TY - JOUR
T1 - Adsorption States of N2/H2Activated on Ru Nanoparticles Uncovered by Modulation-Excitation Infrared Spectroscopy and Density Functional Theory Calculations
AU - Rivera Rocabado, David S.
AU - Noguchi, Tomohiro G.
AU - Hayashi, Shio
AU - Maeda, Nobutaka
AU - Yamauchi, Miho
AU - Ishimoto, Takayoshi
N1 - Funding Information:
We acknowledge funding by JSPS KAKENHI (Nos. JP 18H05517 and JP 19H05062 “Hydrogenomics”) and JST-CREST (No. 15656567).
Funding Information:
This work was supported by the “Advanced Computational Scientific Program” of the Research Institute for Information Technology, Kyushu University.
Publisher Copyright:
© 2021 American Chemical Society.
PY - 2021/12/28
Y1 - 2021/12/28
N2 - The adsorption states of N2 and H2 on MgO-supported Ru nanoparticles under conditions close to those of ammonia synthesis (AS; 1 atm, 250 °C) were uncovered by modulation-excitation infrared spectroscopy and density functional theory calculations using a nanoscale Ru particle model. The two most intense N2 adsorption peaks corresponded to the vertical chemisorption of N2 on the nanoparticle's top and bridge sites, while the remaining peaks were assigned to horizontally adsorbed N2 in view of the site heterogeneity of Ru nanoparticles. Long-term observations showed that vertically adsorbed N2 molecules gradually migrated from the top sites to the bridge sites. Compared to those adsorbed vertically, N2 molecules adsorbed horizontally exhibited a lower dipole moment, an increased N-N bond distance, and a decreased N-N bond order (i.e., were activated), which was ascribed to enhanced Ru-to-N charge transfer. H2 molecules were preferentially adsorbed horizontally on top sites and then rapidly dissociated to afford strongly surface-bound H atoms and thus block the active sites of Ru nanoparticles. Our results clarify the controversial adsorption/desorption behavior of N2 and H2 on AS catalysts and facilitate their further development.
AB - The adsorption states of N2 and H2 on MgO-supported Ru nanoparticles under conditions close to those of ammonia synthesis (AS; 1 atm, 250 °C) were uncovered by modulation-excitation infrared spectroscopy and density functional theory calculations using a nanoscale Ru particle model. The two most intense N2 adsorption peaks corresponded to the vertical chemisorption of N2 on the nanoparticle's top and bridge sites, while the remaining peaks were assigned to horizontally adsorbed N2 in view of the site heterogeneity of Ru nanoparticles. Long-term observations showed that vertically adsorbed N2 molecules gradually migrated from the top sites to the bridge sites. Compared to those adsorbed vertically, N2 molecules adsorbed horizontally exhibited a lower dipole moment, an increased N-N bond distance, and a decreased N-N bond order (i.e., were activated), which was ascribed to enhanced Ru-to-N charge transfer. H2 molecules were preferentially adsorbed horizontally on top sites and then rapidly dissociated to afford strongly surface-bound H atoms and thus block the active sites of Ru nanoparticles. Our results clarify the controversial adsorption/desorption behavior of N2 and H2 on AS catalysts and facilitate their further development.
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U2 - 10.1021/acsnano.1c07825
DO - 10.1021/acsnano.1c07825
M3 - Article
C2 - 34860010
AN - SCOPUS:85120894664
VL - 15
SP - 20079
EP - 20086
JO - ACS Nano
JF - ACS Nano
SN - 1936-0851
IS - 12
ER -