Synthesis and catalytic properties of ZSM-5 zeolite with hierarchical pores prepared in the presence of n-hexyltrimethylammonium bromide

Acid resistance

ZSM-5 zeolite has good acid resistance, it is resistant to various acids except hydrofluoric acid.

Mole Ratio: 15-1000
Nominal Cation Form: Ammonium/Hydrogen

Na₂O Weight %: 0.05
Surface Area, m²/g: 450

Description:

ZSM-5 zeolite properties

Abstract
ZSM-5 samples with hierarchical pores (macropores, mesopores and micropores) were synthesized in the presence of n-hexyltrimethylammonium bromide (HTAB) and tetrapropylammonium hydroxide (TPAOH). The effect of synthesis conditions including the Si/Al ratio, crystallization temperature and time, and the amount of HTAB added to the synthesis system on the final products was examined. The catalytic properties of the hierarchical zeolite were investigated in reactions of Claisen–Schmidt condensation of benzaldehyde and acetophenone, self-condensation of cyclohexanone and methanol conversion. The hierarchical zeolite exhibits superior catalytic performance in Claisen–Schmidt condensation of benzaldehyde and acetophenone and self-condensation of cyclohexanone and has a remarkably high selectivity for dimethyl ether in the methanol conversion reaction at relatively low temperatures, which was attributed to the fast mass transport in the three-dimensional hierarchical pore network. A cooperative assembly mechanism accounting for the formation of the hierarchical zeolite was proposed based on experimental results.

Thermal stability

High thermal stability of ZSM-5 zeolite. This is caused by a skeleton in a stable five-membered ring structure and a high silica to alumina ratio. For example, the sample calcined at 850 ℃ After 2 hours, the crystal structure unchanged. Even can withstand high temperature of 1100 ℃. So far, ZSM-5 zeolites are known to one of the highest qualitative hot temperature. Therefore, it is used in high-temperature process is particularly suitable. For example, use it as a hydrocarbon cracking catalyst, regeneration of the catalyst can withstand passage of time.

Steam stability

The studies have shown that when other zeolites by steam and hot water, and their general structure is destroyed, leading to irreversible deactivation. The Mobil company with ZSM-5 as the conversion of methanol (water is one of the major product) catalyst. This suggests that ZSM-5 to water vapor with good stability. 540 ℃ lower partial pressure of 22mmHg steaming column and HY zeolite HZSM-5 after 24 hours, a crystallinity of HZSM-5 and about 70 percent of fresh catalyst, but under the same conditions, HY zeolite skeleton almost completely damage.

Hydrophobic

ZSM-5 having a high silica to alumina ratio, the smaller the surface charge density. The water molecule is polar, so you will not ZSM-5 is adsorbed. Although water molecules smaller than the diameter of n-hexane, but the amount of adsorption of n-hexane ZSM-5 is generally greater than water.

Easy to coke

ZSM-5 V-shaped aperture effective, pore size and bending, preventing a large condensate formation and accumulation. Meanwhile, ZSM-5 framework is no greater than the bore of the cavity (cage) exist, so limiting the formation of large molecules from the secondary condensation reactions. So that the possibility of ZSM-5 catalyst coke is reduced. ZSM-5 for an alkyl aromatics into the tunnel barrier is formed, and thus the reaction process it can not continue to react in smaller pores, the final condensation formed coke. ZSM-5 so much slower than the rate of coke deposition and Y-type mordenite, difference of almost two orders of magnitude. Capacity of ZSM-5 zeolite carbon content is higher.

Excellent shape-selective selectivity

Zeolite molecular sieve as catalyst, only smaller than the hole crystal molecules can catalyze the reaction out of control pore size crystalline zeolite suffering zeolite catalyst size and shape of reactant and product molecules showed great selectivity. Pore ​​system of ZSM-5 zeolite having a 10-MR constituted medium size orifice diameter, it has a good shape-selective selectivity.

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