(771h) Correlating Treatment Conditions and Atomic-Scale Environments of Pt Supported on NaY Zeolite

Correlating
treatment conditions and atomic-scale environments of

Pt supported on NaY zeolite

Tsatsral
Battsengel,^§ Randall Meyer,^‡ Allen Burton,^‡
Mobae Afeworki,^‡ Robert Carr, ^‡ Pedro
Serna, ^‡ Aaron Sattler, ^‡ Bradley Chmelka^§

^§ Department of
Chemical Engineering, University of California, Santa Barbara, California

^‡ ExxonMobil Research
and Engineering, Clinton, New Jersey

Zeolite-supported
metals are widely used as heterogeneous catalysts for energy and environmental applications,
including hydrocarbon cracking, reforming, and selective reduction of nitrogen
oxides. The reaction properties of these catalysts depend strongly on the
compositions and nanoscale architectures of the zeolite support, as well as the
types and locations of metal species within the zeolite pores, which are
influenced by the catalyst synthesis and treatment conditions.¹ Understanding
the atomic-scale structures of metal-zeolite systems prepared under different
conditions is crucial to the development of strategies to control metal dispersion
and thereby improve catalyst performance.

In this study,
we probe the influences of oxidative processes on the distributions and identities
of Pt on NaY zeolite and the atomic structures of the support framework (Fig 1).
Detailed understanding of Pt environments in Pt-NaY is limited, in part,
because of the broad distributions of local metal environments. To overcome
these challenges, we used powerful multinuclear solid-state NMR techniques, in
combination with XRD, TGA, and XRF analyses, to obtain detailed insights on the
locations and interactions of Pt species, as functions of synthesis conditions.
Specifically, solid- state ²⁷Al and

²⁹Si NMR measurements enabled
the identification and quantification of different framework tetrahedral (T)
sites and their local changes due to proximate Pt species. Solid-state ²³Na
NMR spectra obtained at very high magnetic field strengths (35.3 T, the world’s
highest for NMR at the U.S. National High Magnetic Field Laboratory) provide
unprecedented spectral resolution and reveal the relative populations of ²³Na
cations located at different sites within the Pt-NaY zeolite materials. Advanced
two-dimensional through-bond ²⁷Al{²⁹Si} and through-space
²³Na{²⁹Si} NMR correlation spectra of the parent NaY and
Pt-NaY materials reveal calcination temperature-dependent difference in their
local framework structures that provide information on the locations of the
supported Pt species. Furthermore, different chemical environments of Pt metal
species, among which are the active sites of the catalyst and related to the
catalytic activities, can be directly detected by ¹⁹⁵Pt NMR and
EXAFS measurements. These experimental approaches and techniques are expected
to be broadly applicable to understanding the structure-function relationships
of zeolite supported metal catalysts for diverse applications, providing new
insights to improve their macroscopic reaction properties.

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