PHASE-COMPOSITION OF AL-NI-MO CATALYSTS FOR HYDROTREATMENT PREPARED BY ONE-STEP IMPREGNATION USING DIFFERENT PROCEDURES

X-ray diffraction, Raman and diffuse-reflectance (DR) spectroscopy, co upled with selective extraction of Mo and Ni, are applied to investiga te the phase composition of Al-Ni-Mo catalysts prepared both by a conv entional one-step impregnation with ammonia and phosphoric acid, and b y a new method based on the use of nickel heteropolymolybdate. By comp aring the data obtained by Raman and DR spectroscopy with the data on water extraction, it is shown that the phase removed on washing can be ascribed to heteropolymolybdates. Formation of these compounds is fou nd to be favored by the use of the solution containing H3PO4 to impreg nate the catalyst with Mo and Ni.