高温热稳定性Au/β-Mo2C催化剂的制备及在逆水煤气变换反应中的应用

Preparation of Au/β-Mo2C catalyst with high thermal stability and its performance in the reverse water-gas shift

以程序升温碳化法合成β-Mo2C载体,采用原位沉淀法制备负载量不同的Au/β-M o2C催化剂,利用XRD、STEM和氮气吸附-脱附等手段对Au在载体表面的分散性、微观形貌及孔结构等进行表征,并在逆水煤气变换(RWGS)反应中对其高温热稳定性进行了研究。XRD表征结果表明,在34.44°、38.02°、39.44°、52.12°、61.53°、69.62°和74.65°处出现了β-Mo2C对应的(100)、(002)、(101)、(102)、(110)、(103)和(200)晶面的X射线特征衍射峰;同时,未出现Au物种的特征吸收峰,说明Au负载量较低的0.1%和0.5%的催化剂上Au纳米粒子的分散性较好。STEM表征结果也显示,当负载量较低(0.5%、1.0%和2.0%)时,金纳米粒子以2 nm左右的原子簇形式均匀分散并锚定在β-M o2C载体上。氮气吸附-脱附表征结果表明,催化剂具有良好的介孔结构。反应评价结果表明,0.2%Au/β-Mo2C催化剂在RWGS反应中具有较好的催化活性和较高的CO选择性,且反应后孔结构良好,Au纳米粒子仍然均匀分散,说明Au/β-Mo2C催化剂在此反应中具有较高的催化性能和高温热稳定性。

β-Mo2C support was first prepared by the temperature-programmed carbonization and the Au/β-Mo2C catalysts with different Au loadings were then obtained by using the in-situ precipitation method.The Au/β-Mo2C catalysts were characterized by X-ray diffraction(XRD),scanning transmission electron microscopy(STEM)and nitrogen physisorption;their performance,the thermal stability at the high temperature in particular was then investigated in the reverse water-gas shift(RWGS).The XRD results reveal that the diffraction peaks appeared at 34.44°,38.02°,39.44°,52.12°,61.53°,69.62°and 74.65°correspond to the(100),(002),(101),(102),(110),(103)and(200)planes ofβ-Mo2C,respectively,whereas no characteristic peak of Au species is detected,suggesting the high dispersion of Au nanoparticles on the Au/β-Mo2C catalysts with a low Au loading(0.1%-0.5%).The STEM results illustrate that for the Au/β-Mo2C catalysts with an Au loading of 0.5%-2.0%,gold nanoparticles in the form of atom clusters(about 2 nm)are anchored and uniformly dispersed on theβ-Mo2C surface.The nitrogen physisorption results demonstrate that the Au/β-Mo2C catalysts have plenty of mesopores.The catalytic evaluation results indicate that the 0.2%Au/β-Mo2C catalyst exhibits high activity and high selectivity to CO for the RWGS reaction;moreover,after the reaction,the Au nanoparticles are still evenly dispersed and the pore structure remain intact,suggesting that the Au/β-Mo2C catalyst owns excellent performance and high thermal stability in the he reverse water-gas shift at high temperature.