mechanisms as initiated by the attack of the primary oxidant to the various positions of the parent compound. 

Compositional modulation has been practiced for the FT synthesis in catalytic reactors [126]. It was found that the cyclic feeding of synthesis gas (CO/IT2) had an influence on the selectivity of the FT products. In the early studies, only low conversions could be utilized due to the exothermic nature of the reaction. It was concluded that for an iron catalyst, the methane selectivity increased with periodic operation as did the molar ratio of alkene/alkane. Higher conversion studies were conducted in a CSTR, and it was found that periodic operation had an influence on the selectivity of the products from the FT synthesis using an iron catalyst [127]. First, there was a decrease in the alpha value for synthesis with increasing period. In addition, the alkane/alkene ratio increased with an increase in the period. There was a change in the CO2 production but this could be attributed to the change in CO conversion and not the... 

A Novel PtMo ]/MgO Catalyst for Alkane-to-Alkene Conversion... 

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