Synergistic Strategy for the Fast Dehydrogenation of Liquid Organic Hydrogen Carriers over a Pd/MoO₃ Catalyst

Abstract

We report a synergistic strategy for the dehydrogenation of liquid organic hydrogen carriers (LOHCs) over a Pd/MoO3 catalyst. The effects of Pd loading, temperature, and the variation of H x MoO3 for the catalytic dehydrogenation behavior of LOHCs were investigated systematically. 5 wt % Pd/MoO3 shows the highest catalytic performance. 3.13 wt % release of the stored H2 of perhydro-N-ethylcarbazole (PNEC) was achieved in the initial 5 min, and full dehydrogenation was realized in 1.5 h at 200 °C. The kinetic results suggest that the turn-over frequency (TOF) of PNEC on the 5 wt % Pd/MoO3 catalyst is 191.11 min–1 at 180 °C, which is significantly larger than that of traditional noble metal catalyst 5 wt % Pd/Al2O3 (56.31 min–1). The dehydrogenation mechanism on Pd/MoO3 essentially differs from the traditional noble metal catalysts. The formation of H x MoO3 other than H2 greatly decreases the activation energy barrier of the dehydrogenation reaction and results in the swift desorption of H atoms from PNEC. The results indicate that the synergistic effect between Pd and MoO3 may be an efficient strategy for the fast dehydrogenation of LOHCs.

Beyond Hydrogen Storage: Metal Hydrides for Catalysis

“…The authors reported the existence of bulk-H in the oxide lattice by XRD and XPS characterization of the postreaction catalysts. 113,114 On irreducible oxides like MgO, Al 2 O 3 , and SiO 2 , heterolytic H 2 dissociation was assumed to happen. The hydrogen species generated are strongly dependent on the surface conditions of oxides (such as the density of surface hydroxyl groups and surface defects).…”

“…Recently, Pd/MoO 3 has been utilized in the (de)­hydrogenation of LOHCs. The authors reported the existence of bulk-H in the oxide lattice by XRD and XPS characterization of the post-reaction catalysts. , …”

Catalytic hydrogen storage in liquid hydrogen carriers

“…Synthesis of bimetallic catalysts is also an important strategy for dehydrogenation catalysts, which usually have catalytic activity for both hydrogenation and dehydrogenation. 114,136,137 You et al investigated the effect of interheteromolecular hyperconjugation on heterogeneous (de)hydrogenation catalyzed by Rh-Pd loaded silicon-aluminium oxide supports (Rh-Pd/SAO). 138 Sun et al synthesized reusable bimetallic Pd-Rh nanoparticle catalysts.…”

Reversible Pd Catalysts Supported on Hierarchical Titanate Nanosheets for an N-Methylindole-Based Liquid Organic Hydrogen Carrier

“…Hydrogen-involved catalytic behaviors, including activation, adsorption, migration, and recombination of hydrogen, are closely related to activity enhancement in hydrogen-participating reactions. − Hydrogen spillover (H-spillover) is also an important catalytic phenomenon that is closely related to hydrogen-involved catalytic behavior, influencing the catalytic activity in the hydrogenation and dehydrogenation reactions in LOHC systems. − The Yi group reported that plasma-treated Pt/Al 2 O 3 catalysts increased the catalytic activity in a DBT-based reversible LOHC system because the surface hydroxyl groups generated by plasma treatment promoted H-spillover during hydrogenation and dehydrogenation . Fei et al showed that Pd/MoO 3 catalysts achieved fast dehydrogenation of perhydro-NECs; the Pd species in the catalyst promoted H-spillover to the MoO 3 surface . H-spillover depends on the reaction barriers for hydrogen activation, migration, and adsorption .…”

“…22 Fei et al showed that Pd/MoO 3 catalysts achieved fast dehydrogenation of perhydro-NECs; the Pd species in the catalyst promoted H-spillover to the MoO 3 surface. 23 H-spillover depends on the reaction barriers for hydrogen activation, migration, and adsorption. 24 The choice of catalyst support is crucial to mitigate these reaction barriers.…”