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The coke deposition behaviors and the evolution of hydrocarbon pool species of SAPO‐34 during the methanol to olefins (MTO) process were investigated. Retained hydrocarbon analysis was employed to explore the amount and the category of coke in the cages of thermally quenched SAPO‐34 samples which had been used as the catalyst in the MTO reaction. The coke lead to the distinct microstrain of unit cell. The UV‐vis spectra and GC‐MS studies showed the evolution of hydrocarbon pool species from monocyclic to polyaromatic. Furthermore, the linearly increasing of coke content and linearly reducing of surface area of SAPO‐34 indicated that the deactivation of catalyst was mainly caused by the blockage of SAPO‐34 pore. [ABSTRACT FROM AUTHOR]

• Sn is incorporated into ZSM-5 framework during hydrothermal synthesis. • Incorporation of Sn results in a homogeneous Al spatial distribution. • More Al atoms are enriched in the 10R straight channels when Sn is introduced. • Addition of Sn improves propene selectivity and catalytic stability in MTO reaction. Regulating Al distribution of zeolite is an efficient strategy to enhance its catalytic performance of methanol to olefins (MTO). Herein, controlling spatial and framework Al distribution of ZSM-5 by Sn was firstly investigated. Incorporation of Sn has little impact on the morphology, texture properties, Brønsted acid strength and amount of ZSM-5, but causes a more homogeneous Al spatial distribution, as confirmed by EDS and XPS results. 27Al MAS NMR and 1-hexene cracking probe tests reveal that introduction of Sn leads to an increase in the amount of Al atoms located at 10R straight channels. This fine regulation of Al distribution by Sn is adverse to the aromatic-based cycle, thus generating less aromatics and coke species, as confirmed by in situ DR UV–vis for MTO, GC–MS and TGA results. As a result, the Sn-containing catalysts show a higher propene selectivity and catalytic stability in MTO. [ABSTRACT FROM AUTHOR]

• InCeO x and InCrO x give higher CH 3 OH selectivity, but lower CH 4 selectivity than In 2 O 3. • Doping Ce or Cr into In 2 O 3 lattice sites can generate more surface oxygen vacancies. • HCOO* intermediate has a stronger electronic interaction with InCeO x and InCrO x surfaces. • InCrO x /SAPO-34 shows a C 2 =–C 4 = selectivity of 75.0% at a CO 2 conversion of 33.6%. • The C 2 =–C 4 = yield is 1.5–2.0 times those reported on In 2 O 3 or In–Zr/SAPO-34. Indium-based oxides are potential catalysts for CO 2 hydrogenation to methanol. However, upon complexing with SAPO-34, they give a C 2 =–C 4 = yield below 7.3% due to production of large amounts of CO and CH 4 at high CO 2 conversion. Therefore, a large improvement of the C 2 =–C 4 = yield over indium-based oxide and zeolite composites is a challenge. In this context, InCeO x and InCrO x oxides were prepared and found to produce more methanol than In 2 O 3 or In–Zr oxide. Experimental and DFT calculation results reveal that incorporation of Ce or Cr into In 2 O 3 generates more surface oxygen vacancies and enhances the electronic interaction between HCOO* intermediates and the catalyst surface, which decreases HCOO* and CH 3 OH formation free energy barriers and enthalpy barriers. Compared with InCeO x (0.13) and In 2 O 3 , InCrO x (0.13) shows higher catalytic activity for CO 2 hydrogenation, and by coupling with SAPO-34, it gives a C 2 =–C 4 = yield of 1.5–2.0 times those obtained on In 2 O 3 /SAPO-34 and In-Zr/SAPO-34 at CO 2 conversion of 33.6%. [ABSTRACT FROM AUTHOR]

Adding proper content of Na+ and/or Li+ as well as altering the Si/Al ratio during the synthesis can be used to adjust the Al siting or the distribution of acid sites in ZSM-11 zeolite framework and hence regulate its catalytic performance in MTO. • Al siting or acid sites distribution in ZSM-11 can be adjusted by adding alkali ions. • Adding Na+ or Li+ in synthesis gel can elevate Al fraction in the intersection cavity. • Increasing Si/Al ratio in alkali free system can relatively enrich Al in the strait channel. • Catalytic performance of ZSM-11 in MTO is related to the Al siting in zeolite lattices. • Acid sites in the intersection cavity (strait channel) benefit the aromatic (alkene) cycle. The catalytic performance of acid zeolite in the conversion of methanol to olefins (MTO) is closely related to the location of aluminum (Al) in the lattice sites; however, it is still a great challenge to finely tune the siting of framework Al and thereon purposefully regulate the performance of zeolite catalyst. In this work, adding proper alkali metal ions in the synthesis gel was used to alter the Al siting in ZSM-11 zeolite and the effect of Al siting on the catalytic performance of ZSM-11 in MTO was then investigated. The results indicate that the addition of Na+ and/or Li+ in the synthesis gel can elevate the fraction of Al sited in the intersection cavity of ZSM-11, whereas in the alkali metal ions free synthesis system, an increase in the Si/Al ratio leads to a more prominent decrease of Al sited in the intersection cavity and a relative enrichment of Al distributed in the straight channel. The variation of Al siting has a significant influence on the catalytic performance of ZSM-11 in MTO, which can be well explained by the dual-cycle hydrocarbons pool (HCP) mechanism. More Al atoms located in the straight channel can enhance the alkene-based cycle that produces more propene and butene; in contrast, an increase in the fraction of Al in the intersection cavity can then promote the aromatic-based cycle and facilitate the formation of ethene and aromatics. This work provides an efficient method to finely tune the siting of Al in ZSM-11 zeolite lattices and controllably regulate its catalytic performance in MTO; moreover, the insight shown in this work is also helpful for a better understanding on the relationship between the Al siting/acid sites distribution and the performance of a zeolite catalyst. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The transition period between the initial stage and steady stage of MTO was investigated. • Methylcyclopentadiene and methylbenzene are quickly constructed from lower olefins. • Methylcyclopentadiene and methylbenzene as HCP intermediates open the steady stage. • Methylcyclopropene and methylnaphthalene are less significant in the transition period. • Both pairing and side-chain routes are active in forming olefins from the cyclic HCP species. Abstract In the conversion of methanol to olefins (MTO), it is now well accepted that ethene and propene are formed via a direct mechanism in the initial stage; after a transition period, olefins are then mainly produced via a hydrocarbon pool (HCP) mechanism in the steady stage. However, there was still no clear consensus over what actually occurred in the transition period and how the initial ethene and propene products construct the first HCP intermediates. In this work, the formation of initial HCP intermediates in the transition period and their evolution tendency were investigated for MTO over H-ZSM-5 zeolite by density functional theory and microkinetic modeling. The results illustrate that ethene and propene formed in the initial stage can quickly construct methylcyclopentadiene and methylbenzene; acting as the initial HCP intermediates, these cyclic species can build the light olefins through both the pairing route and the side-chain route and then promote the MTO reactions into the steady stage governed by the HCP mechanism. Meanwhile, the formation of methylcyclopropene and methylnaphthalene needs to conquer a high free energy barrier, which should be less significant as the HCP intermediates in the transition period. The insight attained in this work helps to clarify the origin and evolution of initial cyclic HCP intermediates in the transition period and is thus beneficial for a better understanding of the MTO reaction mechanism. [ABSTRACT FROM AUTHOR]

The mechanism of olefin eliminationin the process of methanol-to-olefins(MTO) over a series of zeolites like HZSM-5, HMOR, HBEA, and HMCM-22was investigated by DFT-D calculations, which is a crucial step thatcontrols the MTO product distribution. The results demonstrate thatthe manners of olefin elimination are related to the pore structureof zeolite catalyst and the interaction between proton transfer reagent(water or methanol) and zeolite acidic framework. The indirect spiromechanism is preferable to the direct mechanism over HMOR, HBEA, andHMCM-22 zeolites with large pores, as suggested by the energy barrierof rate-determining step and the potential energy surface (PES), butis unfavorable over HZSM-5 with medium-sized pores due to the sterichindrance of spiro intermediates. Over various zeolites, water andmethanol perform differently in proton transfer to form the spirointermediates; over HMOR and HBEA with strong acidity, water is superiorto methanol in promoting propene elimination, whereas over HMCM-22with relatively weaker acidity, methanol is more favorable as a protontransfer reagent. [ABSTRACT FROM AUTHOR]