Investigations on stability and reusability of [Pd(2-pymo)2]n as hydrogenation catalyst

Abstract The MOF [Pd(2-pymo) 2 ] n (2-pymo = 2-pyrimidinolate) was used in the liquid-phase hydrogenation of 1-octene and cyclododecene. Up to a reaction time of 4 h, reactant shape selectivity could be observed, i.e. 1-octene was hydrogenated, but not the more bulky molecule cyclododecene. However, if the catalyst was exposed to hydrogen for more than 4 h, also the hydrogenation of cyclododecene took place. Visually a color change of the catalyst was observed and by XRD it was found that Pd 0 nanoparticles were formed and that the MOF [Pd(2-pymo) 2 ] n was transformed into a new crystalline phase, where the Pd 0 seemed to be accessible. Additionally, Pd 0 was leached out and was available for hydrogenation. When reusing the MOF after reaction times less than 1 h, the reaction rate increased with every reuse. We assume that even in the first 4 h Pd 0 was formed, but could not be detected by XRD. In-situ XRD measurements exposing the MOF to hydrogen in the gas phase showed that the MOF was much more stable in gas phase hydrogenation, because the MOF structure remained intact even when Pd 0 was formed.