One step selective hydrogenation of nitroaromatics to obtain symmetric azocompounds with high yields has been performed with a gold supported on cerium oxide catalysts. Au/TiO 2 and Au/CeO 2 catalysts direct the reaction by two different pathways and with different selectivities. In situ FTIR studies reveal that the surface concentration of the intermediate nitrosobenzene is decisive in directing the reaction trough the different reaction pathways. In this way, while on Au/TiO 2 a fast hydrogenation of the nitrosobenzene intermediate leads to a low surface concentration of the nitrosocompound, on Au/CeO 2 nitrosobenzene is more stabilized on the catalyst surface leading to a lower hydrogenation and a higher coupling rate, resulting in high selectivities to azobenzene. On Au/CeO 2 the relative weak adsorption of the azo with respect to the azoxycompound on the catalyst surface, avoids the consecutive hydrogenation of azocompounds to the corresponding anilines until all the azoxy has been consumed. Asymmetric azobenzenes have also been obtained with very high yields on TiO 2 , through the Mills reaction.

The nature of the active sites involved in the gold catalyzed Sonogashira cross-coupling reaction between iodobenzene and phenylacetylene, and in the competitive homocoupling reactions, has been investigated by means of DFT calculations, kinetic measurements, and synthesis of catalysts with different gold surface species. Several catalyst models have been theoretically investigated to simulate gold nanoparticles of different size either isolated, supported on inert materials, or supported on CeO 2 . The mechanistic studies show that IB dissociation occurs on low coordinated Au 0 atoms present in small gold nanoparticles, either isolated or supported, while PA is preferentially adsorbed and activated on Au δ+ species existing at the metal−support interface. When this occurs, the activation energy of the rate-determining step of the Sonogashira reaction, which has been found experimentally to be the bimolecular coupling, is minimized. The product distribution obtained with Au/CeO 2 catalysts containing different ratios of Au 0 /Au δ+ sites confirms the positive role played by cationic gold in the Sonogashira cross-coupling reaction. Importantly, only metallic Au 0 atoms present in gold nanoparticles are required to perform the homocoupling of iodobenzene.

Catalyst design: First principles calculations predict that phosgene can be substituted by dimethyl carbonate (DMC) in the carbamoylation of aromatic amines when using a CeO2 catalyst preferentially exposing the low energy {111} facet. Experimental results confirm the theoretical predictions, and CeO2 nano‐octahedra terminated by low energy {111} facets show high activity and selectivity toward the desired dicarbamoylated product.