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Ye XuAssociate ProfessorDept. of Chemical EngineeringLouisiana State UniversityBaton Rouge, LA
Cerium dioxide (CeO2), or ceria, is an Earth-abundant reducible oxide. The Ce cations can convert readily between the +4 and +3 oxidation states, and upon partial reduction of the oxide, the O anions acquire notable mobility in the bulk. Ceria also anchors metal particles strongly against thermal agglomeration. These properties make ceria a material of choice compared to other oxides when it comes to formulating catalysts for redox reactions such as water-gas shift and total/partial oxidation of hydrocarbons, where oxidative dehydrogenation can play a major role.
In this talk, I will discuss another aspect of ceria catalysis, namely Lewis and sometimes Brønsted acid-base surface chemistry, with Ced+ serving as acid sites and Od- as base sites. It will be illustrated with how acetaldehyde interacts with CeO2(111) using a combination of spectroscopic and theoretical evidence. This understanding is then used to explain ambient-temperature aldol condensation of acetaldehyde, which does not involve a Mars-Van Krevelen mechanism typical of high-temperature reactivity on ceria. Furthermore, I will demonstrate that the reverse of condensation reactions, or hydrolysis, can be effectively catalyzed by ceria for a wide range of organic compounds via pathways including dephosphorylation and deamidation, which rest also on acid-base interactions. These reactions parallel the actions of natural enzymes such as phosphatase and peptidase, highlighting the intriguing potential of ceria for technological applications beyond traditional catalysis, in fields such as biomedicine, nanotechnology, and environmental remediation.