Operando Identification of Dynamic ZrOx–Cu Perimeter Sites during Low-Temperature CO2 Hydrogenation

Abstract

The catalytic conversion of CO2 to methanol over Cu-based catalysts is strongly influenced by oxide–metal interfacial structures, yet the dynamic evolution of these sites under reaction conditions remains insufficiently understood. Herein, a series of ZrOx-modified Cu catalysts with Zr/Cu atomic ratios from 0.015 to 0.120 were prepared by controlled surface deposition and evaluated for CO2 hydrogenation at 220–260 °C and 3.0 MPa. Operando diffuse reflectance infrared Fourier-transform spectroscopy, quasi in situ X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, and Cu K-edge X-ray absorption spectroscopy were combined with kinetic measurements to determine the active interfacial motifs. The catalyst with a Zr/Cu ratio of 0.065 delivered the highest methanol space–time yield of 412.7 gMeOH kgcat⁻¹ h⁻¹ at 240 °C, with CO2 conversion of 13.4% and methanol selectivity of 71.9%. Compared with unmodified Cu, the apparent activation energy decreased from 86.5 to 58.2 kJ mol⁻¹, while the methanol formation rate increased by a factor of 3.6. Operando spectra show that bidentate formate bands at 1584 and 1367 cm⁻¹ intensified rapidly on ZrOx-rich perimeter sites and were subsequently converted into methoxy species at 1048 cm⁻¹. Isotopic switching using D2 revealed a kinetic isotope effect of 2.3, indicating that hydrogen addition to surface formate remains a kinetically relevant step. Long-term testing for 120 h showed only 6.8% activity loss, which was attributed to partial aggregation of surface ZrOx domains rather than Cu sintering. This study demonstrates that highly dispersed ZrOx–Cu perimeters act as dynamic catalytic ensembles and that their structural retention is essential for maintaining methanol selectivity under low-temperature CO2 hydrogenation conditions.