Ab initio DFT study of hydrogen dissociation on MoS₂, NiMoS, and CoMoS: mechanism, kinetics, and vibrational frequencies

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• 作者：Mingyong Sun ; Alan E. Nelson and John Adjaye
• 关键词：Hydrogen dissociation ; Hydrogen migration ; Hydrogen ; MoS₂ ; NiMoS ; CoMoS ; Density-functional theory ; Activation energy ; Transition state
• 刊名：Journal of Catalysis
• 出版年：2005
• 出版时间：2005
• 年：2005
• 卷：233
• 期：2
• 页码：411-421
• 全文大小：1037 K

文摘

The present study provides detailed discussions about the structures, relative stabilities, and vibrational frequencies of hydrogen species on MoS₂, NiMoS, and CoMoS catalyst edge surfaces. The transition states and activation energies for molecular hydrogen dissociation and surface migration of atomic hydrogen on catalyst edge surfaces have been calculated by complete linear synchronous transit (LST) and quadratic synchronous transit (QST) search methods. It has been found that the heterolytic dissociation of molecular hydrogen at a pair of sulfur–metal sites to form an SH group and a metal hydride is energetically preferred. The dissociation of molecular hydrogen on the Ni-promoted andle=V-WA-A-W-WV-MsSAYZW-UUA-U-AABZBBEAVB-AABBEAEEVB-CAYWYUZAA-WV-U&_acct=C000050221&_version=1&_userid=10&md5=cf00e1bca1a3cce816e46c0d415d2549""> metal edge of NiMoS requires slightly lower activation energy than that on the unpromoted andle=V-WA-A-W-WV-MsSAYZW-UUA-U-AABZBBEAVB-AABBEAEEVB-CAYWYUZAA-WV-U&_acct=C000050221&_version=1&_userid=10&md5=73f568a4a2c8fe11b83824caa3635e97""> Mo-edge of MoS₂ (0.87 and 0.91 eV, respectively). The dissociation of molecular hydrogen on the unpromoted andle=V-WA-A-W-WV-MsSAYZW-UUA-U-AABZBBEAVB-AABBEAEEVB-CAYWYUZAA-WV-U&_acct=C000050221&_version=1&_userid=10&md5=0a3bd308635f6fbae8b992914d4a2e51""> S-edge requires a large activation energy (about 1.0 eV), and the addition of cobalt to the andle=V-WA-A-W-WV-MsSAYZW-UUA-U-AABZBBEAVB-AABBEAEEVB-CAYWYUZAA-WV-U&_acct=C000050221&_version=1&_userid=10&md5=795e96acdbbf1c57f62cea16afdb5f25""> S-edge significantly lowers the dissociation energy to approximately 0.6 eV. The atomic hydrogen species on the andle=V-WA-A-W-WV-MsSAYZW-UUA-U-AABZBBEAVB-AABBEAEEVB-CAYWYUZAA-WV-U&_acct=C000050221&_version=1&_userid=10&md5=503c9c52f19e9618251e2748e0844aa6""> S-edge and the Co-promoted andle=V-WA-A-W-WV-MsSAYZW-UUA-U-AABZBBEAVB-AABBEAEEVB-CAYWYUZAA-WV-U&_acct=C000050221&_version=1&_userid=10&md5=09aaf305f07df01d9eee3113c0ede6e1""> S-edge are less mobile than on the andle=V-WA-A-W-WV-MsSAYZW-UUA-U-AABZBBEAVB-AABBEAEEVB-CAYWYUZAA-WV-U&_acct=C000050221&_version=1&_userid=10&md5=a753c80fc809a42ad20f1eb32a6d75cf""> Mo-edge of MoS₂ or the Ni-promoted andle=V-WA-A-W-WV-MsSAYZW-UUA-U-AABZBBEAVB-AABBEAEEVB-CAYWYUZAA-WV-U&_acct=C000050221&_version=1&_userid=10&md5=508397631e626aec1a9060bd2fe35820""> metal edge of NiMoS. The calculated vibrational frequencies of different surface hydrogen species agree well with reported experimental observations and have provided references for further spectroscopic experiments.