Activation of Adsorbed Molecules in Zeolite by Means of Low-temperature Plasma and Photoexcitation

沸石是二氧化硅和氧化铝的混合氧化物，具有离子交换能力和孔隙率，因此，其内部空间可以被用作反应场。最近，我们报道了铜离子交换沸石(ZSM-5型)即使在室温下也能与氮气分子发生强烈的相互作用，其中一价铜离子物种(Cu^+)作为吸附中心。在本研究中，我们打算通过等离子体或光激发的方法在沸石中合成氮化合物，并阐明与氮分子反应的中心状态以及形成的氮化合物的反应活性。我们还尝试利用沸石的内部空间作为反应场来制备新型催化剂。所制备的铜离子交换沸石(CuZSM-5)对氮气的吸附能力因交换溶液中的反离子种类不同而不同，用含有羧基(-COO^-)的溶液制备的CuZSM-5样品具有良好的吸附性能。结果表明，氮气分子可被等离子体激发活化，被强吸附在沸石表面(这些物种只需在573K真空下处理即可脱除)。此外，还制备了银离子交换沸石(AgZSM-5)，通过紫外光激发，在沸石中形成了由大约10个原子组成的银团簇。很明显，这种银团簇和银离子的共存是催化反应(甲烷部分氧化)的充要条件。包括这些结果的两篇论文已经发表在科学期刊上，另外两篇论文正在提交给这些期刊。

Zeolite that is a mixed oxide of silica and alumina has an ability of ion-exchange as well as a porosity, and hence, its internal space can be expected to use as a reaction field. Recently, we have reported that the copper ion-exchanged zeolite (ZSM-5 type) interacts strongly with nitrogen molecules even at room temperature, where the monovalent copper ion species (Cu^+) act as adsorption sites. In the present study, we intended to synthesize nitrogen compounds in the zeolite by means of plasma or photoexcitation and to elucidate the state of sites that reacted with nitrogen molecules as well as the reactivity of nitrogen compound formed. We also tried to prepare new catalysts by making use of the internal space of zeilite as a reaction field.Some results obtained are as follows. The copper ion-exchanged zeolites (CuZSM-5) prepared have different ability to adsorb nitrogen molecules, depending on the kind of counter ions involved in the exchanging solution ; the sample prepared by using a solution involving carboxylato (-COO^-) was found to be excellent in adsorption property. It was evident that the nitrogen molecules can be activated by plasma excitation to be adsorbed strongly on the zeolite surface (these species are removed by only treating at 573 K in vacuo). Furthermore, silver ion-exchanged zeolite (AgZSM-5) was also prepared, and by photoexciting it with ultraviolet rays, silver clusters consisting of about ten atoms were formed in the zeolite. It became cleat that the coexistence of such silver clusters and silver ions was necessary and sufficient condition for catalytic reaction (partial oxidation of methane).Two papers including these results have already been published in the scientific journals, and two more papers are submitted to the journals.