Highly Active Catalysts Based on the Rh₄(CO)₁₂ Cluster Supported on Ce_0.5Zr_0.5 and Zr Oxides for Low-Temperature Methane Steam Reforming

• Main Authors: Andrea Fasolini, Silvia Ruggieri, Cristina Femoni, Francesco Basile
• Format: Article
• Language: English
• Published: MDPI AG 2019-09-01
• Series: Catalysts
• Subjects: hydrogen; low temperature steam reforming; rh₄(co)₁₂ cluster; microemulsion synthesis; cezr oxide; zr oxide
• Online Access: https://www.mdpi.com/2073-4344/9/10/800

Syngas and Hydrogen productions from methane are industrially carried out at high temperatures (900 °C). Nevertheless, low-temperature steam reforming can be an alternative for small-scale plants. In these conditions, the process can also be coupled with systems that increase the overall efficiency such as hydrogen purification with membranes, microreactors or enhanced reforming with CO₂ capture. However, at low temperature, in order to get conversion values close to the equilibrium ones, very active catalysts are needed. For this purpose, the Rh₄(CO)₁₂ cluster was synthetized and deposited over Ce_0.5Zr_0.5O₂ and ZrO₂ supports, prepared by microemulsion, and tested in low-temperature steam methane reforming reactions under different conditions. The catalysts were active at 750 °C at low Rh loadings (0.05%) and outperformed an analogous Rh-impregnated catalyst. At higher Rh concentrations (0.6%), the Rh cluster deposited on Ce_0.5Zr_0.5 oxide reached conversions close to the equilibrium values and good stability over long reaction time, demonstrating that active phases derived from Rh carbonyl clusters can be used to catalyze steam reforming reactions. Conversely, the same catalyst suffered from a fast deactivation at 500 °C, likely related to the oxidation of the Rh phase due to the oxygen-mobility properties of Ce. Indeed, at 500 °C the Rh-based ZrO₂-supported catalyst was able to provide stable results with higher conversions. The effects of different pretreatments were also investigated: at 500 °C, the catalysts subjected to thermal treatment, both under N₂ and H₂, proved to be more active than those without the H₂ treatment. In general, this work highlights the possibility of using Rh carbonyl-cluster-derived supported catalysts in methane reforming reactions and, at low temperature, it showed deactivation phenomena related to the presence of reducible supports.