CO和NO在Rh_2-V/SiO_2催化剂上共吸附的红外光谱

CO or/and NO Adsorption on Reduced Rh_2/SiO_2 and Rh_2-V/SiO_2 Catalysts Characterized by Infrared Spectroscopy

应用CO和NO吸附态原位红外光谱方法研究了还原态Rh2／SiO2，Rh2－V／SiO2催化剂上的活性中心铑的状态和助剂钒的作用。Rh2催化剂用Rh2（CO）4Cl2化合物制备，在还原Rh2／SiO2催化剂上，CO吸附出现四个红外吸收峰：2085，2028cm－1（孪生态吸附RhⅠ（CO）2），2060cm－1（线式吸附RhⅡCO），1867cm－1（桥式吸附RhⅢ2CO）．在还原Rh2－V／SiO2催化剂上，CO在RhⅡ和RhⅢ中心上的吸附峰大大减弱，可以解释为Rh°向钒离子转移电子生成了带正电荷的铑中心（Rhδ＋）；同时RhⅠ（CO）2键能增加，降低了孪生CO被NO置换的程度。

CO and/or NO adsorption on reduced Rh2/SiO2 and An2-V/SiO2 catalystshas been studied by in situ infrared spectroscopy. The catalysts were prepared fromAh2:(CO)4Cl2 as a precursor. Three kinds of Rh sites are identilied by CO adsorption cor responding to absorbance bands at 2085, and 2028cm-1 (RhⅠ(CO)2), 2060cm-1 (RhⅡCO),1867cm-1 (Rh2ⅢCO), respectively. IR bands of NO adsorption on Rh sites appears at 1748and 1648cm-1 ) which can be assigned to Rh-NO and Rh-Noδ- species, respectively. Ad dition of vanadium oxide to Rh2/SiO2 catalyst, decreases reinarkly the number of RhⅡand RhⅢ sites, and enhances the bond energy of RhⅠ(CO)2. The vanadium promotionis suggested as due to the electron transfer from Rh° to vanadium ions on Rh2-V/SiO2catalyst. The results obtained from CO and NO adsorption on supported Rh and Rh-Vcatalysts derived from cluster and metal salt precursors， i. e.， Rh2(CO)4Cl2 and RhCl3,have been compared. It is found tbat the intensity of linear adsorbed CO on Rh2/SiO2catalyst is more intense than that on Rh/SiO2 catalyst, this indicates that more Rh° siteswere produced on Rh2/SiO2 catalyst. Rh2-V/SiO2 catalyst exhibits stronger electronicinteraction between Rh metal and vanadium ions than that on Rh-V/SiO2 catalyst.