Low-temperature RWGS process with a two-stage Cu–Fe/Zn spiral-structured catalyst: the role of intermediate Fe plating in electroless plating

Abstract

The reverse water–gas shift (RWGS) reaction is widely investigated as one of the effective routes to reduce industrial CO₂ emissions and contribute to sustainability through energy recycling. We aim to develop a CFx (carbon fixation of CO₂) system that simultaneously enables CO₂ reduction and the generation of valuable products by integrating multiple reaction processes, with the RWGS reaction as a key step. Our target performance is defined as achieving >40% CO₂ conversion and 100% CO selectivity below 500 °C. To meet this goal, we evaluated the reaction performance of a two-stage catalyst system incorporating a Cu–Fe/Zn spiral-structured catalyst prepared by electroless plating (ELP). This catalyst was fabricated by sequential Zn plating, intermediate Fe plating, and final Cu plating on a spiral-structured aluminum substrate. Notably, employing Fe as the intermediate layer significantly enhanced the performance of the Cu–Fe/Zn spiral-structured catalyst in the two-stage system. Under high flow rate conditions (SV = 12 000 h⁻¹; contact time 0.31 s), CO₂ conversion approached equilibrium at 500 °C. The catalyst was activated by oxidation treatment, demonstrating high activity even at low temperatures below 500 °C. The Cu–Zn alloy formed during oxidation treatment is thought to enhance low-temperature activity. Catalysts with alternative intermediate plating layers (Co, Ni, and Sn) were also investigated. Although Co-plated catalysts showed comparatively high performance, none equaled that of the Fe-plated catalyst. XRD and SEM-EDX analyses indicate that intermediate Fe plating generates fine Fe particles, which act as nucleation sites for Cu deposition and promote well-dispersed Cu precipitation. Furthermore, this process facilitates Zn migration from the underlying Zn plating layer to the surface, resulting in the formation of a relatively thick Cu–Fe–Zn surface layer.