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利用TPD(或TP)-IR动态方法,详细研究了由Rh_4(CO)_(12)衍生的Rh_4/Al_2O_3上金属分散度、CO覆盖和表面碳对CO吸附类型的影响。结果表明,影响CO在Rh_4/Al_2O_3上的吸附类型的主要因素是Rh的分散度,而分散度可以通过适当的制备方法加以控制。CO覆盖度只影响孪生CO谱带的强度;但同时影响线式和桥式CO谱带的位置和强度。在260℃以上,CO解离所产生的表面碳可以完全覆盖Rh~I中心,导致孪生CO谱带消失;对丁线式和桥式中心,只是部分被表面碳覆盖,导致线式样和桥式CO谱带位移到低频。 相似文献
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Five hydrotalcites with Mg/Al molar ratio range of 3-15 were prepared. The structure and basicity of Mg-Al mixed oxides (Mg(Al)O) transformed from hydrotalcites were investigated by TPD, XPS, XRD, FT-IR and NMR techniques. The results of elemental analysis and XPS indicate that Al is enriched in the surface regions of Mg(Al)0, and its amount increases with the Mg/Al molar ratio and the calcination temperature. 27Al-MAS-NMR results show that Al exists in two chemical environments: tetrahedral aluminium (Al(t)) and octahedral aluminium (Al(o)) in Mg(Al)O. The amount of Al(t) increases with the Mg/Al molar ratio and the calcination temperature. It is assumed that Al(t) may be mainly from the surface Al. Temperature-programmed desorption (TPD) of CO2 shows that the number of basic sites of Mg(Al)O samples increases with the Mg/Al molar ratio, and the maximum number of basic sites is obtained for hydrotalcite calcined at 773 K. Infrared spectra of adsorbed CO2 and B(OCH3)3 reveal that there are two kinds of 相似文献
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一氧化碳在Ru/Al2O3上吸附态的相互转化和稳定性的研究 总被引:1,自引:0,他引:1
本文利用差分红外光谱方法研究了不同预处理条件下,CO在4% Ru/Al2O3上的吸附,以及H2和CO在Ru/Al2O3上的共吸附。对CO在Ru上吸附态的红外光谱进行了归属,认为2070cm-1-2060cm-1的中频谱带是孪生CO吸附态的对称伸缩振动和线式CO吸附态的伸缩振动相叠合的谱带。讨论了表面碳(CS)、表面氧(OS)、表面氢(HS)对CO吸附态的影响,认为CO在Ru上发生岐化反应形成的表面碳可使Ru=CO键加强,共吸附H2可使Ru-CO键削弱。表面氧促使形成缺电子的中心,在此中心上生成CO孪生吸附态。CO的孪生吸附是活化吸附过程。 相似文献