DICP OpenIR
学科主题理论物理学
Pt supported 3d transition metal oxide films: a reversed model catalysts for low temperature CO oxidation
Li WX(李微雪)
会议文集242nd ACS National Meeting & Exposition.
会议名称242nd ACS National Meeting & Exposition.
会议日期2011-8-28
2011
会议地点丹佛
页码226-1
出版者待补充
出版地待补充
合作性质分会特邀报告
部门归属507
主办者美国ACS
英文摘要Pt supported 3d transition metal oxide films: a reversed model catalysts for low temperature CO oxidation Wei-Xue Li State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Science, Dalian 116023, China; wxli@dicp.ac.cn Introduction In many catalytic processes, the size of metal containing catalysts supported on oxides falls typically in the range of 1-10 nm. The catalytically active sites in these catalysts are often coordinatively unsaturated metal cations that are able to undergo facile electron transfer and promote catalytic reactions. Among others, characteristic coordinatively unsaturated sites with flexible valent state (CUF) confined by various ensembles such as proteins, ligands and nanopore matrix are essential for their high reactivity and stability in the catalytic oxidation reactions. Preparation of the CUF sites is of great significance but remains a challenge because of their high structural complexity and flexibility under operating conditions. We describe here a strategy to achieve this goal by taking advantage of the confinement effect at interfaces between a variety of nanostructured oxides film with flexible valent states and Pt substrates. The interface-confined CUF sites and neighboring Pt atoms are identified conclusively as the active centers to activate O2 and represent a high activity for low temperature CO oxidation in the presence of excess of hydrogen. Computational Methods All calculations were performed using Vienna ab initio simulation package (VASP) and PAW potential. The wave function was expanded by plane wave with kinetic cutoff 400 eV. The exchange-correlation energy and potential were described by generalized gradient approximation in form of the PW91 and spinpolarized calculations were performed throughout the present paper, and on-site column repulsion between 3d TM d-electrons and magnetic interaction was described by DFT+U method. Adsorption was only allowed on one side of the slabs. The chemisorbed species and metal atoms of the uppermost two layers were allowed to relax till the residual forces less than 0.03 eV/Å, while the remained atoms were fixed at their bulk truncated positions. Transition states (TSs) were located by constrained minimization method and climbing-image nudged elastic band method (CI-NEB). Results and Discussion The interfacial interaction between 3d transition metal (TM)-oxide films and Pt(111) substrates was studied first. We found there is a strong interfacial adhesion stabilizing the 3d TM oxide films, which are essential to keep it in lower valent states with potential ability for O2 activation, instead of complete oxidation. For complete oxidation of 3d TM, O2 activation would be hindered. Moreover, we found that 3d-TM oxide film itself is not active either due to its polar characteristic. Therefore, the coordinated unsaturated sites presented at the perimeters of nano-structural oxide films with flexibility of valent state (so-called CUF sites) will be potential candidate as the active sites for O2 activation. This was indeed found by DFT calculations, as indicated in Figure 1. We found that the CUF sites were very selective for O2 activation, but has a low affinity for CO adsorption. The dual sites presented at the boundary between 3d-TM oxide films and Pt substrate offered an ideal active sites for CO adsorption and O2 activation. The dissociated atomic oxygen has a high activity for CO oxidation. Further calculation showed that the competition between CO adsorption and O2 activation is very sensitive to the 3d-TM. For the 3d-TM at the left side of the periodic table, the significant strong interaction with oxygen molecule leads to oxygen poison. Whereas for the right side of the periodic table, the activity for oxygen molecule decreases gradually, and as a compensation effect, the stability of 3d-TM oxide films increase. As a result, Pt supported early 3d-TM oxide film show up the good activity for CO oxidation in the excess of hydrogen, while for the late 3d-TM oxide film for complete CO oxidation. Figure 1. CO adsorption and O2 activation on Pt-supported FeO and NiO oxide films. Conclusions In conclusion, a strategy of preparing coordinatively unsaturated metal sites with lower valent states on metal substrates is demonstrated by taking advantage of the confinement effects at interfaces between nanostructured oxides and metal substrates. The confined CUF sites and neighboring metal atoms show a high activity and stability in CO oxidation under realistic conditions. The concept of interface confinement and fabrication of coordinately unsaturated low valent cations could be applied widely in various heterogeneous oxides-metals catalytic systems. It illustrates a promising and efficient way to design active sites for nanocatalysts. Acknowledgement. We thank finical supports by NFSC (20873142, 20733008, 20923001), MOST (2007CB815205), and fruitful discussions with Prof. Xin-He Bao and Q. Fu. References (1) Q. Fu, W. X. Li, Y. X. Yao, Y. H. Liu, H. Y. Su, D. Ma, X. H. Bao, Science 2010, 328, 1141.; Pt supported 3d transition metal oxide films: a reversed model catalysts for low temperature CO oxidation Wei-Xue Li State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Science, Dalian 116023, China; wxli@dicp.ac.cn Introduction In many catalytic processes, the size of metal containing catalysts supported on oxides falls typically in the range of 1-10 nm. The catalytically active sites in these catalysts are often coordinatively unsaturated metal cations that are able to undergo facile electron transfer and promote catalytic reactions. Among others, characteristic coordinatively unsaturated sites with flexible valent state (CUF) confined by various ensembles such as proteins, ligands and nanopore matrix are essential for their high reactivity and stability in the catalytic oxidation reactions. Preparation of the CUF sites is of great significance but remains a challenge because of their high structural complexity and flexibility under operating conditions. We describe here a strategy to achieve this goal by taking advantage of the confinement effect at interfaces between a variety of nanostructured oxides film with flexible valent states and Pt substrates. The interface-confined CUF sites and neighboring Pt atoms are identified conclusively as the active centers to activate O2 and represent a high activity for low temperature CO oxidation in the presence of excess of hydrogen. Computational Methods All calculations were performed using Vienna ab initio simulation package (VASP) and PAW potential. The wave function was expanded by plane wave with kinetic cutoff 400 eV. The exchange-correlation energy and potential were described by generalized gradient approximation in form of the PW91 and spinpolarized calculations were performed throughout the present paper, and on-site column repulsion between 3d TM d-electrons and magnetic interaction was described by DFT+U method. Adsorption was only allowed on one side of the slabs. The chemisorbed species and metal atoms of the uppermost two layers were allowed to relax till the residual forces less than 0.03 eV/Å, while the remained atoms were fixed at their bulk truncated positions. Transition states (TSs) were located by constrained minimization method and climbing-image nudged elastic band method (CI-NEB). Results and Discussion The interfacial interaction between 3d transition metal (TM)-oxide films and Pt(111) substrates was studied first. We found there is a strong interfacial adhesion stabilizing the 3d TM oxide films, which are essential to keep it in lower valent states with potential ability for O2 activation, instead of complete oxidation. For complete oxidation of 3d TM, O2 activation would be hindered. Moreover, we found that 3d-TM oxide film itself is not active either due to its polar characteristic. Therefore, the coordinated unsaturated sites presented at the perimeters of nano-structural oxide films with flexibility of valent state (so-called CUF sites) will be potential candidate as the active sites for O2 activation. This was indeed found by DFT calculations, as indicated in Figure 1. We found that the CUF sites were very selective for O2 activation, but has a low affinity for CO adsorption. The dual sites presented at the boundary between 3d-TM oxide films and Pt substrate offered an ideal active sites for CO adsorption and O2 activation. The dissociated atomic oxygen has a high activity for CO oxidation. Further calculation showed that the competition between CO adsorption and O2 activation is very sensitive to the 3d-TM. For the 3d-TM at the left side of the periodic table, the significant strong interaction with oxygen molecule leads to oxygen poison. Whereas for the right side of the periodic table, the activity for oxygen molecule decreases gradually, and as a compensation effect, the stability of 3d-TM oxide films increase. As a result, Pt supported early 3d-TM oxide film show up the good activity for CO oxidation in the excess of hydrogen, while for the late 3d-TM oxide film for complete CO oxidation. Figure 1. CO adsorption and O2 activation on Pt-supported FeO and NiO oxide films. Conclusions In conclusion, a strategy of preparing coordinatively unsaturated metal sites with lower valent states on metal substrates is demonstrated by taking advantage of the confinement effects at interfaces between nanostructured oxides and metal substrates. The confined CUF sites and neighboring metal atoms show a high activity and stability in CO oxidation under realistic conditions. The concept of interface confinement and fabrication of coordinately unsaturated low valent cations could be applied widely in various heterogeneous oxides-metals catalytic systems. It illustrates a promising and efficient way to design active sites for nanocatalysts. Acknowledgement. We thank finical supports by NFSC (20873142, 20733008, 20923001), MOST (2007CB815205), and fruitful discussions with Prof. Xin-He Bao and Q. Fu. References (1) Q. Fu, W. X. Li, Y. X. Yao, Y. H. Liu, H. Y. Su, D. Ma, X. H. Bao, Science 2010, 328, 1141.
文献类型会议论文
条目标识符http://cas-ir.dicp.ac.cn/handle/321008/115960
专题中国科学院大连化学物理研究所
通讯作者Li WX(李微雪)
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Li WX. Pt supported 3d transition metal oxide films: a reversed model catalysts for low temperature CO oxidation[C]. 待补充:待补充,2011:226-1.
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