Study on the structure of active phase in NiMoP impregnation solution using Laser Raman spectroscopy II. Effect of organic additives

Laser Raman spectroscopy (LRS) was used to characterize the NiMoP impregnant with different contents of glycol and citric acid as well as dried Al2O3 impregnated with this NiMoP impregnant. The effect of glycol and citric acid on the structure of active phases in NiMoP impregnant and during the impregnation process was investigated. The results indicated that with glycol as the additive in the NiMoP(0.063) impregnant, the active phases like Hx[PMo11O39](7−x)− or Hx[PMo9O31](3−x)−) and Hx[PMo12O40](3−x)− are converted to Hx[P2Mo5O23](6−x)−. With citric acid as the additive, Hx[P2Mo5O23](6−x)−, (Hx[PMo11O39](7−x)− or Hx[PMo9O31](3−x)−) and Hx[PMo12O40](3−x)− are present together in the NiMoP(0.063) impregnant; however, citric acid leads a decrease of Hx[P2Mo5O23](6−x)− content but an increase of Hx[PMo12O40](3−x)−. Compared with glycol, during the impregnation of alumina with the NiMoP impregnant, citric acid is more effective in preventing the active phases from being decomposed in the cavities of alumina.