(135c) Tuning Bulk and Surface Properties of Mixed Metal Oxides for Partial Oxidation Applications via Chemical Looping Schemes

Authors: 
Li, F., North Carolina State University
Using metal oxide based oxygen carriers as the reaction intermediate, the chemical looping strategy intensifies carbonaceous fuel conversion processes via a cyclic redox scheme. Although conventional chemical looping combustion processes aim to fully oxidize carbonaceous fuels for carbon capture, a similar principle can be applied to generate value added products such as syngas and olefins. The product selectivity requirement calls for oxygen carriers, also known as redox catalysts, with tailored bulk and surface properties.

Monometallic oxides of Cu, Fe, or Ni are among the most frequently investigated oxygen carriers for chemical looping. However, they have limited applicability for selective product generations. The present study discusses the limitation of monometallic oxides for such applications as well as the potential advantages of mixed metal oxide based redox catalysts. Specifically, iron and manganese containing mixed oxides are exemplified for methane partial oxidation, oxidative dehydrogenation (ODH) of ethane, and water/CO2-splitting. Redox catalyst selection criteria and the effect of its bulk and surface properties on redox activity and product selectivity are also presented. The underlying redox reaction pathways and mechanisms are also revealed by experiments and simulations. Compared to traditional heterogeneous catalysts, we demonstrate that mixed metal oxide based redox catalysts can potentially be more selective. Moreover, significant decrease in redox reaction temperatures can be achieved by tailoring the bulk and surface properties of the mixed oxides. In terms of methane partial oxidation, we report excellent redox activity and over 90% syngas selectivity at temperatures as low as 600 °C. In terms of ethane ODH, over 70% single-pass olefin yield was achieved by redox catalysts with tailored surface properties. Rationally designed, iron containing mixed metal oxides demonstrated close to 100% water and CO2 splitting efficiencies.