Influence of composition and morphology of the active phase on the catalytic properties of cobalt-nickel catalysts in the steam reforming of ethanol

Abstract

Potassium promoted monometallic and bimetallic cobalt-nickel catalysts with CeO2 support were characterized in the fresh, reduced and after steam reforming of ethanol (SRE) form. TEM studies of reduced catalysts showed the formation of Co0 or Ni0 forms of active phase with fcc structure in the monometallic catalysts and Co–Ni alloys (fcc) with different proportion Co and Ni in the bimetallic catalysts.Among all tested catalysts, the nickel catalyst indicated the smallest crystallites of active phase (8.4 nm), while the cobalt catalyst indicated the largest crystallites of active phase (12.2 nm). The more cobalt in the active phase of catalysts was, the larger the crystallite size of active phase were.The catalytic studies showed that the increase in the content of nickel in the active phase of catalysts increased the selectivity of the SRE to methane, while the increase in the content of cobalt in the active phase caused an increase in the production of acetaldehyde and acetone. Furthermore, the more nickel in the active phase was, the more stable catalysts were.After 24 h work of catalysts in the SRE, nickel and Co–Ni (fcc) active phases were stable forms under SRE conditions, while the cobalt active phase was observed in two forms: metallic cobalt (fcc) and cobalt oxide (CoO). Moreover, on the cobalt catalyst dominated the encapsulating carbon deposit, whereas on the nickel catalyst the fibrous deposit was dominated. Encapsulating carbon deposit cause faster deactivation of the catalyst than fibrous deposit which explained the various stability of both catalysts in the SRE.