Structure/activity relationships applied to the hydrogenation of α,β-unsaturated carbonyls: The hydrogenation of 3-butyne-2-one over alumina-supported palladium catalysts

The gas phase hydrogenation of 3-butyne-2-one, an alkynic ketone, over two alumina-supported palladium catalysts is investigated using infrared spectroscopy in a batch reactor at 373 K. The mean particle size of the palladium crystallites of the two catalysts are comparable (2.4 ± 0.1 nm). One catalyst (Pd(NO 3 ) 2 /Al 2 O 3 ) is prepared from a palladium(II) nitrate precursor, whereas the other catalyst (PdCl 2 /Al 2 O 3 ) is prepared using palladium(II) chloride as the Pd precursor compound. A three-stage sequential process is observed with the Pd(NO 3 ) 2 /Al 2 O 3 catalyst facilitating complete reduction all the way through to 2-butanol. However, hydrogenation stops at 2-butanone with the PdCl 2 /Al 2 O 3 catalyst. The inability of the PdCl 2 /Al 2 O 3 catalyst to reduce 2-butanone is attributed to the inaccessibility of edge sites on this catalyst, which are blocked by chlorine retention originating from the catalyst’s preparative process. The reaction profiles observed for the hydrogenation of this alkynic ketone are consistent with the site-selective chemistry recently reported for the hydrogenation of crotonaldehyde, an alkenic aldehyde, over the same two catalysts. Thus, it is suggested that a previously postulated structure/activity relationship may be generic for the hydrogenation of α,β-unsaturated carbonyl compounds over supported Pd catalysts.