Carbon Coated Silica Doped With Cerium/Zirconium Mixed Oxides as NO2 Adsorbent at Ambient Conditions

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• 作者：Amani M. Ebrahim ; Teresa J. Bandosz
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：May 1, 2014
• 年：2014
• 卷：118
• 期：17
• 页码：8982-8992
• 全文大小：723K
• 年卷期：v.118,no.17(May 1, 2014)
• ISSN：1932-7455

文摘

Silica gel (Si-60) was modified by carbon grafting to produce carbon coated silica composites. The resulting materials were doped with cerium zirconium mixed oxide and tested as NO₂ adsorbents at ambient conditions. The textural and chemical features were characterized using SEM-EDX, adsorption of nitrogen, potentiometirc titration, thermal analysis and FT-IR. Modification with mixed oxides enhanced the adsorption of NO₂. While the composites with the lowest content of carbon exhibited the best performance in dry conditions, the composites with the highest carbon content showed the best performance in moist conditions. This trend is linked to the hydrophobic nature of the carbonaceous phase, which repels water but allows NO₂ accessibility to reactive sites introduced in the form of mixed oxides. Moreover, with an increase in the carbon content homogeneity of mixed oxide deposition on the surface increases. The release of NO is governed by the ability of the carbon surface to reduce nitrate species. Weakly adsorbed NO₂ molecules existing in the form of transient complexes with those metal sites undergo disproportionation reactions. As a result of these reactions, some NO₂ is converted to NO. Additionally, the percentage of NO released is higher in moist conditions than that in dry conditions. Exposure to NO₂ results in surface acidification due to the oxidation of Ce³⁺ and due to the formation of nitrogen bound species (NO₃^{2鈥?/sup>). The carbonaceous phase is rich in weakly acidic phenolic groups, which are additional sites for NO₂ interactions by nitration pathways.}