W量对Pt/GaWZrO_(x)催化剂结构及甘油选择氢解性能的影响

Effect of W Content on Structure and Catalytic Performance of Pt/GaWZrO_(x) Catalysts in Glycerol Selective Hydrogenolysis

在甘油选择氢解制1,3-丙二醇(1,3-PDO)反应中, Pt-WO_(x)催化剂体系因其高活性和高选择性而受到研究者的广泛关注.本工作制备了W量不同的Ga掺杂GaWZrO_(x)固体酸(GaWZ),然后作为载体采用浸渍法制备了Pt/GaWZ催化剂,系统考察了W的量对催化剂物化性质和催化性能的影响.CO化学吸附和X射线光电子能谱(XPS)表征发现,随着GaWZ载体中W量的增加,其上负载的Pt的分散度先增加,在10%(w) W的Pt/GaWZ(10)催化剂上达到最高值86%,然后在15%(w) W时降低.紫外-可见漫反射(UV-Vis DRS)、傅里叶变换红外(FTIR)和XPS表征表明, Pt/GaWZ催化剂中的W与四方相ZrO_(2)表面的Zr—OH基团存在较强作用,形成了单分散的WO_(x)物种;当大于7.5%(w) W时,开始出现第二层WO_(x)物种.单分散的WO_(x)物种可能是Pt分散度提高的重要原因.由程序升温氨脱附(NH_(3)-TPD)和吡啶吸附红外(Py-IR)表征结果可见,W的量越高,催化剂的酸量越大,Brφnsted酸和Lewis酸同时增加.在甘油氢解反应中,随着W的增加, Pt/GaWZ催化剂上的甘油转化率呈火山型变化趋势,而目标产物1,3-PDO的选择性则持续提高. 1,3-PDO得率在Pt/GaWZ(10)催化剂上达到最高,为47.5%,而且该催化剂有良好的套用稳定性.根据表征结果,我们推测Pt的分散度及Pt与WO_(x)物种之间的协同作用决定了Pt/GaWZ催化剂在甘油氢解反应中的活性;而1,3-PDO选择性与Brφnsted酸量之间呈现的良好的线性关系,说明WO_(x)物种上的Brφnsted酸位是决定Pt/GaWZ催化剂上1,3-PDO选择性的关键.

The Pt-WO_(x)catalyst system has received much attention for its high activity and selectivity in glycerol hydrogenolysis to 1,3-propanediol(1,3-PDO).In this work,the Ga-doped GaWZrO_(x) solid acid supports(GaWZ)with different W contents were prepared,and then Pt/GaWZ catalysts were prepared by the wetness impregnation method.The effects of the W contents on the physicochemical properties and catalytic performance of the Pt/GaWZ catalysts were systematically investigated.CO chemisorption and X-ray photoelectron spectroscopy(XPS)characterizations revealed that the dispersion of Pt on the GaWZ supports first increasesd with the increase in the W content,reached a maximum of 86%on the Pt/GaWZ(10)catalyst with 10%(w)of W,and then decreased at 15%(w)of W.UV-Vis diffuse reflectance(UV-Vis DRS),Fourier transform infrared(FTIR),and XPS characterization showed that the W in the Pt/GaWZ catalysts interacted with the Zr—OH functional groups on the tetragonal phase ZrO_(2),thus forming mono-dispersed WO_(x)species.When the W content was greater than 7.5%(w),the second layer of the WO_(x)species began to emerge.The mono-dispersed WO_(x)species may be conducive to the high dispersion of Pt.The results of the temperature-programmed desorption of NH_(3)(NH_(3)-TPD)and pyridine adsorption infrared(Py-IR)characterizations showed that the higher the W content,the higher the amount of the acid on the catalyst,with the simultaneous increase in the amounts of both the Brφnsted acids and Lewis acids.In glycerol hydrogenolysis over the Pt/GaWZ catalysts,with the increase in the W content,the glycerol conversion evolved in a volcano-shaped trend,while the selectivity to the target product 1,3-PDO increased monotonically.The highest yield of 1,3-PDO of 47.5%was achieved over the Pt/GaWZ(10)catalyst,and the catalyst also displayed excellent recycling stability.On the basis of the characterization results,we propose that the Pt dispersion and the synergistic interaction between Pt and WO_(x)species determine the activity of the Pt/GaWZ catalysts in glycerol hydrogenolysis,and the Brφnsted acid site pertaining to the WO_(x)species is the key to determine the selectivity to 1,3-PDO over the Pt/GaWZ catalysts,as evidenced by the good linear relationship between the 1,3-PDO selectivity and the amount of the Brφnsted acid sites.