Selective Introduction of Acid Sites in Different Confined Positions in ZSM-5 and Its Catalytic Implications

Abstract

Controlling the location of acid sites in zeolites can have a great impact on catalysis. In this work we face the objective of directing the location of Al into the 10R channels of ZSM-5 by taking advantage of the structural preference of B to occupy certain positions at the channels intersections, as suggested by theoretical calculations. The synthesis of B-Al-ZSM-5 zeolites with variable Si/Al and Si/B ratio, followed by B removal in a post synthesis treatment, produces ZSM-5 samples enriched in Al occupying positions at 10R channels. The location of the acid sites is determined on the basis of the product distribution of 1-hexene cracking as test reaction. The higher selectivity to propene and lower C4 = /C3 = ratio in the samples synthesized with B and subsequently deboronated can be related to a larger concentration of acid sites in 10R channels, where monomolecular cracking occurs. Finally, several ZSM-5 samples have been tested in the methanol to propene reaction, and those synthesized through the B assisted method show longer catalytic lifetime, higher propene yield and lower yield of alkanes and aromatics.

Regioselective generation and reactivity control of subnanometric platinum clusters in zeolites for high-temperature catalysis

“…For instance, attempts have been reported to preferentially locate framework Al atoms in the intersectional sites or within the 10MR channels of ZSM-5 (MFI-type zeolite). [5][6][7] However, when functional metals, such as Pt or Pd, have been introduced by including the metal precursor during the synthesis or through inter-zeolite transformations, nanoparticles of 1-2 nm instead of subnanometric metal species (single atoms or clusters) have been obtained within MFI zeolite. [8][9][10][11] As far as we know, the metal particles show random distribution within the zeolite crystallites.…”

Location of the Active Sites for Ethylcyclohexane Hydroisomerization by Ring Contraction and Expansion in the EUO Zeolitic Framework

“…8 This is first of all due to the limited number of zeolites with more or less known location of aluminum atoms. 5,[9][10][11][12][13][14][15][16][17] Then, even once the location is known, it is generally not unique so that identifying the precise location of the most stable intermediates and transition states is not straightforward. This is however a condition for the design of better catalysts.…”

Site‐Specific Iron Substitution in STA‐28, a Large Pore Aluminophosphate Zeotype Prepared by Using 1,10‐Phenanthrolines as Framework‐Bound Templates

“…Incorporation of metal cations into AlPO frameworks can introduce catalytic activity and there is interest in being able to control the location of substituting cations and so of catalytic sites. The related challenge of locating Al in zeolites is an ongoing research area: significant progress has been made in preparing materials that have differing Al distributions, as assessed indirectly from their catalytic properties, for example. Preferred Al positions have also been inferred from the scanning transmission electron microscopic (STEM) observation of Mo atoms thought to bind at framework O atoms adjacent to Al .…”