Chemical Looping Ammonia Synthesis with High Performance Supported Molybdenum-based Nitrogen Carrier

Abstract

Ammonia is not only a vital source of fertilizers production, but also a hydrogen carrier with high energy density, which has the potential to replace the traditional fossil fuels. However, the industrial route for ammonia production (Haber-Bosch process) is a highly energy-intensive process owing to the harsh operating conditions requirement. It is important to develop a novel ammonia synthesis process with mild operating conditions. Chemical looping ammonia synthesis (CLAS) is known to be an innovative and environmentally-friendly low-pressure ammonia synthesis technology, which separates the overall ammonia synthesis reaction into nitrogen release and replenish reactions facilitated with a nitrogen carrier (NC). NC with high efficiencies is the key to the the practical feasibility of CLAS technology. In this work, the supported molybdenum-based NCs were prepared with ammonium molybdate, hexamethylenetramine, and ZSM-5 zeolites through a facile pyrolysis method at different temperatures, and the performance of N-release, N-fixation, and the cyclic CLAS of NCs were studied in detail. The results indicate that the supported molybdenum-based NC pyrolyzed at 450 ℃ outperformed other NCs with an average NH3 production rate of ca. 20000 μmol•g −1 •h −1 , which is two or three orders of magnitude higher than that of the known metal nitrides under similar conditions. Bulk and surface analyses of NCs indicated the migration of lattice nitrogen of NC during the direct hydrogenation step for NH3 formation. At N-fixation stage, the nitrogen vacancy of molybdenum-based NC is expected to be recharged from N2. However, the low kinetics is an important problem of NC nitridation. With the introduction of H2, the nitridation kinetics of NC was significantly enhanced, improving the NC regeneration. During a 12-cycle test at 600 ℃ and atmospheric pressure, and the ammonia production rate was stabilized at ca. 1500 μmol•g −1 •h −1 for each cycle. This article investigated the preliminary feasibility of the supported molybdenum-based nitride as NC during the process of CLAS and could provide a theoretical basis for the design and development of new types of NCs.

Advances in Nitrogen Carriers for Chemical Looping Processes for Sustainable and Carbon-Free Ammonia Synthesis

“…Molybdenum nitride (Mo 2 N) has also shown promising potential as a nitrogen carrier in the CLAP process. Mo 2 N has been widely used as a high-performance electrocatalyst for converting N 2 to NH 3 via the Mars-van Krevelen mechanism. , The N vacancy generation and consumption steps in this mechanism are similar to the N-desorption and N-sorption steps in the CLAP process. Michalsky et al also conducted thermodynamic and economic analyses, suggesting that Mo 2 N had the potential to be a nitrogen carrier in CLAP.…”

Dinitrogen Activation by Heteronuclear Metal Carbide Cluster Anions Y1‐3CoC1,2−: An Experimental and DFT Study

“…[4][5][6] To promote green and sustainable development, there is a need for efficient nitrogen fixation catalysts that can realize nitrogen reduction reaction (NRR) under mild conditions. [7][8][9][10] Sabatier principle is a widely adopted concept in designing NRR catalysts. [11,12] Generally, early transition metals have a high ability to activate N 2 but are limited by the desorption of products due to too strong binding of N species, while late transition metals bind with N 2 too weakly and are limited by the activation of N 2 .…”

“…The amount of nitrogen‐containing compounds produced through lightning and plant root nitrogen fixation during natural processes cannot meet the demands of modern society, and thus it is necessary to use the energy‐intensive and potentially polluting Haber‐Bosch ammonia synthesis process to convert N 2 and H 2 into NH 3 in industrial production [4–6] . To promote green and sustainable development, there is a need for efficient nitrogen fixation catalysts that can realize nitrogen reduction reaction (NRR) under mild conditions [7–10] …”