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Irreversible phase transformation of layered structure into spinel structure is considered detrimental for most of the layered structure cathode materials. Here we report that this presumably irreversible phase transformation can be rendered to be reversible in sodium birnessite (NaxMnO2·yH2O) as a basic structural unit. This layered structure contains crystal water, which facilitates the formation of a metastable spinel-like phase and the unusual reversal back to layered structure. The mechanism of this phase reversibility was elucidated by combined soft and hard X-ray absorption spectroscopy with X-ray diffraction, corroborated by first-principle calculations and kinetics investigation. These results show that the reversibility, modulated by the crystal water content between the layered and spinel-like phases during the electrochemical reaction, could activate new cation sites, enhance ion diffusion kinetics and improve its structural stability. This work thus provides in-depth insights into the intercalating materials capable of reversible framework changes, thereby setting the precedent for alternative approaches to the development of cathode materials for next-generation rechargeable batteries., The irreversible layered-to-spinel phase transformation is detrimental for many cathode materials. Here, the authors show that reversibility can be realized in crystal water containing sodium birnessite by controlled dehydration, leading to enhanced ion diffusion kinetics and improved structural stability.

Fischer–Tropsch synthesis was carried out over precipitated iron-based catalysts with different amounts of CO2 in the feed stream while maintaining both total reaction pressure (1.5 MPa) and partial pressure of H2 + CO (0.75 MPa) using an inert balance gas, N2. The CO2 in the feed stream decreased the rate of hydrocarbon formation, but it had no significant influence on the carbon number distribution of hydrocarbons. The CO2 in the feed stream also suppressed CO2 formation, decreasing both CO conversion and CO2 selectivity. We attribute the decreased reaction rate to the partial competition in the adsorption behavior between CO and CO2 as revealed in the temperature-programmed desorption.

Yellow-colored exhaust gas streams from internal engines or gas turbines, frequently referred to as “yellow plume,” contain nitrogen dioxide (NO2) at concentrations as low as 15 ppm. The process developed in this work for decolorizing the yellow plume is based on reduction of NO2 to NO utilizing a combination of a Pt catalyst and a reducing agent. A stoichiometric excess of carbon monoxide, diesel oil, methanol or ethanol were used as reducing agents. Depending on the type of the reductant, the active temperature window of NO2 reduction was varied with methanol and CO being active at lower temperatures and ethanol and diesel oil at higher temperatures. By changing the Pt loading of the catalysts the active temperature window of NO2 reduction was also changed, higher loading Pt catalysts being active at lower temperatures. This scheme of NO2 reduction process was verified in a pilot-scale test with the real exhaust gas from the gas turbine power plant, showing 96% of NO2 reduction at the stack temperatures of 102–123 °C and at space velocities of 28,000–95,000 h−1 with inherent CO in the exhaust gas as the reducing agent.