Highly Active Catalysts Based on the Rh4(CO)12 Cluster Supported on Ce0.5Zr0.5 and Zr Oxides for Low-Temperature Methane Steam Reforming

Andrea Fasolini,Silvia Ruggieri,Cristina Femoni,Francesco Basile

doi:10.3390/catal9100800

Abstract

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 Ce0.5Zr0.5O2 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 Ce0.5Zr0.5 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.

Highlights

Methane steam reforming (SR) is a leading reaction in syngas production with a wide employment on an industrial scale [1,2,3,4,5,6]
This paper describes the synthesis, characterization and catalytic behavior of Rh-based catalysts, obtained by using the Rh4 (CO)12 neutral cluster as the active-phase precursor
At high Rh loadings (0.6%) the CZOm-supported catalyst was active at 350 ◦ C and was able to reach the equilibrium conversion, especially at low S/C ratio or at high pressures at 450 and 500 ◦ C

Summary

Introduction

Methane steam reforming (SR) is a leading reaction in syngas production with a wide employment on an industrial scale [1,2,3,4,5,6]. The hydrogen removal from the retentate allows to increase the hydrogen yield and methane conversion with regard to a classical reactor, allowing to realize an effective process [11,12] For these reasons, very active, selective, and stable catalysts are required to efficiently perform LTSR in a membrane reactor. Very active, selective, and stable catalysts are required to efficiently perform LTSR in a membrane reactor These must be able to activate methane at low temperatures, improving the performances with respect to high active SR and CPO (catalytic partial oxidation) catalysts [16]. Rh was reported to have both higher activity and stability in steam reforming than other active phases [17,18,19,20,21]

Methods

Results

Conclusion