2020-07-27T19:07:58Z (GMT) by Johnny Zhuchen
As shale gas exploitation has been developed, production of shale gas in the US has rapidly increased during the last decade. This has motivated the development of techniques to covert shale gas components (mainly C1 to C3) to liquid fuels by catalytic conversion. The main goal of the dissertation is to study the geometric and electronic structures of the metal catalysts, which are crucial for understanding the structure-property relationship.

The fi?rst project studies bimetallic Pt-Bi catalyst for non-oxidative coupling of methane. In a recent publication published in ACS catalysis, Pt-Bi/ZSM-5 catalyst
has been shown to stably convert methane into C2 for 8 hours under non-oxidative conditions. In this thesis, structure of the Pt-Bi/ZSM-5 was shown with HAADF
imaging, synchrotron XAS and XRD. A new surface cubic Pt3Bi phase on Pt nanoparticles with Pt-Bi bond distance of 2.80 A was formed. Formation of noble metal intermetallic alloys such as Pt3M may be the clue for non-oxidative conversion of methane.

The second and third project highlight strong metal-support interaction catalysts for propane dehydrogenation. Chemisorption showed partial coverage of the SMSI oxides
on the surface of the nanoparticles. In situ X-ray absorption near edge (XANES), resonant inelastic X-ray scattering (RIXS), X-ray photoelectron spectroscopy (XPS)
have shown that little electronic effect on the metal nanoparticles. The catalyst activity per mol of metal decreased due to the partial coverage of the SMSI oxides on the surface of the catalysts. The catalysts, however, had higher selectivity due to smaller ensembles inhibiting hydrogenolysis.

In the fourth project Pt-P catalyst was investigated to understand the promoting effect of P.Pt-P catalysts had much higher selectivity for propane dehydrogenation
(>95%). These give two types of catalysts, a PtP2-rich surface on Pt core and full PtP2 ordered structure, which were con?rmed by scanning transmission electron microscopy (STEM), and in situ methods of EXAFS, synchrotron XRD, XPS, and Resonant Inelastic X-ray Spectroscopy (RIXS). The PtP2 structure has isolated Pt
atoms separated by P2 atoms. In addition XANES, XPS and RIXS indicate a strong electronic modi?cation in the energy of the valence orbitals.

It can be concluded from the Pt-Bi catalyst that intermetallic alloys might be selective for NOCM. Therefore, promoters with higher reduction temperature, such as Mn and Cr, should be used to have stable catalysts at high temperature. Moreover, both Pt-Bi and Pt/CeO2 suggest that selective catalysts for propane dehydrogenation and NOCM may have some correlation. Further studies would be conducted to understand the correlation between the two reactions.