Impacts of dopants on the catalytic activity of geometrically well-defined $CeO_2$ -based Nanoparticles

Abstract

$CeO_2$ (ceria) has attracted much attention in applications of chemical and electrochemical catalysis given its unusual surface redox chemistry in combination with high oxygen storage capacity. Over the past few decades, there have been many attempts to improve the reactivity of ceria by tailoring its nanoscale architecture. However, the influence of dopants on the inherent catalytic activity of ceria was rarely studies and even their conclusions remained controversial. This is partly because that most of the previous studies used ill-defined particle structures in terms of morphology, which may strongly affect catalytic performances of ceria nanoparticles. Here, we address this issue by synthesizing particle with nearly identical geometries, while varying a choice of rear-earth (RE) dopants. This, in combination with DFT calculations and quantitative reactivity tests, enables to understand the true impacts of dopants on ceria catalysis. Both undoped and RE-doped $CeO_2$ nanoparticles were synthesized by means of a EDTA-citrate complexing method. Precise control of accessible process parameters such as pH value, and the ratio of precursors allowed maintaining the key geometric factors (e.g., shape, size and surface area) of ceria particles constant. The physical and chemical at-tributes of each catalyst were characterized using a broad range of analytical tools, such as TGA, XRD, TEM, BET and ICP-MS. The catalytic reactivity of RE-doped ceria has been tested for CO oxidation reaction in a fixed bed reactor with a gas mixture of 0.5% CO and 20% $O_2$ in Ar with structurally controlled catalysts. Our results showed the negative effects of RE dopants on reactivity of ceria nanoparticles, in contrast to other previous literatures. With aid of DFT simulation, we were able to reveal that oxygen vacancy formation energy is a key descriptor on ceria catalysts toward CO oxidation and obtain new candidate dopant compositions for achieving high performance ceria-based catalysts.