The combination of milli-scale processing and microwave heating has been investigated for the Cu-catalyzed Ullmann etherification in fine-chemical synthesis, providing improved catalytic activity and selective catalyst heating. Wall-coated and fixed-bed milli-reactors were designed and applied in the Cu-catalyzed Ullmann-type C-O coupling of phenol and 4-chloropyridine. In a batch reactor the results show clearly increased yields for the microwave heated process at low microwave powers, whereas high powers and catalyst loadings reduced the benefits of microwave heating. Slightly higher yields were found in the Cu/ZnO wallcoated as compared to the Cu/TiO 2 fixed-bed flow-reactor. The benefit here is that the reaction occurs at the surface of the metal nanoparticles confined within a support film making the nano-copper equally accessible. Catalyst deactivation was mainly caused by Cu oxidation and coke formation; however, at longer process times leaching played a significant role. Catalyst 2 activity could partially be recovered by removal of deposited by-product by means of calcination. After 6 h on-stream the reactor productivities were 28.3 and 55.1 kg prod /(m R 3 •hr)for the fresh Cu/ZnO wall-coated and Cu/TiO 2 fixed-bed reactor, respectively. Comparison of single-and multimode microwaves showed a three-fold yield increase for single-mode microwaves. Control of nanoparticles size and loading allows to avoid high temperatures in a single-mode microwave field and provides a novel solution to a major problem for combining metal catalysis and microwave heating. Catalyst stability appeared to be more important and provided two-fold yield increase for the CuZn/TiO 2 catalyst as compared to the Cu/TiO 2 catalyst due to stabilized copper by preferential oxidation of the zinc. For this catalyst a threefold yield increase was observed in single-mode microwaves which, to the best of our knowledge, led to a not yet reported productivity of 172 kg prod /(m R 3 •hr) for the microwave and flow Ullmann C-O coupling.