Red Mud as an Efficient, Stable, and Cost-Free Catalyst for COx-Free Hydrogen Production from Ammonia.

Alper Uzun,Samira Fatma Kurtoğlu

doi:10.1038/srep32279

Abstract

Red mud, one of the mostly produced industrial wastes, was converted into a catalyst with exceptionally high and stable performance for hydrogen production from ammonia. Results showed that iron species produced after reduction of the HCl digested red mud were converted into ε-Fe2N during the induction period of ammonia decomposition reaction at 700 °C. The catalytic performance measurements indicated that the modified red mud catalyst provides a record high hydrogen production rate for a non-noble metal catalyst at this temperature. For instance, stable hydrogen production rates were measured as 72 and 196 mmol H2 min−1 gcat−1 for the corresponding space velocities of 72 000 and 240 000 cm3 NH3 h−1 gcat−1, respectively, at 700 °C. These results offer opportunities to utilize one of the key hazardous industrial wastes as an eco-friendly, efficient, stable, and almost cost-free catalyst for COx-free hydrogen production from ammonia decomposition.

Highlights

High surface area with improved iron content and reduced alkali amount
Temperature programmed reduction (TPR) of as-received RM (Eti Seydişehir Aluminum Factory, Konya-Turkey, contents are listed in Table S1 in Supplementary Information, SI) indicates that the conversion of iron oxide into bulk Fe is completed upon reduction in hydrogen at temperatures exceeding 650 °C (Figure S1 in SI) consistent with the results of Costa et al.[27] and with the TPR of Fe2O3 as shown in Figure S2, SI
X-Ray diffraction (XRD) of the used RM-700R@600 catalyst given in Fig. 1c shows that the metallic iron was still present together with some newly-formed iron nitride species (Fe3Ny) indicated by 2θpeaks at 38.7°, 41.4°, and 44.0° (XRD results for a complete 2θrange of 10–90° are provided in Figure S3, SI)

Summary

Introduction

High surface area with improved iron content and reduced alkali amount. After reduction at 700 °C, the resulting sample provided exceptionally high and stable hydrogen production rate for ammonia decomposition. Detailed characterization of the used catalyst unveiled that all metallic Fe species formed after the reduction step were converted into ε-Fe2N readily available on the surface during the reaction, suggesting that these newly formed iron nitride sites are responsible for this high and stable performance. Results presented here offer opportunities to utilize one of the key hazardous industrial wastes as an environmentally friendly, efficient, and almost cost-free catalyst for COx-free hydrogen production from ammonia decomposition

Methods

Results

Conclusion