Molecular beam scattering measurements on anatase TiO2(001) and rutile TiO2(110)
EMSL Project ID
17500
Abstract
Heterogeneous catalysis is a key industry in our modern technological world. Despite the pertinent economic impact of heterogeneous catalysis, the mechanistic understanding of chemical reaction dynamics/kinetics is still surprisingly poor. Multi-component catalysts are necessarily optimized by intelligent trial-and-error approaches. Therefore, we propose studies on planar model catalysts with the aim of obtaining a more comprehensive mechanistic understanding, including the structure-activity relationship (SAR) on “simpler” but well-defined model systems by means of surface chemistry techniques. The ultimate goal is to tune structural properties for optimizing the electronic, mechanical, and catalytic performance. Proposed is a surface science study of the adsorption dynamics and kinetics of probe molecules (CO, NO, O2, CO2, H2O) on the catalytically more active anatase polymorph of TiO2(001). Supplementary rutile TiO2(110) will be considered. The probe molecules are important for the CO oxidation and NOx reduction reactions. Furthermore, reactive scattering measurements will be conducted to further characterize the CO oxidation reaction on Au nanoclusters supported on anatase TiO2(001). Thus, we will attempt to bridge the structure gap in catalysis. We will use molecular beam scattering techniques to map the gas-surface energy transfer mechanisms and surface reactions as well as thermal desorption spectroscopy (TDS), He atom TDS, and molecular beam relaxation spectroscopy (MBRS) to study the adsorption kinetics. The TiO2 samples will be characterized by a variety of techniques, including X-ray diffraction (XRD), low energy electron diffraction (LEED), auger electron spectroscopy (AES), and elastic He atom scattering. The results will be compared with prior measurements on rutile TiO2 from the PI’s group as well as published work from other groups to address the question of whether anatase samples are indeed more reactive than rutile surfaces for a given adsorption/reaction process, as proposed in a number of studies.
Significance/broader impact
Besides the most well-known application of Au-TiO2, low temperature CO oxidation used for exhaust emission reduction in the three-way catalyst, numerous other industrial applications have been documented. Au-based catalysts enhance propylene epoxidation and are used in material science applications such as CO, NOx, NH3, and trimethylamine sensors. PROX (preferential oxidation of CO in the presence of excess hydrogen) catalysts are another example. PROX is important for lean-burn gasoline engines (trucks), which have a higher energy consumption efficiency than gasoline-powered engines, as well as for fuel cells. Long-term stability of nano-gold catalysts for PROX has been reported. Furthermore, the rather inexpensive TiO2 material is used for batteries, photo-catalytic water decomposition, as a pigment in paints and cosmetics, as a protective coating, as a biocompatible material, for the conversion of solar energy and for SCR (selective catalytic reduction) of NOx specifically on anatase TiO2 powder catalysts. Thus, numerous applications with an impact on our daily lives are already known for the systems we will study.
PNNL support (Dr. Laxmikant Saraf) is required to manufacture and characterize anatase samples.
Project Details
Project type
Exploratory Research
Start Date
2006-03-10
End Date
2007-01-13
Status
Closed
Released Data Link
Team
Principal Investigator