Abstract
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•Ni–Co/SBA-15 catalysts has been prepared from highly dispersed Ni/Co silicate.•Nickel yields a high dispersed metallic phase and a stable catalytic performance.•A bimetallic phase is formed mainly located in the channels of SBA-15 support.•Co segregation to the surface destabilizes and increases the particle size.
Three mono and bimetallic NixCo1−x/SBA-15 catalysts (x=1, 0.5 and 0) with a total metallic content of 10wt% have been prepared by a deposition–precipitation (DP) method. The catalytic performances on the dry reforming of methane reaction (DRM) have been determined and correlated with their physical and chemical state before and after the catalytic reaction. So, while the nickel monometallic system presents a high activity and stability in the DRM reaction, the Co/SBA-15 catalytic system turns out completely inactive. For its part, the Ni0.5Co0.5/SBA-15 has initially a catalytic performance similar to the Ni/SBA-15 monometallic system, but rapidly evolving to an inactive system, therefore resembling the behavior of the cobalt-based catalyst. The characterization by TEM and in situ XPS techniques has allowed us to ascribe these differences to the initial state of metallic particles after reduction and their different evolution under reaction conditions. So, while after reduction both nickel containing NixCo1−x/SBA-15 catalysts (x=1 and 0.5) present a well dispersed metallic phase, the cobalt monometallic catalyst yields big metallic particles with a heterogeneous distribution of sizes. Additionally, unlike the Ni/SBA-15, the NiCo/SBA-15 system increases during reaction the metallic particle sizes.
Besides indicating that the particle size is a major reason determining the catalytic performances, these results suggest that in the Ni–Co system both metals form after reduction a bimetallic phase mainly located inside the mesoporous channels of SBA-15 support. Under DRM reaction conditions, the cobalt is segregated to the surface of the bimetallic particles, which seems to determine the interaction with the support surface SBA-15. This feature gives rise to a much less stable metallic phase which suffers an important sintering process under DRM catalytic conditions.