Effect of Sn on Isobutane Dehydrogenation Performance of Ni/SiO₂ Catalyst: Adsorption Modes and Adsorption Energies of Isobutane and Isobutene

The reaction of isobutane over Ni/SiO₂ catalyst changes from hydrogenolysis to dehydrogenation when Sn is introduced. The adsorption modes and energies of isobutane and isobutene over the Ni/SiO₂ catalyst with and without Sn addition were determined by in situ FTIR and a novel transient response adsorption approach. In the absence of Sn, isobutane is adsorbed in a double-site mode with H atoms in two methyl groups of isobutane, facilitating hydrogenolysis of isobutane. After the addition of Sn, a single-site adsorption mode with the H atom in the methylidyne group is speculated instead, which is beneficial to the rupture of the C-H bond rather than the C-C bond. Moreover, the double-site adsorption mode of isobutene with the C═C bond and the H atom in a methyl group is turned into single-site mode with the C═C bond after the introduction of Sn. As for the adsorption energy of isobutene, the introduction of Sn leads to an obvious decrease from 74 to 50 kJ mol^-1 and facilitates the prompt desorption of isobutene, resulting in a high selectivity of 81.9 wt %.