화학공학소재연구정보센터
Applied Catalysis A: General, Vol.359, No.1-2, 62-68, 2009
Ecofriendly liquid phase oxidation with hydrogen peroxide of 2,6-dimethylphenol to 2,6-dimethyl-1,4-benzoquinone catalyzed by TiO2-CeO2 mixed xerogels
Titania-ceria mixed xerogels were prepared with 10% (w/w) CeO2 and different pH values during the sol-gel process. The gels were dried in air and calcined at different temperature. Moreover, a sample without cerium, 100% (w/w) TiO2, was prepared to be kept as reference material. The prepared solids were characterized by means of XRD, SEM, DRS, FT-IR, TEM and EDX Their textural properties were determined by adsorption-desorption isotherms of N-2 at 77 K. The xerogels were tested as catalysts in the liquid phase oxidation of 2,6-dimethylphenol at 20 degrees C, using ethanol as solvent and aqueous hydrogen peroxide as a clean oxidizing agent. The 2,6-dimethyl-p-benzoquinone yield achieved was of 85-96% using the mixed xerogels as catalysts, and of 49% when the catalyst of titania without cerium was used. The best performance was achieved by the mixed xerogel synthesized at pH 4 and calcined at 200 degrees C; 100% of conversion of 2,6-dimethylphenol and 96% of yield in 2,6-dimethyl-p-benzoquinone were obtained in this case after 6 h of reaction. The reactions were again carried out with the catalyst recovered after its first use. Only a light yield decrease, lower than 2%, was observed. The use of an ethanol-water mixture as solvent (35:65% (v/v)) in the reaction was studied in order to make the reaction more environmentally friendly. Total conversion of the initial reactant, after 4 h of reaction at 20 degrees, with 70% yield in 2,6-dimethyl-p-benzoquinone (2,6-DMBQ), was observed. Under these conditions a red by-product, insoluble in the reaction solution, was formed. This by-product was isolated and characterized and it was possible to identify it as 2,6-DMBQ dimmer (3,3',5,5'-tetramethyl-4.4'-diphenoquinone). This by-product was observed in very few amounts when ethanol (96% (v/v)) was used as solvent. (C) 2009 Elsevier B.V. All rights reserved.