(K,Mo)Y分子筛中钼组分的EXAFS研究

应用同步辐射Extended X-ray Absorption Fine Structure (EXAFS)技术研究固态法制备的KHMoY分子筛的氧化态和硫化态样品以及硫化态KHY/MoO3样品中钼组分的局域配位环境结构,并与KHMoY和KHY/MoO3样品催化加氢活性结果进行对照.结果表明,随原子比(K+2Mo)/Al的变化,钼原子周围的配位环境有显著的差异.当(K+2Mo)/Al＜1时,KHMoY和KHY/MoO3硫化后,钼组分主要以MoS2小原子簇分散在分子筛超笼中;(K+2Mo)/Al＞1时,钼组分则有两种存在环境,即分子筛超笼中的和分子筛外表面的钼组分.分子筛超笼中的MoS2原子簇的催化加氢合成醇选择性较高;分子筛外表面的MoS2微小颗粒的尺寸相对于超笼中的要大许多,其合成醇选择性较低.

Study of Molybdenum Components in (K, Mo) Y-Zeolites by EXAFS

The local structures of the oxidic and sulfided molybdenum loaded KHMoY zeolites prepared by solid-state reaction and the sulfided mixtures of KHY/MoO3have been investigated by EXAFS. The alcohol synthesis of CO hydrogenation is used to characterize catalytic performance for the sulfided (K, Mo)Y catalysts which is well explained by the EXAFS results. The results indicate that the local structures of Mo(VI) species depend on the atomic ratio of (K+2Mo)/Al. At the ratio of (K+2Mo)/Al lower than the exchange capacity, i.e., 1, the molybdenum species are completely dispersed into the supercages of the zeolites as small atomic cluster of MoS2. At the ratio of (K+2Mo)/Al lager than 1, the molybdenum species could exist in two phases, including both inside and outside of the zeolite supercages. Moreover, the size of MoS2located at the out-surface of the zeolite supercages is much larger than the one in the zeolite supercages. We present that MoS2cluster in the zeolite supercages of zeolites has a higher selectivity of alcohol synthesis for the CO hydrogenation than the MoS2particles located at the out-surface of the zeolite supercages.