Batch synthesis: 300 mL of a solution of Mg(NO3)2•6H2O (0.15 mol) and Al(NO3)3•9H2O (0.05 mol) was added dropwise over 2 h to 300 mL of 0.083 M Na2CO3. The pH was maintained between 9.5 and 10.5 by addition of 1 M NaOH. After completing the addition, the solution was heated to 65 °C for 2 h. The resulting solid was filtered and washed with DI water until the pH of the filtrate was neutral. This procedure was consistent for all doped HTs except the copper-doped sample. In this case we found it is important to wash the precipitate formed in the continuous synthesis from residual salts and base, as the reaction appears to be incomplete. Failure to do so results in formation of additional phases. The formed precipitate was thus filtered, washed with DI water until the pH of the filtrate was neutral, collected and placed into a beaker containing 100 mL of DI water. The following procedure was identical to all other flow synthesized samples. The composition of the doped HTs was set to be Mg:Al:Me = 2.4:1:0.6, when doped with Me 2+ , and Mg:Al:Me = 3:0.4:0.6, when doped with Me 3+ . The HTs doped with Fe 3+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , targeting a 15% mole fraction over the sum of all metal species, were prepared in an analogous synthetic protocol by adding the respective metal nitrate salt to solution A (details of compositions are given in Table in ESI). Table shows designations used subsequently in the text and compositions for all the synthesized hydrotalcites, as well as the results of their ICP-AES analyses. To distinguish between samples prepared at different aging conditions, temperature will be added after sample designation, for example "Fe HT80" corresponds to the Fe-doped hydrotalcite aged at 80 °C.