摘要
合成了NaY超笼捕捉六核羰基簇合物Rh_6(CO)_(16)。IR和EXAFS考察结果表明,它的簇骨架Rh_6/NaY在氧化还原处理时具有较好的稳定性。Rh_6/NaY室温吸附CO后,对^(13)CO同位素交换反应的活性明显高于母体Rh_6(CO)_(16)/NaY。这些实验结果说明:可以在NaY超笼中合成稳定的Rh_6簇骨架,它在室温吸附CO时能形成与母体Rh_6(CO)_(16)类似的簇合物,可能是Rh_6(CO)_(16)的棱边桥式异构体。Rh_6/NaY对CO和H_2的化学吸附量分别为CO/Rh-2.6,H/Rh=0.8。化学吸咐量之比CO/H=3.3。
The structure of NaY zeolite entrapped Rh8(CO)16 , Rh6/NaY and CO, H2 chemisorption behavior of Rh6/NaY have been studied by FTIR and EXAFS. Rh6(CO)16 entrapped in NaY supercage was synthesized from Rh3+ ion-exchanged NaY by the reaction with CO + H2O at 393K. It showed the charateris-tic IR spectrum with bands at 2098 (vs), 2060 (w) cm-1 for twin carbonyls and 1760 (s) cm-1 for face-bridging carbonyl of Rh6(CO)18 entrapped in NaY (Fig.1A).Rh K edge EXAFS studies on the Rh6(CO)16/NaY also supported the formation of hexanuclear Rh6(CO)16 within NaY supercage ( Rh-Rh. R=2.74 A.C.N. =3.1; Rh-COL. R = 1.88A, C.N. = 1.5;Rh-COTri:R=2.15A, C.N. =1.6), as summarized in Table 1. The Rh6 framework was still maintained after the H2 reduction at 673K. From EXAFS analysis, the bond distances and coodination numbers of Rh-Rh, Rh-COL, Rh-COB bond for the CO-chemi-sorbcd Rh6/NaY were similar to those of the original Rhe(CO) i 6/NaY. However, the C-O vibration frequencies revealed by FTIR speclroscopy were different from the original Rh6(CO)16/NaY, and the adsorbed-CO was more active toward 13CO isotopic exchange reaction. It is suggested that the chemisorption of CO on Rh6/NaY leads to the formation of edge-bridging isomer of Rh6-(CO)16/NaY within the supercage.The results of CO-adsorption isotherms for Rh8/NaY supported the transformation from Rh6 into Rh6(CO)16 isomer due to CO chemisorption at 300K. The chemisorbed CO/Rh ratio was 2.6, almost the same as the CO/Rh ratio in Rh8(CO)16 molecule. The chemisorbed H2 was H/Rh = 0.8, and the ratio of chemisorbed CO to H2 on Rh6/NaY was CO/H=3.3.
基金
日本文部省科学研究基金(No.62470069)
