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.

中文翻译：

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调整孔隙扩散行为的分层催化剂的定制形态：利用台式脉冲场梯度（PFG）核磁共振（NMR）的合理指南

这项工作的目的是通过调整多孔材料的质地特性来开发和量化其迁移特性的调节。为此，通过改变制备条件由勃姆石制备氧化铝催化剂载体，以生产具有不同孔径和大孔含量的载体。孔尺寸和大孔含量随着勃姆石的混合时间而降低，并且由于煅烧温度的增加而归因于氧化铝相变的发生。使用低场台式NMR仪器，通过脉冲场梯度NMR扩散技术研究了不同材料中的传质，其中n-辛烷作为探针分子。扩散结果表明，通过对这种行为进行全面和定量的描述，在具有较大孔径和大孔含量的载体中，传质更容易发生。尤其是，最大孔径为17.0 nm时，扩散会随着孔径的增加而迅速增加。在孔径大于17.0 nm且大孔含量大于27％的情况下，消除了由孔结构对探针分子施加的主要几何限制，客体分子的扩散率达到了恒定平台，这表明孔径大于17.0 nm和大孔含量大于27％不会导致传质的显着进一步改善。使用水，甲醇和乙醇进行扩散研究，带有能与表面相互作用的功能性羟基的探针分子表明，在具有小孔且无大孔的样品中，这些客体分子与孔表面的表面相互作用对确定扩散运动也有重要影响物理孔结构的影响。对于较大的孔和较大的大孔含量，孔壁的表面化学性质对多孔基质内部的扩散运动的影响要小得多。这项工作对如何定制载体制备程序以调整质量运输提供了全面而定量的概述，提供了对多孔材料的设计，制备和应用具有重要意义的合理指导。这些客体分子与孔表面的表面相互作用，除了对物理孔结构的影响外，对确定扩散运动也有重要影响。对于较大的孔和较大的大孔含量，孔壁的表面化学性质对多孔基质内部的扩散运动的影响要小得多。这项工作对如何定制载体制备程序以调整质量运输提供了全面而定量的概述，提供了对多孔材料的设计，制备和应用具有重要意义的合理指导。这些客体分子与孔表面的表面相互作用，除了对物理孔结构的影响外，对确定扩散运动也有重要影响。对于较大的孔和较大的大孔含量，孔壁的表面化学性质对多孔基质内部的扩散运动的影响要小得多。这项工作对如何定制载体制备程序以调整质量运输提供了全面而定量的概述，提供了对多孔材料的设计，制备和应用具有重要意义的合理指导方针。孔壁的表面化学性质对多孔基质内部的扩散运动的影响要小得多。这项工作对如何定制载体制备程序以调整质量运输提供了全面而定量的概述，提供了对多孔材料的设计，制备和应用具有重要意义的合理指导。孔壁的表面化学性质对多孔基质内部扩散运动的影响要小得多。这项工作对如何定制载体制备程序以调整质量运输提供了全面而定量的概述，提供了对多孔材料的设计，制备和应用具有重要意义的合理指导。