Understanding the mechanism of CO₂ hydrogenation to methanol is important in the context of renewable energy storage from societal and technological point of view. We use density functional theory calculations to study systematically the effect of the size of Cu clusters on the binding strengths of reactants and reaction intermediates as well as the activation barriers for the elementary reaction steps underlying CO₂ hydrogenation. All the elementary reaction barriers exhibit linear scaling relationships with CO and O adsorption energies. Used in microkinetics simulations, we predict that medium-sized Cu₁₉ clusters exhibit the highest CO₂ hydrogenation activity which can be ascribed to a moderate CO₂ coverage and a low CO₂ dissociation barrier. The nanoscale effect is evident from the strong variation of CO and O adsorption energies for clusters with 55 or less Cu atoms. The reactivity of larger clusters and nanoparticles is predicted to depend on surface atoms with low coordination number. Optimum activity is correlated with the bond strength of reaction intermediates determined by the d-band center location of the Cu clusters and the extended surfaces. The presented size-activity relations provide useful insight for the design of better Cu catalysts with maximum mass-specific reactivity for CO₂ hydrogenation performance.

从社会和技术的角度来看，在可再生能源存储的背景下，了解CO ₂加氢成甲醇的机理很重要。我们使用密度泛函理论计算系统地研究了铜簇的大小对反应物和反应中间体的结合强度以及CO ₂加氢基本反应步骤的活化势垒的影响。所有基本反应势垒均表现出与CO和O吸附能成线性比例关系。在微动力学模拟中，我们预测中等大小的Cu ₁₉团簇表现出最高的CO ₂氢化活性，这可归因于中等的CO ₂的覆盖范围和低的CO ₂解离壁垒。对于包含55个或更少Cu原子的团簇，CO和O吸附能的强烈变化可以证明纳米级效应。较大的团簇和纳米颗粒的反应性预计将取决于具有低配位数的表面原子。最佳活性与反应中间体的键合强度相关，反应中间体的键合强度由Cu团簇和延伸表面的d-带中心位置决定。提出的尺寸-活性关系为更好的Cu催化剂的设计提供了有用的见识，该催化剂具有针对CO ₂加氢性能的最大质量比反应性。