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Abstract

A series of NaY zeolite catalysts with varied Ru loadings was prepared by ion-exchange using Ru(NH₃)₆Cl₃in aqueous solution. During the ion-exchange oxidative hydrolysis was found to occur resulting in oligomeric compounds like Ru red within the zeolite framework. The purple-coloured precursors were transformed into the active state by slowly heating in a N₂/H₂= 1/3 synthesis gas mixture. The Ru/NaY samples proved to be high-temperature and long-term stable NH₃catalysts both at atmospheric pressure and at 20bar. The stability under the reducing reaction conditions is rationalized by the ship-in-the-bottle model, i.e., the zeolite framework prevents the Ru clusters from sintering. When heating in O₂at 723K, Ru was found to segregate to the outer surface forming large RuO₂particles which could easily be rereduced. The various states of the Ru/NaY samples were characterized by a combination of surface-sensitive and bulksensitive methods.