Palladium–Tin nanocatalysts in high concentration acetylene hydrogenation: A novel deactivation mechanism

In the present study, tin-promoted Pd/MWNTs nanocatalysts were prepared via polyol method for further application in highly concentrated acetylene hydrogenation. Particle sizes decreased drastically with addition of tin, indicating a narrow particle size distribution. The particle sizes and the associated distribution remained constant, even after aging the nanocatalyst upon the reaction for a long time. Addition of tin to Pd catalysts showed good propensity towards the highly-stabilized catalysts, in particular, at the molar ratios of Sn/Pd more than 0.25 up to 1. To characterize the catalysts examined, TEM, XRD, TPR, XPS, SIM DIS, FTIR and TPO were applied. XPS and XRD experiments confirmed the formation of intermetallic compounds and Pd2Sn alloy, respectively. The results showed that the presence of these structures on the catalyst surfaces were responsible for the higher catalytic performance, especially, for the catalysts with higher molar ratios of Sn/Pd. Also, a novel mechanism was proposed based on which the higher values of Sn/Pd were more unaffected in contrast to deactivation. This was attributed to the lower ability of the catalyst to dehydrogenate carbonaceous species, which in turn, decreased the spillovers of carbonaceous species from the catalyst surface to the support, increasing the life time of the catalyst.