Showing papers in "Studies in Surface Science and Catalysis in 1988"
1,003 citations
Eni1
TL;DR: In this article, the synthesis of titanium containing zeolites and their catalytic properties when used in oxidations of organic substrates with H 2 O 2 are described, and the special cases of phenol to hydroquinone/catechol mixture and of propylene to propylene oxide are discussed.
Abstract: The synthesis of titanium containing zeolites and their catalytic properties when used in oxidations of organic substrates with H 2 O 2 are described. The special cases of phenol to hydroquinone/catechol mixture and of propylene to propylene oxide are discussed. It is assumed that Ti IV enters the silicalite structure at random during synthesis: each Ti IV is surrounded by Si IV and isolated from other Ti IV by long Si-O-Si-O sequences. It is proposed that isolated Ti IV have properties different from those of Ti IV having other Ti IV as near neighbours, in particular that isolated Ti ,v have a reduced rate for H 2 O 2 decomposition; this, together with “restricted transition state selectivity” typical of medium pore zeolites gives rise to high yields of useful oxidation products. Analogies and differences with catalysts consisting of TiO 2 deposited on high surface area SiO 2 are discussed.
347 citations
TL;DR: The structure-directing role of the template is dominated by stereospecific space-filling and stoichiometry between the template and the framework, and is influenced to a lesser extent by framework charge compensation as mentioned in this paper.
Abstract: The aluminophosphate-based molecular sieves represent new generations of crystalline microporous oxides with one or more of an additional thirteen elements, Li, B, Be, Mg, Si, Ti, Mn, Fe, Co, Zn, Ga, Ge, As, incorporated into the AlPO4 framework. More than two dozen structure types have been reported and include framework topologies analogous to zeolites and a large number of novel structures. Proposed structural rules, coupled with TO2 stoichiometry elucidate the T-O bonding sequences, the mechanism of framework element incorporation, and the generation of negatively charged frameworks. The structure-directing role of the template is dominated by stereospecific space-filling and stoichiometry between the template and the framework, and is influenced to a lesser extent by framework charge compensation. Incorporation of many of the framework elements generates negatively charged frameworks, hydroxyl structure and Bronsted acidity. The hydroxyl infrared characteristics and the Bronsted acidity as measured by n-butane cracking rates depend both on the nature of the element and the structure type. The relationship of Bronsted acidity and hydroxyl structure appears to be much more complex than in the aluminosilicate zeolites.
256 citations
TL;DR: The world's first commercial SMDS plant is being constructed on a site adjoining the Bintulu LNG plant in Sarawak, Malaysia, and will come on stream in the last quarter of 1992 as mentioned in this paper.
Abstract: Since the early 1970s Shell's research has been involved in syngas chemistry with special focus on routes to convert (remote) natural gas into easily transportable liquid hydrocarbons. This has resulted in the development of the SMDS process. The world's first commercial SMDS plant is being constructed on a site adjoining the Bintulu LNG plant in Sarawak, Malaysia, and will come on stream in the last quarter of 1992.
163 citations
TL;DR: In this paper, a detailed investigation of supported platinum catalysts modified with cinchona alkaloids for the enantioselective hydrogenation of pyruvic acid esters has been carried out.
Abstract: A detailed investigation of supported platinum catalysts modified with cinchona alkaloids for the enantioselective hydrogenation of pyruvic acid esters has been carried out. It was confirmed that pretreatment of the catalysts has a strong effect on their performance, which is dependent both upon the catalyst type and the solvent used. Modified catalysts are up to 100 times more active than without cinchona alkaloids. Many commercially available catalysts are active with enantioselectivities of 20-90%. There is no simple correlation between performance and either the total or metal surface area. The most important process variables are pressure, temperature and modifier concentration. Any change in the combination Pt catalysts / cinchona alkaloid / α-ketoester leads to almost complete loss of enantioselectivity. Some mechanistic aspects of this interesting catalytic system are discussed.
142 citations
TL;DR: In this paper, the conversion of glycerol in aqueous solution under 3 MPa hydrogen pressure in the presence of Ru, Ni, Rh, Ir based catalysts leads to hydrocarbons, mainly methane: these metals hydrogenolyse both C-C and C-0 bonds.
Abstract: The conversion of glycerol in aqueous solution at 513 K under 3 MPa hydrogen pressure in the presence of Ru, Ni, Rh, Ir based catalysts leads to hydrocarbons, mainly methane: these metals hydrogenolyse both C-C and C-0 bonds. Hydrogenolysis reactions are not observed with copper. Glycerol dehydrogenation and strong adsorption of dehydrogenated species on this metal lead to selective dehydroxylation (C-0 cleavage) and retro-CLAISEN (C-C cleavage) reactions. These reactions determine the nature of the products obtained from erythritol, xylitol and sorbitol conversions, but, for the two latter polyols, there is also a retro-MICHAEL reaction. This reaction yields selectively glycerol from sorbitol and is favoured on certain copper-based catalysts.
111 citations
TL;DR: The cinnamaldehyde (CAL) hydrogenation into Cinnamyl alcohol (COL) has been performed under 4MPa of H 2 in liquid phase as mentioned in this paper.
Abstract: Noble metal catalysts (Ir, Pt, Ru, Rh Pd) have been prepared with a very homogeneous dispersion on graphite (300 2 m 1 g) and carbon support (1400 m 2 g 1 ). On graphite the particles decorate the edges of the basal planes and there is an electron transfer to the metal. The cinnamaldehyde (CAL) hydrogenation into cinnamyl alcohol (COL) has been performed under 4MPa of H 2 in liquid phase. The factors affecting the selectivity to COL are: (i) the nature of the metal (0=Pd
98 citations
TL;DR: In this paper, the fixed-bed methanol-to-gasoline (MTG) process was successfully scaled up by a factor of 100 to a demonstration unit size of 4 B/D.
Abstract: Mobil recently commercialized its fixed-bed methanol-to-gasoline (MTG) process in a 14, 500 B/D (gasoline) plant, based on natural gas, which is located in New Zealand. Process development studies were carried out in a small pilot plant to define conditions for producing gasoline in good yield and with acceptable product quality while also insuring satisfactory catalyst life. The process was successfully scaled-up by a factor of 100 to a demonstration unit size of 4 B/D. The scale-up factor from the demonstration unit to the commercial plant was in excess of 3000. The characteristics of the fixed-bed MTG process, its development, scale-up to demonstration unit, and assurance of acceptable product quality are discussed.
78 citations
Abstract: A new low investment process for the conversion of natural gas to gasoline is presented. The process incorporates the MTG process into a combined MeOH and dimethylether synthesis. The conversion of synthesis gas to gasoline is carried out in one single synthesis loop. The process has been demonstrated in a 1 MTPD gasoline process demonstration unit.
72 citations
TL;DR: In this article, the authors summarized the limits of the steam reforming process and discussed concepts such as CO 2 -reforming, preconversion, and autothermal reformulation, which can be used to improve the utilization of the process for the manufacture of CO-rich syngases.
Abstract: Better understanding of the steam reforming allows better utilisation of the process for manufacture of CO-rich syngases. The paper summarizes the limits and discusses concepts as CO 2 -reforming, preconversion and autothermal reforming.
69 citations
TL;DR: In this article, the synthesis of silicon-rich SAPO-5 is reported, which is demonstrated by 27Al, 29Si and 31P MAS NMR, IR spectroscopy and catalytic test reactions.
Abstract: The synthesis of silicon-rich SAPO-5 is reported. The Incorporation of silicon in the framework of SAPO-5 is demonstrated by 27Al, 29Si and 31P MAS NMR, IR spectroscopy and catalytic test reactions.
TL;DR: In this article, the crystal structures of CoAPO-44, CoAPSO-46, MAPO-46 and CoAPS-47 were determined from single crystal x-ray data.
Abstract: The crystal structures of CoAPO-44, CoAPSO-44, MAPSO-46, CoAPSO-47 and CoAPO-50 were determined from single crystal x-ray data. All five structures have the tetrahedral framework phosphorus or silicon alternating with the tetrahedral aluminum or the metal (cobalt or magnesium). The crystal structures of the 44's and 47 are topologically similar to the mineral chabazite, but with framework distortions which reduce the symmetry from rhombohedral to triclinic (Plbar). The framework topologies of MAPSO-46 and CoAPO-50 are novel and form a new series of structures based on capped six membered rings with a unidimensional 12-ring channel system having a free aperature between 7A and 8A crossed-linked through 8 rings. CoAPO-50 is the end member of the series and is built from double four rings (a six ring capped top and bottom) only previously observed in Linde type A zeolite. Unlike the other metal aluminophosphate structures described here, the cobalt in CoAPO-50 occupies both the same crystallographic site as aluminum and a unique tetrahedral site.
TL;DR: In this article, a new reforming process (AROMAXSM) is described for selectively converting C6-C7 paraffins to high octane aromatics, which fills an important industrial need, since conventional processes are not very effective for these compounds and since lead additives are being phased out of gasoline.
Abstract: A new reforming process (AROMAXSM) is described for selectively converting C6-C7 paraffins to high octane aromatics. Since conventional processes are not very effective for these compounds and since lead additives are being phased out of gasoline, the AROMAX process fills an important industrial need. This process employs a catalyst comprising platinum on L-zeolite. Pure component studies are used to show that the high selectivity of the catalyst results from a different reaction network than conventional bifunctional reforming catalysts. Pilot-scale tests are used to show how unleaded gasoline or aromatic chemicals can be produced from refinery light naphthas with dramatically better yields than conventional reforming.
TL;DR: In this paper, the medium pore zeolite ZSM-5 catalyst was used to combine two Mobil processes: Methanol to olefins (MTO) and Mobil olefin to gasoline and distillate (MOGD).
Abstract: Gasoline and distillate fuels can be produced from methanol by combining two Mobil processes: Methanol to olefins (MTO) and Mobil olefins to gasoline and distillate (MOGD). Both processes use the medium pore zeolite ZSM-5 catalyst. The combined process offers gasoline and distillate in various proportions, as well as light olefinic byproducts if needed. Liquid fuel yields of up to 95 weight percent of hydrocarbons can be obtained. Flexibility, high yields and excellent product quality make this combined process an attractive alternative for producing a wide range of hydrocarbon products from natural gas or coal. The MTO process was successfully demonstrated in a 100 B/D fluid-bed semi-works unit in Germany. The MOGD process was demonstrated in fixed-bed reactors in a Mobil refinery.
TL;DR: In this paper, a combination of two existing process concepts has been examined and appears capable of producing higher hydrocarbons from methane with high yield and selectivity, such as paraffins, olefins, aromatics, and cycloparaffins.
Abstract: The chemical activation of methane and its subsequent conversion to oxygenates or higher hydrocarbons have been the objects of intensive research in the past several years. At the Pittsburgh Energy Technology Center, a novel combination of two existing process concepts has been examined and appears capable of producing higher hydrocarbons from methane with high yield and selectivity. Methane, oxygen, and hydrogen chloride are reacted over an oxyhydrochlorination catalyst in the first stage to produce methyl chloride and water. In the second stage, the methyl chloride is converted to higher hydrocarbons, namely paraffins, olefins, aromatics, and cycloparaffins, over a zeolite, such as ZSM-5. In the process concept described, the final hydrocarbon mixture is largely in the gasoline (C 4 , C 10 ) boiling range.
TL;DR: The concepts of Bronsted and Lewis acidity in zeolites were examined in this paper in relation to selected experimental and theoretical studies, and the results showed that the acidity of zeolite is positively correlated with the Bronsted acidity.
Abstract: The concepts of Bronsted and Lewis acidity in zeolites are examined in relation to selected experimental and theoretical studies.
TL;DR: In this paper, the Sanderson electronegativity of various zeolites has been estimated using Sanderson electrophoresis, and it was shown that the actual basic strength depends not only on the chemical composition but also on the structural environment of the framework oxygen.
Abstract: The basic strength of various zeolites has been estimated using the Sanderson electronegativity. Comparison of those results with experimental measurements using pyrrole and benzene show that the actual basic strength depends not only on the chemical composition but also on the structural environment of the framework oxygen. In addition to a general trend for an increase in basic strength as Al content and alkaline cation radius rise, very specific effects are noted. They are related to the influence of the zeolite structure and of the distribution of Al and cations in the framework in the neighbourhood of oxygen atoms interacting with a molecule.
TL;DR: In this article, the αs method was used to estimate the effective micropore size distribution in the context of gas adsorption in micropores of width < 2nm.
Abstract: In the IUPAC classification micropores are defined as pores of width < 2nm. The physisorption of gases by microporous solids can occur in two ways: (a) as a primary process in pores of molecular dimensions, or (b) as a secondary, or cooperative, process in the wider micropores. The primary process involves enhanced adsorbent-adsorbate interactions and takes place at very low p/po, whereas the secondary process occurs mainly over the range of p/po from 0.02 to 0.2 and is accompanied by very little enhancement of adsorption energy. Because of the proximity of the pore walls, the total micropore volume cannot be readily evaluated and in the context of physisorption it seems prudent to refer to it as the effective pore volume available to a particular adsorptive. With the aid of the αs method and the application of a number of probe molecules of different size it is possible to arrive at a semi-quantitative estimate of the effective micropore size distribution.
TL;DR: In this article, a non-trivial polymerization of a straight chain aliphatic polymethylene (polymethylene) from CO and H 2 is modelled as a "non trivial polymerization" which occurs on the surface of the solid catalyst.
Abstract: When comparing the competing processes for making hydrocarbons from synthesis gas – the Fischer Tropsch CO hydrogenation and the MTG conversion -the process flow sheets show as the main difference the additional step of methanol synthesis for the MTG route. However, product selectivity is basically different for both the conversions. And from this point of view the one or the other route can be the more favourable option as fitting best the particular demand pattern. Selectivity differences fundamentally result from the different kinds of chemistry which are involved: Hydrogenation on special metal type catalysts in case of the Fischer Tropsch reaction and a conversion via car-benium ion intermediates on acidic sites, which is additionally constrained by shape selectivity in case of the MTG process. The kinetics of the mechanism of Fischer Tropsch hydrocarbon formation from CO and H 2 are modelled in this paper as a “non trivial polymerization” which occurs on the surface of the solid catalyst. The term “non trivial” relates to the fact that producing a straight chain aliphatic “polymethylene” respectively a “methylen oligomer”, from CO and H 2 involves as the repeating polymerization step of prolonging the growing chain by one CH 2 a set of reactions, of activation and transfer of hydrogen, activation of CO and splitting of the C/O bond and formation of a new C/C bond. A kinetic model of this surface polymerization is presented in the paper. It starts with the ideal system and adopts stepwise additional assumptions which regard essential features of observed types of product distributions. The ideal system is described with only one parameter, the quotient of the rate constants of chain propagation and chain termination and it is related easily to the macrokinetics of the CO consumption rate. Actual real cases of product distribution are described as extensions of the ideal model, taking into account the following functions (1) Formation of 3 kinds of primary products (olefins, paraffins and alcohols plus aldehydes) (2) Methyl branching during chain growth (3) Carbon number dependence of chain prolongation rate constants (4) Carbon number dependence of chain branching rate constants. In addition experimental product distributions can seriously be affected by instationarity of the system, errors during sampling and analysis and by-product formation or secondary reactions of the compounds which are produced through the Fischer Tropsch CO hydrogenation.
TL;DR: The use of zeolites as supports for active components has been studied in this paper, whereby their intrinsic properties such as acidity and form-selectivity supplement the catalytic effects of the active components.
Abstract: Heterogeneous catalysis is gaining in importance in the synthesis of chemical intermediates and fine chemicals. In the shift away from homogeneous catalysis, zeolites will play a major role. The experience gained with zeolitic catalysts in the petrochemical industry has, in recent years, been increasingly applied to the selective synthesis of organic compounds. Zeolites, as acidic, form-selective heterogeneous catalysts find most widespread use in proton- and Lewis-acid-catalyzed reactions. Furthermore, zeolites are particularly suitable for use as supports for active components, whereby their intrinsic properties such as acidity and form-selectivity supplement the catalytic effects of the active components. A number of such examples are presented in this article.
TL;DR: In this paper, the shape and position of the hysteresis relative to the pressure axis has been found to be affected by the aluminium content of the zeolite, the type of framework cation and the sorption temperature.
Abstract: In comparison to polycrystalline powder large ZSM-5 crystals are best suited for high resolution sorption experiments. The nitrogen isotherms on HZSM-5 at 77 K reveal a pronounced hysteresis loop. The shape and position of the hysteresis relative to the pressure axis has been found to be affected by the aluminium content of the zeolite, the type of framework cation and the sorption temperature. The occurence of the hysteresis and its changes are assigned to a transition from a liquidlike to a solid-like adsorbed phase of nitrogen. The micropore volume v mp derived from the argon and nitrogen isotherm (s. Fig. 2b, first plateau) and calculated according to DUBININ-RADUSHKEVICH was consistent with the pore volume obtained from the apparent densities with respect to helium and mercury.
TL;DR: The Synfuel gas-to-gasoline complex is sited within 180 hectares of land at Motunui, Taranaki as mentioned in this paper, which is designed to convert 52-55 PJ per annum of natural gas into 570, 000 tonnes (14, 450 barrels per stream day) of high octane gasoline.
Abstract: The Synfuel gas-to-gasoline complex is sited within 180 hectares of land at Motunui, Taranaki. It is designed to convert 52–55 PJ per annum of natural gas into 570, 000 tonnes (14, 450 barrels per stream day) of high octane gasoline. The conversion of gas to gasoline (GTG) takes place in two stages: first gas to methanol (GTM) and second methanol to gasoline (MTG). The two stages are integrated into a single complex to achieve optimum efficiency in management and operation. The GTM plant employs the ICI low-pressure Methanol Process sub-licensed from Davy McKee, and incorporates two methanol trains each capable of producing 2200 tonnes per day of methanol. The MTG plant employs Mobil's fixed bed catalytic process using the Mobil proprietary zeolite catalyst, ZSM-5. The process is very similar to conventional vapour phase catalytic petroleum refinery processes, such as hydro-treating and platinum reforming. The plant is owned and operated by New Zealand Synthetic Fuels Corporation Limited (Synfuel) with a shareholding of Government 75 percent and Mobil 25 percent. Mobil provides technical and management services to the company. The plant was mechanically complete by June 30, 1985, ahead of schedule and about 17 percent under the original budget of US$1475 million. Commissioning and startup proceeded satisfactorily with the first gasoline produced on October 17, 1985. The gasoline is within specification and 739, 000 tonnes have been produced to the end of March 1987.
TL;DR: The use of zeolites as selective catalysts and adsorbents in organic syntheses is a field of growing importance as mentioned in this paper, and a brief discussion of structure, modification and catalytic properties of Zeolites relevant to the topic is given.
Abstract: The use of zeolites as selective catalysts and adsorbents in organic syntheses is a field of growing importance. A brief discussion of structure, modification and catalytic properties of zeolites relevant to the topic is given. Some non- and semicatalytic applications of zeolites in fine chemical preparation are mentioned. Examples of use of zeolites as catalysts in organic reactions are chosen from the fields of isomerization, aromatic substitution, oxidation, cyclization and heterocyclic ring formation.
TL;DR: In this paper, the theoretical values of the mean free path of xenon adsorbed in various zeolites were calculated and the dependence of the chemical shift δ S on the internal void space of the solid was deduced.
Abstract: The chemical shift δ S of xenon adsorbed on zeolite and extrapolated to zero concentration depends only on the internal void space of the solid The smaller the channels or cavities, or the more restricted the diffusion, the greater δ S becomes We have calculated the theoretical values of the mean free path of xenon adsorbed in various zeolites We deduce from them the dependence of the chemical shift δ S on It is now possible to determine the dimensions of any void space in which xenon can be adsorbed
TL;DR: In this paper, the dispersion of Pd on γ-Al 2 O 3 and MgO-SiO 2 was found to be higher than on SiO 2 and mgO.
Abstract: Methane reforming reaction by CO 2 and H 2 O over supported Pd, Pt, and Rh catalysts has been studied. The Pd/γ-Al 2 O 3 , Pt/γ-Al 2 O 3 , Rh/γ-Al 2 O 3 and Pd/MgO-SiO 2 showed high activity in the CH 4 reforming by CO 2 . The adsorption experiments of NH 3 and pyridine showed that the γ-Al 2 O 3 and MgO-SiO 2 supports used here retain a large amount of Lewis acidity, The dispersion of Pd on γ-Al 2 O 3 and MgO-SiO 2 was found to be higher than on SiO 2 and MgO. These results may show that Lewis acid sites make the dispersion of Pd high.
TL;DR: In this paper, a deformation model for the role of translational and vibrational energy in promoting dissociative chemisorption of CH 4 on Ni(111) was proposed.
Abstract: The mechanism for the dissociation of CH 4 on Ni(111) is studied by molecular beam techniques coupled with high resolution electron energy loss spectroscopy. The probability of the dissociative chemisorption of CH 4 increases exponentially with the normal component of the incident molecule's translational energy and with vibrational excitation. Dissociation can also be induced by the impact of an Ar atom incident on a monolayer of CH 4 physisorbed on Ni(111). The nascent products of the dissociation are identified as an adsorbed methyl radical and a hydrogen atom. The chemistry and stability of these adsorbed methyl radicals have also been studied. These results, which have shown that there is a barrier to the dissociative chemisorption, are interpreted in terms of a deformation model for the role of translational and vibrational energy in promoting dissociative chemisorption. The barrier arises largely from the energy required to deform the molecule sufficiently to allow a strong attractive interaction between the carbon and the Ni surface. Tunneling is suggested as the final process in the C-H bond cleavage. The presence of this barrier to dissociative chemisorption and collision-induced dissociation of adsorbates present plausible explanations for the pressure gap in heterogeneous catalysis.
TL;DR: In this paper, it is suggested that to obtain successful substitution into the AlPO 4 structure first requires substitution into a poorly crystalline metavariscite/variscite intermediate.
Abstract: We have studied the synthesis and some of the properties of AlPO 4 -5 and AlPO 4 -11 and their Si-substituted (SAPO), Co-substituted (CoAPO) and Fe substituted (FAPO) analogues. The reactivity of reagents selected for the syntheses has been investigated, with phosphoric acid and hydrolysed Al( i PrO)3, giving the best yields of AlPO 4 's. A poorly crystalline metavariscite/variscite intermediate has been identified as the first product of gel transformation. It is suggested that to obtain successful substitution into the AlPO 4 structure first requires substitution into the metavariscite/variscite intermediate. Desorption of the amines and water from the unsubstituted and substituted AlPO 4 precursors has been followed by thermal desorption/mass spectrometry. The acid-site concentration has been measured by amine desorption. In a series of SAPO-5 samples it has been found that the number of acid sites agrees with the number of substituting atoms only up to about 1% substitution. Above this, the number of acid sites falls rapidly until at a nominal 6% Si substitution only about half of the Si appears to generate acid sites. These substituted AlPO 4 's convert methanol to hydrocarbons with a rate of deactivation due to coke formation, which is low relative to zeolites with one-dimensional channel systems such as mordenite, although they deactivate faster than ZSM-5.
TL;DR: In this article, the number of nickel atoms in an ensemble needed to catalyse steam reforming or coking is discussed, which can result in a small loss of steam reforming activity coupled to a marked diminution of coking.
Abstract: Although the production of hydrogen by steam reforming is a well established process, some problems remain with the industrial operation. Thermodynamics dictates that the reaction be carried out at high temperatures, where coking or sintering of the catalyst may occur. Coking is dictated by the balance between coke formation and removal. One important factor is the number of nickel atoms in an ensemble needed to catalyse steam reforming or coking, control of which can result in a small loss of steam reforming activity coupled to a marked diminution of coking. Different methods of ensemble size control are discussed. The kinetics of nickel and alumina sintering have also been studied and the effect of different stabilisers explored. Some possible sintering processes can be rejected, leading to a better definition of factors important to the process.
TL;DR: In this article, different types of extra-framework aluminium (EFAL) species have been detected and their catalytic activity for cracking n-heptane and vacuum gas-oil has been measured.
Abstract: Y zeolites dealuminated by steam, SiCl 4 . and (NH 4 ) 2 F 6 Si have been characterized by XPS, i.r., pyridine adsorption-desorption and nitrogen adsorption. Their catalytic activity for cracking n-heptane and vacuum gas-oil has been measured. Different behaviour of the samples for the two reactants has been observed. In all samples different types of extraframework aluminium (EFAL) species have been detected. A type of amorphous material related with EFAL, probably as amorphous silica-alumina, shows hydroxyl groups at 3600 cm~l with strong acidity and catalytic activity. In the case of n-heptane the framework Si/Al ratio and the amount of the active EFAL related with amorphous material plays a predominant role on the activity observed. In the case of gas-oil cracking, even if EFAL is active the textural characteristics of the zeolite (pore volume distribution) play a determinant role in the final behaviour of the sample.
TL;DR: The mechanism of the crucial step of initial C-C bond formation from MeOH/DME is an unsolved problem and is the subject of ongoing controversy as discussed by the authors, however, it is known that the intermediate in DME formation from methanol over solid-acid catalysts is a protonated surface methoxyl, which is subject to nucleophilic attack by methanoline.
Abstract: Publisher Summary This chapter discusses the mechanism of hydrocarbon formation from methanol. Hydrocarbon formation from methanol has been intensively investigated along with the description of the conversion of methanol to aromatic gasoline using zeolite catalysts. Methanol dehydrates initially to an equilibrium mixture with dimethyl ether (DME) and water. The mechanisms of acid-catalyzed DME formation from methanol and aromatization of olefins were widely investigated in the years before the discovery of the methanol-to-gasoline reaction. The intermediate in DME formation from methanol over solid-acid catalysts is a protonated surface methoxyl, which is subject to nucleophilic attack by methanol. Aromatization of olefins precedes along classic carbenium pathways with concurrent hydrogen transfer. The mechanism of the crucial step of initial C–C bond formation from MeOH/DME is an unsolved problem and is the subject of ongoing controversy.