Role of Manganese Oxide in Syngas Conversion to Light Olefins

The key of syngas (a mixture of CO and H-2) chemistry lies in controlled dissociative activation of CO and C-C coupling. We demonstrate here that a bifunctional catalyst of partially reducible manganese oxide in combination with SAPO-34 catalyzes the selective formation of light olefins, which validates the generality of the OX-ZEO (oxide-zeolite) concept for syngas conversion. Results from in situ ambient pressure X-ray photoelectron spectroscopy, infrared spectroscopy, and temperature-programmed surface reactions reveal the critical role of oxygen vacancies on the oxide surface, where CO dissociates and is converted into surface carbonate and carbon species. They are converted to CO2 and CHx in the presence of H-2. The limited C-C coupling and hydrogenation activities of MnO enable the reaction selectivity to be controlled by the confined pores of SAPO-34. Thus, a selectivity of light olefins up to 80% is achieved, far beyond the limitation of Anderson-Shultz-Flory distribution. These findings open up possibilities to explore other active metal oxides for more efficient syngas conversion.