Metal-catalysed reactions are often hypothesized to proceed on bifunctional active sites, whereby colocalized reactive species facilitate distinct elementary steps in a catalytic cycle^{1,2,3,4,5,6,7,8}. Bifunctional active sites have been established on homogeneous binuclear organometallic catalysts^9,10,11. Empirical evidence exists for bifunctional active sites on supported metal catalysts, for example, at metal–oxide support interfaces^2,6,7,12. However, elucidating bifunctional reaction mechanisms on supported metal catalysts is challenging due to the distribution of potential active-site structures, their dynamic reconstruction and required non-mean-field kinetic descriptions^7,12,13. We overcome these limitations by synthesizing supported, atomically dispersed rhodium–tungsten oxide (Rh-WO_x) pair site catalysts. The relative simplicity of the pair site structure and sufficient description by mean-field modelling enable correlation of the experimental kinetics with first principles-based microkinetic simulations. The Rh-WO_x pair sites catalyse ethylene hydroformylation through a bifunctional mechanism involving Rh-assisted WO_x reduction, transfer of ethylene from WO_x to Rh and H₂ dissociation at the Rh-WO_x interface. The pair sites exhibited >95% selectivity at a product formation rate of 0.1 g_propanal cm⁻³ h⁻¹ in gas-phase ethylene hydroformylation. Our results demonstrate that oxide-supported pair sites can enable bifunctional reaction mechanisms with high activity and selectivity for reactions that are performed in industry using homogeneous catalysts.

金属催化的反应通常被假设为在双功能活性位点上进行，由此共定位的活性物质促进催化循环^{1,2,3,4,5,6,7,8}中不同的基本步骤。双功能活性位点已在均相双核有机金属催化剂^9,10,11上建立。负载型金属催化剂上存在双功能活性位点的经验证据，例如，在金属-氧化物载体界面^2,6,7,12。然而，由于潜在活性位点结构的分布、它们的动态重建和所需的非平均场动力学描述，阐明负载型金属催化剂的双功能反应机制具有挑战性^7,12,13. _{我们通过合成负载型、原子级分散的氧化铑-钨 (Rh-WO x} ) 对位催化剂克服了这些限制。对位点结构的相对简单性和平均场建模的充分描述使实验动力学与基于第一原理的微观动力学模拟相关联。Rh-WO _x对位点通过涉及Rh辅助WO _x还原、乙烯从WO _x转移到Rh和H ₂在Rh-WO _x界面解离的双功能机制催化乙烯加氢甲酰化。_{在 0.1 g丙醛} cm ^-3  h的产物形成速率下，这对位点表现出 >95% 的选择性^-1在气相乙烯加氢甲酰化中。我们的结果表明，氧化物支持的对位点可以使双功能反应机制具有高活性和选择性，适用于在工业中使用均相催化剂进行的反应。