【摘要】 常压下乙烯在Rh-Y分子筛催化剂上的氢甲酰化反应存在一定的诱导期。在反应条件下,加氢反应和氢甲酰化反应同时进行。在反应初期,含氧化合物活性的增加伴随着乙烷活性的降低,反应达到平衡的时间取决于对催化剂的预处理条件,反应前后,催化剂的颜色有明显变化（淡黄色变成红棕色）:根据XPS的研究结果,新鲜催化剂与用过催化剂的Rh₃d5/2结合能为309.1和306.9eV,分别对应于铑的三价态和零价态。这预示着金属态的铑粒子可能是乙烯氢甲酰化反应的活性中心或它的前身。另外,反应条件下的红外光谱清楚地表明,催化剂的H₂还原处理在活性中心的形成过程中起着非常重要的作用。更多还原

【Abstract】 Hydroformylation of ethylene over Rh-Y zeolite catalyst was carried out in a continuous-flow system under atmospheric pressure. Hydroformylation and hydrogenation of ethylene occurred simultaneously over the catalyst in a reactant stream consisting of H2-CO-C2H4 (1:1:1). In the first hours, the activity for hydrogenation of C2H4 decreased while that for hydroformylation of C2H4 increased. The induction periods were found to be: a) 3 h for reduction at 473 K for 3 h; b) 4 h for carbonylation at 433 K for 3 h; c) 5. 5 h for flushing with He at 433 K for 3 h, dependent on the pretreatment of the catalyst. The enhancement of the catalytic activity for hydroformylation seems to be accompanied by color changes of the catalyst from light yellow to deep red-purple. The used catalyst that showed a deep red-purple color exhibited adsorption bands at 436, 475 and 504 nm in the visible spectrum, while the fresh catalyst did not show those adsorption bands. An identical spectrum was obtained from Na-Y zeolite on which propionaldehyde had been adsorbed. The XPS binding energies of Rh3d5/2 for fresh and used catalysts are 309. 1 and 306. 9 eV, respectively. This can be assigned to Rh(Ⅲ) for the fresh catalyst and Rh(0) for the used one. Depending on the XPS profile (Rh3d) of the dried catalyst changing from broad (reaction for 0. 5 h) to sharp (reaction for 3 h), we suggest that the former catalyst contains a small amount of Rh(Ⅱ) and Rh(Ⅰ) besides Rh(0). And then all Rh(Ⅱ) and Rh(Ⅰ) convert to Kh(0). The results may indicate that metallic rhodium particles are the active species for ethylene hydroformylation or their precursors. Moreover, based on the IR results of the Rh- Y zeolite at ethylene hydroformylation conditions after different pretreatments, the rate of propionaldehyde formation for the reduced catalyst is greater than that for the carbonylated or dried one. It clearly shows the important role of hydrogen in the formation of active rhodium species for ethylene hydroformylation.更多还原