The theory tends to support this view but putting this into practice may be a challenge.

* It should be better to avoid converting N2 + H2 to NH3 and then converting NH3 back to N2 + H2, if there is a way of using the H2 locally or shipping this (not sure of the technology status here). New processes/catalysts for NH3 cracking may exist but the established technology uses a Ni based catalyst at very high temperature, probably necessary to drive the reaction equilibrium to leave very low NH3 slip.

* Conventional NH3 production starts from natural gas and largely feeds into the fertilizer production industry. Often ammonia is used on site to make urea (with CO2 from the steam reforming process) or nitric acid, and so is not shipped.

* Existing NH3 storage and transportation capacity is committed to existing industries using NH3. Therefore, excess shipping and storage capacity may not be available for NH3 as an energy source without investment in additional facilities.

* NH3 for this brave new future will not be made from natural gas by steam reforming. New facilities to make "green" NH3 from H2 ex water electrolysis and N2 from an ASU may not be close to locations with existing NH3 storage/shipping facilities. Therefore, new infrastructure may be required.

* At the far end of the "green" NH3 shipment, there needs to be NH3 storage in order to feed the NH3 cracking to generate the "green" H2 from the NH3. This may be possible with existing NH3 storage facilities but then requires the development of the NH3 cracking facilities and resultant H2 distribution. Another question is whether the cracked NH3 gas (N2 + 3H2) needs to be separated to derive pure H2 due to the local energy consuming network.

As a carbon-free molecule, ammonia has gained great global interest in being considered a significant future candidate for the transition toward renewable energy. Numerous applications of ammonia as a fuel have been developed for energy generation, heavy transportation, and clean, distributed energy storage. There is a clear global target to achieve a sustainable economy and carbon neutrality. Therefore, most of the research's efforts are concentrated on generating cost-effective renewable energy on a large scale rather than fossil fuels. However, storage and transportation are still roadblocks for these technologies, for example, hydrogen technologies. Ammonia could be replaced as a viable fuel for a clean and sustainable future of global energy. More efforts from governments and scientists can lead to making ammonia a clean energy vector in most energy applications. In this review, ammonia synthesis was assessed, including conventional Haber–Bosch technology. Current hydrogen technologies as the key parameters for ammonia generation are also evaluated. The role of ammonia as a hydrogen-based fuel and generation roadmap are discussed for future utilization of energy mix. Further, ammonia generation processes are addressed in depth, including blue and green ammonia generation. A survey of ammonia synthesis catalytic materials was conducted and the role of catalyst materials in ammonia generation was compared, which showed that the Ru-based catalyst generated the maximum ammonia after 20 h of starting experiment. An end-use plan for using ammonia as a clean energy fuel in vehicles, marines, gas turbines as well as fuel cells, is briefly discussed to recognize the potential applications of ammonia use. The practical and future end-use vision of energy sources is proposed to achieve great benefits at low carbon emissions and costs. This review can provide prospective knowledge of large-scale aspects and environmental considerations of ammonia. Herein, we conclude that ammonia will become the “clean energy carrier link” that will achieve the global energy and economy sustainability targets.

DOI: 10.1016/j.ijhydene.2022.09.061

Article Recent advances in ammonia synthesis technologies: Toward fu...

I agree with Peter Broadhurst, that It should be better to avoid converting N2 + H2 to NH3 and then converting NH3 back to N2 + H2, if there is a way of using the H2 locally. I think the best thing that can happen with green hydrogen is its use at the production site. This will help reduce the carbon footprint or increase energy efficiency. EU laws prescribe that products with a low carbon footprint must be transported to the EU. Therefore, it is most advantageous not to import green hydrogen into the EU, but to import products made using green hydrogen.

But I also think that green ammonia is one of the best carriers of green hydrogen.

After listening to all the concerns about using hydrogen transported through the existing natural gas pipeline infrastructure, such as hydrogen embrittlement and other degradation mechanisms, it became clear that NH3 transport through pipelines is not an issue.

I do not have the metallurgical knowledge to comments here but your pint about H2 embrittlement which affects some metallurgies is worth noting. I don't have the knowledge either to comment about the potential effects of ammonia also.

The bottleneck in using ammonia to deliver green hydrogen around the world is the inability to produce ammonia at low pressure with high efficiency. The HB-synthesis is the most effective right now. Catalysts are being developed that show high efficiency at 10 atm, but they have not yet been introduced into industry. Other technologies (electrochemical synthesis of ammonia from H2O and N2, low-temperatures plasma from N2 and H2) don't have enough efficiency to industrial synthesis of ammonia. The bottleneck of HB-synthesis of ammonia under low pressure (less than 10 atm) is the separation of ammonia from the gas mixture. What do you think about this problem?