Negative thermal expansion in silicalite-1 and zirconium silicalite-1 having MFI structure |
| |
| Affiliation: | 1. Universidade Federal do Rio Grande do Norte, Laboratório de Peneiras Moleculares, 59078-970, Natal, RN, Brazil;2. Instituto de Tecnología Química, Universitat Politècnica de València-Consejo Superior de Investigaciones Científicas, 4602, Valencia, Spain;1. School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China;2. State Key Laboratory of Green Chemical Engineering and Industrial Catalysis, SINOPEC Shanghai Research Institute of Petrochemical Technology, Shanghai 201208, China;1. Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering, East China Normal University, North Zhongshan Rd. 3663, Shanghai 200062, China;2. Shanghai Key Laboratory of Magnetic Resonance, School of Physics and Materials Science, East China Normal University, North Zhongshan Rd. 3663, Shanghai 200062, China;1. Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Dalian 116023, China |
| |
| Abstract: | In situ high temperature X-ray diffraction (HTXRD) studies on monoclinic silicalite-1 (S-1, silica polymorph of ZSM-5) and an orthorhombic metallosilicate molecular sieve, zirconium silicalite-1 (ZrS-1) with MFI structure (Si/Zr = 50) have been carried out using a laboratory X-ray diffractometer with an Anton Parr HTK 1600 attachment. While the structure of the S-1 collapsed at 1123 K forming α-cristobalite. S-1 and ZrS-1 showed a complex thermal expansion behavior in the temperature range 298–1023 K, ZrS-1 was stable. Powder X-ray diffraction (PXRD) data taken in this region have shown strong negative lattice thermal expansion coefficient, αV = ?6.75 × 10?6 and ?17.92 × 10?6 K?1 in the temperature range 298–1023 K?1 for S-1 and ZrS-1 samples, respectively. The thermal expansion behavior of S-1 and ZrS-1 is anisotropic, with the relative strength of contraction along a axis is more than that along b and c axes. Three different thermal expansion regions could be identified in the overall temperature range (298–1023 K) studied, corroborating with the three steps of weight loss in the TG curve of ZrS-1 sample. While the region between 298 and 423 K, displays positive thermal expansion coefficient with αV = 2.647 × 10?6 and 4.24 × 10?6 K?1, the second region between 423 and 873 K shows strong negative thermal expansion (NTE) coefficient αV = ?7.602 × 10?6 and ?15.04 × 10?6 K?1, respectively, for S-1 and ZrS-1 samples. The region between 873 and 1023 K, shows a very strong NTE coefficient with αV = ?12.08 × 10?6 and ?45.622 × 10?6 K?1 for S-1 and ZrS-1, respectively, which is the highest in the whole temperature range studied. NTE seen over a temperature range 298–1023 K could be associated with transverse vibrations of bridging oxygen atoms in the structure which results in an apparent shortening of the Si–O distances. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
