The methanol-to-olefins (MTO) reaction is an interesting and important reaction for both fundamental research and industrial application. The Dalian Institute of Chemical Physics (DICP) has developed a MTO technology that led to the successful construction and operation of the world’s first coal to olefin plant in 2010. This historical perspective gives a brief summary on the key issues for the process development, including studies on the reaction mechanism, molecular sieve synthesis and crystallization mechanism, catalyst and its manufacturing scale-up, reactor selection and reactor scale-up, process demonstration, and commercialization. Further challenges on the fundamental research and the directions for future catalyst improvement are also suggested.

http://pubs.acs.org/doi/pdf/10.1021/acscatal.5b00007

Methanol to Olefins (MTO): From Fundamentals to Commercialization

The methanol to hydrocarbon (MTH) process provides an efficient route for the conversion of carbon-based feedstocks into olefins, aromatics and gasoline. Still, there is room for improvements in product selectivity and catalytic stability. This task calls for a fundamental understanding of the formation, catalytic mechanism and degradation of active sites. The autocatalytic feature of the MTH process implies that hydrocarbons are active species on the one hand and deactivating species on the other hand. The steady-state performance of such species has been thoroughly studied and reviewed. However, the mechanism of formation of the initial hydrocarbon species (i.e.; the first C–C bond) and the evolution of active species into deactivating coke species have received less attention. Therefore, this review focuses on the significant progress recently achieved in these two stages by a combination of theoretical calculations, model studies, operando spectroscopy and catalytic tests.

The formation and degradation of active species during methanol conversion over protonated zeotype catalysts

As the conversion of methanol to olefins (MTO) over a zeolite catalyst is conducted on acid sites derived from framework aluminum (AlF), it is possible to enhance the catalytic performance by altering the siting of AlF if one knows the catalytic behavior of specified AlF located at certain sites. In this work, two series of H-ZSM-5 zeolites, viz., S-HZ-m and T-HZ-m, were synthesized with silica sol and tetraethyl orthosilicate, respectively, as the silicon source. Both series of H-ZSM-5 zeolites exhibit similar acidity, morphology, and textual properties. However, they are quite different with respect to AlF siting, as determined by UV–vis–DRS of Co(II) ions and 27Al MAS NMR; AlF of S-HZ-m is enriched in the sinusoidal and straight channels, whereas AlF of T-HZ-m is concentrated in the channel intersections. When they are used as the catalyst in MTO, T-HZ-m gives higher selectivity to ethene and aromatics and a larger hydrogen transfer index (HTI) than S-HZ-m, whereas S-HZ-m exhibits higher selectivity to...

Conversion of Methanol to Olefins over H-ZSM-5 Zeolite: Reaction Pathway Is Related to the Framework Aluminum Siting

Methanol conversion to olefins, as an important reaction in C1 chemistry, provides an alternative platform for producing basic chemicals from nonpetroleum resources such as natural gas and coal. Methanol-to-olefin (MTO) catalysis is one of the critical constraints for the process development, determining the reactor design, and the profitability of the process. After the construction and commissioning of the world's first MTO plant by Dalian Institute of Chemical Physics, based on high-efficiency catalyst and fluidization technology in 2010, more attention has been attracted for a deep understanding of the reaction mechanism and catalysis principle, which has led to the continuous development of catalysts and processes. Herein, the recent progress in MTO catalyst development is summarized, focusing on the advances in the optimization of SAPO-34 catalysts, together with the development efforts on catalysts with preferential ethylene or propylene selectivity.

Recent Progress in Methanol-to-Olefins (MTO) Catalysts.

ConspectusSolid acid materials with tunable structural and acidic properties are promising heterogeneous catalysts for manipulating and/or emulating the activity and selectivity of industrially important catalytic reactions. On the other hand, the performances of acid-catalyzed reactions are mostly dictated by the acidic features, namely, type (Bronsted vs Lewis acidity), amount, strength, and local environment of acid sites. The latter is relevant to their location (intra- vs extracrystalline), and possible confinement and Bronsted–Lewis acid synergy effects that may strongly affect the host–guest interactions, reaction mechanism, and shape selectivity of the catalytic system. This account aims to highlight some important applications of state-of-the-art solid-state NMR (SSNMR) techniques for exploring the structural and acidic properties of solid acid catalysts as well as their catalytic performances and relevant reaction pathway invoked. In addition, density functional theory (DFT) calculations may be ...

Acidic Properties and Structure-Activity Correlations of Solid Acid Catalysts Revealed by Solid-State NMR Spectroscopy.

Over zeolite H-ZSM-5, the aromatics-based hydrocarbon-pool mechanism of methanol-to-olefins (MTO) reaction was studied by GC-MS, solid-state NMR spectroscopy, and theoretical calculations. Isotopic-labeling experimental results demonstrated that polymethylbenzenes (MBs) are intimately correlated with the formation of olefin products in the initial stage. More importantly, three types of cyclopentenyl cations (1,3-dimethylcyclopentenyl, 1,2,3-trimethylcyclopentenyl, and 1,3,4-trimethylcyclopentenyl cations) and a pentamethylbenzenium ion were for the first time identified by solid-state NMR spectroscopy and DFT calculations under both co-feeding ([C-13(6)]benzene and methanol) conditions and typical MTO working (feeding [C-13]methanol alone) conditions. The comparable reactivity of the MBs (from xylene to tetramethylbenzene) and the carbocations (trimethylcyclopentenyl and pentamethylbenzium ions) in the MTO reaction was revealed by C-13-labeling experiments, evidencing that they work together through a paring mechanism to produce propene. The paring route in a full aromatics-based catalytic cycle was also supported by theoretical DFT calculations.

New Insight into the Hydrocarbon‐Pool Chemistry of the Methanol‐to‐Olefins Conversion over Zeolite H‐ZSM‐5 from GC‐MS, Solid‐State NMR Spectroscopy, and DFT Calculations

Surface methoxy species bound to an extra-framework Al (SMS-EFAL) was unambiguously identified by advanced 13 C-{27 Al} double-resonance solid-state NMR technique in the methanol-to-olefins reaction on H-ZSM-5 zeolite. The high reactivity of the SMS-EFAL leads to the formation of surface ethoxy species and ethanol as the key intermediates for ethene generation in the early reaction stage. A direct route for the initial C-C bond formation in ethene was proposed and corroborated by density functional theory calculations.

Extra‐Framework Aluminum‐Assisted Initial C−C Bond Formation in Methanol‐to‐Olefins Conversion on Zeolite H‐ZSM‐5

Methylbenzene hydrocarbon pool in methanol-to-olefins conversion over zeolite H-ZSM-5

The methanol to olefins conversion over zeolite catalysts is a commercialized process to produce light olefins like ethene and propene but its mechanism is not well understood. We herein investigated the formation of ethene in the methanol to olefins reaction over the H-ZSM-5 zeolite. Three types of ethylcyclopentenyl carbocations, that is, the 1-methyl-3-ethylcyclopentenyl, the 1,4-dimethyl-3-ethylcyclopentenyl, and the 1,5-dimethyl-3-ethylcyclopentenyl cation were unambiguously identified under working conditions by both solid-state and liquid-state NMR spectroscopy as well as GC-MS analysis. These carbocations were found to be well correlated to ethene and lower methylbenzenes (xylene and trimethylbenzene). An aromatics-based paring route provides rationale for the transformation of lower methylbenzenes to ethene through ethylcyclopentenyl cations as the key hydrocarbon-pool intermediates.

Experimental Evidence on the Formation of Ethene through Carbocations in Methanol Conversion over H‐ZSM‐5 Zeolite

Zeolite-catalyzed dehydration of ethanol offers promising perspectives for the sustainable production of ethene. Complex parallel-consecutive pathways are proposed to be involved in the reaction network of ethanol dehydration on zeolites, where the initial step of ethanol dehydration is still unclear particularly for the favorable production of ethene at lower temperature. Here we report the observation of a triethyloxonium ion (TEO) in the dehydration of ethanol on zeolite H-ZSM-5 by using ex situ and in situ solid-state NMR spectroscopy. TEO is identified as a stable surface species on the working catalyst, which shows high reactivity during reaction. Ethylation of the zeolite by TEO occurs at lower temperature, leading to the formation of surface ethoxy species and then ethene. The TEO-ethoxide pathway is found to be energetically preferable for the dehydration of ethanol to ethene in the initial stage, which is also supported by theoretical calculations.

/pdf/observation-of-an-oxonium-ion-intermediate-in-ethanol-1ux264c1oz.pdf

Chao Wang

Papers

New Insight into the Hydrocarbon‐Pool Chemistry of the Methanol‐to‐Olefins Conversion over Zeolite H‐ZSM‐5 from GC‐MS, Solid‐State NMR Spectroscopy, and DFT Calculations

Extra‐Framework Aluminum‐Assisted Initial C−C Bond Formation in Methanol‐to‐Olefins Conversion on Zeolite H‐ZSM‐5

Methylbenzene hydrocarbon pool in methanol-to-olefins conversion over zeolite H-ZSM-5

Experimental Evidence on the Formation of Ethene through Carbocations in Methanol Conversion over H‐ZSM‐5 Zeolite

Observation of an oxonium ion intermediate in ethanol dehydration to ethene on zeolite.