Hierarchical ZSM-5 Zeolites with Tunable Sizes of Building Blocks for Efficient Catalytic Cracking of i-Butane

Abstract

Hierarchical ZSM-5 zeolites have been receiving increasing attention from both fundamental research and industrial applications. From the chemical engineering viewpoint, the introduction of building block of ZSM-5 could give consideration to both external surface acidities and diffusion properties which are important in parallel sequence reaction for the final product distribution. In this work, hierarchical ZSM-5 with different sizes of building blocks were successfully prepared by tuning the water/silica ratio during the synthesis. With varying the size of building blocks, the diffusion property and external surface acidity were finely regulated, and it significantly influences the performances of ZSM-5 during catalytic cracking reaction. The catalyst with proper size of building blocks exhibited the optimized yield of olefins and lowest carbon deposition during 72 h reaction in catalytic cracking of i-butane. The strategy proposed herein could be helpful for the engineering design of hierarchical zeolites for industrially important catalytic reactions.

Modified Acid‐Base ZSM‐5 Derived from Core‐Shell ZSM‐5@ Aqueous Miscible Organic‐Layered Double Hydroxides for Catalytic Cracking of n‐Pentane to Light Olefins

“…[70] To verify this perspective, the effect of different Brønsted acid density related to using different LDH loading in the composite on the catalytic performance was further studied. Interestingly, the composites with the highest and lowest LDH content (ZSM-5@MgAlO x (38) and ZSM-5@MgA-lO x (19), respectively) exhibit a significantly lower light olefins yield compared with the one with moderate LDH content (ZSM-5@MgAlO x (33)). The highest LDH loaded catalyst also relates to a lack of Brønsted acid sites, and therefore there are a few available active sites for catalytic cracking.…”

“…To overcome these drawbacks, zeolite catalysts have been modified by several approaches, for example, the creation of the additional mesoporosity in zeolite frameworks [12,13,14,15] as well as the modification with rare earth and metals, such as metal oxides and alkaline-earth metals. [16,17,18,19] However, there is the limitation of an excessive number of strong Brønsted acid sites on external surfaces of zeolites, leading to competing hydride transfers and further side reactions, such as oligomerization, isomerization, cyclization, and aromatization. [20,21] To deal with these issues, the modification of external acidity of zeolites has been investigated.…”

“…However, it often suffers from some disadvantages, such as, a short catalyst lifetime, and a very low yield of light olefins. To overcome these drawbacks, zeolite catalysts have been modified by several approaches, for example, the creation of the additional mesoporosity in zeolite frameworks as well as the modification with rare earth and metals, such as metal oxides and alkaline‐earth metals . However, there is the limitation of an excessive number of strong Brønsted acid sites on external surfaces of zeolites, leading to competing hydride transfers and further side reactions, such as oligomerization, isomerization, cyclization, and aromatization .…”

Butane Isomerization as a Diagnostic Tool in the Rational Design of Solid Acid Catalysts

“…Liu et al demonstrated that the conversion and selectivity of isobutane cracking may be tuned through controlling the mesoporosity of ZSM-5 catalysts. More mesoporous samples demonstrated higher conversion and selectivities due to an improved diffusion, as well as improved catalyst stabilities and lifetimes [91]. The introduction of mesoporosity has also been found to improve resistance to coking, much like when comparing channel versus cage topologies.…”

Insight into the Selection of the Post-Treatment Strategy for ZSM-5 Zeolites for the Improvement of Catalytic Stability in the Conversion of Methanol to Hydrocarbons

“…The catalytic conversion of methanol over acidic zeolite has become an eminent route to produce hydrocarbon products, such as olefins, gasoline, and aromatics. , ZSM-5 is a representative catalyst for the abovementioned reactions attributed to its plentiful active sites and shape-selective pore structure (0.53 nm × 0.51 nm sinusoidal channels and 0.56 nm × 0.53 nm straight channels). , However, such typical micropores cause space limitation for the diffusion of bulky product molecules. These molecules would be trapped in the channels and undergo condensation, hydrogen transfer, and elimination reactions to form coke precursors. , The coke precursors finally convert into coke and deposit in micropores, cover the active sites, and block zeolite channels, resulting in catalyst deactivation. , Especially for the ZSM-5 with a low Si/Al ratio, the high acid density and strong acid strength promote the coke formation, leading to a fast catalyst deactivation. , Therefore, optimization of pore structure and surface acidity should be considered to improve catalytic stability. , …”