Insights into the deactivation and reactivation of Ru/TiO2 during Fischer-Tropsch synthesis

Abstract

The catalytic performance of Ru/TiO2 for the production of hydrocarbons via Fischer–Tropsch synthesis (FTS) has been evaluated in this work. Ru/TiO2 exhibits high CO conversion rates (523 K, 2.5 MPa H2, 1.25 MPa CO) that decrease significantly with time-on-stream. To recover the initial catalytic performance, different treatments using H2 or air have been tested. The evolution of the catalyst structure during FTS and after the re-activation protocols have been explored by a combination of ex situ and in situ techniques. Ru agglomeration, oxidation, and formation of Ru–volatile species are not responsible for the observed deactivation. However, Raman and infrared (FTIR) spectroscopy have confirmed the presence of coke and alkyl chains on the spent catalysts. These species hinder the adsorption of the reactants on the active sites and are the primary reason for the observed decrease in the catalytic activity. These carbonaceous species can be removed by severe thermal treatments in air. However, this latter treatment drastically alters the morphology of the Ru/TiO2, which leads to a substantial loss of catalytic activity.