I’ve spent my entire chemistry career not only using catalysts but designing new molecules that act as catalysts. It was the subject of my Ph.D. thesis, and I have several patent-pending technologies concerning new catalysts. Catalysis is a fascinating area of science. It’s the process by which an otherwise difficult reaction can become very easy to perform. Catalysts lower the required temperatures and reaction times, and give higher yields of the desired products. Probably the most famous example of a catalyst (and certainly one of my favorite catalysis stories) involves work done over 100 years ago by a German chemist named Fritz Haber.
At the time, the planets population was rising rapidly yet the only source of quality fertilizer was Chilean saltpeter, dug out of the ground and transported at great expense across the ocean to starving populations everywhere. Chemists knew that it was the nitrogen in saltpeter that was the “active ingredient” that made the material a good fertilizer. Chemists also knew that over 70% of the air we breathe is nitrogen gas. However, the problem was the “fixation” of nitrogen; nitrogen gas is so stubbornly unreactive that chemists were convinced the gas could never be “fixed” into a solid form for use as a fertilizer.
Haber proved them wrong. His design took years to perfect, and strained the steel industries of the time to their breaking point in terms of tolerances and engineering perfection, but eventually he developed a solid catalyst that could (through a sequence of chemical reactions) turn atmospheric nitrogen into ammonia. This could then be further reacted to become a fantastic fertilizer. It was hailed as a miraculous discovery – “turning air into bread”. No-one was really sure how the solid catalyst (an iron-osmium powder) worked; it’s very difficult to study reactions at solid interfaces, as even nowadays we don’t have many probes that allow us to visualize what’s transpiring at the surface of the solid catalyst.
Given my long-standing interest in catalyst chemistry, and given the famous story of Haber’s catalytic process (a process still in use today!), I was fascinated to read a recent journal article in Science magazine that discussed new insights into this century old reaction. Science is arguably the top science journal in the world, eclipsed only partially by the European publication Nature. The article described how chemists avoided the difficulty of studying a solid catalyst by using soluble forms of iron. Instead of using a powdered catalyst, they used an iron-potassium complex that (when dissolved in a solvent) could break the strong bonds between nitrogen atoms in nitrogen gas. This formed a complex that required three iron atoms for every two nitrogens; further reaction with hydrogen then formed ammonia.
This approach is fantastic because there are so many more tools for studying liquid-phase reactions, as opposed to reactions which take place on a solid surface. Everything becomes less clouded when everything is dissolved into a solvent, as much more sophisticated techniques can be brought to bear. As a result, chemists can now take this articles results and design more efficient solid-state catalysts for the Haber reaction. Instead of just using the current catalyst “because it works” (which is not a very satisfying reason for a scientist), the precise method of action will be known, and so the catalyst can be optimized.
This result excites me because the battle between heterogeneous (solid) catalysts and homogeneous (liquid) catalysts is an old one, and both types have pros and cons. It’s a subject I’ve tried to address in various technologies that I have patented, but this article is a fresh approach to the subject that I hadn’t previously considered. It uses the power of analytical chemistry to investigate liquid reactions and then applies the results to reactions which take place on solid surfaces. If enough scientists pick up on this articles results and work to improve Habers 100-year old catalyst system, the result will be cheaper ammonia, cheaper fertilizer, and ultimately cheaper food. This is something that our planet, with its ever increasing population, could put to great use, and is a discovery which makes me proud to be a chemist with catalysis experience.
The source of this article can be found at:
Rodriguez, M.M; Bill, E.; Brennessel, W.W.; Holland, P.L. “Nitrogen Reduction and Hydrogenation to Ammonia by a Molecular Iron-Potassium Complex”. Science 2011, 334, 780.