Aqueous Interfacial Chemistry in the Catalyst Preparation of NiMo/Al2O3 System by EDTA-Containing Impregnation
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- 作者：Hongbin Zhao ; Zisheng Zhang ; Farzaneh Shemshaki ; Jin Zhang ; Zbigniew Ring
- 刊名：Energy & Fuels
- 出版年：2006
- 出版时间：September 2006
- 年：2006
- 卷：20
- 期：5
- 页码：1822 - 1827
- 全文大小：99K
- 年卷期：v.20,no.5(September 2006)
- ISSN：1520-5029
文摘
The present work studies the effect of organic chelating agents on the solution-support interfacial processduring the catalyst preparation. EDTA-Ni(II)-Mo(VI)-
-Al2O3-H2O is used as a representative catalystsynthesis system. It has been found that Ni(II) adsorption increases with pH value starting from pH 6 andreaches a maximum at pH 8 without EDTA, whereas the adsorption vs pH is reversed (maximum at pH 3.5and no adsorption at pH 9) when EDTA is introduced into this system with a molar ratio of EDTA/Ni(II) =1. According to ion-exchange theory, Ni(II) possibly forms a surface ternary complex with the alumina surfacesites through EDTA acting as a bridge. It has also been found that Mo(VI) adsorption decreases with pH(maximum at pH 3 and no adsorption at pH 9) in the absence of EDTA. EDTA suppresses the adsorption ofMo(VI), although the adsorption of Mo(VI) vs pH remains the same. EDTA has a higher coordinating constantwith the surface Al3+ than do Mo(VI) anions. Free EDTA competes with Mo(VI) on the alumina surface sites.Because EDTA has a preference to chemically bond with Ni(II), which forms a stable complex, Ni-EDTAcould be selectively adsorbed on the alumina surface. On the basis of these experimental results, it can berationalized that EDTA promotes the dispersion of both Ni(II) and Mo(VI) on alumina. Meanwhile, EDTAalso limits strong interactions between the metal ions and alumina, thereby contributing to the formation ofmore vigorous sites.
-Al2O3-H2O is used as a representative catalystsynthesis system. It has been found that Ni(II) adsorption increases with pH value starting from pH 6 andreaches a maximum at pH 8 without EDTA, whereas the adsorption vs pH is reversed (maximum at pH 3.5and no adsorption at pH 9) when EDTA is introduced into this system with a molar ratio of EDTA/Ni(II) =1. According to ion-exchange theory, Ni(II) possibly forms a surface ternary complex with the alumina surfacesites through EDTA acting as a bridge. It has also been found that Mo(VI) adsorption decreases with pH(maximum at pH 3 and no adsorption at pH 9) in the absence of EDTA. EDTA suppresses the adsorption ofMo(VI), although the adsorption of Mo(VI) vs pH remains the same. EDTA has a higher coordinating constantwith the surface Al3+ than do Mo(VI) anions. Free EDTA competes with Mo(VI) on the alumina surface sites.Because EDTA has a preference to chemically bond with Ni(II), which forms a stable complex, Ni-EDTAcould be selectively adsorbed on the alumina surface. On the basis of these experimental results, it can berationalized that EDTA promotes the dispersion of both Ni(II) and Mo(VI) on alumina. Meanwhile, EDTAalso limits strong interactions between the metal ions and alumina, thereby contributing to the formation ofmore vigorous sites.