Sourav Sagar, Wang Yixiao, Kiani Daniyal, Baltrusaitis Jonas, Fushimi Rebecca R, Wachs Israel E
Biological and Chemical Science and Engineering, Energy Environment Science & Technology, Idaho National Laboratory, Idaho Falls, ID, 83415, USA.
Department of Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, PA, 18015, USA.
Angew Chem Int Ed Engl. 2021 Sep 20;60(39):21502-21511. doi: 10.1002/anie.202108201. Epub 2021 Aug 24.
The complex structure of the catalytic active phase, and surface-gas reaction networks have hindered understanding of the oxidative coupling of methane (OCM) reaction mechanism by supported Na WO /SiO catalysts. The present study demonstrates, with the aid of in situ Raman spectroscopy and chemical probe (H -TPR, TAP and steady-state kinetics) experiments, that the long speculated crystalline Na WO active phase is unstable and melts under OCM reaction conditions, partially transforming to thermally stable surface Na-WO sites. Kinetic analysis via temporal analysis of products (TAP) and steady-state OCM reaction studies demonstrate that (i) surface Na-WO sites are responsible for selectively activating CH to C H and over-oxidizing CH to CO and (ii) molten Na WO phase is mainly responsible for over-oxidation of CH to CO and also assists in oxidative dehydrogenation of C H to C H . These new insights reveal the nature of catalytic active sites and resolve the OCM reaction mechanism over supported Na WO /SiO catalysts.
催化活性相的复杂结构以及表面-气体反应网络阻碍了人们对负载型Na₂WO₄/SiO₂催化剂上甲烷氧化偶联（OCM）反应机理的理解。本研究借助原位拉曼光谱和化学探针（H₂-TPR、TAP和稳态动力学）实验表明，长期以来推测的结晶态Na₂WO₄活性相不稳定，在OCM反应条件下会熔化，部分转变为热稳定的表面Na-WOₓ位点。通过产物的时间分析（TAP）和稳态OCM反应研究进行的动力学分析表明：（i）表面Na-WOₓ位点负责将CH₄选择性地活化生成C₂H₆，并将CH₄过度氧化生成CO；（ii）熔融的Na₂WO₄相主要负责将CH₄过度氧化生成CO，并且还协助将C₂H₆氧化脱氢生成C₂H₄。这些新的见解揭示了催化活性位点的本质，并解析了负载型Na₂WO₄/SiO₂催化剂上的OCM反应机理。
