EXAFS on noble metal promoted Co/TiO2

Abstract

During a 5 month project, noble metal promoted Co/TiO2 catalysts for the Fischer-Tropsch process were studied with x-ray absorption fine structure techniques (XAFS). This project was performed during an internship at the ESRF in Grenoble from February to June 2015. The internship is part of the master program Nanomaterials: Chemistry & Physics at the University of Utrecht.

The catalyst that were studied are noble metal (Pt, Ag, Re, Ru) promoted Co/TiO2 catalysts with a cobalt weight loading of approximately 9 wt. % and have a cobalt/noble metal ratio of 0.0143 at. The catalysts used during this project were synthesized and tested during a master project performed in the group of Inorganic Chemistry and Heterogeneous Catalysis before the internship. During this project, turnover frequencies were obtained by measuring the dispersion of the cobalt particles on the catalysts with transmission electron microscopy and catalytic tests under industrial conditions at a temperature of 220°C and a pressure of 20 bar. The noble metal promoted catalyst were found to have higher activities than the unpromoted catalysts. For the ruthenium, platinum and silver catalyst a threefold increase in the apparent turnover frequency was observed, while for the rhenium promoted catalyst a fourfold increase in the apparent turnover frequency was observed.1,2 The aim of this project is to use XAFS to gain a deeper insight into the fundamental reasons of the increased activity of the noble metal promoted Co/TiO2. By the average coordination number and the elements surrounding the noble metal atom, the location of the promoting noble metal was determined. From the EXAFS measurements on the platinum, ruthenium and rhenium promoted catalysts it was concluded that the noble metals were near or at the surface of cobalt particles. For the silver promoted catalyst, small silver particles of ~10 atoms appeared to be present on the surface of the catalyst