Air-Stable Calcium Cyanamide-Supported Ruthenium Catalyst for Ammonia Synthesis and Decomposition
Kazuhisa Kishida, Masaaki Kitano, Masato Sasase, Peter V. Sushko, Hitoshi Abe, Y. Niwa, Kiya Ogasawara, Toshiharu Yokoyama, Hideo Hosono
Abstract
Efficient ammonia synthesis and decomposition processes under mild conditions are important to meet the expanding demand in major applications of ammonia as the energy carrier and to provide feedstock for chemical industry. Here, we report that air-stable calcium cyanamide-supported ruthenium (Ru/CaCN2) works as an efficient and stable catalyst for ammonia synthesis and decomposition. Ru/CaCN2 exhibits greater catalytic performances for both reactions than Ru/Ca2N electride and Ru–Cs/MgO. The kinetic analysis for ammonia synthesis suggests that Ru/CaCN2 exhibits low apparent activation energy and high resistance to hydrogen poisoning, which has characteristics similar to the kinetic parameters of Ru-supported electride catalyst. H2-temperature programmed reaction and temperature programmed desorption revealed that Ru promoted the formation of CN2 vacancies on the CaCN2 surface which in turn capture hydrogen as H– ions during the reaction. Density functional theory calculations provide insights into how the formation of CN2 vacancies is promoted by Ru, which leads to the decrease in the work function of the CaCN2 surface and the hydrogen capture at the Ru-support interface. These results suggest that the high catalytic performance of Ru/CaCN2 can be attributed to the formation of a quasi-electride structure at the Ru–CaCN2 interface.