反应条件对固相合成负载羰基铑原子簇催化剂及其性能的影响

本文报告了由金属盐直接固相合成负载铑络合物或原子簇催化剂的新方法及IR谱表征。CO容易使表面吸附有水分子的RhCl_3/SiO_2还原并生成表面羰基物Rh~+-(CO)_2/SiO_2;CO、CO/H_2和CO/2H_2等不同还原气对表面络合物的生成没有影响。采用H_2还原只能得到金属Rh催化剂。水是重要影响因素,如果RhCl_3/SiO_2先抽空脱水,再用含水的CO还原,就会使Rh~+(CO)_2/SiO_2转化为Rh_6(CO)_(16)/SiO_2。此外,还考察了负载原子簇的CO加氢和热分解反应性能。采用CO还原RhCl_3/SiO_2制备的催化剂同负载原子簇催化剂的反应行为非常相近,而且比传统催化剂具有更高的反应活性。

Effect of Reaction Conditions on the preparation of Supported Rhodium Clusters from Rhodium Salts in solid state and their Catalytic Properties

Here we report a new method of preparing supported rhodium complexes/clusters directly from supported rhodium chloride in controlled atmosphere. The formed surface complexes/clusters were characterized by IR spectroscopy. The results showed that CO easily reduces RhCl3/SiO2 preadsorbed with water molecules to give the surface carbonyl species Rh+(CO)/SiO2. The percentage of H2 in CO/ H2 atmosphere affected little on the* formation of the surface complexes. But reduction of RhCl3/SiO2 with pure H2 resulted in metallic rhodium catalyst (traditionally prepared metallic catalyst). Water played an important role in the process of the formation of the surface species. The surface species Rh+ (CO)2/SiO2 prepared from RhCl3/SiO2 which had been pretreated by vacuum to remove water would convert into Rh6(CO)16/SiO2 quickly when treating with water-saturated CO gas. The behaviors of CO hydrogenation and thermal decomposition of supported rhodium complexes/clusters were also studied. The supported rhodium complex/cluster catalysts prepared by our new method exhibited a good quality of catalytic properties close to the relevant ones prepared traditionally, but much higher than those of the traditional metallic catalysts.