Y沸石中不同状态铁离子的还原和催化性质

Reductibility and Catalytic Properties of Different Fe( Ⅲ ) Species in Zeolite Y

制备了Fe(Ⅲ)处于骨架四面体内、阳离子位及以氧化物形式分散在沸石表面的含铁Y沸石.用TPR方法测定样品的可还原性,发现不同形态的Fe(Ⅲ)其还原情况不同,在800℃以下均不能被还原成金属Fe.以异丙醇脱水和脱氢为探针,考察了样品的酸碱性,证实在沸石结构内引入不同形态的Fe(Ⅲ)可调变沸石的酸碱性.用乙苯脱氢和裂解反应考察了样品的脱氢活性.当样品表面金属离子和强酸位同时存在时,由于二者的协同作用,裂解反应有可能占主导地位.消除强酸位,增加碱性位,可显著提高脱氢的选择性.

Y zeolites containing Fe( Ⅲ ) in framework sites, as the counterions and as the oxide dispersed on zeolite surface were prepared. The reductibility of the zeolite samples was studied by TPR method. Below 800℃ , the Fe( Ⅲ ) cations were reduced to Fe( Ⅲ ), the dispersed α-Fe2O3 was reduced to low valent iron oxide, but the framework Fe(Ⅲ) ions were unchanged. Unlike pure α-Fe2O3, none of the Fe( Ⅲ ) species in the zeolite could be reduced to Fe metal. The dehydration and dehydrogenation of isopropanol on the zeolites were used as the probe reactions for measuring the relative acidity and basicity of the samples. It has been verified that the adjustment of the acidity and basicity of zeolites through incorporation of Fe( Ⅲ ) ions into the various sites of the zeolite structure is realizable. The dehydrogenation and cracking of ethylbenzene were chosen as the probe reactions to measure the dehydrogenation activity of the different types of Fe(Ⅲ) ions incorporated into the zeolite. Cracking of ethylbenzene can become the major reaction due to the synergism of the metal ions and the strong acid sites on the zeolites. Elimination of the strong acid sites and addition of new basic sites on the zeolite surface through incorporation of Fe(Ⅲ ) species can enhance the dehydrogenation selectivity considerably.