Integrating Direct Air Capture and In Situ Reverse Water–Gas Shift over FeNi-Modified CaZr Dual-Functional Materials

This study develops CaZr-based dual-functional materials (DFMs) for integrated direct air capture (DAC) and an in situ reverse water–gas shift (RWGS) reaction, termed IDACU-RWGS. The baseline CaZr material, composed of Ca(OH)2 and ZrO2, exhibited limited CO2 conversion efficiency. To address this, six non-noble metal catalysts (K, Ce, Co, Cu, Ni, and Fe) were screened, with Fe identified as the optimal single catalyst due to its ability to enhance CO2 capture and conversion while maintaining 100% CO selectivity via a redox mechanism. In contrast, Ni improved capture and conversion but favored methanation, resulting in low CO selectivity. A bimetallic Fe–Ni catalyst system was subsequently designed to combine the advantages of both metals. The optimized CaZrFe2Ni1 DFM demonstrated good performance at 650 °C, achieving a CO2 capture capacity of 8.33 mmol/g, CO2 conversion of 83.4%, CO selectivity >99%, and stable performance over five cycles with minimal degradation. Characterization results (XRD, SEM, BET, CO2-TPD, H2-TPR, and XPS) revealed that the incorporation of Fe and Ni promotes the formation of oxygen vacancies and enhances CO2 activation. This work presents a promising DFM strategy for efficient and selective integrated DAC and RWGS conversion.