%0 Journal Article
%T Surface Modification of Fly Ash for Active Catalysis
%A Deepti Jain
%A Renu Hada
%A Ashu Rani
%J Journal of Catalysts
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/723957
%X Fly ash based effective solid base catalyst (KF/Al2O3/fly ash473, KF/Al2O3/fly ash673, and KF/Al2O3/fly ash873) was synthesized by loading KF over chemically and thermally activated fly ash. The chemical activation was done by treating fly ash with aluminum nitrate via precipitation method followed by thermal activation at 650¡ãC to increase the alumina content in fly ash. The increased alumina content was confirmed by SEM-EDX analysis. The alumina enriched fly ash was then loaded with KF (10 wt%) and calcined at three different temperatures 473£¿K, 673£¿K and 873£¿K. The amount of loaded KF was monitored by XRD, FTIR spectroscopy, SEM-EDX, TEM and Flame Atomic Absorption Spectrophotometer. The catalytic activities of the catalysts were tested in the Claisen-Schmidt condensation of benzaldehyde and 4-methoxybenzaldehyde with 2¡ä-hydroxyacetophenone to produce 2¡ä-hydroxychalcone and 4-methoxy-2¡ä-hydroxychalcone respectively. Higher conversion (83%) of benzaldehyde and (89%) of 4-methoxybenzaldehyde reveals that among these heterogeneous catalysts KF/Al2O3/fly ash673 is very active. 1. Introduction Fluoride ion is useful as weakly basic, nonnucleophilic in many organic chemical processes involving hydrogen abstraction or hydrogen bond formation [1]. Fluoride has been reported as effective basic catalyst in Cannizzaro reaction to replace classical methods employing hydroxide base which gave large amount of Cannizzaro side reactions [2]. Potassium fluoride is a well-known source of fluoride and possesses a number of advantages of both solution and solid phase chemistry. Among the supported fluoride systems, potassium fluoride on activated alumina has been found to be more reactive than nonsupported KF, KF-silica gel, KF-celite£¿and KF-molecular sieves [3]. When KF is loaded on alumina, it shows high catalytic activity towards organic reactions namely. Michael addition [4], aldol condensation£¿[5] and transesterification reactions [6]. The basic sites on KF/alumina may be related to a very hard anion F£¿; the catalyst may show the characteristic performances which differentiate KF/alumina from the oxide-type solid base catalysts such as alkaline earth oxides [7]. In contrast to many applications of KF/alumina to organic synthesis as a base catalyst, mechanisms of the appearance of the basicity of KF/alumina are not clarified. Insufficient coordination of KF only with surface OH groups may result in the formation of active F£¿ ions [8]. This possibility was supported by 19F MAS NMR [9]. Three basic species or mechanisms of the appearance of the basicity of KF/alumina
%U http://www.hindawi.com/journals/jcat/2013/723957/