Novel Recovery of Nano-Structured Ceria (CeO2) from Ce(III)-Benzoxazine Dimer Complexes via Thermal Decomposition

Abstract

N,N-bis(2-hydroxybenzyl)alkylamines, benzoxazine dimers, are the major product produced from benzoxazine monomers on mono-functional phenol by the one step ring opening reaction. Due to the metal responsive property of benzoxazine dimers, in this present work, N,N-bis(5-methyl-2-hydroxybenzyl)methylamine (MMD), N,N-bis (5-ethyl-2-hydroxybenzyl)methylamine (EMD), and N,N-bis(5-methoxy-2-hydroxybenzyl) methyl amine (MeMD), are considered as novel ligands for rare earth metal ion, such as cerium(III) ion. The complex formed when the clear and colorless solutions of cerium nitrate and benzoxazine dimers were mixed, results in a brown colored solution. The metal-ligand ratios determined by the molar ratio and the Job’s methods were found to be in a ratio of 1:6. To clarify the evidence of the complex formation mechanism, the interactions among protons in benzoxazine dimers both prior to and after the formation of complexes were determined by means of 1H-NMR, 2D-NMR and a computational simulation. The single phase ceria (CeO2) was successfully prepared by thermal decomposition of the Ce(III)-benzoxazine dimer complexes at 600 °C for 2 h, was then characterized using XRD. In addition, the ceria powder investigated by TEM is spherical with an average diameter of 20 nm.

Preparation of Palladium-Impregnated Ceria by Metal Complex Decomposition for Methane Steam Reforming Catalysis

“…Note that structural characteristics of the three metal complex precursors have been thoroughly investigated and reported in our previous works [22,25] and are not discussed further in this recent work. The obtained ceria powders exhibit high crystallinity indexed to be the face-centered cubic CeO 2 (JCPDS number 34-0394) and no crystalline impurity is observed in the XRD patterns (as demonstrated in Figure 1(a) in both red and blue curves).…”

“…Recently, the use of benzoxazine dimer derivatives as ligand for metal complex precursors has revealed a promising choice for synthesizing ceria through thermal decomposition of metal complex [25]. Therefore, in this work, we extend the state of the art toward the study of the influences of precursor choices used for the metal complex formations on characteristics of the obtained ceria materials and consequently on the catalytic activity after impregnation of palladium catalysts onto the ceria solid support.…”

“…Hereinafter, we call the ligand "benzoxazine dimer. " Cerium(III) nitrate hexahydrate and the benzoxazine dimer with the molar ratio of 1 : 6 were mixed together in ethanol in order to form cerium-benzoxazine dimer complex [25]. The complexation occurred very rapidly, since there was an immediate color change to dark purple after mixing two colorless substances together.…”

“…According to the thermogravimetric analyses in the previous works [19,22,25], the calcination temperature was selected to be 600 ∘ C. Therefore, all the prepared cerium complexes were subjected to calcination at 600 ∘ C for 2 h under air atmosphere to turn into ceria powders via thermal decomposition. The ceria powders obtained after the heat treatment of the complexes were pale-yellow colored.…”

“…Therefore, in this work, we extend the state of the art toward the study of the influences of precursor choices used for the metal complex formations on characteristics of the obtained ceria materials and consequently on the catalytic activity after impregnation of palladium catalysts onto the ceria solid support. Specifically, three different combinations of metal sources and organic ligands have been used to prepare metal complex precursors, namely, (a) cerium(III) nitrate hexahydrate (Ce(NO 3 ) 3 ⋅6H 2 O) and triethanolamine ligand, (b) cerium(III) chloride heptahydrate (CeCl 3 ⋅7H 2 O) and triethanolamine ligand, and (c) cerium(III) nitrate hexahydrate and benzoxazine dimer, N,Nbis(5-methoxy-2-hydroxybenzyl) methyl amine (MeMD), of which the structure was reported previously [25]. Note that the metal complex precursor prepared by combining cerium(III) chloride heptahydrate and benzoxazine dimer MeMD ligand is excluded from this study due to the less stability of this metal complex.…”