A methanol to olefins review: Diffusion, coke formation and deactivation on SAPO type catalysts

SAPO-34 materials with comparable Bronsted acid site density but different crystal sizes were applied as methanol-to-olefin (MTO) catalysts to elucidate the effect of the crystal size on their deactivation behaviors. 13C HPDEC MAS NMR, FTIR, and UV/vis spectroscopy were employed to monitor the formation and nature of organic deposits, and the densities of accessible Bronsted acid sites and active hydrocarbon-pool species were studied as a function of time-on-stream (TOS) by 1H MAS NMR spectroscopy. The above-mentioned spectroscopic methods gave a very complex picture of the deactivation mechanism consisting of a number of different steps. The most important of these steps is the formation of alkyl aromatics with large alkyl chains improving at first the olefin selectivity, but hindering the reactant diffusion after longer TOS. The hindered reactant diffusion leads to a surplus of retarded olefinic reaction products in the SAPO-34 pores accompanied by their oligomerization and the formation of polycyclic a...

Mechanisms of the Deactivation of SAPO-34 Materials with Different Crystal Sizes Applied as MTO Catalysts

Methanol-to-olefin (MTO) conversion has proven to be one of the most successful non-petrochemical routes for producing light olefins. Silicoaluminophosphate (SAPO) zeolite SAPO-34 is one of the best industrial catalysts for MTO conversion, but suffers from rapid deactivation due to the inherent diffusion bottleneck limited by the narrow eight-ring pore openings. To improve the MTO performance, considerable synthetic efforts have been devoted to decrease the crystal size of zeolites or introduce secondary larger pores in zeolite crystals to form hierarchical structures. This review mainly focuses on presenting the state-of-the-art synthetic strategies for nanosized and hierarchical SAPO-34 catalysts with excellent MTO performance. Furthermore, the industrialization of SAPO-34 catalysts for the MTO reaction, and some current problems and future prospects for the synthesis of SAPO-34 catalysts, are also pointed out. We expect that this review can not only shed some light on the preparation of SAPO-34 catalysts, but also stimulate the future development of high-performance SAPO-34 catalysts to meet the increasing demands of the chemical industry.

The state-of-the-art synthetic strategies for SAPO-34 zeolite catalysts in methanol-to-olefin conversion

Nano-SAPO-34 molecular sieves synthesized in a microwave environment with 20 nm crystal size showed a longer lifetime than SAPO-34 prepared by the conventional hydrothermal method in the reaction of methanol to olefins. It has been found that silicon distribution strongly affects the lifetime and selectivity. Thus, silicon at the border of the silicon islands gives a higher lifetime and lower C2/C3 ratio. This change in activity and selectivity is better explained in terms of different silicon distribution than by preferential diffusion of ethene through the 8MR pores and agrees with transition-state selectivity. The effects of equilibrium of olefins and deactivation by coke were isolated, showing that after full formation of the hydrocarbon pool, selectivity is independent of deactivation by coke.

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Methanol to olefins: activity and stability of nanosized SAPO-34 molecular sieves and control of selectivity by silicon distribution

Recent advances of the nano-hierarchical SAPO-34 in the methanol-to-olefin (MTO) reaction and other applications

The synthesis of SAPO-34 with mixed template and its catalytic performance for methanol to olefins reaction

Hydrothermal synthesis of high-silica mordenite by dual-templating method

A novel zirconosilicate with the MWW topology (Zr-MWW) is hydrothermally synthesized for the first time using hexamethyleneimine (HMI) or piperidine (PI) as a structuring direct agent (SDA) and boric acid as a crystallization-supporting agent in an alkali media, which implies new route for preparing MWW-type metallosilicate Highly crystalline Zr-MWW is crystallized from the gels even with a Si/Zr ratio of 50 Zr-MWW is shown to be efficient for the Lewis acid-catalyzed reduction of cyclic ketones with secondary alcohols_in Meerwein-Ponndorf-Verley (MPV) reactions

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Papers

The synthesis of SAPO-34 with mixed template and its catalytic performance for methanol to olefins reaction

Hydrothermal synthesis of high-silica mordenite by dual-templating method

Hydrothermal synthesis of MWW-type zirconosilicate