高分散负载型Rh簇催化剂的研究

A STUDY OF HIGH DISPERED Rh CLUSTER DERIVED CATALYSTS

利用化学吸附及原位红外吸附态的测定装置和连续流动微反研究了用非传统方法制备的Rh_4/Al_2O_3和Rh_2/Al_2O_3。结果表明:催化剂具有高的金属分散度和均一的金属粒度;CO在催化剂上只有一种吸附方式,孪生吸附态;CO和H_2共吸附时,观测到的2035cm^(-1)谱带,归属为吸附态;在CO加氢反应中,催化剂具有高活性和高选择性,归结于高的金属分散度和均一的金属粒度。

Rh4/Al2O3 and Rh2/Al2O3 catalysts have been prepared by unconventional method to be highly dispersed and the metal supported has been determined by H2 chemisorption variation of IR spetra and their attributions in the process of heating adsorbed CO in vacuum, in CO atmosphere, in H2 atmosphere and in H2 and CO atmosphere have been studied by in situ IR spectra methods. The activity and selectivity of the catalysts under a series of H2/CO ratio have been investigated in a micro flow reactor. The results showed that there is a high metal dispersion degree and a uniform metal particle size on both the catalysts. In the process of heating in vacuum or in CO atmosphere, only the twin chemisorbed CO type RhI <COCO appeared , neither the spectra of the liner type nor that of bridge type has been observed. The spectra of twin chemisorbed type disappeared in H2 and CO atmosphere, only the band at 2035 cm-1 has been noticed. This is probably due to the influence of adsorbed H2 on the twin chemisorped CO, we assign this band to RhI< HCO, and in CO hydrogenation reaction RhI<HCO is the active type that results in CO dissociation. The activi- ty of the two catalysts has been observed increase with temperature rising and with higher H2/CO ratio, both the two catalysts had high rnethanation activity and selectivity which is assigned to the high metal dispersion degree and uniform metal particle size. But under the same condition, Rh4/Al2O3 had a higher activity than Rh2/Al2O3.