The physicochemical property of extremely small Ru clusters supported on Y zeolite has been investigated with X-ray absorption fine structure (XAFS). The Ru clusters were prepared according to the following procedure. First a Ru red complex ion was obtained in the supercage of zeolite by the reaction of $RuCl_3$ and $NH_3$ aqueous phase at 330 K. Ru red complex ion was decomposed under vacuum at 673 K, during which the Ru species was partially reduced spontaneously. Third, Ru species was fully reduced to form a cluster in the supercage by heating in $H_2$ flowing at 623 K. The resulting Ru cluster size has been controlled with heating rate for the complex decomposition, as indicated by the average number of Ru atoms per cluster which was obtained from the xenon adsorption measurements.
Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) have been measured for the Ru cluster under He and $H_2$ at room temperature and 110 K. The coordination number of the nearest Ru-Ru pairs obtained from the standard curve fitting analysis of the EXAFS appeared to be underestimated at room temperature and 110 K, when compared with the cluster size estimated by the xenon adsorption method. This difference has been attributed to the static disorder, i.e., surface reconstruction in the small Ru cluster. Nevertheless, there was a good correlation between the coordination number from EXAFS and the results from the xenon adsorption measurement.
The electronic structure of the Ru cluster probed by XANES under dihydrogen atmosphere at room temperature did not change over the range of cluster size corresponding to 20 - 60 Ru atoms per cluster. Hydrogen chemisorption and the activity of ethane hydrogenolysis on Ru cluster were not affected significantly by the change of Ru cluster size. This has been attributed to the same electronic structure of Ru clusters over the cluster size range. However, the results of $^129Xe$ NMR spectrum as a function of Ru cluster size indicated that the surface of these small Ru clusters changed somewhat in the electronic structure. As the dihydrogen atmosphere was replaced by helium during the X-ray absorption measurement, the Ru-Ru bond distance contracted and the coordination number decreased due to the surface reconstruction, which resulted in the change of the XANES spectrum above the Ru K edge.
Y 제올라이트에 담지된 루테늄 금속 클러스터의 크기와 위치를 크세논 흡착법과 크세논 핵자기 공명 분광법을 이용하여 연구한 결과, 수퍼케이지내에 약 20 개에서 60 개의 루테늄 원자의 덩어리임을 알 수 있었다. 이 루테늄 금속 클러스터의 물리 화학적 성질을 연구하기 위하여 X 선 흡광 실험을 여러 가지 실험조건에서 한 후, 흡광분석 결과를 루테늄 금속 클러스터의 크기와 관련지어 보고자 하였으며, 흡착 및 반응성과 연관성도 연구하였다. 실험결과에 따르면 제올라이트 수퍼케이지에 존재하는 매우 작은 루테늄 금속 클러스터는 재배열 (reconstruction) 현상이 수소 기체가 흡착된 상태에서도 현저히 일어남을 알 수 있었다. 그리고 수소 흡착법으로는 10Å 이하의 작은 루테늄 금속 클러스터의 크기를 결정할 수가 없었다. 에탄의 분해 반응 실험결과 루테늄 금속 클러스터의 크기가 감소함으로서 생기는 분해반응점의 감소 때문에 촉매반응성이 루테늄 금속 클러스터의 크기에 감소함에 따라 감소함을 볼 수 있었다.
