# 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
#### 4.2.5 Additive Manufacturing for Microreactors and Miniaturized Devices  
Microreactors, and other microstructured devices, are compact pieces of equipment designed for mass and heat transfer in structures typically smaller than 1 mm. This scale presents numerous advantages over conventional chemical engineering operations at larger scales, particularly in terms of the ease of mixing due to reduced dimensions that facilitate diffusion, as well as high conversion and selectivity. Furthermore, their high area-volume ratio contributes to more efficient heat and mass transfer [159]. Inherent challenges in these devices primarily revolve around the manufacturing process, where the ability to produce three-dimensional structures of extremely small dimensions is critical, and other determining factors that must be taken into account include cost, processing time, and required precision [160]. Additive manufacturing emerges as an alternative technology that mitigates challenges associated with manufacturing costs while offering significant advantages for rapid prototyping. This technique provides remarkable flexibility for the agile manufacturing of virtually any channel geometry alongside the ability to utilize a wide range of materials and customized designs. However, one of the main challenges when printing more complex microreactors via additive manufacturing lies in multi-level connectivity [161].  
Some examples of miniaturized devices produced by means of additive manufacturing used in chemical engineering applications can be commented on. Among these found applications, the use of silicone microreactors for photocatalytic hydrogen generation can be highlighted [162], whose microchannels were coated with an Au/TiO\({}_{2}\) photocatalyst (Figure 18A). The successful operation of the microreactor with 500 \(\upmu\)m width channels at ambient temperature and pressure was demonstrated under different water-ethanol gaseous mixtures, photocatalyst loadings, and light irradiance conditions. Other research work developed a polyvalent electrochemical microreactor, which was validated in three different electrosynthesis processes: the synthesis of tailor-made mixtures of paraffins by Kolbe electrolysis, the \"cation flow\" method for generating and accumulating carbocations, and the synthesis of peroxodicarbonate [163], highlighting its precision in process control, uniform mass flow, and short residence time (Figure 18B). High conversion rates, yields, selectivities, and Faraday efficiency levels were reported. Lastly, another example included the study of steam reforming of methanol performance using 3D-printed porous stainless-steel microsupports for microreactors [164], demonstrating their viability for hydrogen production under specific reaction conditions.  
Figure 17: Examples of Fe/SiC catalysts with different patterned structures: (**a**) square cells, (**b**) triangular cells, and (**c**) radial pattern, (**d**) with a general view of the monoliths (Reprinted with permission from Ref [156]. 2021, Elsevier); (**e**) SAPO-34 zeolite adsorbents produced by Direct Ink Writing (Reprinted with permission from Ref [157]. 2017, Elsevier).