摘要
在甲醇氧化制甲醛反应中,银催化剂表面微量的铁将导致甲醛选择性下降,从而降低催化剂的使用寿命.研究其表面的结果表明,毒化的银催化剂表面的铁以氧化物形式存在.铁含量较低时,低氧化态的FeO为主要表面物种,铁借助于与之配位的氧原子与银表面发生强相互作用,形成四氧配位的平面结构;表面铁覆盖度的增加,导致了平面结构向八面体结构的转变,表面逐渐生成高氧化态的α-Fe_2O_3并趋向于聚集成岛,此时银铁间的相互作用消失.本文报道了用表面反应谱仪(TPRS)和表面功函数测量等方法研究氧、甲醇在毒化催化剂表面吸附和氧化反应机理的实验结果.
The temperature programmed reaction spectroscopy (TPRS) and work function measurement have been employed to study the oxidation reaction of meth-anol on electrolytic silver catalyst poisoned by iron. Two possible mechanisms are suggested for the poisoning action. First, the oxygen coordinating with Fe2+ on the surface attacks on the hydrogen in the surface methoxy species, which leads to the decomposition of the intermediate and the evolution of CO and H2. Second,the reactive adsorbed oxygen species on Fe2O3 islands (Ed = 44.4kJ/mol) bypasses the reaction path to form methoxy intermediate, so that combustion dominates and CO2 increases.
