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氘反同位素效应是合理阐明过渡金属催化剂上氨合成催化反应机理的重要实验依据之一. 在 N2/H2 (或 D2) 体积比 1/3, 0.2 MPa, 633~733 K 和 GHSV = 24 000 或 12 000 h?1 的条件下, 检测到了 Ru 基 (纯 Ru, Ru/?-Al2O3, K-Ru/?-Al2O3, Ru/MgO, K-Ru/MgO 和 Ba-Ru/MgO) 和 Fe 基 (纯 Fe 和 A110-3) 催化剂上强的氘反同位素效应 (rD/rH ? 2), 其数值随催化剂和反应温度的变化而变化. 这可能是动力学同位素效应与热力学同位素效应二者相互强竞争的结果. 相似文献
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本文在400—450℃和常压下,分别对暴露于N_2/3H_2,10N_2/H_2,N_2或H_2流动气体体系中的双促进铁催化剂A110-3上的化学吸附物种进行了反应条件下现场动态激光Raman光谱观测,并对暴露于D_2或~(15)NH_3/H_2流动或稳态气体体系的同一催化剂,在迅速冷至室温后进行了现场光谱观测。对于N_2/3H_2/A110-3体系观测到的Raman谱峰2040cm~(-1)(ms),1940cm~(-1)(m)和423cm~(-1)(m)与443cm~(-1)(w)可能分别归属于α-Fe(111)面活性中心上多核络合的斜插(或直插)式与平躺式两种不同化学吸附N_2物种的v_(N-N)和v_(Fe-N_2)。没有观测到可能归属于v_(Fe-N)的1088cm~(-1)和v_(Fe-NH)的890cm~(-1)(对于10N_2/H_2/A110-3或N_2/A110-3-残留H体系,从450℃迅速冷至室温后可观测到这两个Raman谱峰)。实验表明在上述远离平衡的氨合成反应条件下(常压,400—450℃),N或NH都不可能是主要的含氮化学吸附物种。因此,已知的氘反同位素效应就不可能基于NH或N为最大量的含氮吸附物种的假设,从热力学与解离式机理来解释。结果支持了氨合成反应的缔合式机理,主要反应途径看来是以N_2的化学吸附及其与化学吸附H(可归属于v_(Fe-H)的Raman谱峰位于1950cm~(-1),1901cm~(-1)等处)的加氢反应为速度控制步骤,而可能与之竞争的是按解离式机理的次要反 相似文献
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研究了三组份Cu-ZnO-Al_2O_3催化剂添加Cr_2O_3后.铬在催化剂中的存在形式,助催作用本质及其与甲醇含成催化活性的关联。结果表明:在ZnO-Cr_2O_3催化剂中,铬以Cr~(3 )和ZnCr_2O_4形式存在于ZnO晶格中,Cu-ZnO-Al_2O_3-Cr_2O_3催化剂的催化活性与CR~(3 )在ZnO晶格中诱导出来的正一价缺位和催化剂的其它顺磁性物种的ESR强度能很好地关联,在活性测试中,以含1%Cr(原子比)的Cu-ZnO-Al_2O_3-Cr_2O_3的催化活性最高。 相似文献
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碳纳米管负载铑催化剂上丙烯氢甲酰化 总被引:21,自引:0,他引:21
Effect of carbon nanotubes, as a novel support material, on the performance of Rh-catalyst supported by them was studied. Catalysts based on carbon nanotubes, SiO2, carbon molecular sieves, active carbon, and GDX-l02(a copolymer of styrene with divinylbenzene),were prepared, and their catalytic behaviors for propene hydroformylation were investigated and compared. The results showed that, over the carbon nanotubes-supported Rh-catalyst, C3H6 conversion and regioselectivity of butyric aldehyde (represented by n/i, a ratio of n-butyric aldehyde to its isomer, i-butyric aldehyde, in the products) were pronouncedly improved: the average turnover frequency(TOF) for the catalytic hydroformylation of propene was 0.079 s-1 at 393K, which was 2.1 times faster than that over the Rh catalyst based on SiO2, and the n/i ratio of the aldehyde products reached to 11.6, which was 1.9 times higher than that over the catalyst based on SiO2. The roles of six-membered C-ring at the surface of the carbon-nanotubes on the stability of the catalytically active Rh-complexes and of the tubular nano-channel on the spatiospecific seletivity of reaction intermediate state and butyric aldehyde produced were discussed. 相似文献