植物营养元素的含量和δ~(13)C值随海拔而变化的特征及营养元素相互作用对碳同位素分馏作用的影响

为了研究植物营养元素的含量和δ~(13)C值随海拔而变化的相关关系,沿着海拔450 m的贵州茂兰至海拔1330 m的贵州安顺一线,采集和分析研究了C_3植物——小果蔷薇(R.cymosa Tratt)的叶片。分析结果表明,植物叶片中营养元素含量随着海拔的上升而产生的变化是:氮、磷和钾的含量会在增高,而钙和镁的含量却会降低。植物叶片的δ~(13)C值会增大,其变幅为+2.4‰/1000m。

The stability of nanosized HZSM-5 zeolite: a high-resolution solid-state NMR study

The thermal and hydrothermal stabilities of HZSM-5 zeolites with crystal sizes less than 100 nm have been studied by multinuclear solid-state NMR, combined with BET and XRD. As evidenced by Al-27 and Si-29 MAS as well as their corresponding cross-polarization/MAS NMR investigations, the thermal stability of nanosized HZSM-5 is not so good as that of microsized HZSM-5. This is due to two processes concerning dealumination and desilicification involved in the calcination of nanosized HZSM-5, while only the dealumination process is conducted in microsized HZSM-5 under the similar calcination process. The hydrothermal stability of nanosized HZSM-5 is, contrary to what was expected, not so bad as that of the microsized HZSM-5 in the course of steam treatment. The actual resistance of the hydrothermal stability to the crystal size of HZSM-5 can be ascribed to an active reconstruction of zeolitic framework through an effective filling of amorphous Si species into nanosized HZSM-5 during hydrothermal treatment. (C) 2001 Published by Elsevier Science B.V.