Ru-Ni bimetallic catalyst supported on CeO₂ boosts chemoselective methoxycarbonylation of olefins

In this study, the bimetallic RuM-CeO₂ (M = Ni, Fe, Cu, K and Cs) catalysts were facilely fabricated by taking the commercially available CeO₂ (99.95 % metals basis, Aladdin, < 50 nm of diameter) as the support. They displayed distinct catalytic performance, especially the chemo-selectivity, on the methoxycarbonylation of styrene with CO and CH₃OH. Impressively, Ru₂Ni_0.6-CeO₂ provided an up to 90.1 % yield of methyl phenylpropionate with satisfied linear selectivity (L/B = 91/9). The characterization and mechanistic results demonstrated that the doping of proper amount of Ni species enriches the local oxygen vacancy (Vö) at the surface but slightly reduces the charge at Ru sites, thereby modulating the interfacial Lewis acid − base pair (Ru-O-Ce-Vö) for catalysis. It thus enhances the CH₃OH dissociation, leading to high coverage of OCH₃ species with low adsorption energy and relatively weak acidity. Further, the insertion of CO becomes readily due to the weak Ru-CO affinity at electron-deficient Ru center therein. As such, the apparent activation energies (E_a) of styrene methoxycarbonylation over Ru₂-CeO₂ (71.2 kJ mol⁻¹) is nearly half-reduced by doping Ni element (Ru₂Ni_0.6-CeO₂: 37.5 kJ mol⁻¹). Meanwhile, the competitive side reactions at the surface of Ru₂Ni_0.6-CeO₂ is inhibited without sufficient acid strength and acid sites. Both aromatic olefins and cyclic olefins were well tolerated under such a system.