Ptnc-FeOx界面作用提升Pt团簇催化CO氧化性能

Role of Ptnc-FeOx metal-oxide interface in enhancing the catalytic activity for CO oxidation

金属-氧化物界面作用对于调节金属催化剂的电子结构、提升催化剂的催化活性和稳定性起到重要影响,在纳米催化研究领域受到广泛关注。利用尿素沉积沉淀法合成了与FeOx形成界面作用的负载型Pt团簇(Ptnc,尺寸为(1.4±0.2)nm),它表现出相对单金属Ptnc催化剂显著提升的CO催化氧化活性。与具有类似Pt负载量的Pt/SiO2相比,Ptnc-FeOx/SiO2催化剂在同等条件下催化CO氧化的完全转化温度从180°C大幅降低至90°C,表观活化能从60 kJ·mol^−1降低到19 kJ·mol^−1,并具有高出20倍的转换频率(Turnover Frequency,TOF)。采用同步辐射X射线吸收谱学技术、原位漫反射傅里叶变换红外光谱、球差电镜等多种表征手段,对Ptnc-FeOx之间的界面相互作用进行了探讨。结果表明:Ptnc与FeOx之间通过形成的Pt-Fe金属键发生了从Fe向Pt的电荷转移,从而降低了Ptnc的d带中心位置,减弱了CO在Ptnc表面的吸附强度,有助于实现催化活性和反应动力学速率的提升。

[Background]Metal-oxide interface plays critical roles in promoting the catalytic activities of metal catalysts in a vast diversity of reactions.Maximizing this interfacial interaction so as to optimize the catalytic performance is an active subject of research that is worthy of intensive exploration.[Purpose]This study aims to develop new Pt-group catalysts that are highly active towards cryogenic CO catalytic oxidation,and explore effective strategies to engineer metal-oxide(hydroxide)interfaces to weaken the adsorption of CO and to enhance the adsorption/activation of O2.[Methods]Supported ultrasmall Pt nanoclusters(Ptnc-FeOx/SiO2)of(1.4±0.2)nm were synthesized using deposition-precipitation with urea(DPU).The catalytic performance towards CO oxidation was examined by using a fixed-bed U-shape flow quartz reactor.Extended X-ray absorption fine structure(EXAFS),in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS),transmission electron microscopy(TEM),high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM),and energy-dispersive Xray spectroscopy(EDX)techniques were combined to study the Ptnc-FeOx interfacial interaction.[Results]The Ptnc-FeOx/SiO2 catalyst shows superior catalytic performance than Pt/SiO2 towards the CO oxidation reaction.Kinetics tests show that both the apparent activation energy and turnover frequency of Ptnc-FeOx/SiO2 are greatly enhanced as compared with Pt/SiO2(19 kJ·mol^−1 vs.64 kJ·mol^−1;0.044 s^−1 vs.0.002 s^−1 at 37°C).[Conclusion]The charge transfer from Fe to Pt results in the downshifted d-band center of Pt and reduces the CO adsorption strength,and hence,playing important roles in promoting the catalytic activity of Pt catalysts.