Pd Catalyzed, Acid Accelerated, Rechargeable, Liquid Organic Hydrogen Carrier System Based on Methylpyridines/Methylpiperidines

Efficient, solvent-free, liquid to liquid hydrogen storage systems based on reversible dehydrogenation and hydrogenation using a single heterogeneous supported Pd catalyst are reported, including (a) 2-picoline/2-methylpiperidine, and (b) 2,6-lutidine/2,6-dimethylpiperidine, having 6.1 and 5.3 wt % theoretical hydrogen storage capacity, respectively. By a simple blend of Pd(OAc)(2), activated carbon, and methylpiperidines, a very active supported Pd/C-HS (Pd/C-HS = Pd on activated carbon for hydrogen storage) and catalytic acetic acid were generated in situ, which catalyzed the dehydrogenation of 2-methylpiperidine or 2,6-dimethylpiperidine to 2-picoline or 2,6-lutidine in excellent yields (91% and 100% yields, respectively), and releasing H-2 at a fast rate under mild conditions. Our studies revealed that mild acids or acidic groups on the support surface significantly accelerate the dehydrogenation. The reverse hydrogenation of both 2-picoline (2-7 bar) and 2,6-lutidine (1.6-5 bar) was achieved under exceptionally low H-2 pressure. Furthermore, the Pd/C-HS catalyst can be easily recovered and reused without a decrease in catalytic activity.