Constantinou Costas L, Costa Costas N, Efstathiou Angelos M
Department of Chemistry, Heterogeneous Catalysis Laboratory, University of Cyprus, P.O. Box 20537, CY 1678 Nicosia, Cyprus.
Environ Sci Technol. 2007 Feb 1;41(3):950-6. doi: 10.1021/es061392y.
The selective catalytic reduction of nitrates (NO3-) in pure water toward N2 formation by the use of gaseous H2 and in the presence of O2 (air) at 1 atm total pressure and 25 degrees C has been investigated over Pd-Cu supported on various mixed metal oxides, x wt % MO(x(/gamma-Al2O3 (MO(x) = CeO2, SrO, Mn2O3, Cr2O3, Y2O3, and TiO2). It is demonstrated for the firsttime that a remarkable improvement in N2 reaction selectivity (by 80 percentage units) can be achieved when oxygen is present in the reducing feed gas stream. In particular, significantly lower reaction selectivities toward NH4+ and NO2- can be obtained, whereas the rate of NO3- conversion is not significantly affected. Moreover, it was shown thatthe same effect is obtained over the Pd-Cu-supported catalysts irrespective to the chemical composition of support and the initial concentration of nitrates in water used. The Pd-Cu clusters supported on 4.8 wt%TiO2/gamma-Al2O3 resulted in a solid with the best catalytic behavior compared with the rest of supports examined, both in the presence and in the absence of oxygen in the reducing feed gas stream. DRIFTS studies performed following catalytic reduction by H2 of NO3- in water revealed that the presence of TiO2 in the Pd-Cu/TiO2-Al2O3 system enhanced the reactivity of adsorbed bidentate nitrate species toward H2. Nitrosyl species adsorbed on the alumina and titania support surfaces are considered as active intermediate species of the selective catalytic reduction of NO3- by H2 in water. Pd-Cu/TiO2-Al2O3 appears to be the most selective catalyst ever reported in the literature for the reduction of nitrates present in pure water into N2 by a reducing gas mixture of H2/air.
在1个大气压总压和25℃条件下，利用气态H₂并在O₂（空气）存在的情况下，研究了负载在各种混合金属氧化物x wt% MO(x)/γ-Al₂O₃（MO(x) = CeO₂、SrO、Mn₂O₃、Cr₂O₃、Y₂O₃和TiO₂）上的Pd-Cu对纯水中硝酸盐（NO₃⁻）选择性催化还原生成N₂的过程。首次证明，当还原进料气流中存在氧气时，N₂反应选择性可显著提高（提高80个百分点）。特别是，可以获得显著更低的对NH₄⁺和NO₂⁻的反应选择性，而NO₃⁻的转化率没有受到显著影响。此外，研究表明，负载Pd-Cu的催化剂无论载体的化学成分和所用水中硝酸盐的初始浓度如何，都能获得相同的效果。与其他所研究的载体相比，负载在4.8 wt%TiO₂/γ-Al₂O₃上的Pd-Cu簇在还原进料气流中存在和不存在氧气的情况下，都表现出最佳的催化性能。通过H₂对水中NO₃⁻进行催化还原后进行的漫反射红外傅里叶变换光谱（DRIFTS）研究表明，Pd-Cu/TiO₂-Al₂O₃体系中TiO₂的存在增强了吸附的双齿硝酸盐物种与H₂的反应活性。吸附在氧化铝和二氧化钛载体表面的亚硝酰基物种被认为是水中H₂选择性催化还原NO₃⁻的活性中间物种。Pd-Cu/TiO₂-Al₂O₃似乎是文献中报道的通过H₂/空气还原气体混合物将纯水中的硝酸盐还原为N₂的最具选择性的催化剂。
