Abstract
Heteropoly compounds in the solid state are ionic crystals (sometimes amorphous) consisting of large polyanions, cations, water of crystallization, and other molecules. Heteropolyacids (HPAs) have several advantages as catalysts. On the one hand, they have a very strong Bronsted acidity, especially the cobalt and cesium salts; on the other hand they are exhibiting fast reversible multielectron redox transformations under mild conditions. The cobalt and cesium salts of wells- Dawson HPAs were synthesized and characterized using elemental analysis and spectroscopic techniques ( 31 P-NMR, FT-IR). The wells-Dawson anions possess the ability to accept or release electrons through an external potential or upon exposure to UV radiation (photochemical reactions). The catalytic tests of these salts were investigated on phenol degradation where the UV photodegradation of acidified aqueous solutions (pH = 2) were studied in a batch photoreactor under ambient temperature and continuous circulation of phenol solution. The results reveal high catalytic activity for two HPAs, the best catalyst is the salt of cesium; where the presence of cesium improves significantly both the photcatalytic activity and the selectivity to oxalic acid.
Highlights
Solid state photochemical studies have recently become important due to their relevance in catalysis technologies.The chemical, photochemical and electrochemical properties of heteropolyanions have been subject of great interest primarily due to their wide ranging catalytic applications [1]
The results reveal high catalytic activity for two HPAs, the best catalyst is the salt of cesium; where the presence of cesium improves significantly both the photcatalytic activity and the selectivity to oxalic acid
Photodegradation of phenol were monitored using, an high performance liquid chromatography (HPLC) apparatus consisted of a water (Merck-Hitachi) model L-6200 A pump associated with a waters Model 6200 gradient controller, a reversed phase C18 analytical column (250 mm × 4.6 mm ID, 5 μm), and UV/Vis detector (L-4250. 190–700 nm) mark
Summary
Solid state photochemical studies have recently become important due to their relevance in catalysis technologies. Heteropolyacids (HPAs) and transition metalsubstituted heteropolyacids have more attracted interest as catalysts in many reactions than heteropolyanion salts because of their, their stronger Brønsted acidity, thermal, chemical stability and the possibilities for modification [10, 11]. These are come to be widely used as homogeneous and heterogeneous acidic oxidative catalysts by virtue of their unique physicochemical properties [12]. Because their insolubility in aqueous medium; cesiumsubstituted HPA Dawson-type was synthesized and characterized and used as a heterogeneous catalyst. Catalytic tests of several prepared HPAs were examined by photodegradation process in phenolic aqueous solution
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