Synthesis of Submicron-Sized SAPO-34 as Efficient Catalyst for Olefin Generation from CH3Br

Highly Enhanced Aromatics Selectivity by Coupling of Chloromethane and Carbon Monoxide over H-ZSM-5

The transformation of methane into high value-added chemicals such as aromatics provides a more desired approach towards sustainable chemistry but remains a critical challenge due to the low selectivity of aromatics and poor stability. Herein, we first report a coupling reaction of CH₃ Cl and CO (CCTA) based on methane conversion, which achieves extremely high aromatics selectivity (82.2 %) with the selectivity of BTX up to ca. 60 % over HZSM-5. The promoting effects have been demonstrated on other zeolites especially 10-membered rings (10 MR) zeolites. Multiple characterizations show that 2,3-dimethyl-2-cyclopentene-1-one (DMCPO) is generated from acetyl groups and olefins. Furthermore, isotopic labeling analysis confirms that CO is inserted into the DMCPO and aromatics rings. A new aromatization mechanism is proposed, including the formation of the above intermediates, which conspicuously weakens the hydrogen transfer reaction, leading to a considerable increase of aromatics selectivity and a dramatic drop in alkanes.

Synthesis of SAPO-34 Nanoplates with High Si/Al Ratio and Improved Acid Site Density

Two-dimensional SAPO-34 molecular sieves were synthesized by microwave hydrothermal process. The concentrations of structure directing agent (SDA), phosphoric acid, and silicon in the gel solution were varied and their effect on phase, shape, and composition of synthesized particles was studied. The synthesized particles were characterized by various techniques using SEM, XRD, BET, EDX, and NH₃-TPD. Various morphologies of particles including isotropic, hyper rectangle, and nanoplates were obtained. It was found that the Si/Al ratio of the SAPO-34 particles was in a direct relationship with the density of acid sites. Moreover, the gel composition and preparation affected the chemistry of the synthesized particles. The slow addition of phosphoric acid improved the homogeneity of synthesis gel and resulted in SAPO-34 nanoplates with high density of acid sites, 3.482 mmol/g. The SAPO-34 nanoplates are expected to serve as a high performance catalyst due to the low mass transfer resistance and the high density of active sites.

Investigation of synthesis time and type of seed along with reduction of template consumption in the preparation of SAPO-34 catalyst and its performance in the MTO reaction

SAPO-34 catalysts were synthesized through the seeding approach under different seed conditions. The different seed synthesis times (6 h, 12 h, and 24 h) and three types of seeds were evaluated: the dried seed, the calcined seed, and the mother liquor from an unseeded synthesis, called the solution seed. Pure SAPO-34 was obtained using 12 h and 24 h solution seeds, in which a 40% reduction of template consumption was achieved simultaneously. All seeding induced samples represented higher catalytic performance in the MTO process than conventional SAPO-34 due to the smaller crystallite/particle sizes and larger external surface areas and mesopore volume. Furthermore, the changes in the acidity of samples affect their performance. The maximum olefin selectivity under industrial feed conditions (72 wt% methanol in water) was 91.79% for the sample prepared from the 12 h solution seed, which was 14.43% higher than the unseeded sample. Although this sample did not have the longest lifetime, it showed a 330 min lifespan, which was at least twice more than that of the conventional one (150 min). The sample prepared from the 6 h solution seed showed the longest lifetime of more than 500 min among all catalysts, although it was contaminated with a little SAPO-5.

SAPO-34 catalysts were synthesized through the seeding approach under different seed conditions.

Synthesis, characterization, and catalytic application of hierarchical nano-ZSM-5 zeolite

Hierarchical nano-ZSM-5 zeolites (Z5-X) with different grain sizes were synthesized by varying amounts of 3-glycidoxypropyltrimethoxysilane (KH-560) in the hydrothermal synthesis strategy. Moreover, the conventional ZSM-5zeolite(Z5), which was prepared without KH-560, was used as the reference sample. The crystalline phases, morphologies, porous characteristics, Si/Al molar ratios and acidic properties of all fresh catalysts were characterized using the X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), scanning electron microscopy (SEM), N₂ adsorption–desorption, inductively coupled plasma atomic emission spectroscopy (ICP) and temperature programmed desorption of ammonia (NH₃-TPD) techniques. Results show that the grain size and strong acid amount of zeolite decreased with the increasing amount of KH-560. The micropore surface areas and the corresponding volume of Z5-X changed less compared with Z5. Consequently, the high shape-selectivity of zeolite was preserved well under the addition of KH-560. However, the mesopore surface areas and the corresponding volume increased significantly with the increasing amount of KH-560. Benefiting from the abundant hierarchical structure, the Z5-X catalysts exhibited a larger coke capacity than the Z5 catalyst. The coke depositions of all the deactivated catalysts were characterized by the thermogravimetric technique (TG), and the results are indicative of the decreased average rate of coke deposition with an increasing amount of KH-560, which could result from the gradually reduced strong acid amount and the nano-sized crystallites. The catalytic performance of methanol-to-aromatics (MTA) indicates that the Z5-0.12 catalyst exhibited higher catalytic activity and selectivity of BTX as the reaction was prolonged, which could result from the synergistic effect among the proper strong acid amount, the smaller zeolite grain size, and the abundant hierarchical structure.

The crystal size and strong acid amounts of ZSM-5 decrease and the mesopores increase with increasing of KH-560. High MTA catalytic performance could be obtained under synergistic effect of proper strong acid amount, smaller crystal size and abundant hierarchical structure.