Abstract
The M1 phases of the Mo-V-Te-Nb mixed-metal oxides are highly promising catalysts for direct propane (amm)oxidation. Nb is beneficial to the activity and selectivity for acrylonitrile, but direct evidence for Nb location is lacking because structural methods cannot distinguish Nb (Z = 41) from Mo (Z = 42). We have employed high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) and density functional theory (DFT) to study the Ta (Z = 73) location in a Mo-V-Te-Ta-O M1 phase produced via hydrothermal synthesis, which possesses uniform Ta distribution compared to M1 phases previously synthesized via slurry evaporation. The HAADF STEM and DFT results indicate that Ta predominantly occupies the pentagonal bipyramidal site (S9). Moreover DFT results validate the previous hypothesis that Ta and Nb both prefer the S9 site.
| Original language | English |
|---|---|
| Pages (from-to) | 68-72 |
| Number of pages | 5 |
| Journal | Catalysis Communications |
| Volume | 29 |
| DOIs | |
| State | Published - Dec 5 2012 |
Funding
This study was supported by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, U.S. Department of Energy , under Grant # DE-FG02-04ER15604 . The HAADF STEM studies were supported in part by ShaRE user facility, and part of the DFT studies were performed at the Center for Nanophase Materials Sciences, which are both sponsored at Oak Ridge National Laboratory (ORNL) by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. We would like to thank Shawn Reeves (ORNL) for her help for preparing sectioned samples. The resources of the National Energy Research Scientific Computing Center, supported by DOE Office of Science under Contract DE-AC02-05CH11231 , are gratefully acknowledged.
Keywords
- DFT
- HAADF STEM
- Heterogeneous catalysis
- Mixed metal oxides
- Mo-V-Te-Ta(Nb)-O M1 phase
- Propane (amm)oxidation