Reactor design via scan line patterning: An implicit approach to create scalable microstructured parts in selective laser melting

The adaptation of additive manufacturing for chemical flow reactors has recently gained momentum as the methods become more advanced and equipment is increasingly affordable. With the design of periodic open cellular structures (POCS) from metal selective laser melting (SLM), structured catalyst substrates can be realized in a much more ordered fashion than well-established metal foams with a random structure. Hence, tailored transport properties are achieved and flow profiles are homogenized, eliminating flow channeling and stagnant flow zones. However, with current SLM methods, the minimal achievable feature size and therewith the specific surface area is still limited. Moreover, the size of finely resolved STL files that define the structure grows exponentially with decreasing feature sizes, further limiting the scalability of methods with direct structure definition. In this work, we present a method for implicit structure design by metal SLM with specific surface areas and porosities that compete with established catalyst substrates. The definition of the microstructure is realized by control of the laser scan lines, where single scan lines create fine struts. The general applicability of our method to various metal materials is demonstrated by production from stainless steel and copper. In a numerical study for a model steam reforming application, we show that the POCS provide mass transfer coefficients and volumetric reaction rates that compete with benchmark substrates. Scan line patterning therefore provides a promising method to create highly ordered, well-scalable substrates for heterogeneous catalysis from a wide range of materials, e.g., for the application in highly efficient small-scale reactors.