Large Oblate Hemispheroidal Ruthenium Particles Supported on Calcium Amide as Efficient Catalysts for Ammonia Decomposition

Kazuhisa Kishida; Masaaki Kitano; Yasunori Inoue; Masato Sasase; Takuya Nakao; Tomofumi Tada; Hitoshi Abe; Yasuhiro Niwa; Toshiharu Yokoyama; Michikazu Hara; Hideo Hosono

doi:10.1002/chem.201800467

Large Oblate Hemispheroidal Ruthenium Particles Supported on Calcium Amide as Efficient Catalysts for Ammonia Decomposition

Chemistry. 2018 Jun 4;24(31):7976-7984. doi: 10.1002/chem.201800467. Epub 2018 May 8.

Authors

Kazuhisa Kishida^{1

2}, Masaaki Kitano¹, Yasunori Inoue³, Masato Sasase¹, Takuya Nakao⁴, Tomofumi Tada¹, Hitoshi Abe^{2

5

6}, Yasuhiro Niwa⁵, Toshiharu Yokoyama^{1

2}, Michikazu Hara^{2

4}, Hideo Hosono^{1

2

4}

Affiliations

¹ Materials Research Center for Element Strategy, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan.
² ACCEL (Japan) Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012, Japan.
³ Institute for Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan.
⁴ Laboratory for Materials and Structures, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan.
⁵ Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan.
⁶ Department of Materials Structure Science, School of High Energy Accelerator Science, SOKENDAI (the Graduate University for Advanced Studies), 1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan.

PMID: 29603479
DOI: 10.1002/chem.201800467

Abstract

Ammonia decomposition is an important technology for extracting hydrogen from ammonia toward the realization of a hydrogen economy. Herein, it is reported that large oblate hemispheroidal Ru particles on Ca(NH₂ )₂ function as efficient catalysts for ammonia decomposition. The turnover frequency of Ru/Ca(NH₂ )₂ increased by two orders of magnitude when the Ru particle size was increased from 1.5 to 8.4 nm. More than 90 % ammonia decomposition was achieved over Ru/Ca(NH₂ )₂ with large oblate hemispheroidal Ru particles at 360 °C, which is comparable to that of alkali-promoted Ru catalysts with small Ru particle sizes. XAFS analyses revealed that Ru particles are immobilized on Ca(NH₂ )₂ by Ru-N bonds formed at the metal/support interface, which lead to oblate hemispheroidal Ru particles. Such a strong metal-support interaction in Ru/Ca(NH₂ )₂ is also substantiated by DFT calculations. The high activity of Ru/Ca(NH₂ )₂ with large Ru particles primarily originates from the shape and appropriate size of the Ru particles with a high density of active sites rather than the electron-donating ability of Ca(NH₂ )₂ .

Keywords: heterogeneous catalysis; metal-support interactions; nanoparticles; ruthenium; supported catalysts.