Dynamics of transition-metal complex in supercritical CO_2 as studied by NMR

1999年，我们设计并建造了一种新型的高压核磁共振探头，该探头可以在超临界CO_2(T_c=31.0℃，P_c=72.9 atm)的非均相体系中使用。利用该探头可在-70℃至+150℃的温度范围内进行原位核磁共振测量，并可在低于20 Mpa的压力范围内进行测量。Xe的临界参数为：T_c=289.8 K，P_c=5.8 Mpa，ρ_c=1.15gcm~(-3)~(-3)。在第一阶段，我们研究了对Xe吸附很弱的聚合物的自由体积。在下一阶段，我们对大孔二氧化硅FSM-16进行了第一次高压核磁共振测试。使用了三种类型的样品，它们具有不同的中孔直径(D)，即d=1.9、2.7和4.1 nm。结果表明，在d=1.9 nm的中孔中存在两个不同的Xe。另一方面，在d=4.1 nm的中孔中观察到单一的共振线。最后，我们用高压核磁共振技术研究了5A和13X分子筛的吸附性能。因此，不仅微孔内的水分子影响Xe在分子筛中的吸附，而且颗粒的大小也会影响Xe在分子筛中的吸附。

In 1999 we designed and built a new high-pressure NMR probe which can be used in a heterogeneous system under the supercritical condition of CO_2 (T_c = 31.0℃, P_c = 72.9atm). In situ NMR measurements can be performed in a temperature range between - 70 ℃ and + 150 ℃ , and in a pressure range below 20 MPa by using this probe.^<129>Xe NMR was recorded on a Bruker MSL-200 spectrometer to investigate physico-chemical properties of micropores and/or mesopores in various porous systems. The critical parameters of Xe are Tc = 289.8 K, Pc = 5.8 MPa, and ρ_c = 1.15 gcm^<-3>.At the first stage, we studied the free volumes in polymers which can adsorb Xe very weakly. The size of the micropore in each polymer was determined by ^<129>Xe NMR and was compared with the result of the positron annihilation experiment.In the next stage, we applied the first high-pressure ^<129>Xe NMR to the meoporous silica, FSM-16. Three types of samples were used, which have different diameters (d) of the mesopore, being d = 1.9, 2.7, and 4.1 nm. It was found that there are two inequivalent Xe inside the mesopore with d = 1.9 nm. On the other hand, a single resonance line was observed in the mesopore with d = 4.1 nm. It was concluded that at least a diameter of d = 2.7 nm is necessary to detect the evidence of the critical phenomenon in the mesopore.Finally we are now studying adsorption properties of molecular sieves 5A and 13X by using high-pressure ^<129>Xe NMR. It follows that not only water molecules inside the micropores but also the particle sizes affect Xe adsorption into these molecular sieves.