铂是光催化二氧化碳（CO₂）还原制甲烷（CH₄）最有效的助催化剂之一，但仍面临CO₂还原速率和CH₄选择性低的难题。本研究利用原子层沉积（ALD）制备了Pt颗粒尺寸可调（0.55−1.80 nm）的Pt/TiO₂催化剂并将其用于光催化还原CO₂制CH₄反应。Pt/TiO₂催化CO₂还原速率和CH₄选择性随Pt颗粒尺寸增加呈现出先增加后降低的火山型趋势，其中，Pt颗粒尺寸为1.35 nm时，催化剂的甲烷收率最高（71.9 μmol/(g·h)）且没有检测到H₂的生成；烷烃产物（CH₄、C₂H₆、C₃H₈）选择性为100%，CH₄的电子选择性和碳基产物选择性分别高达81.69%和90.20%。CO-DRIFTS、XPS、CO₂-TPD、H₂O-TPD、H₂-TPD等分析结果表明，Pt颗粒尺寸为1.35 nm时，具有最优的活化CO₂能力、合适的活化H₂O能力和较高的氢脱附温度，使H₂O活化生成活性氢速率与CO₂还原消耗活性氢速率相匹配，展示出最佳性能。本研究对开发高活性和高选择性的光催化CO₂还原催化剂具有重要参考价值。

Platinum is one of the most efficient cocatalysts for photocatalytic reduction of carbon dioxide (CO₂) to methane (CH₄), but it still suffers from low CO₂ reduction rate and low selectivity of CH₄. In this study, Pt/TiO₂ catalysts with adjustable Pt particle size (0.55−1.80 nm) were prepared by atomic layer deposition (ALD) and used for photocatalytic reduction of CO₂ to CH₄. The CH₄ yield and selectivity of the Pt/TiO₂ catalysts showed a volcanic variation trend with the increase of Pt particle size. The 10Pt/TiO₂ with Pt particle size of 1.35 nm exhibit the highest methane yield (71.9 μmol/(g·h)). Especially, a high electron-based selectivity of 81.69% for CH₄ (product-based selectivity of 90.20%), and 100% for hydrocarbons (CH₄, C₂H₆ and C₃H₈) are achieved, no H₂ formation was detected. The CO-DRIFTS, XPS, CO₂-TPD, H₂O-TPD, and H₂-TPD characterizations suggest that the 10Pt/TiO₂ exhibited optimal CO₂ adsorption/activation capacity, suitable H₂O activation capacity, and higher hydrogen desorption temperature, making the generation rate of active hydrogen species from H₂O matches their consumption rate for CO₂ hydrogenation. This study opens an avenue for rationally designing highly efficient and selective photocatalysts for photocatalytic CO₂ reduction.