Pt-based intermetallic nanoparticle has drawn much research interest in dehydrogenation of light alkanes for their excellent performance. As a well-defined material, intermetallic has advantages over its solid solution counterpart in its long-range periodicity and therefore exhibit some unique catalytic behaviors. This study focuses on the design and synthesis of Pt-Zn intermetallic nanocatalysts and their application in non-oxidative dehydrogenation (DHE) and oxidative dehydrogenation of ethane (ODHE). Two types of Pt-Zn intermetallics are successfully synthesized via atomic layer deposition (ALD) and incipient wetness impregnation (IWI) sequentially: Pt3Zn1 and Pt1Zn1. The formation of silica-supported Pt1Zn1 and Pt3Zn1 intermetallic nanoparticles were observed by both X-ray diffraction (XRD) and synchrotron X-ray absorption spectroscopy (XAS). STEM images showed that the 2-3 nm Pt-based intermetallic nanoparticles were uniformly dispersed on SiO2 support. The relationships between Pt-Zn intermetallic phases and synthesis conditions were established. In situ XAS measurements at Pt L3 and Zn K edges during hydrogen reduction provided a detailed image on surface species evolution. Owing to a combined electronic and geometric effect, Pt1Zn1 exhibited ca. 1.2 times and 15 times higher reactivity than Pt3Zn1 and Pt in DHE reaction. Pt1/Zn1/SiO2 also exhibit excellent performance in ODHE reaction compared with Pt3Zn1/SiO2 and Pt/SiO2, yet it deactivated considerably during the reaction. Understanding the deactivation mechanism of a catalyst in a chemical reaction is helpful for the future design of more stable catalysts. Identification of the influencing factors in the deactivation mechanism is vital to tackling the problem in the right direction. Using in situ XAS and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in conjunction with kinetics studies, we demonstrate that for ODHE over Pt1Zn1 intermetallic nanocatalyst, the rearrangement of the active sites caused by oxidation of Zn in the Pt-Zn alloy phase poses more harm to the catalyst than coke deposition. Sintering of Pt particle size may be the strongest influencing factor in the early stage of the ODHE.

Design and synthesis of Pt-Zn intermetallic nanocatalysts for dehydrogenation of ethane

ACS Spring Meeting 2021

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