Structure-dependent activity and stability of Al2O3 supported Rh catalysts for the steam reforming of n-dodecane

Steam reforming of liquid hydrocarbon fuels is an appealing way for the production of hydrogen. In this work, the Rh/Al2O3 catalysts with nanorod (NR), nanofiber (NF) and sponge-shaped (SP) alumina supports were successfully designed for the steam reforming of n-dodecane as a surrogate compound for diesel/jet fuels. The catalysts before and after reaction were well characterized by using ICP, XRD, N-2 adsorption, TEM, HAADF-STEM, H-2- TPR, CO chemisorption, NH3-TPD, CO2-TPD, XPS, Al-27 NMR and TG. The results confirmed that the dispersion and surface structure of Rh species is quite dependent on the enclosed various morphologies. Rh/Al2O3-NR possesses highly dispersed, uniform and accessible Rh particles with the highest percentage of surface electron deficient Rh-0 active species, which due to the unique properties of Al2O3 nanorod including high crystallinity, relatively large alumina particle size, thermal stability, and large pore volume and size. As a consequent, Rh/Al2O3-NR catalyst exhibited superior catalytic activity towards steam reforming re-actions and hydrogen production rate over other two catalysts. Especially, Rh/Al2O3-NR catalyst showed the highest hydrogen production rate of 87,600 mmol gfuel-1 gRh-1min-1 among any Rh-based catalysts and other noble metal-based catalysts to date. After long-term reaction, a significant deactivation occurred on Rh/Al2O3-NF and Rh/Al2O3-SP cata-lysts, due to aggregation and sintering of Rh metal particles, coke deposition and poor hydrothermal stability of nanofibrous structure. In contrast, the Rh/Al2O3-NR catalyst shows excellent reforming stability with negligible coke formation. No significantly sin-tering and aggregation of the Rh particles is observed after long-term reaction. Such great catalyst stability can be explained by the role of hydrothermal stable nanorod alumina support, which not only provides a unique environment for the stabilization of uniform and small-size Rh particles but also affords strong surface basic sites. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

Steam reforming of liquid hydrocarbon fuels using Rh/Al2O3 catalysts with different morphologies of alumina support was studied. The catalyst with nanorod morphology showed superior catalytic activity and stability, achieving the highest hydrogen production rate compared to other catalysts. This research is significant for improving hydrogen production efficiency.