Effects of calcination treatment on samples of mono-metallic Pd and Pd77-Ag23 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% H2 in N2 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 o):  i.e., chemisorption of oxygen on particle surface upon calcination at T o < 373 K, reconstruction into a surface PdO structure at 473 K and incorporation into sublayers to form bulk PdO structure at high T o. Minimum temperature (T r) required for reduction of oxidized palladium by the hydrogen stream was generally low (150 K < T r < 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 Ag77−Pd23 primary particles. The freshly prepared alloy was inhomogeneous in composition but became homogeneous upon calcination at T o > 673 K.

evolution strongly depends on gas adsorption conditions, and we still do not know the exact correspondence between the gas desorption site and the gasification site. Further work is required to clarify this point. ConclusionsTPD patterns of H20-gasified and 02-chemisorhed chars from various types of coals showed some sharp desorption peaks and/or broad desorptions. The appearance of a sharp peak depends on whether the sample contains catalytically active mineral matter or not. The gasification mechanism for the formation of the sharp peak was closely associated with the mechanism for the gasification reaction catalyzed by mineral matter. The broad desorption patterns were common for both raw and demineralized chars, and they were very similar among various chars. There-fore, this desorption emanates from the carbon substrate itself. The effect of the char type on the formation of surface oxygen complex is not so significant. The TPD experiments on chars prepared under different adsorption conditions (as in H20-gasified and 02-chemisorbed chars) revealed different kinds of useful information on the surface oxygen-containing complexes.Acknowledgment. This work was supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture, Japan, Special Project for Energy (No. 60040034). Acknowledgment is also made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support of this activity.Registry No. H20, C02,

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