Journal
JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL
Volume 425, Issue -, Pages 297-309Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.molcata.2016.10.031
Keywords
4H-chromene; 2-amino-2-chromene; CaO-ZrO2; Raman; Urea hydrolysis
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Funding
- Board of Research in Nuclear Sciences (BRNS), Mumbai [37(2)/14/23/2015/BRNS]
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A series of CaO-ZrO2 nanocomposite oxides containing 2-50 mol% of CaO were synthesized employing urea as a mild hydrolyzing agent. The nanocomposite systems were characterized using XRD, Fourier analysis, TPD, Raman, XPS, TGA-DSC, FESEM, HRTEM, and BET surface area measurement techniques. XRD study indicated selective stabilization of the tetragonal zirconia phase in the composite oxide. Upto 20 mol% CaO, the Ca2+ ions substituted for Zr4+ ions in the zirconia lattice to form a substitutional solid solution. Beyond 20 mol% CaO, the presence of a mixed phase system consisting of the solid solution phase, CaO and nonstoichiometric Zr-0.93 O-2 phase was observed. The composite oxides contain crystallites with size <20 nm as observed from Fourier and HRTEM analysis. TPD study revealed a significant enhancement in the basicity of zirconia as a result of Ca2+ incorporation. XPS study confirmed presence of different lattice oxygen as potential basic sites. Raman spectral data indicated the presence of oxygen vacancy and distortion in oxygen sublattice due to Ca2+ incorporation to zirconia. Microscopic investigation of the composite oxide suggested a gradual morphological change from rod shape particles to flake like and subsequently to cubic morphologywith increase in CaO content in the composite. The CaO-ZrO2 nanocomposite oxides were used as an efficient and recyclable heterogeneous base catalyst for synthesis of chromene analogues. Structurally diverse 2-amino-4H-chromenes and 2-amino-2-chromenes were synthesized in high yield and purity under mild condition using CaO-ZrO2 material as catalyst and multicomponent condensation approach. (C) 2016 Elsevier B.V. All rights reserved.
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