Bi- and trimetallic Ni catalysts over Al₂O₃ and Al₂O₃-MO_x (M=Ce or Mg) oxides for methane dry reforming: Au and Pt additive effects

The effects of Au and Pt addition (in very low concentrations, 0.2wt%) on the catalytic performances of 4wt% Ni catalysts supported over Al₂O₃ and Al₂O₃-10wt%MO_x (M=Ce or Mg) oxides were studied in the dry reforming of methane (DRM). The properties of the catalysts, before and after long-run tests, were investigated employing N₂ adsorption-desorption isotherms, XRD, H₂-TPR, XPS, TEM, EDX microanalysis and O₂-TPO. It was shown that addition of a small amount of Au and Pt (0.2wt%) to Ni catalyst leads to formation of a synergistic interaction, which induces easy reduction of NiO species and decrease of particle size. It was also found that the small amount of Au and Pt addition plays an important role on catalytic performance of bi-/trimetallic catalysts and carbon poisoning. The improvement of catalytic activity and stability obtained for the trimetallic NiAuPt/Al₂O₃ catalyst was attributed to the formation of high active Ni-Au-Pt nanoparticles, synergistically interacting, where growth of small amount of bamboo-like carbon nanotubes occurs. Conversely, abundant amorphous carbon and both, amorphous and carbon nanotubes, were detected in the bimetallic, NiAu and NiPt, and monometallic Ni alumina supported catalysts.The effect of Al₂O₃ doping with MgO or CeO₂ also significantly improves the catalytic performance of monometallic Ni catalyst and the nature and amount of carbon deposits as well. However, the support effect was weakened in both Mg and Ce doped trimetallic catalysts due to the dominant role of Ni-Au-Pt interaction responsible of the enhanced activity for DRM.