3D-printed capillary force trap reactors (CFTRs) for multiphase catalytic flow chemistry

In this paper, we introduce the 'Capillary Force Trap Reactor' (CFTR), which leverages additive manufacturing (AM) methods and small-scale fluid physics to enable intensified catalytic reactions such as hydrogenations with facile catalyst replenishment. The central concept of this reactor paradigm is the temporary trapping of colloidal solutions of metallic nanoparticle catalysts via capillary forces on 3D-printed traps on the walls of a milli-scale flow reactor. We discuss the design, fabrication, operation, and analysis of such reactors, along with demonstrations of online catalyst recovery and replenishment. We start by establishing the operating limits of the capillary force traps in a CFTR with a simple proof-of-concept flow cell design. We then implement a model reaction to evaluate the performance of the CFTR, demonstrating complete conversion of hydrogenation of 1-hexene to n-hexane catalyzed by polyvinylpyrrolidone (PVP)-stabilized rhodium nanoparticle (RhNP) catalysts suspended in water. Lastly, we show a facile method to replenish used catalyst to maintain performance over a prolonged period of reactor operation, and discuss tuning reactor performance when catalyst deactivation occurs. This work illustrates the possibility of harnessing 3D printing for novel capillary flow trap designs, and opens up new routes for 'designer' flow reactors for multiphase catalytic reactions.