Аннотация
Calcium hydroxyapatites (HAP) containing cobalt or copper were
synthesized and catalytically evaluated in the dehydration of glycerol
for valuable chemical intermediates production. The solids were
characterized by chemical analysis, X-ray diffraction (XRD), Scanning
Electron Microscopy and Energy Dispersive X-ray Spectroscopy (SEM-EDS),
acid-base measurements, Raman spectroscopy and nitrogen adsorption
desorption isotherms. Cobalt-containing HAPs had the characteristic
hydroxyapatite (Ca10-x(HPO4)(PO4)(6-x)(OH)(2-x)x(H2O)(x)) and monetite
Ca(HPO4) phases, independently of the cobalt contents, being mesoporous
materials. This was proven to be due to Ca2+ ions replaced by Co2+ ones
in HAP structure; since the cobalt amount increased, a dispersion of
nanosized cobalt species was suggested. Copper-containing
hydroxyapatites showed the HAP and monetite phases. Increased copper
contents provided the ionic exchange of Ca2+ by Cu2+ and resulted in the
libethenite (Cu-2(OH)(PO4)) phase formation as well as the deposition of
CuO on solid surface. These solids possessing distinct morphologies had
micro and mesopores and preserved the HAP and monetite phases, even
increasing the copper content. The catalytic evaluation in the
dehydration of glycerol was dependent on the content of the metals as
well as the nature of the active phase. Generally, copper-containing
samples were more active than those possessing cobalt, probably due to
the either stable libethenite phase presence or great acidity of the
formers. The catalytic performance of the solids with low copper
contents showed the elevated selectivity to 1-hydroxyacetone and
products from its dimerization-cyclysation reactions whereas samples
possessing cobalt were selective to 1-hydroxyacetone and light products.
(C) 2013 Elsevier B.V. All rights reserved.
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