User Program study with R. England of Cummins Engine Co.
| The catalytic
activity is to a large extent controlled by the surface area of the
active components. Upon extended operation at high temperatures, the
surface area of some of these components decrease, reducing the
activity of the catalyst. Transition frequencies and bandwidths of
Raman bands of support materials are sensitive to the surface area of
these active components. One percent doping of Pt can
significantly alter the Raman Bands of the substrate. The band
broadening is an indication of the relaxation process with surrounding
lattice modes, and the correlation length is a function of the
crystallite size of the Pt. Raman vibrational spectroscopy has been
used to characterize surface adsorbing species. In this study, the goal was to test the correlation of the Raman response with a physical measurement of the catalyst crystal size in the bulk material. Calibration of Raman using XRD and TEM will permit Cummins Engine to subsequently use the Raman technique as a particle size probe to delineate catalyst degradation pathways which are critical in developing a fundamental under-standing of aging mechanisms in NOx/SOx absorbers. The new Philips X’Pert Pro MPD Diffractometer was used to scan the (200) Pt peak on titania substrates, which were corrected for instrumental broadening by the (220) reflection of Si. Good correlation was observed between the XRD and Raman tech-niques for specimens containing 3.62wt%Pt on titania. Raman data were also obtained for 1.66 wt%Pt. TEM results for one specimen confirmed the XRD crystallite sizes. |
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Acknowledgments
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