Browse Publications Technical Papers 2008-01-0416
2008-04-14

Bridging the Gap between Theory and Experiments - Nano-structural Changes in Supported Catalysts under Operating Conditions 2008-01-0416

Computational approaches have been limited to examining catalytic processes using models that have been greatly simplified in comparison to real catalysts. Experimental studies, especially on emission treatment catalysts, have primarily focused on fully formulated systems. Thus, there remains a knowledge gap between theory and experiments. We combine the power of theory and experiment for atomistic design of catalytically active sites that can translate the fundamental insights gained directly to a catalyst system suitable for technical deployment. In this article, we describe our results on a model platinum-alumina catalyst that is a common constituent of emission treatment catalysts such as three-way, NOx trap, oxidation, and HC-SCR catalysts.
We present theoretical and experimental studies of the oxidation and reactivity of Pt catalyst clusters towards O, CO, and NOx. Our theoretical studies indicate that the reaction energetics are strongly dependent on the size of the clusters as well as the extent of oxidation of the clusters, and the energetics of CO and NO oxidation may be more favorable on the oxidized clusters than metallic clusters because of the weakened adsorption of O, CO and NO. Experimentally, we have observed that the aberration-corrected HA-ADF STEM images of Pt/γ-alumina support show that there are single atoms, 2-3 atom clusters, and several 10-20 atom clusters of Pt.
We also found that the Pt particles size has an impact on CO oxidation initiation and completion temperatures. Substrate effects were studied for equivalent Pt particle size distributions on both θ-alumina and γ-alumina supports. Particle size effects were investigated on Pt/γ-alumina catalysts with Pt particle size distribution centered at 1 nm and 12 nm, respectively. We will describe our results on substrate and Pt particle size effects. In addition, we will also present our study of nano-structural changes in model catalysts on exposure to various reaction conditions.

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