(461e) Correlating Nanoscale Compositions, Structures, and Reaction Properties of Bifunctional Pt-H+usy Zeolite Catalysts

Pt-zeolite catalysts exhibit diverse hydrocarbon conversion properties that depend strongly on the chemical compositions and nanoscale structural features of zeolite support. In particular, reaction properties are influenced by the Si/Al ratio and architecture of the zeolite framework, the types and locations of metal species, and the presence of mesopores induced by dealumination treatments. Understanding the atomic-scale compositions and structures of Pt-zeolite systems is crucial to to improve and prolong catalyst activity. Detailed understanding of Pt environments and functions in zeolite catalysts however have been limited, due in part to the broad distributions of local Pt environments, low metal loadings, and diverse interactions with non-stoichiometric framework compositions and exchangeable cations, all of which tend to lack long-range order. These challenges are exacerbated for bifunctional Pt-H⁺USY catalysts, which also have high Si/Al ratios and therefore low numbers of Brønsted acid sites.

To overcome these challenges, we use complementary X-ray diffraction, electron microscopy, infrared spectroscopy, and powerful solid-state NMR techniques to obtain detailed insights on the locations and interactions of Pt species for different type USY zeolites. Interestingly, different Pt-H⁺USY catalysts exhibit significantly different hydroisomerization properties, the origins of which are not apparent from conventional techniques. By comparison, two-dimensional (2D) ²⁷Al{²⁹Si} and ²⁹Si{¹H} MAS NMR spectra show differences in the distributions and quantities of framework Al atoms, Brønsted acid sites, and silanol groups. These results are correlated with in situ ¹³C and ¹H MAS NMR analyses, which provide information on the types and relative quantities of reactants and products over the Pt-H⁺USY catalysts for industrially significant reactions, such as n-hexadecane dehydroisomerization, under conditions up to 100 bar and 240 ^oC.The resulting atomic-level insights on the compositions, structures, and reaction properties of Pt-H⁺USY zeolite are expected to yield new criteria for the design and preparation of heterogeneous zeolite catalysts with improved reaction properties.