Above the bar: operando spectroscopy of ammonia production at high pressure

by Dr Christopher Goodwin (ALBA Synchrotron)

Tuesday 14 Feb 2023, 14:15 → 15:00 Europe/Berlin

FLASH seminar room

The Haber-Bosch reaction to form ammonia from air and hydrogen feeds over half the earth’s population. Yet, there has been no comprehensive study of the atomic nature of the catalyst’s surface while active since 100 years after the inception of the reaction. The fundamental issue is nitrogen’s inert nature, which needs high pressure to proceed, yet the pressure requirements inhibit all atomic spectroscopy. To this effect, Nobel Lorette Gerhard Ertl wrote, “… spectroscopic measurements may never be performed under pressure conditions as applied for the [Haber-Bosch] reaction.” For almost 40 years, this was true with the most valuable atomic spectroscopy, ambient pressure x-ray photoelectron spectroscopy, limited to 20-50 mbar compared to the formation of ammonia, requiring over 10x higher pressure. Yet with the development of POLARIS, a high-pressure XPS, we have been able to study the surface state of the catalyst, intermediates, and activity simultaneously. The XPS system installed at DESY in P22 can reach a pressure of over 1 bar while maintaining high data quality. Many surface states have been proposed to describe ammonia formation, including oxides, nitrides, metallic, and atomic nitrogen-covered surfaces. We have proven the chemical state of the surface for all of the most active surfaces for ammonia synthesis. Finally, we evaluated the effects of temperature, pressure, and gas composition, providing new insight into the most important reaction of the 20th century.