Selective hydrogenation finds many applications in the chemical industry. The high exothermicity of the reaction, together with potential side hydrogenations and hydrogenolysis, however, make high catalytic selectivity a challenge. A common approach to the problem is to use very active metal catalysts (e.g.: Pt/Pd) and boost their selectivity via poisoning and\or dilution with more forgiving metals (e.g: Ag). However, thanks to the development of nanomaterials synthesis we are nowadays able to design catalysts basically to atomic level precision. The newly added degree of freedom permits us not only to re-design the commonly used noble-metal based catalysts, but also bring back to life previously overlooked hydrogenation metals, such as copper. This base metal, in fact, appears to be remarkably promising in poly- to mono-unsaturated conversions, and potentially stable in fouling/oligomerization conditions. However, little is known about Cu particle size effects and the nature of the catalyst selectivity. Herein, we discuss the catalytic behaviour of differently sized (2-10 nm) Cu nanoparticles supported on silica and carbon. We investigated the selectivity and activity of these catalysts for two reactions, namely the gas-phase selective hydrogenation of 1,3-butadiene in presence of a 100-fold excess of propene and the liquid-phase hydrogenation of 3-methyl-1-butyn-3-ol. The catalysts, prepared via thermal decomposition of Cu(NO3)2-impregnated supports, exhibited clear particle size dependent activity and selectivity up to 5-7 nm, with the 7 nm Cu being the most selective one (e.g.: up to 99% in the hydrogenation of 1,3-butadiene to butenes as measured at 95% 1,3-butadiene conversion). We identified the hydrogen insertion step to be the rate determining, while the selectivity was rationalized by exploring the adsorption behaviour of the alkyne/alkadiene vs alkene moieties over Cu. A more in-depth discussion of the reaction mechanism and kinetics will be presented at the conference.

Nanosized copper particles for selective hydrogenation

ACS Spring 2022

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