Large manufacturing plants, such as the one shown above, can make hundreds of thousands of tons of ammonia each year using the Haber–Bosch process. At least 80% of that yield serves as crop fertilizer. Its synthesis consumes nearly 2% of the global energy output and, in the process, produces 500 million tons of carbon dioxide.
The synthesis is so energy intensive largely because the Haber–Bosch process requires brute force—high temperature (up to 650 °C) and high pressure (200 atmospheres)—to split apart the triply bonded nitrogen atoms, which then react with hydrogen over an iron catalyst. Iron is effective and inexpensive as an industrial catalyst. But chemical engineers have been searching for decades for alternatives to catalyze the reaction in milder, environmentally friendlier conditions.
For several years, researchers have been aware of alternatives to iron, such as nickel and cobalt. But both of those metals are normally unreactive with nitrogen and can be turned into effective catalysts only in the proximity of particular additives, known as promoters. A collaboration between Technical University of Denmark researchers, led by theorist Jens Nørskov and experimentalist Ib Chorkendorff, now propose a mechanism by which cobalt becomes a particularly good catalyst of ammonia in the presence of lanthanum.
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