On the potential of nickel catalysts for steam reforming in membrane reactors

Abstract

Hydrogen membrane reactors have been identified as a promising option for hydrogen production for power generation from natural gas with pre-combustion decarbonisation. While Pd or Pd-alloy membranes already provide good hydrogen permeances the most suitable catalyst design for steam reforming in membrane reactors (SRMR) is yet to be identified. This contribution aims to provide insight in the suitability of nickel based catalysts in SRMR. The use of nickel (Ni) catalysts would benefit the cost-effectiveness of membrane reactors and therefore its feasibility. For this, the activity of nickel catalysts in SRMR was assessed with kinetics reported in literature. A 1D model was composed in order to compare the hydrogen production rates derived from the kinetics with the rate of hydrogen withdrawal by permeation. Catalyst stability was studied by exposing the catalysts to reformate gas with two different H/C ratios to mimic the hydrogen lean reformate gas in the membrane reactor. For both the activity (modeling) and stability study the Ni-based catalysts were compared to relevant catalyst compositions based on rhodium (Rh). Using the high pressure kinetics reported for Al 2O 3 supported Rh and MgAl 2O 4 and Al 2O 3 supported Ni catalyst it showed that Ni and Rh catalysts may very well provide similar hydrogen production rates. Interestingly, the stability of Ni-based catalysts proved to be superior to precious metal based catalysts under exposure to simulated reformate feed gas with low H/C molar ratio. A commercial (pre-)reforming Ni-based catalyst was selected for further testing in an experimental membrane reactor for steam reforming at high pressure. During the test period 98% conversion at 873 K could be achieved. The conversion was adjusted to approximately 90% and stable conversion was obtained during the test period of another 3 weeks. Nonetheless, carbon quantification tests of the Ni catalyst indicated that a small amount of carbon had deposited onto the catalyst. The activity of the Ni catalyst for carbon formation is expected to eventually cause performance loss due to plugging or fouling. Ongoing research efforts are devoted towards the preparation of cost-effective nickel based catalysts with suppressed carbon formation activity.