Dry reforming of methane over Ni–ZrOx catalysts doped by manganese: On the effect of the stability of the structure during time on stream

Abstract

Ni–Mn–ZrOx catalyst prepared by a one-step urea hydrolysis method was tested in the dry reforming of methane (DRM) reaction at medium temperature. The catalyst was characterized by H2-TPR, CO2-TPD, XRD, XPS, TGA, Raman, and TEM. On Ni–Mn–ZrOx catalyst, the catalytic activity increased with time on stream, while a decrease was observed on Ni–ZrOx catalyst. In order to understand this phenomenon, the catalysts were characterized at pre-reaction and during reaction for different time on stream such as 100 min, 300 min, and 480 min. According to the XPS results, it was shown that the Zr species on Ni–ZrOx were reduced during the reaction, whereas the Zr species was almost in equilibrium on Ni–Mn–ZrOx catalyst. In combining the results of XRD and activity in DRM, we can conclude that a stable ZrO2 structure on Ni–Mn–ZrOx catalyst might promote the redox of nickel species during the reaction, and further promote the redistribution of nickel species. However, on the Ni-ZrOx catalyst, the unstable ZrO2 support might result in a decrease of surface nickel content while an increase of Ni particle size, thus led to a decrease of activity for DRM.