Metal-free carbocatalyst for room temperature acceptorless dehydrogenation of N-heterocycles

Abstract

Catalytic dehydrogenation enables reversible hydrogen storage in liquid organics as a critical technology to achieve carbon neutrality. However, oxidant or base-free catalytic dehydrogenation at mild temperatures remains a challenge. Here, we demonstrate a metal-free carbocatalyst, nitrogen-assembly carbons (NCs), for acceptorless dehydrogenation of N-heterocycles even at ambient temperature, showing greater activity than transition metal–based catalysts. Mechanistic studies indicate that the observed catalytic activity of NCs is because of the unique closely placed graphitic nitrogens (CGNs), formed by the assembly of precursors during the carbonization process. The CGN site catalyzes the activation of C─H bonds in N-heterocycles to form labile C─H bonds on catalyst surface. The subsequent facile recombination of this surface hydrogen to desorb H 2 allows the NCs to work without any H-acceptor. With reverse transfer hydrogenation of various N-heterocycles demonstrated in this work, these NC catalysts, without precious metals, exhibit great potential for completing the cycle of hydrogen storage.

Cobalt nanoparticles supported on microporous nitrogen-doped carbon for an efficient catalytic transfer hydrogenation reaction between nitroarenes and N-heterocycles

“…44–46 Subsequent isomerization of 3,4-dihydroquinoline generates 1,2-dihydroquinoline ( 3 ). 47 Then, the dehydrogenation of 1,2-dihydroquinoline ( 3 ) to quinoline ( 4 ) occurs, similar to the dehydrogenation of 1,2,3,4-tetrahydroquinoline to 3,4-dihydroquinoline. At the same time, the catalytic hydrogenation of nitrobenzene ( 5 ) generates nitrosobenzene ( 6 ) and a molecule of water.…”

Highly Efficient Hydrogen Production from Dehydrogenation Reaction of Nitrogen Heterocycles via Pd0–Pdδ+ Synergistic Catalysis

“…6,7 Based on the reversible chemical hydrogen storage mechanism (hydrogenation/dehydrogenation cycle of unsaturated organic liquids), the purity of released hydrogen reaches 99.99%, which meets the demand of on-board hydrogen source systems. 8,9 Among various LOHC molecules, the N-ethylcarbazole vs dodecahydro-N-ethylcarbazole (NECZ vs 12H-NECZ) cycle system offers a desirable candidate with a high hydrogen gravimetric capacity (5.79 wt %) and a relatively low reaction temperature. 10−13 For such a structure-sensitive reaction, noble metal catalysts (e.g., Pd and Pt) have shown good catalytic performance toward dehydrogenation of 12H-NECZ at a relatively benign temperature (below 200 °C).…”

“…Compared with several hydrogen storage technologies ( e.g. , pressurized liquid hydrogen, metal hydrides, and nanomaterials), the liquid organic hydrogen carrier (LOHC) provides a promising route for large-scale hydrogen storage and transportation with advantages of high gravimetric capacity, convenient usability, and infrastructure compatibility. , Based on the reversible chemical hydrogen storage mechanism (hydrogenation/dehydrogenation cycle of unsaturated organic liquids), the purity of released hydrogen reaches 99.99%, which meets the demand of on-board hydrogen source systems. , …”

Continuous Room‐Temperature Hydrogen Release from Liquid Organic Carriers in a Photocatalytic Packed‐Bed Flow Reactor

“…For example, it has been demonstrated that iron (Fe) could achieve dehydrogenation of THQ in 18 h at 145 °C, but at a lower yield (88 %) than that obtained by precious metals, [10] while nitrogen assembly carbons can achieve > 99 % yield at 150 °C in 4 h or at room temperature in five days. [11] From a sustainability perspective, a more energy-efficient acceptorless dehydrogenation process relies on the photo activation of the catalyst. [12] Metal-organic frameworks (MOFs) with narrow distance between their active sites have been shown to catalyze the dehydrogenation of THQ in 3 h under ultraviolet (UV) illumination (390 nm).…”

“…Non‐precious metal catalysts have also been investigated to overcome the high cost of the precious metals. For example, it has been demonstrated that iron (Fe) could achieve dehydrogenation of THQ in 18 h at 145 °C, but at a lower yield (88 %) than that obtained by precious metals, [10] while nitrogen assembly carbons can achieve >99 % yield at 150 °C in 4 h or at room temperature in five days [11] …”