Product selectivity in methanol to hydrocarbon conversion for isostructural compositions of AFI and CHA molecular sieves

Yuen, L.T.; Zones, Stacey I.; Harris, Thomas V.; Gallegos, E.J.; Auroux, A.

doi:10.1016/0927-6513(93)e0039-j

Cited by 107 publications

(76 citation statements)

References 17 publications

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“…In general, the presence of weaker Brønsted acidities on small pore SAPO catalysts tends to decrease the catalyst deactivation rate for the MTO process, [22] but in contrast, higher reaction temperatures (i.e. 400ºC) are required to afford total methanol conversions compared to aluminosilicate counterparts.…”

Section: -Introductionmentioning

confidence: 99%

“…[17] This methodology allows synthesizing SAPO-18 materials 4 with limited silicon distributions, detecting the formation of large amounts of agglomerated silicon species within the crystals. [17] It is worth noting that the siliconrich domains are formed by the multiple substitution of P 5+ and Al 4+ atoms in the zeolitic framework by Si 4+ atoms, resulting in materials with lower Brønsted acidities and hydrothermal stabilities.In general, the presence of weaker Brønsted acidities on small pore SAPO catalysts tends to decrease the catalyst deactivation rate for the MTO process, [22] but in contrast, higher reaction temperatures (i.e. 400ºC) are required to afford total methanol conversions compared to aluminosilicate counterparts.…”

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confidence: 99%

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Improving the catalytic performance of SAPO-18 for the methanol-to-olefins (MTO) reaction by controlling the Si distribution and crystal size

Martínez-Franco

Martínez‐Triguero

et al. 2016

Catal. Sci. Technol.

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The physico-chemical properties of the small pore SAPO-18 zeotype have been controlled by properly selecting the organic molecules acting as organic structure directing agents (OSDAs). The two organic molecules selected to attempt the synthesis of the SAPO-18 materials were N,N-diisopropylethylamine (DIPEA) and N,N-dimethyl-3,5-dimethylpiperidinium (DMDMP). On one hand, DIPEA allows achieving small crystal sizes (0.1-0.3 µm) with limited silicon distributions when the silicon content in the synthesis gel is high (Si/TO 2 ~ 0.8). On the other hand, the use of DMDMP directs the formation of larger crystallites (0.9-1.0 µm) with excellent silicon distributions, even when the silicon content in the synthesis media is high (Si/TO 2 ~ 0.8). It is worth noting that this is the first description of the use of DMDMP as OSDA for the synthesis of the SAPO-18 material, revealing not only the excellent directing role of this OSDA to stabilize the large cavities present in the SAPO-18 structure, but also to selectively place the silicon atoms in isolated framework positions. The synthesized SAPO-18 materials have been characterized by different techniques, such as powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), N 2 adsorption, solid NMR, or ammonia temperature programmed desorption (NH 3 -TPD). Finally, their catalytic activity has been evaluated for the Methanol-to-Olefin (MTO) process at different reaction temperatures (350 and 400ºC), revealing that the SAPO-18 catalysts with optimized silicon distributions and crystal sizes show excellent catalytic properties for the MTO reaction. These optimized SAPO-18 materials present improved catalyst lifetimes compared to standard SAPO-34 and SSZ-39 catalysts, even when tested at low reaction temperatures (i.e. 350ºC). 3 1.-IntroductionThe Methanol-to-Olefins (MTO) process has received a significant attention in the last years since it has been considered as an alternative route for the production of light olefins, such as ethylene and propylene, which are currently mainly achieved from fluid catalytic cracking or steam cracking of hydrocarbons. [1,2] Small pore silicoaluminophosphate (SAPO) materials containing large cavities in their structures, have been described as the most efficient catalysts for the MTO reaction. [2,3] Indeed, SAPO-34 material, which is the silicoaluminophosphate form of the crystalline structure of CHA, [4] is being applied as commercial catalyst for this process. [3,5] It is claimed that the unique crystalline structure of CHA, combining the presence of large cavities (~ 6.7x10.9 Å) and small pores (~ 3.8 Å), allows the formation of the required bulky aromatic intermediate states, known as "hydrocarbon pool", and permits the preferential diffusion of the desired light olefins, respectively. [6,7,8,9,10] In addition to the SAPO-34 catalyst, other small pore SAPO materials presenting large cavities in their structure have also been studied as catalysts for the MTO process. [11,12] From the different SAPO materials, SAPO-18 has sho...

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Section: -Introductionmentioning

confidence: 99%

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confidence: 99%

Improving the catalytic performance of SAPO-18 for the methanol-to-olefins (MTO) reaction by controlling the Si distribution and crystal size

Martínez-Franco

Martínez‐Triguero

et al. 2016

Catal. Sci. Technol.

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“…Zeolites with the CHA topology are of industrial interest, primarily as potential highly selective catalysts for application in the methanol to olefins (MTO) reaction [1]. The presence and concentration of Al in the zeolite framework determines the acidity of the material in the hydrogen form.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of high silica CHA zeolites with controlled Si/Al ratio

Eilertsen

Nilsen

Wendelbo

et al. 2008

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Zeolites with the CHA topology have been synthesized with Si/Al ratios ranging from 15 to 133. ICP-AES analysis shows that the Si/Al ratio in the material is close to linearly related to the Si/Al ratio in the reaction mixture, while powder XRD shows that the unit cell parameters decrease with increasing Si/Al ratio. The difference between the unit cell parameters for the as-synthesized and the calcined samples show that the structure directing agent sterically hinders the contraction in the c-axis direction for the as-synthesized samples. A relationship between the Si/Al ratio in the material and the a-axis has been established. The particle size of the material also shows a dependency on the Si/Al ratio of the material.

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“…With the addition of CTAB, the process of assembling and growth of the precursors is delayed permitting the control of the size of the crystals. 38 SSZ-13 the aluminosilicate homologue of SAPO-34 with CHA topology 39,40 offers an alternative for MTO. Due to its higher acidity strength, the reaction of methanol to olefins could starts at lower temperature or to allow a shorter contact time or higher throughput.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of nano-SSZ-13 and its application in the reaction of methanol to olefins

Navarro

Martínez‐Triguero

et al. 2016

Catal. Sci. Technol.

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Nanosized SSZ-13 has been obtained from a one-pot synthesis procedure with the addition of CTAB to the synthesis precursor solution. Nano-SSZ-13 zeolite showed high intracrystalline mesoporosity and comparing to standard SSZ-13 presented much longer lifetime and higher conversion capacity for the reaction of methanol to olefins. The improved properties were attributed to a more efficient utilization of microporosity by easier diffusion of reactants and products and slower deactivation by coke. A higher C2/C3 ratio was found for nano-SSZ-13 pointing to a lower deactivation of the aromatics cycle of the hydrocarbon pool.

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Product selectivity in methanol to hydrocarbon conversion for isostructural compositions of AFI and CHA molecular sieves

Cited by 107 publications

References 17 publications

Improving the catalytic performance of SAPO-18 for the methanol-to-olefins (MTO) reaction by controlling the Si distribution and crystal size

Improving the catalytic performance of SAPO-18 for the methanol-to-olefins (MTO) reaction by controlling the Si distribution and crystal size

Synthesis of high silica CHA zeolites with controlled Si/Al ratio

Synthesis of nano-SSZ-13 and its application in the reaction of methanol to olefins

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