Regenerating Spent Solutions of Vanadium-containing Heteropoly Acids in the Presence of Additives

Vanadium-containing heteropoly acid solutions of Keggin H3+xPMo12-xVxO40 and modified HaPzMoyVxOb types (P-Mo-V HPAs) are promising nanosized inorganic metal-oxygen cluster compounds with the property of reversible oxidability (V-V V-IV). The oxidation of reduced P-Mo-V HPAs at a temperature of 130-170 degrees C and an oxygen pressure of 4 atm is a convenient method for their regeneration, but results in regeneration degree of only 75-88%. Various materials with electron transfer or oxidative properties, such as nitrogen doped carbon nanofibers (N-CNFs), Sibunit-4, HNO3, and MoO2, were investigated as additives to facilitate and accelerate the regeneration of HPA solutions. Among the studied additives HNO3 was found to show the best efficiency, resulting in regeneration degree of higher 95%. Rapid and efficient regeneration of spent HPA catalysts is an important criterion for achieving high productivity and sustainability of oxidative processes on their basis.