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Chemical Weathering of Alumina in Aqueous Suspension at Ambient Pressure: A Mechanistic Study
Author(s) -
Abi Aad Jane,
Casale Sandra,
Michau Mathieu,
Courty Philippe,
Diehl Fabrice,
Marceau Eric,
Carrier Xavier
Publication year - 2017
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201700145
Subject(s) - gibbsite , hydroxide , dissolution , chemical engineering , aqueous solution , nucleation , weathering , precipitation , crystallinity , catalysis , chemistry , inorganic chemistry , aluminium , materials science , mineralogy , organic chemistry , geology , physics , engineering , geomorphology , meteorology
Transition aluminas rank among the main supports used for heterogeneous catalysis. Their stability in the aqueous phase is a key issue for catalytic processes, as their hydration can be strongly detrimental to their physicochemical and mechanical properties. As a consequence, the design of more stable alumina‐based supports relies on a better understanding of the mechanisms leading to their chemical and physical degradation. It is shown here that if suspended in water at atmospheric pressure and at temperatures up to 70 °C, all transition aluminas (from γ to θ‐Al 2 O 3 ) transform into Al(OH) 3 polymorphs (bayerite, gibbsite, and nordstrandite), although to different extents. A quantitative study of the aluminum concentration in solution and of the amount of hydroxides demonstrates that Al 2 O 3 hydration occurs through a two‐step dissolution/heterogeneous precipitation process, with nucleation of Al(OH) 3 on the surface of the alumina grains followed by particle growth. The grains become more fragile because of chemical weathering; the ensuing mechanical degradation by attrition, in turn, brings the weathering process to completion. The nature of the main hydroxide polymorph is a function of aluminum concentration and ageing time: first the kinetic product, bayerite, then nordstrandite and eventually gibbsite, the most thermodynamically stable hydroxide. Increasing crystallinity and decreasing specific surface area of alumina leads to a reduced amount in hydroxide formation.