Electron microscopy investigations of metal-support interaction effects in M/Y₂O₃ and M/ZrO₂ thin films (M=Cu, Ni)

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• 作者：Ramona Thalinger ; Michael St枚ger-Pollach ; Walid Hetaba ; Michael Feuerbacher ; Bernhard Kl枚tzer ; Simon Penner
• 关键词：Oxides ; Phase transitions ; Electron microscopy ; Thin films
• 刊名：Materials Chemistry and Physics
• 出版年：16 December, 2013
• 年：2013
• 卷：143
• 期：1
• 页码：167-177
• 全文大小：4346 K

文摘

Model systems of the clean and pure oxides Y₂O₃ and ZrO₂, as well as Cu/Cu₂O and Ni/NiO particles embedded in the respective oxides have been used to study the reduction behavior of the oxides and the eventually associated metal-support interaction effects in oxide-supported systems. Particular emphasis has also been given to the influence of the phase transformation in ZrO₂-containing systems on metal-support interaction. Whereas Y₂O₃ has been found to be an outstandingly structurally and thermally stable oxide even upon reduction in hydrogen up to 1073聽K, ZrO₂ was found to undergo a series of phase transformations from amorphous ZrO₂ to polycrystalline tetragonal ZrO₂ (鈭?73聽K) and subsequently to monoclinic ZrO₂ (above 873聽K). Both phase transformations were found to be basically dependent on gas partial pressure and annealing rate. However, substantial reduction of the oxides did not take place during the phase transformations. In turn, both Cu- and Ni-containing systems were not observed to be substantially affected by any (strong) metal-support interaction effects such as encapsulation by sub-stoichiometric oxides or reductive formation of intermetallic phases, at least up to temperatures of 1073聽K. Equally, for the ZrO₂-containing systems, also the phase transformations occurring at elevated temperatures did not cause structural or thermo-chemical alterations of the Cu or Ni-particles. Differences in the metal-support interaction between Cu- and Ni-particles have only been obtained in the structural 鈥渞eference鈥?systems, that is, if supported on SiO₂. Whereas Cu/Cu₂O particles on SiO₂ are basically unaffected by the reductive treatment at elevated temperatures, a Ni₃Si₂ intermetallic phase is formed if SiO₂-supported Ni/NiO particles are treated in hydrogen at 673聽K and above.