Surface Properties and Catalytic Activities of Niobic Acid Treated with Diluted Phosphoric Acid

A surface treatment of niobic acid using about l mol dm−3 of phosphoric acid was effective for the enhancement of the surface acidity and the catalytic activity for some acid-catalyzed reactions such as cyclohexanol dehydration and alkylation of benzene with methanol. However, a treatment with phosphoric acid of higher concentration might form a deposit on the surface, which would prevent the penetration of reactants and/or products and, thus, decreased the catalytic activity of niobic acid. The P component added to the niobic acid was hardly removed by steaming at 400 °C, although it could be taken off by soaking in water at room temperature for twelve hours.