In a remarkable breakthrough, scientists have uncovered an astonishing ability of calcium to outshine chromium as a catalyst in the production of ammonia. Working together harmoniously, a trio of unassuming calcium atoms has defied expectations by effectively dismantling one of the most robust chemical bonds known to science. These atoms form a crucial component of a catalyst that can cleave the triply bonded nitrogen molecule (N2), a pivotal stage in the synthesis of ammonia-based fertilizers. This discovery has the potential to ignite innovative and more sustainable approaches to manufacturing fertilizers and other vital chemicals.
Yoji Kobayashi, a distinguished inorganic materials chemist from KAUST, co-led this groundbreaking research. He expressed his astonishment at calcium’s newfound prowess in catalyzing ammonia production from nitrogen, a revelation that caught the scientific community off guard. Presently, industrial ammonia production relies on an iron catalyst, which demands high temperatures and pressures during the process, prompting a quest for alternative methods.
Kobayashi explained, “Conventional catalysts for ammonia synthesis are typically effective when based on materials like ruthenium, iron, or cobalt, but they exhibit poor performance with early transition metal compounds such as chromium.” However, recent years have witnessed the emergence of more potent hydride catalysts rooted in titanium, vanadium, and chromium, reigniting the exploration for novel ammonia catalysts.
The team, led by Kobayashi, recently stumbled upon a novel chromium nitride hydride material, serendipitously containing calcium, and demonstrated its ability to function as an ammonia synthesis catalyst. Intrigued by this unexpected finding, they embarked on a comprehensive investigation into the catalyst’s mechanism, employing a combination of experimental and computational techniques.
Collaborating with Luigi Cavallo’s group at the KAUST Catalysis Center, Kobayashi delved into the catalyst’s complex structure, denoted as Ca3CrN3H. The intricate architecture presented multiple potential reaction sites, each requiring scrutiny to determine their feasibility for converting nitrogen into ammonia.
The ensuing analysis yielded astonishing results, as Kobayashi elaborated, “The role of calcium was truly unforeseen. The N2 molecule binds to a trio of calcium atoms on the catalyst’s surface, undergoing hydrogenation to transform into ammonia.” Contrary to expectations, the chromium atom, typically anticipated as the central player, does not play a direct role in activating the N2 molecule for conversion into ammonia.
Despite the catalyst’s relatively modest activity in ammonia synthesis, it has opened up an innovative avenue for exploring catalyst materials, diverging from the conventional dependence on transition metal elements. Kobayashi emphasized, “Numerous other inorganic structures possessing analogous atomic arrangements warrant investigation. Our study underscores that a touch of creativity can perpetually expand the realm of promising catalyst materials.”