화학공학소재연구정보센터
Applied Catalysis A: General, Vol.441, 108-118, 2012
Synthesize 2-methylpyrazine using aqueous glycerol and ethylenediamine over zinc oxide-zinc chromite catalysts: Structure-activity relationship
ZnO-ZnCr2O4 mixed oxides (Zn-Cr-O) were obtained by decomposition of Zn-Cr hydrotalcite precursors synthesized by co-precipitation method at pH similar to 7 and 9, with a constant Zn/Cr ratio of 2. Based on the product distribution, mechanisms were proposed. The differences in dehydrocyclization activity of Zn-Cr-O mixed oxides were established based on adsorption and spectroscopic data that emphasized changes in the structural properties of Zn-Cr-O obtained at different pHs. X-ray photoelectron (XPS) lines indicated Cr6+ and these species were reduced to Cr3+ during H-2-temperature programmed reduction (H-2-TPR) analysis. The higher NH3 and O-2 uptakes of Zn-Cr-O (pH 7) than Zn-Cr-O (pH similar to 9) are attributed to the presence of Cr6+ ions on the catalyst surface. Disorder in the cubic ZnCr2O4 sub-lattice may result in multiple Raman bands appeared in the Zn-Cr-O samples. The characteristic bands of Lewis and Bronsted acid sites at 1450 and 1540 cm(-1) assigned by FT-IR spectra of pyridine adsorbed on Zn-Cr-O samples, and their relative peak intensities corresponding to Lewis and Bronsted suggested higher ratios for Zn-Cr-O (pH similar to 7) than for Zn-Cr-O (pH similar to 9). It is demonstrated that the dehydrocyclization reaction proceeds on ZnO and/or ZnCr2O4 resulting in 2MP synthesis, and catalysts that possess mainly acid sites show intermolecular cyclization of EDA leading to high selectivity of pyrazine. (C) 2012 Elsevier B.V. All rights reserved.