Sequential Oxygen Vacancy Formation Governs Cu Size-Dependent Methanol Synthesis at Cu–ZrO2 Interfaces

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Methanol synthesis at Cu–ZrO2 interfaces requires CO2 activation, H2 dissociation, and conversion of oxygenated intermediates to proceed in concert, yet how Cu aggregation coordinates these functions remains unclear. Electronic-structure calculations, molecular dynamics, and catalytic experiments show that Cu size governs sequential oxygen vacancy formation and the adsorption landscape of HCOO*. Isolated Cu atoms favor formation of the initial vacancy and lower the HCOO* formation barrier to 17.41 kcal mol–1, consistent with high methanol selectivity and the highest apparent turnover frequency at 240 °C. When a second vacancy is introduced near isolated Cu in the calculation, HCOO* adsorption strengthens by 31.41 kcal mol–1 and creates a deep thermodynamic trap. Cu clusters instead change HCOO* adsorption by only 4.66 kcal mol–1 as the second vacancy forms and couple bidentate CO2 activation at the vacancy with H2 dissociation on adjacent Cu atoms. This balanced interface gives the highest CO2 conversion and methanol space–time yield of 562.90 mgMeOH gcat–1 h–1 at 280 °C and remains stable for 100 h. Cu nanoparticles, despite their higher Cu loading, interact weakly with CO2 and have the highest HCOO* formation barrier of 27.28 kcal mol–1, giving the lowest productivity. Controlled-reduction EPR reveals Cu-size-dependent changes in defect-related signals, while transient DRIFTS shows distinct reduction- and treatment-dependent changes in the observable HCOO-related surface pools. Their correspondence with the calculated vacancy energetics and adsorption responses supports a Cu-size-dependent balance among defect formation, reactant activation, and intermediate conversion. Cu clusters couple reactant activation with intermediate conversion to sustain methanol production.