CO和NO在Rh2-V/SiO2催化剂上共吸附的红外光谱

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

CO and/or NO adsorption on reduced Rh2/SiO2 and Rh2-V/SiO2 catalysts has been studied by in situ infrared spectroscopy. The catalysts were prepared from Rh2 (CO)4Cl2 as a precursor. Three kinds of Rh sites are identified by CO adsorption corresponding 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. Addition of vanadium oxide to Rh2/SiO2 catalyst, decreases remarkly the number of RhⅡ and RhⅢ sites, and enhances the bond energy of RhⅠ(CO)2. The vanadium promotion is suggested as due to the electron transfer from Rh°to vanadium ions on Rh2-V/SiO2 catalyst. The results obtained from CO and NO adsorption on supported Rh and Rh-V catalysts derived from cluster and metal salt precursors, i.e., Rh2 (CO)4Cl2 and RhCl3, have been compared. It is found that the intensity of linear adsorbed CO on Rh2/SiO2 catalyst is more intense than that on Rh/SiO2 catalyst, this indicates that more Rh°sites were produced on Rh2/SiO2 catalyst. Rh2-V/SiO2 catalyst exhibits stronger electronic interaction between Rh metal and vanadium ions than that on Rh2-V/SiO2 catalyst.