We have prepared and investigated the structural and mechanistic properties of an array of active Cu/CeO2/ZSM-5 catalysts for the reverse water-gas shift (RWGS) reaction, where the roles of Cu and CeO2 as a promoter were studied under reaction conditions. The concentration of copper was varied between 0 and 10 wt %, while the concentration of CeO2 was varied between 0 and 48 wt % in several permutations of Cu/CeO2/ZSM-5 catalysts. RWGS reactivity trends revealed that all three components of the catalyst system are essential for promoting and sustaining the optimum catalytic activity. The dynamic chemical states of copper and cerium were probed using in situ X-ray absorption spectroscopy (X-ray absorption near-edge structure and extended X-ray absorption fine structure), revealing reduced copper and mostly oxidized ceria in the active state. In situ X-ray diffraction data revealed the presence of copper aggregates, as well as copper within the ZSM-5 lattice. In situ and isotopic switching diffuse reflectance infrared Fourier transform spectroscopy analyses were used to unambiguously establish copper speciation within the ZSM-5 lattice and CeO2 surface sites as participatory in the RWGS mechanism, with surface formate species on CeO2 being a reaction intermediate. Based on a robust set of real-time structural, electronic, and surface chemical data, we proposed a reaction mechanism that involves the participation of all three components of this catalyst system.

The nine-arm inverter integrates two modular multilevel converters (MMCs) into one compact inverter to diminish the number of power semiconductor devices. It can be used for dual-motor driving or connecting two AC power sources in a multi-terminal high voltage direct current (HVDC) system, etc. Although the half-bridge based modular multilevel converter has the fewest components, it is generally not resistant to the DC-side faults. In order to achieve a DC fault blocking capability with high efficiency and low cost, this paper proposes a hybrid nine-arm high-voltage inverter, which is consists of a full-bridge sub-module (FBSM) and a half-bridge sub-module (HBSM). Firstly, the topology, operation modes, and modulation strategy of the proposed hybrid inverter are presented. Then, by analyzing the potential short-circuit current paths between different ports, the ability of the proposed hybrid inverter to block the DC faults is described and the appropriate ratio of HBSM and FBSM is determined to further reduce the number of devices and the losses of the proposed hybrid inverter. Finally, simulation results based on MATLAB/Simulink are provided to demonstrate the effectiveness and feasibility of the proposed hybrid nine-arm high-voltage inverter under normal operation and DC fault condition.