TY - JOUR
T1 - First-Principles and Microkinetic Study on the Mechanism for Ammonia Synthesis Using Ru-Loaded Hydride Catalyst
AU - Nakao, Takuya
AU - Tada, Tomofumi
AU - Hosono, Hideo
N1 - Funding Information:
This work was supported by funds from a Kakenhi Grant-in-Aid (No. 17H06153) from the Japan Society for the Promotion of Science (JSPS) and the Ministry of Education, Culture, Sports, Science and Technology (MEXT) Element Strategy Initiative to form a research core (Grant Number JPMXP0112101001).
Publisher Copyright:
Copyright © 2019 American Chemical Society.
PY - 2020/1/23
Y1 - 2020/1/23
N2 - Ru-loaded hydride is an efficient catalyst for ammonia (NH3) synthesis under mild conditions. Metal hydrides such as Ca2NH with surface anionic electrons at hydrogen vacancies (Ca2NH1-xex-) function well as active catalytic support materials for Ru. The resultant catalysts exhibit good performance for NH3 synthesis with a large reduction of the apparent activation energy and the suppression of hydrogen poisoning of Ru. However, the reaction mechanism and the rate-determining step (RDS) have not yet been clarified from a microscopic viewpoint. Here, we have successfully reproduced the experimental results of NH3 synthesis by microkinetic modeling using density functional theory (DFT) calculations. Three essential mechanisms were identified: (i) the promotion of nitrogen cleavage with electron injection from Ca2NH1-xex- to Ru, (ii) the formation of NHx species promoted at the Ru/Ca2NH1-xex- interface, and (iii) hydrogen poisoning suppression of Ru by fast hydrogen migration at the Ru/Ca2NH1-xex- interface. Microkinetic modeling also revealed that NH3 formation (NH2 + H → NH3) at the Ru/Ca2NH1-xex- interface is the RDS. These findings are consistent with the experimental results and validate the reaction mechanism dealt with in this research.
AB - Ru-loaded hydride is an efficient catalyst for ammonia (NH3) synthesis under mild conditions. Metal hydrides such as Ca2NH with surface anionic electrons at hydrogen vacancies (Ca2NH1-xex-) function well as active catalytic support materials for Ru. The resultant catalysts exhibit good performance for NH3 synthesis with a large reduction of the apparent activation energy and the suppression of hydrogen poisoning of Ru. However, the reaction mechanism and the rate-determining step (RDS) have not yet been clarified from a microscopic viewpoint. Here, we have successfully reproduced the experimental results of NH3 synthesis by microkinetic modeling using density functional theory (DFT) calculations. Three essential mechanisms were identified: (i) the promotion of nitrogen cleavage with electron injection from Ca2NH1-xex- to Ru, (ii) the formation of NHx species promoted at the Ru/Ca2NH1-xex- interface, and (iii) hydrogen poisoning suppression of Ru by fast hydrogen migration at the Ru/Ca2NH1-xex- interface. Microkinetic modeling also revealed that NH3 formation (NH2 + H → NH3) at the Ru/Ca2NH1-xex- interface is the RDS. These findings are consistent with the experimental results and validate the reaction mechanism dealt with in this research.
UR - http://www.scopus.com/inward/record.url?scp=85079822468&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85079822468&partnerID=8YFLogxK
U2 - 10.1021/acs.jpcc.9b10850
DO - 10.1021/acs.jpcc.9b10850
M3 - Article
AN - SCOPUS:85079822468
SN - 1932-7447
VL - 124
SP - 2070
EP - 2078
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 3
ER -