Partially oxidizing methane into syngas via a two-step chemical looping scheme was a promising option for methane transformation. Ce 2 (SO 4 ) 3 was selected to explore the performance and mechanism of methane chemical looping partial oxidation (CLPOM) to syngas. Thermodynamic and kinetic analysis forecast the Ce 2 (SO 4 ) 3 as a promising candidate for CLPOM. Compared with literature, Ce 2 (SO 4 ) 3 not only had an outstanding syngas selectivity, but also an appropriate CH 4 conversion and molar ratio, and CH 4 conversion could reach 90.5 % of thermodynamic result. As revealed via characterization, Ce 2 (SO 4 ) 3 (1 0 2) surface had the highest peak intensity and the migration of lattice oxygen played an important role in CLPOM. Some of them were tend to agglomeration and these small particles were less than 5 μm. Density functional theory calculations demonstrated that CH 4 series dehydrogenation products tended to adsorb at O site and CH 3 → CH 2 + H was the rate-determining step. The reaction of surface lattice oxygen atoms and migration of the internal lattice oxygen atoms could inhibit carbon deposition, promote CH 4 conversion and syngas generation in experiment. Compared with NiO, Ce 2 (SO 4 ) 3 had a lower energy barrier of lattice oxygen migration, which could increase the reaction rate.
The occurrence of NH 3 -SCR (selective catalytic reduction of NO with NH 3 ) reaction on catalyst surface typically requires acid and redox sites. However, the role of acid-redox interaction on NH 3 -SCR performance is still obscure due to complex acidities and entangled acid-redox sites. Herein, three types of model Ce 2 (SO 4 ) 3 -CeO 2 catalysts with distinct interfaces are constructed to reveal the effect of acid-redox interaction on NH 3 -SCR performance. That is, SO 4 2- /CeO 2 -VS (vapor sulfation of ceria) with strong acid-redox interfacial contact, SO 4 2- /CeO 2 -WI (wet impregnation), and SO 4 2- /CeO 2 -SG (solid grinding) with limited interfaces. It is found the redox property is significantly disturbed as a result of the electron-withdrawing effect from the sulfate. Theoretical result unravels that the introduction of Ce 2 (SO 4 ) 3 retards the oxygen vacancy formation over CeO 2 . Due to restricted interfaces in SO 4 2- /CeO 2 -SG, the negative influence from acid sites is greatly alleviated. Further mechanism study discloses the weakened acid-redox interaction actually changes the nature of surface NO x species, resulting in the generation of reactive species (*O-N-O* and cis -N 2 O 2 2- ) and the promotion of surface reaction via Langmuir-Hinshelwood (L-H) mechanism.
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