Memory Effect of Activated Mg–Al Hydrotalcite: In Situ XRD Studies during Decomposition and Gas‐Phase Reconstruction

Chemistry - A European Journal - Tập 13 Số 3 - Trang 870-878 - 2007
Javier Pérez‐Ramírez1,2, Sònia Abelló2, N. M. van der Pers3
1Catalan Institution for Research and Advanced Studies (ICREA), Pg. Lluís Companys 23, 08010 Barcelona, Spain
2Laboratory for Heterogeneous Catalysis, Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, 43007 Tarragona, Spain,
3Department of Materials Science and Engineering, Delft University of Technology, Faculty of 3 mE, Mekelweg 2, 2628 CD Delft, The Netherlands

Tóm tắt

AbstractThe thermal decomposition of Mg–Al hydrotalcite and the subsequent reconstruction of the decomposed products in the presence of water vapor (2 vol. % H2O in N2) have been investigated by in situ XRD. Thermographic analysis and temperature‐programmed desorption MS results complemented the diffraction data. Valuable mechanistic and kinetic insights into these processes, which are of prime importance for optimal activation of this type of material for catalytic applications, were obtained. Hydrotalcite decomposition to the mixed oxide proceeds via formation at 423–473 K of an intermediate phase, consisting of a highly disordered, dehydrated, layered structure. The latter evolves by removal of interlayer water on heating, causing a shrinking of the interlayer space (it is up to 45 % smaller than in the as‐synthesized hydrotalcite). Above 623 K, Mg(Al)Ox oxide with the periclase structure is formed. Reversion of the intermediate dehydrated structure to hydrotalcite upon contact with water vapor is complete and very fast at room temperature. Recovery of hydrotalcite from the oxide calcined at 723 K is two orders of magnitude slower than rehydration of the intermediate layered structure and one order of magnitude slower than the typically practiced liquid‐phase reconstruction. In contrast to the decomposition, the reconstruction mechanism does not involve an intermediate phase. The gas‐phase rehydration and reconstruction was interrupted above 303 K. This is attributed to the poor wetting of the surface of the decomposed materials induced by hampered H2O adsorption above room temperature at the water vapor pressure applied. The Avrami–Erofe′ev model describes the reconstruction kinetics well.

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Tài liệu tham khảo

10.1016/0920-5861(91)80068-K

Braterman P. S., 2004, Handbook of Layered Materials, 313

10.1039/B510313B

10.1107/S0567740868003511

10.1180/minmag.1973.039.304.01

10.1023/B:CATT.0000007166.65577.34

10.1016/0021-9517(85)90219-2

10.1016/S0010-8545(98)00216-1

10.1016/S0169-1317(98)00058-1

10.1016/j.jpcs.2003.08.034

10.1016/S0169-1317(00)00026-0

10.1016/j.ijpharm.2003.09.043

10.1039/a707655j

10.1006/jcat.1994.1202

10.1006/jcat.1999.2734

10.1016/S0021-9517(02)00120-3

10.1039/a708431e

10.1016/S1381-1169(00)00209-0

10.1006/jcat.1997.1878

10.1023/A:1016626521403

10.1002/chem.200400409

10.1006/jcat.1995.1008

10.1039/a707874i

10.1016/S1381-1169(99)00099-0

10.1039/b002827o

10.1002/1521-3765(20010316)7:6<1258::AID-CHEM1258>3.0.CO;2-I

10.1021/ic971543l

10.1016/S0167-2738(97)00494-3

10.1016/S0924-2031(01)00119-9

10.1016/S0009-2509(02)00185-9

10.1016/S0926-860X(99)00084-8

Williams G. R., 2006, Structure and Bonding, Vol. 119, 161

10.1039/b009320n

Scherrer P., 1918, Nachr. Ges. Wiss. Göttingen, 2, 98

10.1039/a903231b

10.1021/jp960040i

10.1021/ic980739y

10.1021/la970543v

10.1006/jcat.1998.2161

10.1016/j.tca.2006.02.031

10.1021/j100066a024

10.1021/jp002715u

10.1016/S0025-5408(01)00657-2

10.1016/S0254-0584(02)00024-X

10.1021/cm980478q

10.1039/b006610i

10.1016/S0920-5861(99)00230-8

10.1063/1.1750380

10.1039/b005198p

10.1021/ja049860w

10.1111/j.1151-2916.1972.tb11213.x

10.1002/adma.200600673

10.1021/ja01269a023

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Chemistry - A European Journal

Tập 13 Số 3

870-878

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