Preparation of trimetallic Pt-Re-Ge/Al2O3 and Pt-Ir-Ge/Al2O3 naphtha reforming catalysts by surface redox reaction
Résumé
Preparation of trimetallic Pt-Re-Ge/Al2O3 and Pt-Ir-Ge/Al2O3 naphtha reforming catalysts by means of a surface redox reaction (namely the catalytic reduction method), was studied by varying the concentration of Ge. The catalytic reduction method was chosen in order to favor the interaction of Ge with the active Pt-Re and Pt-Ir phases. The results shows that the deposition of Ge on the bimetallic catalysts does not seemingly depend on the nature of the metal phase (Pt-Ir or Pt-Re). The test reactions indicated that Ge addition modified the properties of both the metal and acid functions of the bimetallic catalysts. The modification of the acidity is due to the deposition of part of Ge on the support. The n-C-7 reforming results show that Pt-Re-Ge/Al2O3 and Pt-Ir-Ge/Al2O3 catalysts with low Ge contents (<= 0.3%) have similar catalytic performances (toluene yield, C-1-C-4 formation, coke deposit) as the presulfided bimetallic samples. This effect is attributed to an efficient passivation of hydrogenolytic activity at low Ge contents. At higher Ge contents a drastic decrease of the toluene yield is observed due to a strong poisoning of the metal phase and the formation of isolated Ge species.