Porous solids in the form of adsorbents and catalysts play a crucial role in various industrially important chemical, energy, and environmental processes. Formulating them into structured configurations is a key step toward their scale up and successful implementation at the industrial level. Additive manufacturing, also known as 3D printing, has emerged as an invaluable platform for shape engineering porous solids and fabricating scalable configurations for use in a wide variety of separation and reaction applications. However, formulating porous materials into self-standing configurations can dramatically affect their performance and consequently the efficiency of the process wherein they operate. Toward this end, various research groups around the world have investigated the formulation of porous adsorbents and catalysts into structured scaffolds with complex geometries that not only exhibit comparable or improved performance to that of their powder parents but also address the pressure drop and attrition issues of traditional configurations. In this comprehensive review, we summarize the recent advances and current challenges in the field of adsorption and catalysis to better guide the future directions in shape engineering solid materials with a better control on composition, structure, and properties of 3D-printed adsorbents and catalysts.

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Amine-functionalized metal−organic frameworks (MOFs) are facile adsorbents for CO 2 removal from enclosed environments. In this study, we prepared polyethylenimine (PEI) and tetraethylenepentamine (TEPA) impregnated MOFmonoliths using a 3D printing technique, through pre-and postfunctionalization approaches, and evaluated their CO 2 capture performances. For preimpregnation, the MIL-101 powder was impregnated with PEI or TEPA and printed to form the monoliths. Meanwhile, the postimpregnation technique directly printed the MOF powder and secondarily impregnated the monoliths with TEPA or PEI. The adsorption analysis results indicated that all impregnated monoliths showed improved CO 2 capacities from the pristine monolith at dilute concentrations, and preimpregnation yielded higher CO 2 uptakes than postimpregnation. Specifically, the preimpregnated TEPA and preimpregnated PEI monoliths, with 3.5 and 5.5 mmol N/g amine content, respectively, displayed a capture capacity of 1.6 and 1.4 mmol/g, respectively, at 3000 ppm and 25 °C. From CHN analysis, postimpregnation yielded ∼50 wt % less N content than preimpregnation which was attributed to reduced diffusion of aminopolymers into the MOF pores. This was further evidenced by the textural properties which showed nearly a 3fold increase in pore volume and a 2-fold increase in surface area for postimpregnation over preimpregnation. In turn, preimpregnated TEPA-MIL-101 exhibited the highest amine efficiency of 0.46 mmol CO 2 /mmol N. Furthermore, the TEPA grafting occurred during paste densification at 50 °C and resulted in the enhanced stability of TEPA-MIL-101 monoliths. Despite high adsorption capacity, the adsorptions kinetics were found to be relatively slow over 3D-printed amine-loaded MIL-101 monoliths, especially the preimpregnated monoliths, because the adsorption rate was limited by the CO 2 molecular diffusion into the monolith walls. Overall, this study establishes a route to formulate amine-MOF monoliths by a 3D printing technique; however, the monolith dimensions should be tuned to optimize adsorption kinetics.

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