ISSN:
1573-4803
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The solid state reactions occurring at the support throughout the preparation process of lanthana-supported metal catalysts is reported. Specifically it is concerned with the impregnation step. When following the usual procedure, i.e. impregnation of lanthana with an aqueous solution of the precursor, heavy carbonation of the support with formation of a hydroxycarbonate phase, La(OH)CO3, was found to occur. Simulated impregnation treatments with distilled water have shown that the nucleation of the hydroxycarbonate phase, not observed on lanthana simply exposed to air, is not specifically induced by the presence of the precursor salt. Likewise, it has been found that the nucleation of La(OH)CO3 does not take place upon heating the oxide in air at 383 K, as in the drying treatment which follows the wetting step of the impregnation process. Accordingly, nucleation of the new carbonated phase must occur during the wetting step. Once the formation of La(OH)CO3 has begun, the support can slowly take up further amounts of CO2 by simple exposure to air. In this way, impregnated support phases actually consisting of as much as 80% La(OH)CO3 could be observed. It can be concluded from the present work that the occurrence of carbonation phenomena on lanthana constitutes a major feature of its behaviour as a support of the transition metals. To date, however, this is an aspect which has received very little attention.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01161496
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