Propyne and 1,3-butadiene adsorption and co-adsorption over palladium catalysts

The adsorption of propyne, 1,3-butadiene and the co-adsorption of propyne and 1,3-butadiene has been studied over a series of palladium catalysts. The adsorption of propyne shows a “secondary” adsorption region typical of hydrocarbon adsorption over supported metal catalysts. Hydrogenation occurs via the hydrogen associated with the β-palladium hydride formed during reduction. A support effect is seen with the titania support reducing the stability of the palladium hydride resulting in a lower hydrogen concentration in the titania supported hydrides. The behaviour of 1,3-butadiene is similar to that found with propyne. The catalyst with the lowest dispersion, as measured by carbon monoxide adsorption, has the highest butadiene adsorption and vice versa, whereas propyne adsorption followed the same trend as carbon monoxide. This behaviour is linked to the mode of adsorption and site requirements. Sequential adsorption revealed that the catalysts had sites that were specific to each adsorbate. Co-adsorption revealed a reduction in adsorption for both gases but with a larger reduction for 1,3-butadiene due to site requirements.