Fig. 4: NMR characterization of the Ru@PGS catalyst.

a, 2D HSQC NMR (400 MHz, MeOD) spectrum of the Ru@PGS catalyst after reaction with H2/CO2. b, Solid-state 13C CP-MAS NMR (125.7 MHz) spectrum before reaction with H2/CO2. c, Solid-state 13C CP-MAS NMR (125.7 MHz) spectrum after reaction with H2/CO2, showing the presence of ammonium formate species. The asterisks (*) indicate spinning side bands. These spectra evidence the formation of ammonium formate species on the catalyst when hydrogenation reactions are performed using H2/CO2.