【摘要】 在催化剂的制备过程中,常采用浸渍法将金属或活性相负载到多孔固体载体上以获得高性能的负载型催化剂;在浸渍过程中溶剂对载体的浸润能力和效果对负载活性组分的分布和状态至关重要,进而会影响催化剂的催化性能.本文利用磁共振成像（MRI）技术开展了溶剂对γ-Al₂O₃颗粒浸润过程的原位研究.评估了自旋回波（SE）、梯度回波（GRE）和超短时间回波（UTE） 3种不同MRI序列的成像效果,发现UTE序列在观测短横向弛豫时间（T₂）值的¹H MRI信号方面展现出优越的性能,应用小激发角和短恢复时间（TR）可以获得比SE和GRE序列更高时间分辨率（<1 min）的动态图像.利用UTE序列对γ-Al₂O₃在不同极性溶剂中的浸渍过程进行了原位监测,发现极性溶剂水和甲醇均表现出典型的自由扩散过程,即溶剂从颗粒的外缘逐渐扩散到其中心直至饱和;非极性溶剂环己烷展现了不同的浸润行为,γ-Al₂O₃颗粒的整体¹H MRI信号分布呈现出颗粒中心信号强、边缘信号低的特点,并在γ-Al₂O₃颗粒的外层形成了强¹H MRI信号的“液膜”.更多还原

【Abstract】 Impregnation method is commonly used to prepare high-performance catalyst via loading metal or active phase on porous solid support.Solvent infiltration on the support during the impregnation process is essential for the distribution and state of the supported active components,which impact the catalytic property of the supported catalyst.In this study,magnetic resonance imaging（MRI） is implemented for in situ investigation of the solvent infiltration process on γ-Al₂O₃ particles.MRI of γ-Al₂O₃ particles infiltrated with sufficient water was evaluated by three different MRI sequences,i.e.,spin-echo（SE）,gradient-echo（GRE） and ultra-short time of echo（UTE）.It is found that the UTE sequence is superior in the acquisition of ¹H MRI signals with short T₂ values.The selection of very short time of echo（TE） values can significantly alleviate the differences in signal intensity caused by protons with different mobility.Particularly,the signals from the motion-restricted protons that diffuse into interior of γ-Al₂O₃ particles can be observed by using the UTE sequence.Meanwhile,the use of small excitation angle and short time of recovery（TR） in UTE allows to obtain the dynamic images with higher time resolution（<1 min） than that of SE and GRE sequences.The UTE sequence is employed to in situ monitor the infiltration process of γ-Al₂O₃ particles in solvent with distinct polarities.For polar solvent water and methanol,both show a typical free diffusion process that the solvent gradually diffuses from the outer edge of the particle to its center up to saturation.Interestingly,there is a different infiltration behavior for the non-polar solvent cyclohexane,and the overall ¹H MRI exhibits strong central signal and low edge signal in the γ-Al₂O₃ particles after immersed for a certain time.The"liquid film"with a strong signal intensity is formed around the particle,which probably prevents the infiltration of outer cyclohexane into particles,thus affecting the subsequent molecular diffusion and redistribution in the particles.更多还原