Facile and Rapid Synthesis of Durable SSZ-13 Catalyst using Choline Chloride Template for Methanol-to-Olefins Reaction

In the current study, a facile and rapid synthesis approach for a SSZ-13 catalyst using choline chloride (CC) as a template was proposed, and the catalytic performance for the methanol-to-olefins (MTO) reaction was examined. With a proper amount of CC addition (i.e., m(CC)/m(SiO2)=0.14), uniform and homogeneously distributed cubic SSZ-13 crystals were obtained within 4 h with lower aggregation. The synthesized catalyst demonstrated excellent porous features with a total specific surface area and mesopore volume of 641.71 m2·g−1 and 0.04 cm3·g−1, respectively. The optimized strong and weak acid sites on SSZ-13 were obtained by regulating the m(CC)/m(SiO2) ratio. The less strong acid sites and a larger amount of weak acid sites in the synthesized catalyst were conducive to the catalytic performance of the MTO reaction under a lower reaction temperature (450 °C). The appropriate acidity and well-developed pore structure of synthesized SSZ-13 could also slow down the carbon deposition rate and, thus, significantly improve the catalytic lifetime of the catalyst. The methanol conversion rate and initial selectivity of light olefin using the synthesized catalyst could maintain over 95% and 50%, respectively, and a lifetime of 172 min was achieved. Although the low olefin selectivity of the synthesized SSZ-13 catalyst was slightly lower than that of the purchased one, its desirable features were thought to have good potential for industrial application.

Synthesis of nano-ZSM-5 zeolite via a dry gel conversion crystallization process and its application in MTO reaction

Nano-sized ZSM-5 with superior catalytic properties was synthesized from LAPONITE® as one of the Si sources by a dry gel conversion method.

Rational construction of hierarchical SAPO-34 with enhanced MTO performance without an additional meso/macropore template

A facile approach has been developed to fabricate hierarchical SAPO-34 with large intracrystalline meso/macropores and excellent catalytic performance in the MTO reaction.

MTO Synthesis and Characterization of ZnAPO-34 and SAPO-34: Effect of Zn on the Acidity and Catalytic Activity in the MTO Reaction

SAPO-34 and ZnAPO-34 materials (Zn incorporated by isomorphic substitution in AlPO-34 material) were synthesized by hydrothermal synthesis using triethylamine (TEA) as the structure directing agent (SDA). The structure presented by both materials is isomorphic to the chabazite zeolite (CHA). However, they have different properties such as textural properties (Z34 and S34 presented a surface area of ​​485 and 603 m2/g, respectively), different crystal sizes and acid properties. The physicochemical properties of the zeotypes were studied using XRD (X-ray diffraction), N2 adsorption-desorption, temperature programmed desorption of NH3 and SEM (Scanning Electron Microscopy). The catalytic performance of these catalysts was studied in the MTO reaction at 400 °C and atmospheric pressure using a WHSV of 2.12 h-1 in a fixed bed reactor. The incorporation of Zn had an important effect on acidity, generating a higher density of acid sites, increasing selectivity to light olefins. It was observed that when the crystal size decreases (ZnAPO-34), 100 % mol methanol conversion is obtained at short reaction times. The ZnAPO-34 material had a smaller crystal size (0.5 µm) and selectivity for olefins of 78 mol %. On the other hand, the SAPO-34 catalyst showed a larger crystal size (1.5 µm) and lower selectivity to olefins (72 mol %). The Z34 catalyst was compared with a previously reported MeAPSO-36 material, the latter was selective for the formation of aromatic compounds and lower selectivity to olefins (35 % mol) due to the presence of larger channels and lower density of acid sites. Resumen. En este trabajo se han sintetizado materiales SAPO-34 y ZnAPO-34 (Zn incorporado por sustitución isomórfica en material AlPO-34), mediante síntesis hidrotérmica usando trietilamina (TEA) como agente director de la estructura. La estructura presentada por ambos materiales es isomorfa a la de una zeolita chabazita. Sin embargo, ambos materiales tienen diferentes propiedades texturales (Z34 y S34 presentaron un área superficial de 485 y 603 m2/g, respectivamente), diferentes tamaños de cristal y distinta acidez. Las propiedades fisicoquímicas de los catalizadores se estudiaron mediante DRX (difracción de Rayos X), adsorción-desorción de N2, desorción programada a temperatura de NH3 y SEM (Microscopia electrónica de barrido). El rendimiento catalítico de los catalizadores se estudió en la reacción de transformación de metanol a olefinas (MTO) a 400 °C y presión atmosférica en un reactor de lecho fijo operando con un WHSV de 2.12 h-1. La incorporación de Zn tuvo un efecto importante en la acidez generando una mayor densidad de sitios ácidos y aumentando la selectividad a olefinas ligeras. Se observó que cuando el tamaño del cristal disminuye (ZnAPO-34), se obtiene una conversión de metanol del 100 % mol a tiempos cortos de reacción. El material ZnAPO-34 presentó un tamaño de cristal más pequeño (0.5 µm) y selectividad para olefinas de 78 % mol. Por otro lado, el catalizador SAPO-34 mostró un tamaño de cristal más grande (1.5 µm) y menos selectividad a olefinas (72 % mol). El catalizador Z34 fue comparado con un material MeAPSO-36 reportado anteriormente, que presentaba alta selectividad hacia la formación de compuestos aromáticos y menor selectividad a olefinas (35 % mol), debido a la presencia de canales de mayor tamaño y menor densidad de sitios ácidos.

Porosity of CHA Zeolite Driving the Formation of Polyaromatic Coke Species in the Methanol to Olefins Reaction

The pore size of the chabazite structure is exceptionally suitable for the methanol to olefins (MTO) reaction. The reaction has an induction period required for the formation of a hydrocarbon pool (HP), usually composed of aromatic compounds of different sizes. HP is alkylated by methanol and afterward cracked, leading to the formation of olefins. Despite the importance of HP, its formation and growth in size are exceedingly dependent on the porosity of the catalyst. The ideal is that the formed HP remains stable throughout the reaction because the growth in its size causes blockage of the small catalyst pores, decreasing its capacity. Herein we studied chabazite zeolites with different porosity and structure, caused by variation in the particle size and pores’ volume. Porosity influenced the formation of HP species in quantity (as revealed by thermogravimetric analysis (TGA)) and polymerization degree (gas chromatography coupled with mass spectrometer (GC-MS) analysis) and, consequently, the MTO reaction’s performance.

Designing SAPO-18 with Energetically Favorable Tetrahedral Si Ions for MTO Reaction

The silicon site location in silicoaluminophosphate zeolites have significant influences on their acidic and catalytic properties. Herein, AEI analogue silicoaluminophosphates with controlled tetrahedral silicon centers (T sites) were synthesized using...