Scotland PhD competition winner - Yalinu Poya

15 October 2019

Each year, SCI’s Scotland group runs a competition where students are invited to write a short article describing how their PhD research relates to SCI’s strapline: where science meets business.

Yalinu Poya, a Chemistry PhD student from the University of Glasgow, was the winner in this year’s competition. Her article ‘Using Catalysts to Feed the World’ is reproduced here.

Using Catalysts to Feed the World

It is forecast that the world population will reach 9.1 billion by the year 2050. To support this population food production will need to increase (estimates range from 25%) and farmers will require more fertilizer to produce healthy crops. Since ammonia is the key ingredient in fertilizer, its production will also need to increase.     

The Haber–Bosch process is a mature technology originally developed in 1908 and is the cornerstone of industrial fertiliser production. The process currently produces over 180 million tonnes of ammonia annually, establishing the production of over 450 million tonnes of synthetic fertilizer, sustaining 40% of the global population. The Haber–Bosch process involves combining pure H2 and N2 feed streams directly over a promoted iron catalyst at temperatures of around 400°C using pressures of over 100 atmospheres. The reaction is exothermic and is equilibrium limited, and so thermodynamically favoured at lower temperatures. Despite this, the temperature of operation is dictated by the requirement to achieve acceptable process kinetics. Unfortunately, this industrial technology annually consumes 2% of the world’s energy demand and contributes to global warming by releasing 1.6% of man–made carbon dioxide into the atmosphere.

My PhD research is on ‘Supported Transition Metal Catalysts in Ammonia Synthesis,’ using affordable materials to make catalysts able to produce ammonia in a clean way using less harsh reaction conditions and energy.  The Haber–Bosch process uses conventional iron catalysts, that are inexpensive, abundant in nature and highly effective when promoted. For this reason, alternative catalysts should produce high activity whilst using low temperature and/or pressure in the reaction.

Osmium is an active catalyst in ammonia synthesis and was initially considered for the Haber–Bosch process, it is, however, expensive, toxic and rare, and was thus soon discounted. Ruthenium is also highly active, producing ammonia at low pressures. Although it is expensive, it is commercially used in the Kellogg Advanced Ammonia Process.  It is notable that several active ammonia synthesis catalysts comprise cobalt with other active metals. For example, a combination of cobalt and rhenium as a bimetallic catalyst shows high ammonia synthesis activity. Cobalt is cheap and readily available, whilst rhenium is expensive and low in abundance. Despite its low surface area, cobalt rhenium is an active catalyst, however, a more highly dispersed catalytic phase using small amounts of cobalt and rhenium can minimize costs and enhance catalytic performance. This can be obtained by application of a suitable and inexpensive catalyst support. Magnesium oxide is an example as it possesses high surface area and acts as a chemical promoter due to its basicity.

I have prepared novel magnesium oxide supported cobalt rhenium catalysts, applied them to ammonia synthesis and produced excellent results. To yield massive economic and environmental benefits, there is great interest in the development of small-scale local ammonia production plants that use renewable hydrogen generated from water via electrolysis and powered by sustainable electricity, such as wind energy. I believe that my cobalt-rhenium supported on magnesium oxide catalysts are suitable for this.

Additionally, the ammonia produced can also be used as a green energy vector capable of addressing intermittent periodic oversupply.  My research on making catalysts for ammonia production in the Haber–Bosch process offers a new perspective to global sustainability. Ammonia manufacturers need to establish a link where ‘science meets business’ for economic and environmental rewards, affordable and clean energy, industrial innovation, and climate action. Cobalt-rhenium supported on magnesium oxide catalysts could prove to be that missing link.

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