Comparison of water–gas shift reaction activity and long-term stability of nanostructured CuO-CeO 2 catalysts prepared by hard template and co-precipitation methods

Abstract

This study focuses on the characterization and water–gas shift reaction (WGSR) activity of CuO-CeO 2 catalysts containing 10, 15 and 20 mol% CuO synthesized by hard template method (HT) with KIT-6 silica acting as a template and co-precipitation method (CP). The obtained solids were characterized by SEM/TEM microscopy, N 2 adsorption/desorption, XRD, H 2-TPR/TPD, N 2O decomposition and NH 3 chemisorption/TPD methods. The preparation techniques yield fundamentally different products despite the same nominal chemical composition. Catalysts prepared by the HT method exhibited ordered mesoporous structure, which was identified as the negative replica of the KIT-6 silica pore system. Considerable differences in BET surface area (147–166 m 2/g for CuCe HT samples compared to 22–54 m 2/g for CuCe CP solids, respectively) were measured. CuO dispersion values between 28% and 40% were determined for CuCe HT solids, in case of CuCe CP samples, these values were in the range of 8–20%. H 2-TPR/TPD experiments revealed facile and extensive CeO 2 reduction in all tested samples, which increased with CuO loading. Very similar density of surface acidic sites was determined for both CuCe HT and CuCe CP catalyst samples at each CuO loading, with CuCe CP solids exhibiting the absence of strong acidic sites. WGS reaction activity was tested at the stoichiometric CO/H 2O ratio and low contact times in the temperature range from 250 to 450 °C. Despite rigorous reaction conditions, CO conversions up to 62% and 54% were attained for CuCe HT and CuCe CP samples, respectively, with H 2 selectivity above 99% over the entire temperature range. Superior BET surface area and CuO dispersion of CuCe HT samples are decisive factors contributing to higher activity in the investigated WGS reaction, compared to the ones synthesized by the co-precipitation method.