WILL AMMONIA POWER THE WORLD?
Most of us know ammonia as that eye watering stuff in the bottle that is used to clean very dirty spaces. Did you know that ammonia is also essential in the production of agricultural fertilizer? The same chemistry that makes ammonia a great cleaning product and fertilizer may also make for a powerful renewable fuel source.
First world countries are racing toward the use of green energy. These green energies require energy storage via non-renewable batteries. Batteries require the use of minerals mined in third world countries. Green energy may reduce the carbon footprint in the first world but are we trading first world problems on the backs of the third world miners? Could ammonia be a better solution?
Ammonia is a combination of a single nitrogen and three hydrogen atoms. The process for ammonia production (Haber-Bosch process) combines dnitrogen (an unreactive molecular form) and hydrogen in the presence of an iron catalyst. The reaction is driven under high pressure and temperature with a greater than 2% production of CO2. That sounds like a process that uses a lot of energy! Why even consider ammonia?
The reason is an abundance of natural ingredients. The dnitrogen is a biological product of bacteria abundantly found in the air. The other ingredient, hydrogen, is found in water. An energy source, sunshine, is abundant. Ammonia can be easily stored and shipped in liquid form. Today, Australia is leading the way in the research of ammonia production.
Dougals MacFarlane has several patent applications describing the use of an electrochemical cell capable of reduction of dnitrigen to ammonia (WO 2017/132721 A1, published August 10, 2017). A liquid salt catalyst is needed for electrochemical reduction of dnitrogen to ammonia. The use of an electrolyte comprising liquid salts provides an ion conductive, low water medium in which the process reactions occur. The electrolyte needs to have low volatility and high gas solubility. The solution must support N2 reduction but not reduction of water to H2 (have high hydrophobicity). Ammonia is produced at ambient temperature and pressure. A continuous or pulsed current is required to pass between the cathode working electrode and the counter electrode. A catalyst for electrochemical reduction of dnitrogen is a nano-structural material having a high electrochemical working surface area. This requires the use of one or more metals in the form of elemental metal or inorganic compounds comprising transition metals or lanthanide metals.
Schrauzer is a leader in the evolution of use of aqueous systems to generate ammonia. US patent 4113590 claims a method for the photoreduction of nitrogen which comprises reducing nitrogen to ammonia by irradiating metal oxide selected from the group consisting of titanium dioxide and metal-doped titanium dioxide with ultraviolet light in the presence of gaseous nitrogen and water and recovering such ammonia. Nitrogen is reduced to ammonia, hydrazine, and mixtures thereof by reaction with water on a solid metal oxide irradiated with ultraviolet light. Useful metal oxides include titanium dioxide and metal-doped titanium dioxide. Titanium dioxide doped with iron, cobalt, molybdenum or nickel is preferred. The metal oxide is irradiated in the presence of nitrogen and water with ultraviolet light from a source such as a mercury arc lamp or sunlight. The nitrogen and the water may be in the vapor phase, or they may be adsorbed on the metal oxide. In addition, liquid water may be present. The ammonia which is formed may be recovered in a few ways, for example, by heating the metal oxide gently under vacuum, by water extraction, or by adsorption in an acid acceptor.
Schrauzer’s patents are more than 20 years old and are being built on by other research groups. The relative abundance of lanthanide metals, dnitrogen, water, and sunlight may make ammonia a green transportable source of energy.