Growth of Thin Film Model Oxide Catalysts
EMSL Project ID
1683
Abstract
Although oxides are widely used to catalyze partial oxidation reactions and the selective reduction of NO, the relationship between catalytic activity and structure remains poorly understood. It has been suggested that defects play a key role in oxide catalysis. Last year we started a DOE Basic Energy Sciences funded project aimed at using high-speed variable-temperature scanning tunneling microscopy (STM) to characterize the structure and stability of reactive sites on oxide catalyst surfaces. The low conductivity of many oxides presents an obstacle to studying oxide surfaces with STM. We will also shortly begin to study MoO3 and V2O5. For these materials, it is planned to overcome the conductivity constraint by depositing thin films of the insulating oxides on conductive substrates. This proposal focuses on collaborating with EMSL staff with expertise in oxide film growth to develop alternative methods for depositing molybdenum and vanadium oxides, with two major goals in mind: 1) develop a proficiency in the MBE oxygen plasma growth techniques developed at EMSL for oxide growth so that similar capabilities can be developed at Yale; 2) grow molybdena and/or vanadia films for study by STM and other surface science techniques at Yale. We are interested in two different substrates, WO3(001) and Au(111). Molybdena forms two crystal structures, the favored alpha phase and a metastable beta phase. In STM and temperature programmed desorption/reaction (TPD/R) studies at Yale, we will then be able to compare the effect of the metal cation (W vs. Mo) on the reactivity without changing the surface structure. Comparison of results for molybdena on Au(111) and WO3 (001) will allow us to determine how the bulk crystal structure of the oxide affects the reactivity of surface sites. Preparing molybdena and vanadia films will also allow us to address the issues raised above about the reactivity and stability of defects on these surfaces.
Project Details
Project type
Exploratory Research
Start Date
2000-02-07
End Date
2001-01-01
Status
Closed
Released Data Link
Team
Principal Investigator