The Effect of Phosphate Treatment on Nickel Dispersion on MCM-41 Mesoporous Material

다국어 초록 (Multilingual Abstract)

The incorporation of nickel into mesoporous molecular sieves MCM-41 was carried out. Ni-PO/MCM41 and Ni-CI/ MCM41 were prepared by using Ni(Ⅱ) acetate solution adjusted to pH=2.5 with phosphoric acid and hydrochloric acid, respectively, by the incipient wetness method. Photoacoustic spectroscopy(PAS) was used to study the local environments of Ni(Ⅱ) incorporate into mesopores. The PAS of as-prepared Ni/MCM41, Ni-CI/MCM41, and Ni-PO/MCM41 with Ni(Ⅱ) acetate solution exhibits two bands of λ_max around 400nm and 750nm, which could be assigned to the ^2A_2g → ^3T_1g(F) and the ^3A_2g → ^3T1g(P) transition of octahedral Ni(Ⅱ) species. After calcination, Ni ion within Ni-PO/MCM41 dispersed atomically onto the surface of MCM-41 channel as an octahedral species without the transformation to nickel oxide phase, while Ni ion within Ni-CI/MCM41 and Ni/MCM41 transformed to nickel oxide phase. It may be attributed to the fact that each Ni ion is separated by the phosphate grafted to surface silanol group. The effects of phosphoric acid on the dispersity of Ni ion within MCM-41 have been investigated using ^31P and ^29Si MAS NMR spectroscopy and X-ray photoelectron spectrosecopy.