Reversible Transformation of Pt Nanoparticles into Single Atoms inside High-Silica Chabazite Zeolite

Abstract

We report the encapsulation of platinum species in highly siliceous chabazite (CHA) crystallized in the presence of N,N,N-trimethyl-1-adamantammonium and a thiol-stabilized Pt complex. When compared to Pt/SiO or Pt-containing Al-rich zeolites, the materials in this work show enhanced stability toward metal sintering in a variety of industrial conditions, including H, O, and HO. Remarkably, temperatures in the range 650-750 °C can be reached without significant sintering of the noble metal. Detailed structural determinations by X-ray absorption spectroscopy and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy demonstrate subtle control of the supported metal structures from ∼1 nm nanoparticles to site-isolated single Pt atoms via reversible interconversion of one species into another in reducing and oxidizing atmospheres. The combined used of microscopy and spectroscopy is critical to understand these surface-mediated transformations. When tested in hydrogenation reactions, Pt/CHA converts ethylene (∼80%) but not propylene under identical conditions, in contrast to Pt/SiO, which converts both at similar rates. These differences are attributed to the negligible diffusivity of propylene through the small-pore zeolite and provide final evidence of the metal encapsulation.

Achieving Atomic Dispersion of Highly Loaded Transition Metals in Small‐Pore Zeolite SSZ‐13: High‐Capacity and High‐Efficiency Low‐Temperature CO and Passive NOx Adsorbers

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Small-pore zeolites also exhibit enhanced hydrothermal stability in comparison to their medium-and large-pore analogues. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Small-pore zeolites also exhibit enhanced hydrothermal stability in comparison to their medium-and large-pore analogues.…”

“…[22,23] Theintroduction of transition-metal cations of large ionic radii into small pore zeolites using traditional post-synthetic preparation methods (e.g., ion exchange) has proven difficult. [16,[26][27][28][29][30][31][32][33][34] Molliner et al demonstrated ar oute to produce 0.23 wt %a tomically dispersed Pt in SSZ-13 with Si/Al ratio 7t o9 . [24,25] Today,t here is ag reat interest to produce small-pore zeolites loaded with atomically dispersed Pt and Pd at levels higher than 0.3 wt %.…”

“…Therefore,n ew methods in which metal precursors are introduced into the zeolite synthesis gel prior to zeolite crystal nucleation have been proposed. [16] To form ionically dispersed Pt in SSZ-13, aP t 2+ complex with (3mercaptopropyl)trimethoxysilane ligand had to be added to the zeolite synthesis gel prior to crystallization. However,m ethods of loading transition metals ionically into SSZ-13 at practically relevant levels (> 1wt%)a re not known.…”

“…This happened despite the abundance of Brçnsted acid sites in the zeolite structure: for example,f or 1wt% Pd/SSZ-13 with Si/Al ratio 30 the nominal [H + ]/Pd II ratio is approximately 6. [16,34] TheS i/Al ratio of these siliceous materials should be (3 < x < 10) sufficient to utilize all metal and produce enough metal in the micropore. [27][28][29][30][31][32] In those papers,t he materials are prepared via either reaction with H-form of the zeolite (which is not effective) or using materials with high Si/Al ratios (10 and higher).…”

Single Metal Atom Photocatalysis

“…During the synthesis process, the polydopamine‐coated a‐FeOOH nanorod was carbonized, and then leached by HCl, resulting in the isolated Fe atoms on the inner surface of N‐doped carbon ( Figure a) . In addition, by thermal calcination at high temperature in oxidative atmosphere, isolated metal atoms could be derived from bulk metal . For example, Moliner et al found the metal nanoparticles, such as Pt and Pd, can be fragmented into smaller particles or even subnanometric species via calcination treatment in oxidative atmosphere (Figure b) .…”