Rh-Mn-Li／SiO2催化剂的吸附量热和红外研究

Studies of Highly Efficient Rh-Mn-Li/SiO_2 Catalyst by Microcalorimetry and FT-IR

通过在最优Rh含量基础上对金属配比的再优化,成功地改进了Rh-Mn-Li/SiO2催化剂的CO加氢性能;并采用微量吸附量热和红外等表征手段,考察了助剂Mn和Li促进作用的本质.结果表明:助剂Mn和Li的添加,使孪式和线式吸附CO的碳氧键强度增加,并同时削弱了桥式吸附CO的碳氧键或者使其转化为更易于解离的倾斜式CO吸附物种,从而同时增加了Rh基催化剂的CO解离和插入能力,提高了其活性和C2含氧化合物选择性.另一方面,Mn和Li的添加显著地降低了Rh基催化剂表面H的数量和稳定性.催化剂加氢能力显著降低极大地抑制了CH4的生成,从而有利于C2含氧化合物选择性的进一步提高.

A Rh-Mn-Li/SiO2 catalyst that exhibited rhodium efficiency up to 41g/（ g-Rh h） at reaction conditions： 553K, 5.0 MPa, 12 500 h^-1 and H2/CO =2 and excellent stability was developed by the re-optimization of metal ratio, and the effect of promoters such as Mn and Li on CO and H2 adsorption behaviors over Rh/SiO2 catalyst was researched by Microcalorimetry and Fourier Transform infrared （FT-IR）. The results showed that the addition of Mn and Li to Rh/SiO2 catalyst decreased adsorption intensities of linear and geminal CO and strengthened their Rh-C bond, which led to an increase in CO insertion ability of Rh-based catalyst; Meanwhile, the Rh-C bond of bridged CO was weakened or tilted CO appeared over the promoted Rh/SiO2 catalyst, which was favorable for increasing the CO dissociation ability. On the other hand, the number of active sites for dissociatively adsorbing H2 remarkably reduced, accompanied by an obvious decrease of adsorption intensities of H2 with the addition of Mn and Li to Rh/SiO2. The increase of CO insertion and dissociation abilities, and the decrease of hydrogenation ability of Rh-based catalyst were responsible for the dramatic increase of activity and selectivity toward C2-oxygenates with the addition of Mn and Li.