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Liquid hydrocarbon fuels play an essential part in the global energy chain, owing to their high energy density and easy transportability. Olefins play a similar role in the production of consumer goods. In a post-oil society, fuel and olefin production will rely on alternative carbon sources, such as biomass, coal, natural gas, and CO2. The methanol-to-hydrocarbons (MTH) process is a key step in such routes, and can be tuned into production of gasoline-rich (methanol to gasoline; MTG) or olefin-rich (methanol to olefins; MTO) product mixtures by proper choice of catalyst and reaction conditions. This Review presents several commercial MTH projects that have recently been realized, and also fundamental research into the synthesis of microporous materials for the targeted variation of selectivity and lifetime of the catalysts. [ABSTRACT FROM AUTHOR]

Abstract: This study examined the reaction mechanism with respect to both catalyst deactivation and product formation in the conversion of methanol to hydrocarbons over zeolite H-ZSM-5. The reactivity of the organics residing in the zeolite voids during the reaction was assessed by transient 12C/13C methanol-switching experiments. In contrast to previously investigated catalysts (H-SAPO-34 and H-beta), hexamethylbenzene is virtually unreactive in H-ZSM-5 and is thus not a relevant reaction intermediate for alkene formation. However, the lower methylbenzenes are reaction intermediates in a hydrocarbon pool-type mechanistic cycle and are responsible for the formation of ethene and propene. An additional reaction cycle not applicable for ethene also must be taken into account. The C3+ alkenes are to formed through rapid alkene methylation and cracking steps to a considerable extent; thus, methanol is converted to hydrocarbons according to two catalytic cycles over H-ZSM-5. Moreover, in contrast to what occurs for large-pore zeolites/zeotypes, molecules larger than hexamethylbenzenes are not built up inside the H-ZSM-5 channels during deactivation. Thus, deactivation is explained by coke formation on the external surface of the zeolite crystallites only. This is a plausible rationale for the superior lifetime properties of H-ZSM-5 in the methanol-to-hydrocarbon reaction. [Copyright &y& Elsevier]

In order to reach a deeper insight into the reaction mechanism of the zeolite catalyzed methanol to hydrocarbons reaction (MTH), the proposed reaction intermediates, i.e., a series of multiply methyl-substituted benzenium ions has been generated in the gas phase by chemical ionization. The fragmentations of the corresponding long-lived (metastable) ions have been investigated. While expulsion of H2 dominates for the lower homologues, elimination of methane dominates for the higher homologues, accompanied by increasing amounts CH. Loss of larger fragments relevant to the MTH-reaction, in particular ethene, propene and even butene, is also observed in minor amounts. This latter finding is consistent with a proposed reaction cycle in the MTH reaction known as the paring mechanism, and the feasibility of this mechanism has thus been demonstrated. The metastable gas-phase ions studied here are considerably more energetic than those residing in a zeolite catalyst, but they were found to decompose with markedly higher selectivity towards alkenes as compared to those activated by collision-induced dissociation (CID). [ABSTRACT FROM AUTHOR]

Recent studies have pointed to the heptamethylbenzenium cation as a prominent intermediate in the methanol to hydrocarbons (MTH) reaction. The reactions of the heptamethylbenzenium cation in a H-beta zeolite was studied at 300 °C by feeding its corresponding base (WHSV = 0.4 h-1). The reactant was converted completely into aliphatic products, polymethylbenzenes and coke under the employed conditions. The results testify that the proposed reaction intermediate yields the same product spectrum as methanol. The composition of the material retained in the catalyst micropores after 15 min of reaction was determined by dissolving the catalyst in 15% HF. Polymethylated benzenes (predominantly pentamethylbenzene), dihydro-trimethylnaphthalenes, and hexamethylnaphthalene were the major components. The results also support the idea that the lowest naphthalene derivative is formed from the heptamethylbenzenium cation by a molecular rearrangement. Hence, the heptamethylbenzenium cation is inherently linked to both product formation and catalyst deactivation in the MTH reaction. [ABSTRACT FROM AUTHOR]

[13C]Methanol and [12C]benzene were coreacted over zeolite H-beta at different reaction temperatures, ranging from 210 to 330 °C. The main attention was paid to the material being trapped within the zeolite pores. Hexamethylbenzene and the heptamethylbenzenium cations were easily formed by methylation reactions. The arene methylation reactions leading to hexamethylbenzene and the heptamethylbenzenium cation were much faster than the reactions leading to isotopic scrambling, and the isotopomers 12C6(13CH3)6 and 12C6(13CH3)7+ could be synthesized in situ. This achievement was used to elucidate new details in the MTH mechanism. The heptamethylbenzenium cation was the major compound being retained within the pores of the beta zeolite at 250 °C. When the reaction temperature was increased, this species soon vanished and polymethylbenzenes and -naphthalenes became the dominating components. The isotopic distribution observed in both gaseous products and retained material is in excellent agreement with a reaction mechanism where rearrangement of the heptametylbenzenium cation, followed by dealkylation, is the major reaction route for olefin formation in the MTH/MTO reaction over the H-beta zeolite. [Copyright &y& Elsevier]

Conversion of methanol-to-hydrocarbons has been studied over beta-zeolites with varying contents of aluminum, obtained by dealumination of the parent sample with oxalic acid. It was found that the dealumination leads to catalysts which are more resistant to deactivation. The total amount of methanol which might be converted to hydrocarbons before the catalyst becomes completely deactivated increased. The conversion capacity is higher at high reactant feed rates. [Copyright &y& Elsevier]

Abstract: H-ITQ-7 ((Si+Ge)/Al=103) has been synthesized and submitted to thorough characterization, in particular with respect to the acidic properties. The H-ITQ-7 material, being one of very few known zeolite or zeotype materials with a three dimensional large pore channel structure, is of particular interest due to its structural similarities with the well studied and industrially relevant H-beta zeolite. By using a variety of molecular probes (H2O, CH3OH, CO, and pyridine) in combination with FT-IR spectroscopy, detailed insights regarding the acidic character of the various surface sites have been obtained. The use of several probes is required, as complementary knowledge is gained. Al containing H-ITQ-7 possesses strong Brønsted acid sites of at least two families that are clearly seen to interact differently with both CH3OH and CO. The spectral features observed upon adsorption of H2O and CH3OH indicate that the Brønsted acid sites of H-ITQ-7 are of strength comparable to those of H-beta. However, the spectra recorded upon adsorption of the more sensitive CO probe suggest that the acid strength of the Brønsted sites of H-ITQ-7 is slightly lower than those of several other acidic zeolites. H-ITQ-7 is an active catalyst in the conversion of methanol to hydrocarbons at 400°C, a reaction that requires strong Brønsted acidity, and the product shape selectivity observed indicates that the pores of H-ITQ-7 are slightly more restricted than those of H-beta. [Copyright &y& Elsevier]

Abstract: A series of desilicated ZSM-5 catalysts previously shown to have improved catalytic performance in the MTG (methanol-to-gasoline) reaction [M. Bjørgen, F. Joensen, M.S. Holm, U. Olsbye, K.-P. Lillerud, S. Svelle, Appl. Catal. A 345 (2008) 43] was subjected to thorough examination using FTIR. Clearly, defects represented by internal Si-OH sites are removed upon NaOH treatment. In a parallel manner, free Si-OH sites increase in concentration and the results point to a selective mechanism for formation of mesopores as the framework dissolution preferentially takes place at defective sites in the crystallites. The acid properties of the desilicated materials were investigated by applying CO and collidine (2,4,6-trimethylpyridine) as molecular probes. Monitoring the induced frequency shifts upon CO adsorption at liquid N2 temperature revealed that the desilication procedure did not alter the acid strength of the Brønsted sites significantly. This weakens the explanation linking improved catalytic behaviour, such as increase in both catalyst activity and hydrogen transfer activity, to modified Brønsted acid strength. Simultaneous to the mesopore formation resulting from the desilication, strong Lewis acid sites were generated, presumably from dislodged framework aluminium. Collidine, which is too bulky to enter the micropore system of ZSM-5, could access Lewis acidity, suggesting that these sites were predominantly generated on the external surface or in the newly created mesopores. Additionally, by first saturating the zeolite surface with collidine and subsequently adsorbing CO, we show that barely any Lewis acidity was uncoordinated post-collidine saturation while the Brønsted acidity continuously was protected behind the micropore system. It is hypothesized from the present study that the desilication procedure can lead to a slight dealumination of the samples while forming Lewis acidity preferentially at the crystal surface. [Copyright &y& Elsevier]

Due to its fully reversible nature, H2 storage by molecular adsorption could represent an advantage with respect to dissociative processes, where kinetic effects during the charging and discharging processes are present. A drawback of this strategy is represented by the extremely weak interactions that require low temperature and high pressure. High surface area materials hosting polarizing sites can represent a viable way toward more favorable working conditions. Of these, in this contribution, we have studied hydrogen adsorption in a series of zeolites using volumetric techniques and infrared spectroscopy at 15 K. We have found that in H-SSZ-13 zeolite the cooperative role played by high surface area, internal wall topology, and presence of high binding energy sites (protons) allows hydrogen to densify inside the nanopores at favorable temperature and pressure conditions. [ABSTRACT FROM AUTHOR]

The article examines the transmethylation of methylbenzenes over H-zeolites using diphenylmethane. Zeolite is dissolved in hydrofuran and the confined intermediates are liberated and analyzed. Dimethylated diphenylmethane species may be formed at high concentrations in the ZSM-5 zeolite channels when toulene is reacted.