Jurriaan Beckers

Palladium-free and ligand-free Sonogashira cross-coupling

Copper nanoclusters catalyse the cross-coupling of alkynes and aryl halides to give the corresponding disubstituted alkynes. No palladium, ligand, or co-catalyst is needed, and products are isolated in good yields (80–85%) and high selectivity. The clusters are simple to prepare, stable and can be applied to a variety of iodo- and bromoaryls. Mechanistic pathways for homocoupling and cross-coupling of alkynes are examined by comparing the activity of different catalyst and co-catalyst combinations. The copper clusters show different catalytic properties than their homogeneous analogues.

Sustainable selective oxidations using ceria-based materials

This Perspective covers sustainable oxidation processes using doped cerias, ceria-supported catalysts and ceria-based mixed oxides. Firstly, we consider the general properties of ceria-based catalysts. We outline the advantages of the ceria redox cycle, and explain the dynamic behaviour of these catalysts in the presence of metal additives and dopants. We then review three types of catalytic oxidation processes: preferential CO oxidation (PROX), oxidative dehydrogenation and the selective oxidations of hydrocarbons and inorganics. The preferential oxidation of CO from hydrogen-rich mixtures is interesting for fuel cell applications. Copper-ceria catalysts, where the copper species are well dispersed and interact strongly with the ceria surface, show good selectivity and activity. The oxidative dehydrogenation of small alkanes is another important potential application. To avoid mixing oxygen and hydrocarbons at high temperatures, one can run the dehydrogenation over a conventional Pt/Sn catalyst while burning the hydrogen formed using the ceria lattice oxygen. This safer redox process allows separate tuning of the dehydrogenation and hydrogen combustion stages. A combinatorial screening showed good results for ceria doped with Pb, Cr or Bi, amongst others. Finally, we also discuss the catalytic selective oxidation of various hydrocarbons, oxygenates and inorganic molecules (H2S, H2 and NH3). The goal here is either product valorisation or waste stream purification. Ceria-based materials show promise in a variety of such selective oxidations.