Abstract
Despite the extensive studies on the adsorption and activation of hydrogen over metal oxides, it remains a challenge to investigate the structure-dependent activation of hydrogen and its selectivity mechanism in hydrogenation reactions. Herein we take spinel and solid solution MnGaO(x) with a similar bulk chemical composition and study the hydrogen activation mechanism and reactivity in syngas conversion. The results show that MnGaO(x)-Solid Solution (MnGaO(x)-SS) is a typical Mn-doped hexagonal close-packed (HCP) Ga(2)O(3) with a Ga-rich surface. Upon exposure to hydrogen, Ga-H and O-H species are simultaneously generated. Ga-H species are highly active but unselective in CO activation, forming CH(x)O, and ethylene hydrogenation, forming ethane. In contrast, MnGaO(x)-Spinel is a face-centered-cubic (FCC) spinel phase featuring a Mn-rich surface, thus effectively suppressing the formation of Ga-H species. Interestingly, only part of the O-H species are active for CO activation while the O-H species are inert for olefin hydrogenation over MnGaO(x)-Spinel. Therefore, MnGaO(x)-Spinel exhibits a higher activity and higher light-olefin selectivity than MnGaO(x)-SS in combination with SAPO-18 during syngas conversion. These fundamental understandings are essential to guide the design and further optimization of metal oxide catalysts for selectivity control in hydrogenations.