Abstract
Effects of calcination treatment on samples of mono-metallic Pd and Pd <sub>77</sub> -Ag <sub>23</sub> alloy with primary particles around 8 nm were studied with the temperature-programmed reduction technique. Temperature profiles of hydrogen consumption for calcined samples from a stream of 10% H <sub>2</sub> in N <sub>2</sub> were monitored by a thermal conductivity detector. Two distinct peaks, i.e., a consumption of hydrogen for PdO reduction and a subsequent desorption of hydrogen from bulk palladium hydride, were observed. The extent of palladium oxidation upon calcinations increased with the temperature of calcination (T <sub>o</sub> ): i.e., chemisorption of oxygen on particle surface upon calcination at T <sub>o</sub> < 373 K, reconstruction into a surface PdO structure at 473 K and incorporation into sublayers to form bulk PdO structure at high T <sub>o</sub> . Minimum temperature (T <sub>r</sub> ) required for reduction of oxidized palladium by the hydrogen stream was generally low (150 K < T <sub>r</sub> < 320 K) and increased with the extent of oxidation. A quantitative measurement of hydrogen desorbed from reduced samples suggested a formation of alloy phase in freshly prepared Ag <sub>77</sub> -Pd <sub>23</sub> primary particles. The freshly prepared alloy was inhomogeneous in composition but became homogeneous upon calcination at T <sub>o</sub> > 673 K.