The Effect of Phosphoric Acid Treatment on the Catalytic Property of Niobic Acid

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Abstract
The effects of the treatment of niobic acid with phosphoric acid, sulfuric acid, and hydrofluoric acid on its surface area, structure, acidic property, and catalytic activity have been studied. The treatment with phosphoric acid was found to be most effective for maintaining a large surface area and a large amount of strong acid sites and for preventing niobic acid from crystallizing even after the heat treatment at higher temperatures above 600 °C. The XPS study revealed that a large amount of phosphorous exists on niobic acid after high temperature heat treatment. In accordance with these results, niobic acid treated with phosphoric acid and heat-treated at higher temperatures exhibited high catalytic activities for methanol conversion and ethylene hydration, whereas the activities of niobic acid containing no phophoric acid were very low when heat-treated at high temperatures.