(304f) Correlating Atomic-Scale Compositions, Structures, and Reaction Properties of Bifunctional Pt/H+usy Zeolite Catalysts

The reactive properties of platinum-containing zeolite catalysts depend strongly on the atomic-scale composition and structures of the catalyst system. For example, ultra-stable Y-zeolites (USY) containing dispersed platinum are used for hydrocracking and hydroisomerization of hydrocarbons in fuel and chemical production. USY zeolites are formed via dealumination treatments which introduce mesopores and decrease the amount of aluminum, and thus Brønsted acid sites, in the zeolite framework. The catalysts’ reaction properties depend on the aluminum content of the zeolite, the presence of mesopores, and the type and location of exchangeable cations and dispersed metals. Understanding the atomic-scale compositions and structures of Pt-containing zeolite systems is crucial to developing stable catalysts that have favorable activity and selectivity. Until now, however, insights on the local acid and Pt environments in these industrially relevant zeolite catalysts has been limited due to the broad distributions of Pt environments, low metal loadings, and the heterogeneity of the dealuminated zeolite support.

Here, we present detailed insights on the locations and distributions of the acid sites and Pt species in Pt/H⁺USY catalysts under various treatment conditions to the H⁺USY zeolite support. This is completed by powerful solid-state NMR techniques, X-ray diffraction, electron microscopy, and infrared spectroscopy. The distribution of Al atoms and siliceous moieties in the catalysts are revealed via two-dimensional ²⁷Al{²⁹Si} and ¹H{²⁹Si} NMR correlation experiments. These analyses are correlated with in situ ¹³C NMR, which enable the distributions of reactants and products of industrially relevant reactions, such as n-hexadecane hydroisomerization, to be resolved at high temperatures and pressures. In addition, the local chemical environments of the Pt species are probed via novel, indirect ¹⁹⁵Pt NMR techniques, such as ¹H{¹⁹⁵Pt} solid-state NMR. The results yield new atomic-scale criteria that are being used to guide the design, synthesis, and modification of metal-zeolite catalysts to improve their performance.