Cobalt Salts of Decamolybdodicobaltic Acid as Precursors of the Highly Reactive Type II CoMoS Phase in Hydrorefining Catalysts

摘要

Catalysts have been synthesized using the Anderson polyoxometalates (POMs) (NH_4)_4[Ni(OH)_6Mo_6O_(18)] (NiMo_6POM), (NH_4)_6[Co_2Mo_(10)O_(38)H_4] - 7H_2O (Co_2Mo_(10)POM), and H_6[Co_2Mo_(10)O_(38)H_4] (Co_2Mo_(10)HPA) as the precursors and hydrogen peroxide as the solvent. The catalysts have been characterized by lowtemperature nitrogen adsorption, XPS, and HRTEM. Their catalytic properties have been tested in thiophene hydrodesulfurization and in the hydrodesulfurization and hydro- genation of components of diesel oil. The active phase of the catalysts synthesized using the POMs is the type II CoMoS phase in which the mean plate length is 3.6–3.9 nm and the mean number of MoS_2 plate per plate packet is 1.8–2.0. Use of hydrogen peroxide provides an efficient means to reduce the proportion of Co~(2+) promoter atoms surrounded by oxygen in the case of an impregnating solution containing both an ammonium salt of a heteropoly acid and a Co~(2+) salt. In the catalysts synthesized using cobalt salts of Co_2Mo_(10)HPA, the support surface contains the multilayer type II CoMoS phase and cobalt sulfides. These catalyst show high catalytic properties in thiophene hydrogenolysis and diesel oil hydrorefining. Models are suggested for the catalysts synthesized using Anderson POMs.