Fm. Bautista et al., STRUCTURAL AND TEXTURAL CHARACTERIZATION OF ALPO4-B2O3 AND AL2O3-B2O3(5-30 WT-PERCENT B2O3) SYSTEMS OBTAINED BY BORIC-ACID IMPREGNATION, Journal of catalysis, 173(2), 1998, pp. 333-344
A series of AlPO4-B2O3 (APB) and Al2O3-B2O3 (AlB) systems with various
boria loadings (5-30 wt%) were prepared by impregnation of AlPO4 with
boria from a boric acid solution (methanol or water) and characterize
d by XRD, SEM-EDX, TG/DTA, XPS, DRIFT and nitrogen adsorption. B-11, A
l-27, and P-31 MAS NMR were used to determine the local structure. DTA
and XRD analysis showed that crystallization occurred in all cases ab
ove 900 K, yielding alpha-cristobalite-AlPO4 in APB systems, and alumi
num berate in AlB systems. Also, boron oxide remained amorphous (XRD)
for thermal treatments in the range 473-1073 K. SEM showed a non-homog
eneous distribution in morphology, texture and particle size. Also, ED
X and XPS indicated a surface enrichment in boron for APB systems whil
e for AlB ones the reverse is true. Moreover, Al-27 MAS NMR showed the
simultaneous presence of four and six-coordinate Al atoms in AlB syst
ems while in APE ones, Al atoms appeared only in AI(OP)(4) environment
s. P-31 MAS NMR only identified P atoms with tertrahedral coordination
. Besides, the presence of boria did not change the local structure of
the starting AlPO4 or Al2O3 support. B-11 MAS NMR identified both tet
rahedral(BO4) and trigonal (BO3) species as being present; the concent
ration of tetrahedral oxygen coordinated berate (BO4) species were fou
nd to increase with boria loading. Furthermore, DRIFT spectroscopy sho
wed that the incorporation of boron results in the appearance of B-OH
groups and B-O stretches of a berate phase where both Trigonal and tet
rahedral boron exist on the surface of APB and AlB samples. Besides, t
rigonal berate species predominate and tetrahedral berate species incr
ease with boron loading. Finally, the incorporation of boron produces
a decrease in surface area and pore volume that becomes greater as the
boron content increases. (C) 1998 Academic Press.