PdCu bimetallic catalysts for the selective hydrogenation of 2-methyl-3-butyn-2-ol

Abstract

In selective hydrogenation processes, multiple hydrogenation steps are possible, but the desired end product is not fully saturated. A common is the hydrogenation of alkynes to alkenes. In this work PdCu is investigated as a catalyst for the selective hydrogenation of alkynes. Pd is very active for this reaction, but has a low selectivity, while Cu has a high selectivity towards the alkene product. By diluting the active Pd in Cu an increased selectivity towards the desired product is reached. To achieve this, the Pd and Cu have to be mixed well in each nanoparticle. An incipient wetness co-impregnation synthesis method for PdCu/SBA-15 was optimized by varying heat treatments after impregnation. The aim was to create nanoparticles with an even distribution of Pd and Cu in the particles as well as a uniform size distribution of the nanoparticles over the support. This was achieved by a direct reduction at 600°C after impregnation with a total metal loading of 2-3 wt% and drying under vacuum. Catalysts were prepared with 1:1, 1:5 and 1:10 atomic Pd:Cu ratios. These catalysts, together with monometallic Pd and Cu references, were tested for the selective hydrogenation of 2-methyl-3-butyn-2-ol. The PdCu catalysts demonstrated an improved selectivity towards the alkene product compared to monometallic Pd catalysts. Increasing the Cu content in the bimetallic catalysts led to a higher selectivity. The Pd1Cu1 catalyst also had a similar activity compared to the Pd catalyst, while the Pd1Cu5 and Pd1Cu10 were approximately 10 times less active, per mol Pd. The industrial benchmark Lindlar catalyst, consisting of Pd/CaCO3 poisoned with Pb and quinoline, was also compared to the PdCu catalysts. The Lindlar catalyst had a higher selectivity towards the alkene compared to the regular Pd1Cu1 catalyst, but a lower activity. To fully compare the Pd1Cu1 catalyst was also tested with the addition of quinoline. The catalyst’s selectivity improved to reach 98% towards the desired alkene product, the highest of any catalysts tested in this study.