Addressing electronic effects in the semi-hydrogenation of ethyne by InPd2 and intermetallic Ga–Pd compounds

• InPd2 is synthesized and catalytically tested in semi-hydrogenation of acetylene.
• InPd2 has superior stability and high selectivity to ethylene.
• The catalytic activity is influenced by the position of d-band.
• The selectivity is mainly governed by the active-site isolation.

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.

Figure optionsDownload high-quality image (156 K)Download as PowerPoint slide