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キーワード:
carbonaceous deposits; deactivation; potassium; Pt black
Platinum in Catalysis
要旨:
Pt black prepared by reduction with HCHO/KOH contains ca. 2% K impurity (Pt/K). It can be removed by washing it with HNO3 (Pt). Transformation of hexane/H2 was studied on these two samples after regeneration (O2/H2) and after exposure to trans–trans-hexa-2,4-diene at 603 K. XPS showed 47% C after this treatment on both samples, but with different carbon structure: more “graphite-like” entities on Pt, and an excess of “atomic” surface C (“C1”) on Pt/K. The loss of activity and changes in selectivity – related to the regenerated state – were less pronounced on Pt/K. The presence of K on Pt: (i) stabilizes chemisorbed hydrogen, (ii) hinders accumulation of “massive” hydrocarbonaceous deposits, (iii) and promotes their removal during regeneration.