Activity-Composition Relationships of Fe-Ni-Cu Ternary Nanoparticles Supported on Al2O3 as Three-Way Catalysts for NO Reduction

Ternary FexNiyCu1-x-y (x, y: molar fractions) metal nanoparticles supported on Al2O3 were prepared by H-2-reduction treatment at 900 degrees C and investigated as three-way catalysts free of precious metals (Rh, Pd, and Pt). As-prepared nanoparticles consisted of nearly homogeneous alloys, whereas their surfaces were partially oxidized. Further oxidation occurred upon exposure to a reaction gas mixture (NO-CO-C3H6-O-2-H2O) at lower temperatures of <= 400 degrees C. At higher temperatures, however, Cu and Ni regenerated the active metallic states and reconstructed alloy nanoparticles, whereas most Fe was fully oxidized and formed a spinel-like Fe-Ni oxide phase. A contour map analysis revealed that the NO reduction activity and the fraction of metallic states were strongly dependent on the metal composition (x and y). Among the compositions investigated in the ternary system, near-equimolar catalysts (0.2 <= x <= 0.33, 0.2 <= y <= 0.33) exhibited the highest activity and the highest fraction of metallic states. The regenerability and stability of metallic-state Cu and Ni species were improved by the copresence of Fe-Ni oxide, which was found to promote the oxidative adsorption of C3H6 as a carboxylate on the Al2O3 surface. A subsequent reaction with NO formed N-2, which converted the carboxylate to CO and NCO species close to the perimeter of the metal-support interface. As oxidative C3H6 adsorption consumes oxygen, this provides a more reductive surface environment, thereby enhancing the stability of the active metallic state.

Automated summary

Ternary FexNiyCu1-x-y metal nanoparticles supported on Al2O3 were investigated as three-way catalysts without precious metals. Near-equimolar catalysts exhibited the highest activity and the highest fraction of metallic states. The presence of Fe-Ni oxide improved the regenerability and stability of metallic-state Cu and Ni species, enhancing the stability of the active metallic state by promoting the oxidative adsorption of C3H6.