Highly Efficient Hydrogen Production from Dehydrogenation Reaction of Nitrogen Heterocycles <i>via</i> Pd<sup>0</sup>–Pd<sup>δ+</sup> Synergistic Catalysis
Hao Meng, Yusen Yang, Tianyao Shen, Zhiming Yin, Jian Zhang, Hong Yan, Min Wei
Abstract
Hydrogen shows great potential as a clean energy source, but its safe and efficient storage/transportation is a crucial issue for the development of hydrogen economy; therefore, the use of liquid organic hydrogen carriers for reversible hydrogen storage has attracted considerable attention. Herein, we report palladium catalysts supported on a series of rod-like Al 2 O 3 with different crystal phases (amorphous, γ, δ, and α), which are employed in hydrogen production from dehydrogenation reaction of dodecahydro- N -ethylcarbazole (12H-NECZ). The optimized 3Pd/Al 2 O 3 -γ catalyst, which is featured by a high distribution of Pd nanoparticles (∼3 nm) on the Al 2 O 3 -γ support with unique Pd 0 –Pd δ+ interfacial sites, exhibits good catalytic performance with a complete conversion of 12H-NECZ, a hydrogen selectivity of 99% within 2.0 h. The turnover frequency value reaches up to 281.2 min –1, and H 2 production rate attains 0.66 mol H2 g Pd –1 min –1 at 180 °C, which are preponderant to the state-of-the-art catalysts. An in-depth investigation based on in situ characterizations (Fourier transform infrared and temperature-programmed surface reaction with mass spectrometry pulse measurements), kinetic studies, H/D isotope exchange, and density functional theory calculations demonstrates that Pd 0 –Pd δ + synergistic catalysis plays a crucial role in the C–H bond cleavage of 4H-NECZ (the rate-determining step): the surface Pd 0 site facilitates the activation adsorption of 4H-NECZ, which reduces the reaction energy barrier of C–H bond rupture, while the interface Pd δ+ site boosts the desorption of final products (H 2 and NECZ). The high performance dehydrogenation catalyst developed in this work shows potential applications in chemical hydrogen storage.