Alkanes catalytic conversion

Second, we shall present our approach as to how to probe the palladium surfaces in more complex Pd/support catalysts, especially when the so-called metal-support interactions are expected. We shall develop our idea of how to use such chemical probes as a catalytic reaction (alkane catalytic conversion) or chemisorption in order to see important changes in the catalytic behavior. When possible, an adequate reference to available data from more sophisticated physical techniques is made. 

The catalytic conversion of NO was investigated Grst in absence of catalyst (blank). The results reported in Fig. 1 show that the homogeneous gas phase oxidation of the alkane starts at 650 K. No reduction of NO is observed in the homogeneous process, then the production of N2 can be ascribed to the catalytic reduction. The catalytic properties were determined by temperature programmed reaction (ramp 2 K min-l). The temperature was increased from 523 to 673 K and back. 

More than three decades ago, skeletal rearrangement processes using alkane or cycloalkane reactants were observed on platinum/charcoal catalysts (105) inasmuch as the charcoal support is inert, this can be taken as probably the first demonstration of the activity of metallic platinum as a catalyst for this type of reaction. At about the same time, similar types of catalytic conversions over chromium oxide catalysts were discovered (106, 107). Distinct from these reactions was the use of various types of acidic catalysts (including the well-known silica-alumina) for effecting skeletal reactions via carbonium ion mechanisms, and these led... 

The CH-activation of alkanes and especially of methane and their catalytic conversion to alcohols is one of the major challenges for chemists. Methane as the major part of natural gas is currently the cheapest source of hydrocarbons and the need for methanol will increase in the near future. Methane conversion to methanol would make a conveniently transportable fuel and also a new carbon source for the chemical industry. 

Wacker oxidation, a catalytic conversion of alkanes with aerial oxygen to carbonyl compounds, and its potential for large-scale applications has been reviewed.220 Aerobic... 

The interrelationships between activation of H2 and other a-bonded molecules such as alkanes and silanes are highly significant because catalytic conversion of methane and other alkanes is strongly being pursued (17-19). An important question thus is whether C-H bonds in alkanes, particularly CH4, can bind to superelectrophilic metal centers to form a a alkane complex that can be split heterolytically where proton transfer to a cis ligand (or anion) takes place followed by functionalization of the resultant methyl complex (Eq. (3)). 

The abundance and low cost of light alkanes have generated in recent years considerable interest in their oxidative catalytic conversion to olefins, oxygenates and nitriles in the petroleum and petrochemical industries [1-4]. Rough estimates place the annual worth of products that have undergone a catalytic oxidation step at 20-40 billion worldwide [4]. Among these, the 14-electron selective oxidation of -butane to maleic anhydride (2,5-furandione) on vanadium-phosphorus-oxide (VPO) catalysts is one of the most fascinating and unique catalytic processes [4,5] ... 

Ti-p and Ox-Ti-P samples exhibited very low activity in the oxidation of alkanes (Table 3). Literature data indicate that as compared to TS-1, Ti-P has very low catalytic conversions in the oxidation of alkanes [10]. For example conversions of about 0.5 and 0.8 % have been reported in the oxidation of n-hexane and cyclohexane at 333 K and H202/alkane = 0.082. In addition, we found that the conversion does not improve when the ratio of hydrogen peroxide to substrate is increased to 0.5. As for Ox-Ti-P samples, they had higher n-hexane conversions, however the selectivity towards oxygenated products was low. Most of the by-products formed over Ox-Ti-P are likely due to the presence of aluminum (Table 1). 

The dynamics of methane, propane, isobutane, neopentane and acetylene transport was studied in zeolites H-ZSM-5 and Na-X by the batch frequency response (FR) method. In the applied temperature range of 273-473 K no catalytic conversion of the hydrocarbons occurred. Texturally homogeneous zeolite samples of close to uniform particle shape and size were used. The rate of diffusion in the zeolitic micropores determined the transport rate of alkanes. In contrast, acetylene is a suitable sorptive for probing the acid sites. The diffusion coefficients and the activation energy of isobutane diffusion in H-ZSM-5 were determined. 

Microporous and, more recently, mesoporous solids comprise a class of materials with great relevance to catalysis (cf. Chapters 2 and 4). Because of the well-defined porous systems active sites can now be built in with molecular precision. The most important catalysts derived from these materials are the acid zeolites. The acid site is defined by the crystalline structure and exhibits great chemical and steric selectivities for catalytic conversions, such as fluid catalytic cracking and alkane isomerization (cf. Chapter 2). In Section 9.5 we discuss the synthesis of zeolites and, briefly, of mesoporous solids. 

Scheme 1. Proposed mechanism for the partial oxidation of 2-propyl surface species on O/Ni(100) at low oxygen coverages. A similar mechanism is likely to operate during the catalytic conversion of alkanes on substoichiometric nickel oxides.

Activated alkanes, such as cyclohexanone, acetone, and aliphatic nitro compounds, can react with carbon dioxide even without metal catalysis. A typical example is the phenolate-catalyzed reaction of acetophenone with C02 to the corresponding carbon add. A catalytic conversion of the non-activated methane with C02 to give acetic acid was reported by Fujiwara and co-workers [72], The reaction was carried out in the presence of palladium and copper acetate and also stoichiometric amounts of the oxidant K2S208. 

Taking into account the complexity of C2-C4 alkanes functionalization, one of methods of solution of this problem is the conversion of these alkanes into liquid hydrocarbons. The investigations in this direction showed the possibility of one-stage catalytic conversion of lower alkanes into aromatic hydrocarbons [1-3]. Taking into account the reactivity differences of C2-C4 alkanes, it is interesting to elucidate the reactivity of gas mixtures consisted of these molecules and their aromatic products. The present report is devoted to the results of studies in this direction. 

Treatment of an alkyne with Hg in the presence of a transition metal catalyst, most commonly Pd, Pt, or Ni, results in the addition of two moles of H2 to the alkyne and its conversion to an alkane. Catalytic reduction of an alkyne can be brought about at or slightly above... 

The alkane metathesis of highly branched alkanes and product selectivity also follows the same mechanism with catalyst 24. A selective and catalytic conversion of 2-methylpropane into 2,3-dimethylbutane (42%), and ethane (41%) (Scheme 23) [80] was observed when 2-methylpropane was passed over the catalyst 24 at 150°C. Conversion was reached up to 8% and 37 TON was achieved over 43 h (Scheme 23). 

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... 

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). 

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