Methanol-to-hydrocarbon catalysis

Catalysis. As of mid-1995, zeoHte-based catalysts are employed in catalytic cracking, hydrocracking, isomerization of paraffins and substituted aromatics, disproportionation and alkylation of aromatics, dewaxing of distillate fuels and lube basestocks, and in a process for converting methanol to hydrocarbons (54). 

J.F. (2004) Theoretical smdy of the methylbenzane side-chain hydrocarbon pool mechanism in methanol to olefin catalysis. /. Am. Chem. Soc., 126, 2991-3001. 

B.V. (2008) Methanol to hydrocarbons, in Handbook of Heterogeneous Catalysis (eds G. Ertl, H. Knozinger, and J. Weitkamp), Wiley-VCH Verlag GmbH, Weinheim, pp. 2950-2965. 

Elements such as B, Ga, P and Ge can substitute for Si and A1 in zeolitic frameworks. In naturally-occurring borosilicates B is usually present in trigonal coordination, but four-coordinated (tetrahedral) B is found in some minerals and in synthetic boro- and boroaluminosilicates. Boron can be incorporated into zeolitic frameworks during synthesis, provided that the concentration of aluminium species, favoured by the solid, is very low. (B,Si)-zeolites cannot be prepared from synthesis mixtures which are rich in aluminium. Protonic forms of borosilicate zeolites are less acidic than their aluminosilicate counterparts (1-4). but are active in catalyzing a variety of organic reactions, such as cracking, isomerization of xylene, dealkylation of arylbenzenes, alkylation and disproportionation of toluene and the conversion of methanol to hydrocarbons (5-11). It is now clear that the catalytic activity of borosilicates is actually due to traces of aluminium in the framework (6). However, controlled substitution of boron allows fine tuning of channel apertures and is useful for shape-selective sorption and catalysis. 

The accepted papers cover every aspect of catalysis on microporous materials. A significant number of contributions describe the synthesis, modification, instrumental and chemical characterisation of zeolites and other micro- and mesoporous materials. Catalytic reactions involve hydrocarbon cracking, nucleophilic aromatic substitution, methanol to hydrocarbon conversion, hydration of acetylene, various alkylation reactions, redox transformations, Claisen rearrangement, etc. A whole range of appealing chemistry can be enjoyed by reading the contributions. 

Chang. C.D. The Methanol-to-Hydrocarbons Reaction A Mechanical Perspective. In Shape Selective Catalysis, Chemicals Synthesis and Hydrocarbon Proces.sing Song. C., Garces, J.M., Sugi, Y.. Eds. ACS Symp. Series. American Chemical Society, 1999 Vol. 738. 96-114. Chap. 7. 

Stable nano/mesoporous materials with mixed oxides such as zeolites, clays, and other minerals are widely used in various fields catalysis, adsorption, ion-exchange, separation, etc. because of their catalytic activity in acid/base and redox (e.g., materials with titania phase) reactions, ability to sorb selective molecules of diverse types, participate in ion-exchange reactions, providing sieve effects, etc. (Tanabe 1970, Grandjean and Laszld 1989, Rocha and Anderson 2000, Cundy and Cox 2005, Tao et al. 2006). The most important processes that utilize the selective properties of these materials are alkylation and isomerization of aromatic hydrocarbons as well as conversion of methanol to hydrocarbons, and some other reactions. Silicalite is an extreme type of the materials with the ZSM-5 zeolite structure but whose aluminum content is negligible. Therefore, unlike conventional zeolites, silicalite does not possess ion-exchange properties, and its surface has a weak affinity to water. 

Whereas some evidence of the transformation of MTO were present in the prior arts, it is truly the Mobil discovery of the early 1970s that launched the transformation of the methanol to hydrocarbons (MTH), which has led to a new discipline in catalysis and petrochemical or organic chemistry. Since then this discipline has pursued at a continuous pace in other works. Fig. 6 shows the relative number of zeolite-related publications, between 1970 and 2012. 

Mole s reaction path for olefin formation via toluene. Adapted from Mole T, Bett G, Seddon D. Conversion of methanol to hydrocarbons overZSM-5 zeolite an examination of the role of aromatic hydrocarbons using IScarbon- and deuterium-labeled feeds.] Catal 1983 84 435—45 Mole T, WhitesideJA, Seddon D. Aromatic co-catalysis of methanol conversion over zeolite catalysts.] Catal 1983 82 261-6. 

Acid catalysis in hydrocarbon conversion. In terms of the transformation of substrates, our mechanistic understanding has reached a high level, mainly because the systems can be largely (but not totally) explained in terms of classical organic chemistry. Many mechanistic details remain to be elucidated, however, such as how the first C-C bond is formed in the methanol-to-hydrocarbon conversion on zeolites and other solid acids. The steric and topologic constraints that are specific to zeolites have been identified and used to predict catalytic properties. Much more needs to be understood about how structure and composition at the surface sites control the chemistry. 

In shape-selective catalysis, the pore size of the zeoHte is important. For example, the ZSM-5 framework contains 10-membered rings with 0.6-nm pore size. This material is used in xylene isomerization, ethylbenzene synthesis, dewaxing of lubricatius oils and light fuel oil, ie, diesel and jet fuel, and the conversion of methanol to Hquid hydrocarbon fuels (21). 

Currently, low-temperature CO oxidation over Au catalysts is practically important in connection with air quality control (CO removal from air) and the purification of hydrogen produced by steam reforming of methanol or hydrocarbons for polymer electrolyte fuel cells (CO removal from H2). Moreover, reaction mechanisms for CO oxidation have been studied most extensively and intensively throughout the history of catalysis research. Many reviews [4,19-28] and highlight articles [12, 29, 30] have been published on CO oxidation over catalysts. This chapter summarizes of the state of art of low temperature CO oxidation in air and in H2 over supported Au NPs. The objective is also to overview of mechanisms of CO oxidation catalyzed by Au. 

It is clear that these catalysts will provide a very rewarding area for both fundamental and applied research in catalysis as they give rise to a route to hydrocarbon synthesis from methanol and ethanol as an alternative to oil-based routes. 

It is apparent that much resourceful, imaginative experimentation has been done to resolve the question of C-C bond formation from methanol. Although the answer remains elusive, these experiments tell us at least what is probably not involved in the bond formation, particularly in the presence of zeolite catalysts. The Stevens rearrangement of oxonium ylide can be ruled out, as well as the carbocationic route invoking hypervalent carbon transition states. Not excluded are surface-bound species such as carbenoids and ylides. Again there seems to be a consensus that surface methoxyls are precursors to these reactive C- intermediates, which seems somehow to be "coming full circle", since surface methoxyls were early shown to be intermediates in the formation of DME, which is itself an intermediate in hydrocarbon formation. Finally, if the free radical character of the initiation step proves correct, the implications to zeolite catalysis will be far-reaching. 

Iron has played an extremely important role in catalysis in the past, present and increasingly will in the future. The fundamental work carried out over a centuiy ago continues to he relevant and informative to modern catalysis. The discovery and development of heterogeneous iron-hased catalysts used in large-scale ammonia, methanol and hydrocarbon synthesis, amongst others, has undoubtedly sculpted modern science and society. Most crucial to the use of iron in modem catalysis is perhaps the excellent sustainability traits associated with iron. The high natural abundance, low cost and low toxicity of iron oxides and iron salts provides sustainable avenues for molecule diversification. In particular, the ability of simple iron oxides and iron salts to facilitate crosscoupling and olefin hydrofunctionalisation reactions, where noble metals are commonly required, demonstrates a significant advance towards more sustainable synthesis. 

Typic2il examples of acid-catalysis of heteropoly compounds are as follows Dehydration of methanol, - > ethanol, - - propanol - - - -"- "- > and butanol, conversion of metanol or dimethyl ether to hydrocarbons, etheration to form methyl /-butyl ether, esterifications of acetic acid by ethanol and pentanol, decomposition of carboxylic acid and formic acid, alkylation of benzene by ethylene and isomerization of butene, o-xylene and hexane. ... 

Poisoning of platinum fuel cell catalysts by CO is undoubtedly one of the most severe problems in fuel cell anode catalysis. As shown in Fig. 6.1, CO is a strongly bonded intermediate in methanol (and ethanol) oxidation. It is also a side product in the reformation of hydrocarbons to hydrogen and carbon dioxide, and as such blocks platinum sites for hydrogen oxidation. Not surprisingly, CO electrooxidation is one of the most intensively smdied electrocatalytic reactions, and there is a continued search for CO-tolerant anode materials that are able to either bind CO weakly but still oxidize hydrogen, or that oxidize CO at significantly reduced overpotential. 

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