Highly dispersed Pd nanoparticles on a SiO2 support for dehydrogenation of dodecahydro-N-ethylcarbazole

Abstract

Liquid organic hydrogen carriers (LOHC) are regarded as a promising hydrogen storage and transportation technology. However, problems of incomplete dehydrogenation and the high dehydrogenation catalyst costs have hindered the development and application of this technology. Therefore, the research and development of a dehydrogenation catalyst with low cost and high reactivity have become the focus of current research in this field. In this paper, we report on a dehydrogenation catalyst with low noble metal loading prepared using amino silane coupling agent. The catalyst showed excellent catalytic performance on dodecahydro-N-ethylcarbazole (12H-NECZ). At 473 K, the hydrogen release of 0.3% Pd–NH₂(1) catalyst prepared by the amino modification method is 4.44 wt%, which is 2.1 times that of Pd catalyst prepared using the traditional impregnation method. The amino-modified catalysts with increasing Pd loading of 0.5, 0.8, and 1.0 wt% displayed hydrogen release of 4.96, 5.14 and 5.21 wt%, respectively. The characterization of amnio-modified Pd catalysts showed that Pd was uniformly distributed on the SiO₂ support, and the Pd particle size of the 0.3% Pd–NH₂(1) catalyst was only 1.6 nm. The reaction kinetic parameters of two catalysts in the 12H-NECZ dehydrogenation were calculated, and the results indicated that the activation energy of the rate-limiting step (4H-NECZ to NECZ) in dehydrogenation was reduced with amnio-modified catalysts compared to impregnated catalysts. By analyzing the relationship between the Pd particle size and turnover frequency (TOF), the optimal Pd particle size in the overall dehydrogenation reaction and each step of the 12H-NECZ dehydrogenation was obtained.