Competitive hydrogenation of alkynes and olefins: Application for the analysis of size sensitivity

Abstract

In this study, the researchers applied the competitive hydrogenation of two similar terminal alkynes (or olefins) to develop a new kinetic approach to evaluate size effects in catalytic processes and differentiate active sites. This method is based on the analysis of differential selectivity, using phase trajectories of reactions. An analysis of the phase trajectories shows that the hydrogenation of terminal alkynes occurs on the same type of active sites of palladium catalysts (faces). The negative size effect in alkyne hydrogenation, under the action of palladium catalysts with a particle size of 6.6–24 nm, is associated only with the geometric factor. Contrary to alkynes, hydrogenation of olefins takes place on at least two types of active sites. The reasons for the dependence of the apparent turnover frequency of alkyne hydrogenation on the particle size for Ziegler systems are considered. Moreover, the hypotheses about the catalytically active sites of Pd-P nanoparticles in the hydrogenation of alkynes are discriminated.