In-Situ Grown Metal Nanocatalysts from Oxide Host Lattices

Catalysis plays a central role in energy conversion and chemical production. High activity and robustness under operational condition is required for practical utilization of catalysts. Especially for high temperature applications such as solid oxide fuel cells and methane steam reforming, catalyst stability is an important issue. This talk presents three different catalyst systems for efficient energy conversion and chemical production. First, I will discuss metal nanoparticles formed by partial decomposition of oxide. This phenomenon, metal exsolution, has been known for some time and is used in formulations of automotive emission control catalysts. The ability to re-dissolve and exsolve the metal via redox cycling has a merit of nanoparticle regeneration. However, the mechanism by which the transition metal is exsolved from the oxide host is still poorly understood. My recent contribution looks into the mechanism for the evolution of the unique metal-oxide dual phase structure. I have used well-defined model systems and detailed structural analysis to characterize the nucleation and exsolution of Ni particles. I will show how interesting properties of resistance against coarsening and carbon fiber formation are linked to the particle-in-a-pit morphology. Second catalyst system is for membrane reactor application. Syngas production via methane steam reforming is an important industrial process by which hydrogen is produced in mass scale. However, it requires high energy input due to endothermic nature of the reaction. Using oxygen transport membrane, one can combine air separation and methane partial oxidation to reduce energy cost. I will show how catalyst can increase the oxygen flux by reducing the surface resistance, and expand the applicability of exsolution concept to proton conducting membranes.