The Oxidation of Ru in a carbon supported Pt-Ru catalyst
C. Roth (1), T. Hartmann(2)
(1) Angewandte Physikalische Chemie, FB Biologie, Chemie, Pharmazie Physikalische und Theoretische Chemie, FU Berlin, Germany.
(2) STOE & Cie GmbH Darmstadt, Germany
Preliminary tests with the STOE IN-SITU HT2 (Figure 1) to observe the temperature calibration by investigating the phase transitions from a to b-quartz (Figure 2) at 573 °C and from orthorhombic to cubic celestine at 1150 °C (Figure 3) had been carried out with a steady flow of 0.06 l/min N2 in a quartz capillary with 1.5 mm inner diameter for the first, and sapphire capillaries (1 mm diameter) for the latter experiment.
Though these results had already been very encouraging, the combination of the new STOE INSITU HT2 and reactive gases had still to prove functionality. Therefore a series of test measurements have taken place in the laboratories of the Applied Physical Chemistry group at the FU Berlin.
30 to 40 mm3 of a carefully ground carbon supported Pt-Ru catalyst 1) has been fixed between two pads of rock wool in the middle of a quartz capillary with 1.0 mm inner diameter. Then the capillary has been mounted in the STOE INSITU HT2, a flow of 0.5 l/min N2 has been led through the chamber to protect the graphite heating element from ignition. O2 as reactive gas streamed through the capillary with a flow of 0.03 ml/min. The heating rate has been chosen to 5 °C/min.
X-ray patterns from the catalyst exposed to O2 at room temperature, 200 °C, 250 °C and 300 °C have been taken on STOE STADI P powder diffractometer with a sealed molybdenum tube, Ge(111) monochromator yielding pure Mo Ka1 radiation and a Dectris MYTHEN 1K detector (1 mm chip), the X-ray patterns are shown in Figure 4.
Due to the catalyzing effect of Pt, an exposure to pure O2 at 300°C led to a complete combustion of the sample. The big hump at 10° 2q is a signal from the capillary material.
The measurement at room temperature (Figure 5) shows only the reflections of the rather crystalline Pt – Ru nanoparticles which are too small to yield sharp reflections.
At 200 °C and 250 °C the oxidation (and tempering) of the Ru particles starts, additional reflections appear for RuO2 and Ru (Figures 6 and 7).
As a summary, it could be demonstrated that the STOE INSITU HT2 fulfills all requirements to be the first commercially available in-situ heating chamber in Debye-Scherrer mode for small sample amounts in a temperature range from RT to 1600 °C and gas flows (reactive or protective) between 0.01 to 0.1 ml/min.
The STOE IN SITU HT2 fits on all vertical mounted STOE STADI P and STADI MP diffractometers and is fully computer-controlled in the newest WinXPow software version.
1) C. Roth, N. Martz, H. Fuess, ‘Characterization of different Pt-Ru catalysts by X-ray diffraction and transmission electron microscopy’, Phys. Chem. Chem. Phys. 3 (2001) 315-319.