In situ anomalous small-angle X-ray scattering from metal particles in supported-metal catalysts. II. Results

Information about the metal phase in a supported-metal catalyst can be obtained using anomalous small-angle X-ray scattering (ASAXS). The difference between the scattering profiles for SAXS at two different wavelengths near the metal's absorption edge is essentially the scattering of the metal alone. Novel in situ ASAXS measurements are made on mordenite impregnated with platinum metal while the temperature and composition of gas in the sample cell are changed. Measurements are made 62 times during treatment of the catalyst. The metal particles are assumed to be randomly distributed spheres with N(R)dR = number of spheres with radii between R and R + dR. It is found that N(R) is always a monotonically decreasing function of R, and that the average value of R, obtained from N(R), decreases by a factor of two over the time (approximately 6 h) for which the system is observed.