The catalytic mechanism of hydrogen production via formic acid decomposition by pentamethylcyclopentadienyl (Cp*) rhodium­(III) and cobalt­(III) catalysts with proton-responsive 4,4′-dihydroxy-2,2′-bipyridine (4L) and 6,6′-dihydroxy-2,2′-bipyridine (6L) ligands ([Cp*M­(4L)­(H 2 O)] 2+ and [Cp*M­(6L)­(H 2 O)] 2+ ; M = Rh and Co) were explored using density functional theory calculations. The effect of pH on the protonation state of M­(4L) and M­(6L) ligands was studied using the speciation approach, and the fully protonated dihydroxy-2,2′-bipyridine ligand was found to be the dominated species throughout the catalytic mechanism of formic acid decomposition at pH 2.5. For both Cp*Rh­(III) and Cp*Co­(III) catalysts with 4L or 6L ligands, the β-hydride elimination step was found to be the rate-determining step irrespective of the position of the hydroxyl group on the bipyridine ligand. In the case of M­(6L), both formic acid- and water-assisted hydrogen evolution transition states were considered, and from the computed free energy profile, the water-assisted H2 generation was found to be the most favorable pathway. The electronic origin of the difference in the catalytic efficiency of the chosen catalysts was traced by performing natural bonding orbital analysis. These analyses reveal that the second-order stabilizing interactions and hydricity in the reaction intermediates and transition states play a significant role in altering the energetics of the formic acid decomposition reaction. Furthermore, the calculated activation free energies for the β-hydride elimination step catalyzed by the chosen catalysts were in the range of 15.8 to 20.3 kcal/mol, signifying that these catalysts are promising candidates for hydrogen generation with catalytic activities comparable to its Ir analogue. Especially, Co­(6L) with a relatively low activation energy barrier of 15.8 kcal/mol can be considered as an efficient low-cost catalyst for achieving fast dehydrogenation of formic acid. Overall, the present study paves the way for designing novel catalysts for hydrogen generation via formic acid dehydrogenation.

Theoretical investigations have been performed on hydrogen (H-) bonded complexes of two aromatic amines with anisole to investigate the effect of the methyl substituent on N – H⋯O and N – –H⋯π interactions. Natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) analyses were done to elucidate the nature of H- bonding. In 1:1 complexes, the total interaction energy of N-methylaniline complex is higher than that of aniline complex. The existence of bond critical point between N–H of amine and oxygen of anisole confirms weak hydrogen bonding. The energy decomposition analysis showed the role of CT in stabilizing complexes.

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The catalytic activity of nickel nanoparticles (5% Ni w/w loading) dispersed on different metal oxide supports has been explored for the hydrogenation of furfural. Nickel, supported on reducible oxides (CeO2 and TiO2), displays higher (almost 100%) conversion compared to that on non‐reducible oxide supports (SiO2, Al2O3, Mg3AlOx). H2‐TPR and XPS analyses bring out the influence of metal‐support interaction during the reduction of nickel precursor and their electronic properties. The adsorption and activation of furfural on the catalyst has been studied using infrared spectra and DFT calculations. The reaction proceeds via both ring‐rearrangement and ring hydrogenation pathways, with furfuryl alcohol as the primary intermediate. At higher reaction temperature, reducible oxide supported catalysts, particularly titania, favours deep‐hydrogenated products and higher conversion than non‐reducible oxide supported catalysts. Among all the catalysts, nickel on titania displayed maximum conversion of furfural. TiO2 possessing higher acidity than ceria, favoured ring‐rearrangement of furfuryl alcohol to cyclopentanone at high temperatures, while the latter retarded reduction of cyclopentanone due to blockage of active‐sites by unreacted furfural and strongly adsorbing intermediates. The combined effects of the electronic‐state of supported metal and surface acidity of catalyst provide a new strategy to tune catalytic properties for selective transformation during hydrogenation of furfural.