Tailoring morphology of hierarchical catalysts for tuning pore diffusion behaviour: a rational guideline exploiting bench-top pulsed-field gradient (PFG) nuclear magnetic resonance (NMR)
Tailoring morphology of hierarchical catalysts for tuning pore diffusion behaviour: a rational guideline exploiting bench-top pulsed-field gradient (PFG) nuclear magnetic resonance (NMR)
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DOI：
10.1039/d0me00036a
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发表时间：
2020-08-01
影响因子：
3.6
通讯作者：
D'Agostino, Carmine
中科院分区：
文献类型：
--
作者：
Forster, Luke;Lutecki, Michal;D'Agostino, Carmine
这项工作的目的是开发和量化的多孔催化材料中的传输性能的调整，通过定制它们的纹理属性。为了做到这一点，氧化铝催化剂载体制备勃姆石通过改变制备条件，以产生具有不同孔径和大孔含量的载体。孔径和大孔含量随着勃姆石混合时间的增加而减小，随着煅烧温度的升高而增加，这是由于氧化铝发生了相变。采用脉冲场梯度NMR扩散技术，以正辛烷为探针分子，用低场台式NMR仪器研究了不同材料内的质量传递。扩散的结果表明，传质更容易发生在载体具有更大的孔径和大孔含量，通过提供一个全面的和定量的描述这种行为。特别地，高达17.0nm的孔径，扩散随孔径非常迅速地增加;在孔径大于17.0nm和大孔含量大于27%时，除去了孔结构对探针分子施加的主要几何限制并且客体分子的扩散率达到恒定的平台，这表明大于17.0nm的孔径和大于27%的大孔含量不会导致传质性能的显著进一步改善。扩散研究，使用水，甲醇和乙醇，作为探针分子与官能羟基基团能够与表面相互作用，表明，在样品中的小孔和没有量的大孔，这些客体分子与孔表面的表面相互作用有显着的影响上确定的扩散运动，除了物理孔结构的效果。对于较大的孔和较大的大孔含量，孔壁的表面化学对多孔基质内的扩散运动的影响要小得多。本工作给出了一个全面的和定量的概述，如何定制载体制备程序，以调整质量传输，提供了一个合理的指导方针，具有重要意义的设计，制备和应用的多孔材料。
The aim of this work is to develop and quantify the tuning of transport properties in porous catalytic materials by tailoring their textural properties. In order to do this, alumina catalyst carriers were prepared from boehmite by varying preparation conditions to produce carriers with different pore sizes and macropore content. Pore size and macropore content decreased with boehmite mixing time and increased with calcination temperature due to alumina phase transformations occurring. Mass transport within the different materials was studied by pulsed-field gradient NMR diffusion techniques, with a low-field, bench-top NMR instrument, using n-octane as the probe molecule. The diffusion results revealed that mass transport occurs more readily in carriers with greater pore size and macropore content, by providing a comprehensive and quantitative description of this behaviour. In particular, up to a pore size of 17.0 nm diffusion increases very rapidly with pore size; at pore sizes greater than 17.0 nm and macropore content greater than 27% the major geometrical restrictions imposed by the pore structure on the probe molecule were removed and the diffusivity of guest molecules reaches a constant plateau, suggesting that a pore size greater than 17.0 nm and a macropore content greater than 27% do not lead to significant further improvements in mass transport properties. Diffusion studies using water, methanol and ethanol, as probe molecules with functional hydroxyl groups able to interact with the surface, showed that in samples with small pores and no amount of macropores, surface interactions of these guest molecules with the pore surface have a significant effect on determining the diffusive motion, in addition to the effect of the physical pore structure. For larger pores and larger macropore content, the surface chemistry of the pore walls has a much smaller impact on the diffusive motion inside the porous matrix. This work gives a comprehensive and quantitative overview on how to tailor carrier preparation procedures in order to tune mass transport, providing a rational guideline with important implications in design, preparation and applications of porous materials.