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Abstract

The intermetallic compound InPd₂ was prepared as single-phase material and used in an unsupported state as catalyst in the semi-hydrogenation of ethyne in a large excess of ethene. InPd₂ showed high activity and selectivity (up to 93%) toward ethene in the temperature range from 478 to 508 K. In addition, the compound revealed high stability during 20 h time on stream at 473 K at 80% selectivity and >90% conversion. Investigations by differential thermal analysis combined with thermogravimetry (DTA/TG) in H₂ and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) exclude the formation of intermetallic hydrides, phase transitions, decomposition, and the presence of elemental palladium. The stability of InPd₂ under reaction conditions allows addressing the influence of electronic factors on the catalytic properties by comparison with Ga–Pd intermetallic compounds. From the joint results of experiments and first-principles calculations, the electronic influence on the catalytic selectivity is found to be minor; selectivity seems to be largely governed by geometric effects – as suggested earlier by the site-isolation concept – as well as the absence of hydridic hydrogen.