摘要
SiO_2负载的过渡金属催化剂经低温还原对烷烃氢解均呈活性状态,但不同金属彼此相差极大,Ru,Rh较Pt,Pd高5个数最级。高温烧结导致催化能力不同程度的下降,Ru,Rh下降达1000倍,而Ni仅降为原来的一半。透射电镜研究表明载体上各金属在烧结态均呈规则的多面体大颗粒状。该颗粒经充分氧化并低温还原后分裂成众多的无规则小晶粒的簇团。具有更低配位数和更高自由能的表面原子是氢解反应活性中心,溶于金属体内的氢则对氢解反应起抑制作用。
Silica-supported transition metals reduced at low temperature all show their high activities for alkane hydrogenolysis, but differ greatly each other with Ru, Rh being 5 orders of magnitude higher than Pt, Pd. Annealing at high temperature reduces the activities of these metals in different extent, by a factor of 1000 on Ru,Rh and by only 2 on Ni.Transmission electron microscopy studies show the formation of large regular polyhedral particles in the annealed state, which split to form clusters of small irregular particles upon complete oxidation and low-temperature reduction. The surface atoms with low coordination, high free energy are active sites for hydrogenolysis, and hydrogen in metals inhibits the reaction.
