In situ Magnetic Resonance Imaging of Solvent Infiltration on gamma-Al2O3 Particles

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 infil. tration process on gamma-Al2O3 particles. MRI of gamma-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 H-1 MRI signals with short T-2 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 gamma-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 gamma-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 H-1 MRI exhibits strong central signal and low edge signal in the gamma-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.