Solid-state NMR as a tool for investigating paramagnetic Ni containing heterogeneous catalysts

Butene dimerization to C8 hydrocarbons uses Ni-impregnated silica alumina catalysts with Brønsted acid sites (BAS). Using NMR with trimethylphosphine oxide probes, Ga and Al doped MCM-41 catalysts were studied. Ga doping produced stronger BAS than Al, while identifying strong Lewis acid sites and weaker BAS in all supports. Unlike zeolites, no (TMPO)2H+ dimers formed, enabling easier impregnation. Fewer acid sites in Ga-MCM-41 reduced branched products. The study showed strong BAS importance in selective butene dimerization and established TMPO-NMR for characterizing mesoporous acid sites.