(468c) Creation of Single Pt Atoms in Znox Nests in Dealuminated Zeolite Beta for Propane Dehydrogenation

Propylene is an important olefin product used for manufacturing polypropylene, propylene oxide, acrylic acid, and acrylonitrile, and thermal dehydrogenation of propane (PDH) is an attractive route. Pt is the only metal active center used in industrial PDH processes because of its high activity for dehydrogenation and low activity for the undesired cracking process. However, Pt large ensembles bring about detrimental structure-sensitive side reactions including cracking and deep dehydrogenation, leading to coke formation, whereas Pt clusters with smaller size favor high activity and selectivity. Therefore, stabilizing very small Pt clusters and ultimately Pt atoms has received strong interest.

In this study, we build on the idea that new class of improved PDH catalysts might be developed by creating atomically dispersed Pt in Zn containing clusters. To this end, we created ≡SiOZn(OH) nests by grating Zn into the silanol nest of dealuminated zeolite Beta (DeAlBEA) and then used ≡SiOZn(OH) nests to anchor Pt atoms. A catalyst named xPt-yZn-DeAlBEA (x and y indicate atomic ratios) is reported here. This material was characterized with complementary spectroscopic and microscopic methods including HAADF-STEM, ¹H and ²⁹Si NMR, Operando K-edge Zn and Pt XANES and EXAFS to show that Pt is dispersed atomically as cations with an apparent oxidation state ~ +4. The as-prepared catalyst undergoes reduction to form hexa-coordinated Pt⁰ atoms at 823 K, and the structure was characterized as a PtZn₆ intermetallic complex anchored to the zeolite. This new catalyst exhibits a propylene selectivity of nearly 100%, and it shows PDH activity that is 2- to 4.5-fold higher and a deactivation rate that is 18 times slower than that previously reported best PtZn catalysts. By co-feeding a low partial pressure of H₂, the catalyst works with virtually no activity loss after 160 h on stream.