One percent Pt/KL catalysts containing ion-exchanged cations, for example, calcium (Ca), scandium (Sc), and manganese (Mn), were prepared by chemical vapor deposition. Catalysts were reduced at 500 °C in hydrogen and either cooled and fixed in wax directly, or subjected to H2S poisoning at 20.3 ppm for 2 h prior to cooling and fixing in wax. This prevented oxidation of catalyst samples, allowing for characterization by X-ray absorption near-edge spectroscopy (XANES) at the Soft X-ray Microcharacterization Beamline at the Canadian Light Source, Inc. K-edges of S, K, Ca, Sc, and Mn were examined following normalization of XANES spectra. There are two competing theories for the poisoning mechanism of Pt/KL catalysts. The first involves poisoning of charge-compensating cations located on Pt/KL, which is suggested to prevent the cation from assisting in ring closure of the adsorbed hexatriene intermediate on the Pt surface through an electrostatic interaction. The second mechanism involves direct poisoning of Pt surface by H2S. Once formed, Pt particles are proposed to migrate and agglomerate within KL channels, preventing diffusion of reactants and products to Pt clusters located within L-zeolite channels. XANES did not reveal evidence of an interaction between exchanged cations (e.g., Ca, Sc, or Mn) and sulfur, or between potassium cations and sulfur. Rather, XANES spectra at cation K-edges of freshly activated and activated/H2S-poisoned catalysts were virtually identical. Sulfur K-edge spectra showed line shapes consistent with platinum sulfide. In agreement with our prior study with Pt/KL catalysts, sulfur poisoning appears to involve direct poisoning of Pt, with detachment and agglomeration.
|Title of host publication
|Chemistry Solutions to Challenges in the Petroleum Industry
|Parviz Rahimi, Cesar Ovalles, Yunlong Zhang, Jeramie J. Adams
|Number of pages
|Published - 2019
|ACS Symposium Series
Bibliographical noteFunding Information:
The work carried out at the University of Texas at San Antonio was supported by startup funds provided by the State of Texas and the STARS Program. Research at the Center for Applied Energy Research (CAER) was supported by the Commonwealth of Kentucky. Synchrotron experiments were performed at the Canadian Light Source, Inc., which is funded by the Canada Foundation for Innovation, the Natural Sciences and Engineering Research Council of Canada, the National Research Council Canada, the Canadian Institutes of Health Research, the Government of Saskatchewan, Western Economic Diversification Canada, and the University of Saskatchewan.
© 2019 American Chemical Society.
ASJC Scopus subject areas
- Chemistry (all)
- Chemical Engineering (all)