An investigation of the thermal stability, crystal structure and catalytic properties of bulk and alumina-supported transition metal nitrides
An investigation of the thermal stability, crystal structure and catalytic properties of bulk and alumina-supported transition metal nitrides
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DOI：
10.1016/j.jallcom.2007.10.046
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发表时间：
2008-09
影响因子：
6.2
通讯作者：
Z. Yao;Anjie Zhang;Yuan Li;Yuzhuo Zhang;Xiaoqing Cheng;C. Shi
中科院分区：
文献类型：
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作者：
Z. Yao;Anjie Zhang;Yuan Li;Yuzhuo Zhang;Xiaoqing Cheng;C. Shi
采用NH3-程序升温反应法合成了一系列V、Mo、Fe和Co金属氮化物，并用X射线衍射（XRD）和程序升温脱附技术对其进行了表征。X射线光电子能谱分析进一步证实了Co 4 N和Co 4 N/γ-Al 2 O3的形成。评价了这些金属氮化物对NO分解的催化活性。它们对NO的分解活性顺序为Co 4 N> Fe 3 N> Mo 2N>VN和Co 4 N/γ-Al 2 O3> Fe 3 N/γ-Al 2 O3> Mo 2N/γ-Al 2 O3>VN/γ-Al 2 O3。考察了催化剂的晶体结构与催化活性的关系。结果表明，空位浓度越高的金属氮化物具有越高的NO分解活性。金属氮化物与γ-Al 2 O3载体之间存在较强的相互作用。结果表明，Co 4 N/γ-Al 2 O3复合材料的热稳定性明显高于本体材料，这是由于Co 4 N与γ-Al 2 O3载体之间存在较强的相互作用。利用XRD技术研究了Co_4N/γ-Al_2O_3催化剂在反应过程中的结构变化。结果表明，Co 4 N/γ-Al 2 O3催化剂活性的迅速丧失是由于其本体氧化所致。在NO-H2反应中，NO解离过程中产生的氧被H2部分还原，部分进入氮化物晶格。通过在600°C下在原料气中加入H2，可以通过最小化表面氧的存在来保留活性Co 4 N/γ-Al 2 O3相。
A series of bulk and alumina-supported nitrides of metals (V, Mo, Fe and Co) were synthesized by NH3-temperature-programmed reaction and characterized by X-ray diffraction (XRD) and temperature-programmed desorption techniques. The formation of bulk Co4N and Co4N/γ-Al2O3was further confirmed using X-ray photoelectron spectroscopic analysis. The catalytic activities of these metal nitrides for NO decomposition were evaluated. Their activities for NO decomposition ranked in the order of Co4N>Fe3N>Mo2N>VN and Co4N/γ-Al2O3>Fe3N/γ-Al2O3>Mo2N/γ-Al2O3>VN/γ-Al2O3. The relationship between crystal structures and catalytic activities was investigated. The results indicated that metal nitrides with higher vacancy concentration exhibited higher activities for NO decomposition. There was a stronger interaction between the metal nitride phases and γ-Al2O3support. It was suggested that Co4N/γ-Al2O3exhibited thermal stability significantly higher than that of bulk counterpart, owing to the strong interaction between the Co4N phase and γ-Al2O3support. We applied the XRD technique to examine the structural changes of Co4N/γ-Al2O3catalysts during the reactions. The results indicated that the rapidly loss in catalytic activity was due to the bulk oxidation of Co4N/γ-Al2O3. In the NO–H2reaction, the oxygen generated during NO dissociation was partly reduced by H2and partly incorporated into the nitride lattice. By the addition of H2in feed gas at 600°C, one can retain the active Co4N/γ-Al2O3phase by minimizing the presence of surface oxygen.