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 CO(2). 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.

Conversion of Methanol to Hydrocarbons: How Zeolite Cavity and Pore Size Controls Product Selectivity

https://isiarticles.com/bundles/Article/pre/pdf/22294.pdf

A generalized synchronous transit method for transition state location

We use the multiscale simulation approach, which combines the first-principles calculations and grand canonical Monte Carlo simulations, to comprehensively study the doping of a series of alkali (Li, Na, and K), alkaline-earth (Be, Mg, and Ca), and transition (Sc and Ti) metals in nanoporous covalent organic frameworks (COFs), and the effects of the doped metals on CO2 capture. The results indicate that, among all the metals studied, Li, Sc, and Ti can bind with COFs stably, while Be, Mg, and Ca cannot, because the binding of Be, Mg, and Ca with COFs is very weak. Furthermore, Li, Sc, and Ti can improve the uptakes of CO2 in COFs significantly. However, the binding energy of a CO2 molecule with Sc and Ti exceeds the lower limit of chemisorptions and, thus, suffers from the difficulty of desorption. By the comparative studies above, it is found that Li is the best surface modifier of COFs for CO2 capture among all the metals studied. Therefore, we further investigate the uptakes of CO2 in the Li-doped COFs...

/pdf/doping-of-alkali-alkaline-earth-and-transition-metals-in-3ub8m3vi9f.pdf

Doping of Alkali, Alkaline-Earth, and Transition Metals in Covalent-Organic Frameworks for Enhancing CO2 Capture by First-Principles Calculations and Molecular Simulations

The elementary reactions leading to the formation of the first carbon–carbon bond during early stages of the zeolite-catalyzed methanol conversion into hydrocarbons were identified by combining kinetics, spectroscopy, and DFT calculations. The first intermediates containing a C−C bond are acetic acid and methyl acetate, which are formed through carbonylation of methanol or dimethyl ether even in presence of water. A series of acid-catalyzed reactions including acetylation, decarboxylation, aldol condensation, and cracking convert those intermediates into a mixture of surface bounded hydrocarbons, the hydrocarbon pool, as well as into the first olefin leaving the catalyst. This carbonylation based mechanism has an energy barrier of 80 kJ mol−1 for the formation of the first C−C bond, in line with a broad range of experiments, and significantly lower than the barriers associated with earlier proposed mechanisms.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/ange.201704600

Formation Mechanism of the First Carbon-Carbon Bond and the First Olefin in the Methanol Conversion into Hydrocarbons.

A comprehensive DFT study of the possible CO2 adsorption geometries in the MIL-53 (Al, Cr) and MIL-47 hybrid organic−inorganic materials has been performed, as a preliminary step to gain a deeper understanding of the CO2 adsorption mechanism in these systems and to help explain the “breathing” effect displayed by the MIL-53 materials. This technique allows us to explore the possible spatial configurations of the CO2 molecules in the MIL-53 systems depending on the size of the pore opening at different loadings. Our results show that the replacement of the μ2-OH groups by oxo moieties in the MIL-47 material leads to fewer, weaker adsorption sites for CO2 onto the framework itself, whereas a larger number of CO2 geometries are possible in both the large and narrow versions of MIL-53. In the narrow pore form, the double interaction, where a CO2 molecule bridges the pore to simultaneously coordinate with 2 μ2-OH groups on opposite sides of a pore wall, was predicted to be the most energetic arrangement at the...

Probing the Adsorption Sites for CO2 in Metal Organic Frameworks Materials MIL-53 (Al, Cr) and MIL-47 (V) by Density Functional Theory

We report detailed density functional theory (DFT) calculations of important mechanisms in the methanol to gasoline (MTG) process in a zeolite catalyst. Various reaction paths and energy barriers involving C-O bond cleavage and the first C-C bond formation are investigated in detail using all-electron periodic supercell calculations and recently developed geometry optimization and transition state search algorithms. We have further investigated the formation of ethanol and have identified a different mechanism than previously reported [1], a reaction where water does not play any visible role. Contrary to recent cluster calculations, we were not able to find a stable surface ylide structure. However, a stable ylide structure built into the zeolite framework was found to be possible, albeit a very high reaction barrier.

/pdf/zeolite-catalyzed-hydrocarbon-formation-from-methanol-gd0pbew87e.pdf

Kurt Reindel

Papers

Zeolite-Catalyzed Hydrocarbon Formation from Methanol: Density Functional Simulations