Valency and coordination of iron in FeAIPO molecular sieves: an in situ Mossbauer study

摘要

Changes in the valency and coordination states of iron in FeALPO-5 and FeALPO-11 during reduction-oxidation treatments were followed by extracting isomer shift, quadrupole splitting and relative absorption area data from in situ Mossbauer spectra. Facile Fe~(3+) ->Fe~(2+) reduction was detected, and the Fe~(2+) formed was stabilized in a low symmetry coordination state. The bonding strength, characterized by the Debye temperature (#THETA#_D), was considerably smaller for Fe~(2+) than for Fe~(3+) (#THETA#_(D(Fe2+)) approxapprox 170 K, #THETA#_(D(Fe3+)) approxapprox 500 K).