Cobalt

A team from Nanjing University, Hubei Normal University and Zhejiang University has developed a cobalt-doped graphdiyne catalyst for catalytically decomposing ammonia (NH3) to generate H2. The composite catalyst significantly enhances the reactivity and stability of ammonia decomposition.

In a paper in the journal Fuel, the researchers report that the Co-doped graphdiyne catalyst achieved nearly complete decomposition of ammonia at 550 ˚C, and the conversion rate remained stable over 18 h of continuous reaction.

Liu et al.

Graphdiyne (GDY) is a new two-dimensional (2D) carbon allotrope, similar to graphene. However, while graphene is a single layer of carbon atoms arranged in a 2D honeycomb lattice, graphdiyne is composed of both sp2 and sp carbon atoms (sp and sp2 refer to the hybridization state of carbon atoms in molecules), forming a unique structure with a large number of pores, giving it a high surface area—useful for applications in energy storage and catalysis.

Ammonia is by its nature a high-density hydrogen carrier. While noble metal catalysts, such as ruthenium, exhibit superior catalytic performance in ammonia decomposition—i.e., to release the hydrogen—their high cost is a challenge for widespread application, the authors note.

Conversely, low-cost metal catalysts are available but demonstrate suboptimal catalytic effects. Carbon-based catalysts promote interfacial electron transfer, enhancing the adsorption and dissociation potentials of NHx adsorbate at the interface. However, how to enhance the catalytic activity of non-precious metals and carbon-based composite catalysts, decrease the reaction temperature, and obtain a fundamental understanding of novel two-dimensional catalysts have become a major challenge.

Numerous studies have been devoted to discovering and expanding new catalyst materials, with a particular focus on graphdiyne. Graphdiyne is a novel two-dimensional carbon material that exhibits a high potential for catalytic NH3 decomposition, as demonstrated by theoretical studies. The uneven surface charge distribution of graphdiyne provides ample active sites for catalytic reactions. Typically, graphdiyne anchored with metal atoms is employed as a catalyst for thermochemical reactions. However, the interaction effect of cobalt loading on graphdiyne in thermal reactions, particularly in ammonia decomposition performance, has not yet been studied extensively.

In this work, we focus on loading non-noble metal nanoparticles on graphdiyne to investigate the catalytic interactions between two-dimensional carbon materials and transition metals. We discovered that high performance of various transition metals loaded on graphdiyne during ammonia decomposition can be attributed to particle dispersion, metal reducibility, and elemental composition of the catalyst in this study.

For the sstudy, the team synthesized a series of Co-loaded graphdiyne sheets using a facile wet co-precipitation method.

DFT calculations elucidated that the rate-determining step in the reaction kinetics is the dehydrogenation of NHx species, not the recombination of nitrogen as conventionally understood.

Our study highlights the tremendous potential of metal-doped graphdiyne catalysts for facile hydrogen production via NH3 decomposition, enabling safe and scalable hydrogen utilization.

Resources

Lishan Liu, Feng Gong, Yunlong Xie, Sijun Wang, Yu Qiu, Zhihua Wang, Rui Xiao (2023) “Highly-efficient hydrogen production from ammonia decomposition over Co-doped graphdiyne under moderate temperature,” Fuel, Volume 354 doi: 10.1016/j.fuel.2023.129320

Xin Gao, Huibiao Liu, Dan Wang and Jin Zhang (2019) “Graphdiyne: synthesis, properties, and applications” Chemical Society Reviews doi: 10.1039/C8CS00773J

Posted on 06 August 2023 in Ammonia, Catalysts, Hydrogen, Hydrogen Production, Hydrogen Storage, Market Background | Permalink | Comments (0)