Comparison among cobalt and iron perovskite-based catalysts for WGSR

Abstract

The water gas shift reaction (WGSR) has been extensively used in industrial processes, being a fundamental step for the commercial production of high purity hydrogen over the years. For economical purposes, the reaction is performed in two steps, named high temperature shift (HTS) and low temperature shift (LTS). The classic HTS catalyst is chromia-doped hematite, which is toxic and losses specific surface area during industrial processes, demanding for new catalysts. Therefore, considerable effort has been made in recent years to find alternative catalysts for HTS step. With this goal in mind, LaFe1-xCoxO3 (x= 0.0, 0.5 and 1) perovskites were compared in order to find alternative catalysts for WGSR. Samples were prepared by thermal decomposition of amorphous citrate precursors and characterized by Fourier transform infrared spectroscopy, X-ray diffraction, X-ray fluorescence, specific surface area measurements, temperature programmed reduction, UV-Vis diffuse reflectance spectroscopy, scanning electron microscopy and Mössbauer spectroscopy. The catalysts were evaluated in WGSR performed at 1 atm and different temperatures in the range of 250 to 600 °C. Before reaction, samples were reduced under hydrogen flow at 600 °C, for 1 h. All samples exhibited the perovskite phase. The addition of iron makes the production of Co0 species more difficult and the inverse effect was noted for cobalt which makes iron reduction easier. The cobalt-free sample was the least reducible one while the cobalt-free perovskite led to the least active solid. This was assigned to the low reducibility of iron in perovskite structure. At temperatures higher than 450 °C, the addition of cobalt increased the activity of iron-based catalyst, probably due to the ability of cobalt in making iron reduction easier. The cobalt-based perovskite (LaCoO3) was the most active catalyst. This was related to the easy cobalt reduction in perovskite structure, ensuring high activity in WGSR. It can be concluded that LaCoO3 perovskite is a promising precursor for catalysts for WGSR in the range of 350 to 450 °C, while LaFeO3 and LaCo0.5Fe0.5O3 lead to poorly active catalysts.