(Co2+,Ni2+)2SiO4 Bimetallic Olivines: An Investigation on the Influence of Molar Ratio Composition of the Ni–Co Olivine System for the Heck–Mizoroki Reaction

This study systematically investigates the role of Ni in Co2SiO4 in a bimetallic (Co2+,Ni2+)2SiO4 olivine-type system and the materials’ catalytic efficiency in a model Heck–Mizoroki coupling reaction. Thus, a series of olivines with varying (Co2+,Ni2+)2SiO4 compositions (0–100% Ni) was synthesised and characterised by ICP-OES, FTIR/Raman, P-XRD and XPS analysis. Ideal mixing of metals was achieved with (49:51) Co:Ni. Catalytic testing revealed distinct conversion vs. time profiles, with the (69:31) Co:Ni olivine exhibiting the best overall performance, combining good reactivity with near-perfect selectivity (>99%) and improved stability. Mechanistic pathways were probed through product scope analysis, reactant–product temporal profiling, leaching and radical scavenging experiments. Results suggest a radical-assisted Heck–Mizoroki mechanism. Spectroscopic data correlated Co2+ and Ni2+ incorporation with M1 and M2 site occupancy, where Ni2+ M2 sites enhanced reactant activation and intermediate stability and Co2+ in the M1 site enhanced product release, though also homocoupling in Co2SiO4. Minimal leaching was observed for all bimetallic catalysts. These findings highlight the tunability of bimetallic olivines for C–C coupling reactions via controlled cation distribution.