Unveiling the Role of Step Density in CO2 Activation and Hydrogenation on Copper Surfaces

Resolving the mechanistic link between local coordination environments and dynamic surface restructuring is essential for advancing carbon dioxide activation and hydrogenation on copper-based catalysts. Here, we demonstrate that the configuration of steps and terraces governs the restructuring pathways on high-index Cu(hkl) surfaces with varying (111) × (100) step densities by integrating in situ spectroscopy/microscopy and theoretical simulation. On the Cu(211) surface [3(111) × (100)], low-coordinated step sites facilitate CO2 activation and the subsequent reaction-driven fragmentation of Cu into nanoclusters. These metastable ensembles serve as active sites that stabilize key intermediates─formate and methoxy─thereby driving sequential hydrogenation. In contrast, on the Cu(557) surface featuring a lower step density [6(111) × (100)], oxygen atoms derived from CO2 dissociation at step sites migrate onto the terraces, assembling into ordered oxide chains that passivate the active sites. Our findings reveal that modulating the step density could effectively dictate the surface reconstruction and the reaction activity of carbon dioxide hydrogenation over Cu-based catalysts.