Characterization and catalytic activity for ammonia synthesis of ruthenium ion-exchanged zeolites

Ruthenium metal on a zeolite support was found to be active for the catalytic synthesis of ammonia from dihydrogen and dinitrogen at temperatures between 300 and 450{dollar}spcirc{dollar}C and at atmospheric pressure. A triply-promoted iron catalyst exhibited a lower activity under similar conditions. Upon various pretreatment conditions, the ruthenium metal crystallites were either located within the pore structure or on the external surface of the zeolite microcrystals. The catalyst with the ruthenium metal particles located in the pore structure of the zeolite exhibited a higher activity than the catalyst with the ruthenium crystallites on the external surface. Variation of the exchangeable alkali-metal cations altered the activity of the internal ruthenium catalyst. Using Sanderson's Electronegativity calculations for the internal ruthenium zeolite, a relationship was found between the activity for ammonia synthesis of ruthenium zeolites of varied elemental compositions and the effective oxygen charge.