Stabilisation of aluminas by rare earth and alkaline earth ions

Jeffrey S. Church, Noel W. Cant*, David L. Trimm

*Corresponding author for this work

Research output: Contribution to journalArticle

177 Citations (Scopus)

Abstract

The effect of added rare earth and alkaline earth oxides on the resistance of two aluminas to loss of surface area at high temperature has been investigated. In tests of short duration ( ≤ 4 h) at 1100 ° C, La3+ and Ce4+ are equally effective in reducing loss of area for a commercial γ-alumina. However, in extended tests (24 h) La3+is much more effective than Ce4+. X-ray diffraction shows that the latter has segregated as CeO2 and the alumina is largely α-phase. No separate rare earth oxide phase can be observed with La2O3 and θ-alumina is dominant. The same effects are discernable at higher temperature and with a washcoat alumina. Tests with other rare earth oxides and alkaline earth oxides show that an ion size effect is operative. Under severe conditions Ca2+, Yb3+ and Sm3+ are ineffective, Pr3+ and Sr2+are moderately effective while La3+ and Ba2+ are the most effective. Samples containing the latter both exhibit the presence of a hexaaluminate-type phase after tests at 1200° C. Diffuse reflectance infrared spectroscopy has been used to investigate surface hydroxyl groups formed after reequilibration of samples with ambient air. The groups present on sintered alumina differ only slightly from those on unsintered material. There is a good correlation between hydroxyl group band area, in Kubelka-Munk units, and surface area. Samples with added La2O3 and CeO2 show only AlOH groups which also closely resemble those present on alumina alone. However the band area for oxide stabilised samples appears to be slightly below that for pure alumina of equivalent area. At most 30% of the surface is made up of a capping layer of the added oxide. X-ray photoelectron spectroscopy (XPS ) binding energies, and La/ Al and Ce/Al atom ratios determined by XPS, are consistent with the above picture.

Original languageEnglish
Pages (from-to)105-116
Number of pages12
JournalApplied Catalysis A, General
Volume101
Issue number1
DOIs
Publication statusPublished - 26 Jul 1993

Keywords

  • alkaline earth oxides
  • alumina
  • rare earth oxides
  • stabilization
  • surface area

Fingerprint Dive into the research topics of 'Stabilisation of aluminas by rare earth and alkaline earth ions'. Together they form a unique fingerprint.

  • Cite this