X-ray vision spies copper on the move: Copper ions in zeolites help remove noxious nitrogen oxides from diesel exhaust by catalyzing their reaction with ammonia and oxygen. Paolucci et al. found that these copper ions may move about during the reaction (see the Perspective by Janssens and Vennestrom). Zeolite catalysts generally fix metals in place while the reacting partners flow in and out of their cagelike structures. In this case, though, x-ray absorption spectroscopy suggested that the ammonia was mobilizing the copper ions to pair up as they activated oxygen during the catalytic cycle. Science , this issue p. 898 ; see also p. 866

Intense literature and research efforts have focussed on the exploration of complex hydrides for energy storage applications over the past decades. A focus was dedicated to the determination of their thermodynamic and hydrogen storage properties, due to their high gravimetric and volumetric hydrogen storage capacities, but their application has been limited because of harsh working conditions for reversible hydrogen release and uptake. The present review aims at appraising the recent advances on different complex hydride systems, coming from the proficient collaborative activities in the past years from the research groups led by the experts of the Task 40 ‘Energy Storage and Conversion Based on Hydrogen’ of the Hydrogen Technology Collaboration Programme of the International Energy Agency. An overview of materials design, synthesis, tailoring and modelling approaches, hydrogen release and uptake mechanisms and thermodynamic aspects are reviewed to define new trends and suggest new possible applications for these highly tuneable materials.

Aminopolymer-based sorbents are preferred materials for extraction of CO₂ from ambient air [direct air capture (DAC) of CO₂] owing to their high CO₂ adsorption capacity and selectivity at ultra-dilute conditions. While those adsorptive properties are important, the stability of a sorbent is a key element in developing high-performing, cost-effective, and long-lasting sorbents that can be deployed at scale. Along with process upsets, environmental components such as CO₂, O₂, and H₂O may contribute to long-term sorbent instability. As such, unraveling the complex effects of such atmospheric components on the sorbent lifetime as they appear in the environment is a critical step to understanding sorbent deactivation mechanisms and designing more effective sorbents and processes. Here, a poly(ethylenimine) (PEI)/Al₂O₃ sorbent is assessed over continuous and cyclic dry and humid conditions to determine the effect of the copresence of CO₂ and O₂ on stability at an intermediate temperature of 70 °C. Thermogravimetric and elemental analyses in combination with in situ horizontal attenuated total reflection infrared (HATR-IR) spectroscopy are performed to measure the extent of deactivation, elemental content, and molecular level changes in the sorbent due to deactivation. The thermal/thermogravimetric analysis results reveal that incorporating CO₂ with O₂ accelerates sorbent deactivation using these sorbents in dry and humid conditions compared to that using CO₂-free air in similar conditions. The in situ HATR-IR spectroscopy results of PEI/Al₂O₃ sorbent deactivation under a CO₂-air environment show the formation of primary amine species in higher quantity (compared to that in conditions without O₂ or CO₂), which arises due to the C-N bond cleavage at secondary amines due to oxidative degradation. We hypothesize that the formation of bound CO₂ species such as carbamic acids catalyzes C-N cleavage reactions in the oxidative degradation pathway by shuttling protons, resulting in a low activation energy barrier for degradation, as probed by metadynamics simulations. In the cyclic experiment after 30 cycles, results show a gradual loss in stability (dry: 29%, humid: 52%) under CO₂-containing air (0.04% CO₂/21% O₂ balance N₂). However, the loss in capacity during cyclic studies is significantly less than that during continuous deactivation, as expected.