Tuning Co–Co₂SiO₄ interfacial chemistry on SBA-15 for the reverse water–gas shift reaction: An operando TR-XAS and in situ DRIFTS study

Abstract

Transforming CO₂ into CO via the reverse water–gas shift (RWGS) reaction is a pivotal step toward sustainable carbon utilization. Herein, we unveil how tuning the Co/Co₂SiO₄ ratio in Co/SBA-15 catalysts dictates CO₂ activation and product selectivity. Cobalt catalysts were synthesized via pH-controlled impregnation (pH 3.0, 6.0, and 8.0), yielding distinct Co₃O₄/Co₂SiO₄ composites after calcination. Operando time-resolved X-ray absorption spectroscopy coupled with mass spectrometry and gas chromatography (TR-XAS–MS–GC), and in situ DRIFTS provided real-time insight into the materials’ behavior and reaction intermediates. Increasing impregnation pH enhanced cobalt dispersion and metal–support interactions, stabilizing Co²⁺–O–Si species. After reduction, the Co/Co₂SiO₄ ratios decreased in the order Co (pH 3)/SBA-15 (9.30) > Co (pH 6)/SBA-15 (4.41) > Co (pH 8)/SBA-15 (2.78). Remarkably, Co(pH 8)/SBA-15, providing the lowest Co/Co₂SiO₄ ratio, achieved the highest CO₂ conversion (56.6 %) and CO selectivity (99.3 %) at 700 °C. Operando TR-XAS revealed the gradual reduction of Co₂SiO₄ during the reaction, while DRIFTS confirmed that formate and CO species are key intermediates. The synergistic interplay between metallic Co (H₂ dissociation) and Co₂SiO₄ (CO₂ activation) drives exceptional CO selectivity while suppressing methanation. This study demonstrates how simple pH modulation during synthesis tailors the interfacial Co–Co₂SiO₄ chemistry, offering a robust route to next-generation cobalt catalysts for high-temperature CO₂ conversion.