Chlorine-Tolerant Ruthenium Catalyst Derived Using the Unique Anion-Exchange Properties of 12CaO•7Al2O3 for Ammonia Synthesis

Poisoning is defined as deactivation by the strong adsorption of, usually, impurities on active sites, which is a serious problem in many important catalytic processes. For example, the activity of Ru catalysts is significantly degraded by Cl in ammonia synthesis because of its electron-withdrawing properties. Here we demonstrate that 12CaO center dot 7Al(2)O(3) with subnanometer-sized cages prevents the poisoning of a Ru catalyst by Cl-ions in ammonia synthesis. Conventional supported Ru catalysts exhibit a negligible activity if a tiny amount of Cl-ions remain on the catalyst surface. In contrast, the catalytic activity of Ru/C12A7 is not influenced by Cl-ions even though the amount of Cl in Ru/C12A7 is one order of magnitude higher than that in the conventional Ru catalysts. The Cl resistance of Ru/C12A7 is attributed to the unique anion-exchange properties of C12A7; that is, the Cl-ions are trapped preferentially in the positively charged subnanometer-sized cages of C12A7 instead of OH ions under ammonia synthesis conditions.