Ultrafast Encapsulation of Metal Nanoclusters into MFI Zeolite in the Course of Its Crystallization: Catalytic Application for Propane Dehydrogenation

Abstract

Encapsulating metal nanoclusters into zeolites combines the superior catalytic activity of the nanoclusters with high stability and unique shape selectivity of the crystalline microporous materials. The preparation of such bifunctional catalysts, however, is often restricted by the mismatching in time scale between the fast formation of nanoclusters and the slow crystallization of zeolites. We herein demonstrate a novel strategy to overcome the mismatching issue, in which the crystallization of zeolites is expedited so as to synchronize it with the rapid formation of nanoclusters. The concept was demonstrated by confining Pt and Sn nanoclusters into a ZSM-5 (MFI) zeolite in the course of its crystallization, leading to an ultrafast, in situ encapsulation within just 5 min. The Pt/Sn-ZSM-5 exhibited exceptional activity and selectivity with stability in the dehydrogenation of propane to propene. This method of ultrafast encapsulation opens up a new avenue for designing and synthesizing composite zeolitic materials with structural and compositional complexity.

Structure‐Activity Relationships in Highly Active Platinum‐Tin MFI‐type Zeolite Catalysts for Propane Dehydrogenation

“…Several studies using Pt-containing MFI-type zeolites with different balancing cations and/or promoters have been published in the literature over the last decades. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] Small Pt clusters within the 10r channels of ZSM-5 zeolite, containing isomorphously substituted Fe 3 + ions and Na + as balancing cations, have been shown to catalyze propane dehydrogenation with higher rates, selectivity and stability than Pt/Sn-Al 2 O 3 , attributed to the presence of well-dispersed Pt within the zeolite micropores, the weaker acid sites resulting from framework Fe 3 + ions (as compared with Al-containing zeolites), and geometric constraints inhibiting the formation of bulky hydrocarbons. [11][12] More recently, it has been shown to be possible to synthesize in one pot siliceous (K)PtSnMFI zeolites that are highly active, selective and stable in the dehydrogenation of propane; utilizing the zeolite shape-selectivity to favor dehydrogenation over oligomerization and the absence of Brønsted sites to mitigate coke formation.…”

“…Due to their particular properties, zeolites have found use as support for light alkane dehydrogenation catalysts [9–30] . Several studies using Pt‐containing MFI‐type zeolites with different balancing cations and/or promoters have been published in the literature over the last decades [9–25] .…”

“…Due to their particular properties, zeolites have found use as support for light alkane dehydrogenation catalysts [9–30] . Several studies using Pt‐containing MFI‐type zeolites with different balancing cations and/or promoters have been published in the literature over the last decades [9–25] . Small Pt clusters within the 10 r channels of ZSM‐5 zeolite, containing isomorphously substituted Fe 3+ ions and Na + as balancing cations, have been shown to catalyze propane dehydrogenation with higher rates, selectivity and stability than Pt/Sn‐Al 2 O 3 , attributed to the presence of well‐dispersed Pt within the zeolite micropores, the weaker acid sites resulting from framework Fe 3+ ions (as compared with Al‐containing zeolites), and geometric constraints inhibiting the formation of bulky hydrocarbons [11–12] .…”