Regulating the states of Ni species by controlling the silanols of MCM-41 support to promote the hydrogenation of maleic anhydride

Nickel (Ni) supported on MCM-41 zeolite as hydrogenation catalysts have been widely applied in various reactions, however, the synergism between Ni and the support remains obscure. To prepare more efficient catalysts and reveal the metal-support interaction, MCM-41 zeolite was modified with ammonium hexafluorosilicate (AHFS) before Ni loading. Results show that fluoride ions could selectively convert the vicinal silanols into isolated silanols on MCM-41 surface, which weakens the interactions between Ni precursors and the SiO2 supports. Over the modified MCM-41 zeolites, the attenuated interaction results in the agglomeration of NiO particles that is more easily to be reduced, rather than the formation of nickel phyllosilicate which is extraordinarily difficult towards reduction. The easily-reduced Ni particles provided more adsorption sites for C--C bond instead of C--O bond, and the adsorption strength was also regulated. Therefore, the AHFS modified catalyst demonstrated a notable enhancement in hydrogenation of maleic anhydride (MA) into succinic anhydride (SA), presenting 98.4 % MA conversion and 99.8 % SA selectivity at 90 degrees C under 3.0 MPa H2. Moreover, the optimum catalyst was recycled for 5 runs to analyze the deactivation mechanism, it was found out that the loss of activities stems from the leaching of large Ni particles. Overall, our work shed light on the metal-support interactions for Ni/MCM-41 catalyst, determining the vicinal hydroxyl groups were responsible for the state of Ni species, which is helpful for the rational design of other hydrogenation catalysts.