# Additive Manufacturing and Chemical Engineering: Looking for Synergies from a Bibliometric Study
## 4 Review of Research Focused on Additive Manufacturing and Chemical Engineering
### Additive Manufacturing and Chemical Engineering: Future Needs
#### 4.2.4 Catalysts and Sorbents Produced by Additive Manufacturing  
The development of novel catalysts and sorbents is essential for advancing sustainable practices across various industries. From renewable energy production to wastewater treatment, these materials contribute to minimizing environmental impact while optimizing resource efficiency. Innovations in catalyst and sorbent technologies not only improve process economics by reducing energy consumption and waste generation but also pave the way for greener industrial operation conditions [152]. There is particular interest in monolithic structures given their ability to offer significant advantages compared to conventional configurations such as pellets, beads, or granules. Monoliths are structured materials with specifically designed flow channels whose shape and density per cross-sectional area are controllable [153]. Their advantages include low pressure drop, high thermal stability, excellent mechanical integrity, and good mass and heat transfer characteristics [154]. These properties enable overcoming the issues associated with packed beds, such as limitations in heat and mass transfer, high pressure drops, and uneven flows, which can lead to deviations in contact time and decreased selectivity [152].  
One particularly challenging aspect in manufacturing monolithic structures via traditional direct extrusion processes is balancing key design parameters such as active load, mass and heat transfer properties, and channel distribution [153]. When additive manufacturing is employed, it becomes possible to fabricate monoliths with a high degree of freedom, varied cross-sectional shapes, channel sizes, and wall thicknesses, and importantly, manufacturing parameters can be adjusted to achieve final products with enhanced mechanical properties. Currently, the most utilized technologies for manufacturing catalysts and adsorbents by additive manufacturing are based on material extrusion, specifically Direct Ink Writing, followed by Fused Deposition Modeling [155].  
Applications of catalysts and sorbents produced by additive manufacturing have expanded across various fields in chemical engineering. For example, three-dimensional honeycomb monolithic reactors with interconnected channels were employed in the selective production of dihydroxybenzenes such as catechol and hydroquinone (Figure 17a), demonstrating significant improvements in performance, stability, and sustainability compared to conventional commercial methods [156]. In another study, the manufacture of zeolitic monoliths through 3D printing provided an efficient platform for the synthesis of heterogeneous catalysts applied to the catalytic cracking of n-hexane, resulting in increased selectivity towards light olefins and improved stability compared to powder alternatives [154]. SAPO-34 monoliths produced via Direct Ink Writing showed notable affinity and CO\({}_{2}\) adsorption capacity, suggesting enhancements in gas separation efficiency (Figure 17b). Additionally, these 3D-printed SAPO-34 monoliths enabled selective CO\({}_{2}\) and N\({}_{2}\) separation through adsorption, with adaptable geometry and excellent recoverability [157]. Finally, the 3D printing of activated carbon provided a solution for CO\({}_{2}\) capture in post-combustion scenarios, exhibiting high adsorption capacity and selectivity adjustable based on the selected activation conditions [158].