Nitrogen Dissociation via Reaction with Lithium Alloys

Chemical Looping Technology in Mild-Condition Ammonia Production: A Comprehensive Review and Analysis

Ammonia is an efficient and clean hydrogen carrier that promises to tackle the increasing energy and environmental problems. However, more than 90% of ammonia is produced by the Haber-Bosch process, and its enormous energy consumption and CO2 emissions require the development of novel alternatives. Chemical looping technology can decouple the one-step ammonia synthesis reaction into separated nitridation and hydrogenation processes at atmospheric pressure, thereby achieving the mild ammonia synthesis based on renewable energy. The strategy of stepwise reactions circumvents the problem of competing adsorption of N2 and H2 /H2 O at the active sites and provides additive freedom for optimal regulation of sub-reactions. This review introduces the concept and mechanism of chemical looping ammonia production (CLAP), and comprehensively summarizes the state-of-art research from the perspective of reaction pathways and nitrogen carriers. The challenges faced by CLAP and strategies to address them in terms of nitrogen carriers, methods, equipment, and technological processes are also proposed.

Zn Promotes Chemical Looping Ammonia Synthesis Mediated by LiH-Li2 NH Couple

Chemical looping ammonia synthesis (CLAS) is a promising alternative route to ammonia production because of its advantages of avoiding competitive adsorption of N2 and hydrogen source (H2 O or H2 ) and intervening the scaling relations in the catalytic process. Our previous studies showed that NH3 can be synthesized at low temperatures via a CLAS mediated by an alkali or alkaline earth metal hydride-imide couple with the aid of transition metal catalysts. Herein, we demonstrate that a group-IIB metal Zn, which has rarely been studied in the thermal-catalytic process, can significantly promote the performance of the lithium hydride-lithium imide (LiH-Li2 NH)-mediated CLAS process (denoted as Zn-LiH-Li2 NH). The addition of Zn dramatically changes the reaction pathway of the LiH-Li2 NH mediated loop by forming a series of intermediates including Li2 NH, lithium zinc intermetallic compounds (LiZnx ), and a ternary metal nitride (LiZnN). LiZnN together with Li2 NH functions as nitrogen carrier in the Zn-LiH-Li2 NH-mediated CLAS. Because of these properties, the kinetics of N2 fixation is significantly enhanced with a reduction in apparent activation energy from 102 kJ mol-1 to 50 kJ mol-1 . The ammonia production rate reaches 956 μmol g-1  h-1 at 350 °C, which is 19 times higher than that of the neat LiH-Li2 NH-mediated CLAS.

Lithium-based Loop for Ambient-Pressure Ammonia Synthesis in a Liquid Alloy-Salt Catalytic System

The Haber-Bosch process for ammonia (NH₃ ) production in industry relies on high temperature and high pressure and is therefore highly energy intensive. In addition, the activity of the solid transition metal-based catalysts used is typically limited by the scaling relation between activation barrier for N₂ dissociation and nitrogen-binding energy. Here, an innovative Li-based loop in a liquid alloy-salt catalytic system for ambient-pressure NH₃ synthesis from N₂ and H₂ was developed. The looping process consisted of three reaction steps taking place simultaneously. The first step was the nitrogen fixation by Li in the liquid Li-Sn alloy to form lithium nitride (Li₃ N), which floated up and dissolved into the molten salt. The second step was the hydrogenation of the Li₃ N to produce NH₃ and lithium hydride (LiH) in the molten salt. The third step was the decomposition of the LiH to regenerate Li in the presence of Sn. An average NH₃ yield rate of 0.025 μg s^-1 was achieved in an 81 h test at 510 °C and ambient pressure. The floating and dissolution of Li₃ N realized in the liquid catalytic system enabled circumventing the scaling relation exerted on Li, and the remarkable properties of liquid alloy and molten salt offered extraordinary advantages for NH₃ synthesis at ambient pressure.

Facile fabrication of bimetallic Cu–Ag binary hybrid nanoparticles and their application in catalysis

Herein, high efficiency and recyclable Cu–Ag hybrid catalyst (Trp–Cu–Ag) NPs were prepared by the hydrothermal method using l-tryptophan as a reducing agent and protecting reagent.