Metal structured catalysts for hydrogen production

K.Y. Koo, U. Jung
Korea Institute of Energy Research,
Korea

Keywords: hydrogen production, natural gas steam reforming, ammonia decomposition, metal structured catalyst, catalyst coating

Summary:

In typical chemical processes including the natural gas steam reforming (NGSR) for hydrogen production, a packed bed reactor with ceramic pellet catalysts has been used. These ceramic pellet catalyst have a low utilization owing to heat and mass transfer limitations and in order to compensate for this shortcoming, an excessive amount of pellet catalyst are used and it causes difficulties in compactness of reactor. As such, it entails some problems such as slow response characteristics, pressure drop, and channeling. To overcome such problems, metal structured catalysts such as monolith, foam and fin plate etc. have been studied as an alternative. Since a metal structured catalyst provides a large geometric reaction surface area to reaction volume (S/V) and increases the heat transfer rate per unit volume of process flow (US/V), it enables a compact reactor design. Moreover, the radial concentration and temperature gradient as well as pressure drop can be minimized by the well-behaved uniform flow of the metal structures through the regular channel. Although there has been a growing interest in development of the new reactor with metal structured catalysts, the reason why the metal structured catalyst is faced with difficulties for the commercialization is that there is a lack of skill for coating stably the catalyst on the surface of the metal substrate. To address this issue, we developed two key technologies regarding to the surface treatment of the metal substrate and the highly dispersed catalyst coating. First, the developed surface treatment enables to form metal oxide layer uniformly on the surface of the metal structured carrier regardless of the composition and shape. The formed metal oxide layer improves the adherence of coating layer and prevents the detachment of coated catalyst layer from the surface of the metal substrate. Secondly, the proprietary KIER coating method is developed to coat the catalyst layer uniformly and stably on the surface of metal substrate compared to the conventional coating methods such as washcoating and impregnation. In this study, Ru coated metal structured catalysts were prepared by the proprietary KIER coating method and we investigated the catalytic performance in NGSR and ammonia (NH3) decomposition reactions for hydrogen production. In order to apply for NGSR reactor in an actual KIER 1~5 kW-class fuel reformer system for PEMFCs, the Ru catalyst was coated on the surface of FeCralloy plate with ruffled pin type by KIER coating method. It was possible to prepare the metal structured catalyst with high catalytic activity by coating a small amount of Ru catalyst on the surface of the metal substrate using KIER coating method. Furthermore, the Ru coated metal structured catalyst showed a good catalytic performance equivalent to commercial pellet catalyst in fuel processor despite usage of 1/10 Ru metal compared to commercial pellet catalyst. We are developing the Ru coated metal foam catalyst for COx-free hydrogen production via NH3 decomposition and want to share some important results of catalytic performance for 5 Nm3/h H2 production till lately.