Modulating acid site spatial location of Zn/ZSM‐5 catalyst to boost the stable aromatization of hexane

Abstract

Engineering acid site spatial location of zeolite catalyst harbors tremendous potential to boost catalytic performance but still remains a grand challenge for aromatization reaction. Herein, we successfully manipulate acid site spatial location inside the ZSM‐5 channels to promote the hexane aromatization via the simple SiO2 coating treatment. Multi‐techniques demonstrated that the medium strong L acid in the channel originated from the Si(Al)OZn structure is mainly retained in the Zn/ZSM‐5‐Si catalyst by covering the acid sites outside the channel. Surprisingly, there is a good linear relationship between BTEX yield and this medium strong L acid content. Based on the reaction kinetics, in situ FT‐IR and theoretical calculations, it is found that the L acid with confinement effect served as the main active site could prominently enhance the cyclization of propene intermediate and the dehydrogenation of cycloalkane due to the strong affinity between the C/H and ZnOx, and control the desorption of BTEX (mainly benzene, toluene, ethylbenzene, and p‐xylene) by weakening the binding of hydrogen proton to π electrons. Compared with the ordinary Zn/ZSM‐5 catalyst, the yield of BTEX is increased by nearly 10%, and the Zn/ZSM‐5‐Si catalyst exhibits excellent anti coking deactivation ability. This strategy together with mechanistic results may pave the rational design of efficient Zn/ZSM‐5 catalysts for aromatization reaction.

Insight into catalytic cracking pathways of n‐pentane over bifunctional catalysts to produce light olefins

“…Compared with the ZSM‐5, the introduction of Ag could decrease the content of the Si‐(O‐Si) 2 from 9.5% to 8.7% accompanied by an increase in the content of Si‐(O‐Si) 3 from 8.9% to 9.2%. It is highly possible that Ag species interact with ZSM‐5 skeleton to form corresponding Ag‐O‐T structure, resulting in the reconstruction of coordination environment of Si species 26 . Meanwhile, the 27 Al MAS‐NMR in Figure 1E shows the change of aluminum characteristic peaks in different coordination forms after Ag modification, while the most obvious one is that the characteristic peak representing extra‐framework Al at 0 ppm is significantly reduced 27 .…”

“…The adsorption peak of alkane resonance with the end Si‐OH of the skeleton appears near 3500 cm −1 , which is caused by the adsorption of n‐pentane or some saturated alkanes in the product on the catalyst surface 33 . Meanwhile, the absorption peak at 2800–3000 cm −1 corresponds to the stretching vibration of CH bond, which mainly comes from the n‐pentane adsorbed in the gas phase and on the catalyst surface 26 . The absorption band increases with time, indicating that the conversion rate of n‐heptane decreases gradually with time.…”

“…33 Meanwhile, the absorption peak at 2800-3000 cm À1 corresponds to the stretching vibration of C H bond, which mainly comes from the n-pentane adsorbed in the gas phase and on the catalyst surface. 26 The absorption band increases with time, indicating that the conversion rate of n-heptane decreases gradually with time. Moreover, the characteristic peak at 1400-1600 cm À1 corresponds to the C H bond bending vibration of the aromatic ring.…”

Low-Temperature Thermocatalytic Coupling of CH4 and CO2 to Ethanol over Zn–Ce/ZSM-5 by a Stepwise Technique

“…Afterward, the pyridine-adsorbed IR spectra of different catalysts are displayed in Figure C. The peaks centered at ∼1450 and ∼1540 cm –1 were attributed to the L acid sites and B acid sites for pristine HZSM-5, respectively. , The peaks at ∼1490 cm –1 were constructed from the L+B acid sites for all catalysts. Based on the integrated peak area, the amounts of L and B acid sites of all catalysts were calculated and listed in Table S4.…”

The process of obtaining aromatic hydrocarbons by catalytic aromatization of normal hexane on the (2%LA*2%CU*8%ZN/Н-HSZ-30) catalyst

“…The volume of the reaction zone is calculated by setting the length of the "area" at equal temperature. The catalyst with high activity selected aromatization of hexane with a linear structure to obtain aromatic hydrocarbons was activated at 600 °C for 2 hours in an air stream, followed by 40 minutes in a helium stream [12][13][14][15].…”