Pd/C催化剂的表面性质对1,8-二硝基萘加氢反应的影响

1,8-二氨基萘(1,8-DAN)是一种重要的精细化工中间体,其在染料、医药中间体和感光材料等行业有着广泛的应用。目前,主要采用化学还原剂还原的方法来合成,此工艺具有产生废渣、原子经济性低等缺点。因此,发展一种绿色环保的催化加氢方法具有重要意义。笔者以具有不同Pd纳米平均粒径的Pd/C为催化剂,通过1,8-二硝基萘催化加氢制备,考察了Pd纳米粒子尺寸对1,8-二硝基萘(1,8-DNN)加氢性能的影响,探索了催化剂表面结构与催化性能的关系。首先,以椰壳炭化料为原料,经水蒸气活化法制备出孔隙发达的载体活性炭,通过不同的还原方法制备出具有不同粒径的Pd/C催化剂,以1,8-DNN的加氢反应来评价其催化性能。应用X-射线衍射(XRD)、透射电镜(TEM)、X-射线光电子能谱(XPS)、N_2吸附等手段对催化剂表面性质进行表征。结果表明:在一定粒径范围内,钯纳米颗粒的尺寸越小,催化剂的活性越高,1,8-DAN的产率和选择性越高。氢气还原使得钯纳米颗粒严重团聚,而使用甲酸和NaBH_4还原的Pd/C催化剂,Pd纳米颗粒分散性较好,并且具有良好的均一性。使用NaBH_4还原的Pd/C催化剂催化1,8-DNN加氢制备1,8-DAN的转化率和产率可分别达到100%和99%,其催化性能高于商业化的Pd/C催化剂。循环回收实验结果表明,Pd/C催化剂在回收反应过程中十分稳定,连续循环5次,活性并没有明显降低。

The effect of surface properties of Pd/C catalyst on 1,8-dinitronaphthalene hydrogenation reaction

1,8-diaminonaphthalene (1,8-DAN) is an important chemical raw material, which has been widely used in the industrial production of fine chemicals, especially in dye, pharmaceutical intermediates and photosensitive materials. At present, 1,8-DAN is mainly synthesized through chemical reduction of 1,8-dinitronaphthalene (1,8-DNN) using iron or zinc, etc, as the catalyst. The process would produce many solid wastes and has low atomic economy. Therefore, it is of great significance to develop an environmentally friendly hydrogenation process to synthesize 1,8-DNN. In this work, we firstly prepared activated carbon support by steaming activation of coconut shell carbon followed by loading Pd nanoparticles by impregnation method. The physiochemical properties of these catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption, etc. The catalytic performances were evaluated through the catalytic hydrogenation of 1,8- DNN to 1,8-DAN. The effect of reduction methods on the mean particle size of Pd and shape of Pd/C was investigated, and the relationship between Pd particle size, shape, and surface properties of these catalysts and their catalytic performances was also examined. The results showed that the reduction method has a significant impact on the Pd particle size. The use of H2 readily resulted in severe agglomeration of Pd nanoparticle, whereas the use of HCOOH and NaBH 4 could afford a small Pd nanoparticle with uniform size distribution. The smaller the size of the palladium nanoparticles, the higher the yield and selectivity of 1,8-DAN was obtained within a certain particle size range. The order for their hydrogenation activity of 1,8-DNN increased as follows: 5%Pd/C-NaBH 4 ,1%Pd/C-NaBH 4 ,1%Pd/C-HCOOH, 1%Pd/C-H2.In addition, it was found that besides the Pd average size and the surface oxygenated groups have a remarkable effect on the catalytic performances. Pd/C obtained by the reduction of NaBH 4 has more hydroxyl groups, which has effectively promoted its hydrogenation activity. The conversion of 1,8-DNN and yield of 1,8-DAN were 100% and 99%, respectively, could be achieved under mild reaction conditions. N2 adsorption results indicated that the surface area, pore volume, and pore size of the catalyst all decreased after the loading of Pd nanoparticles, suggesting that Pd nanopraticles could introduce to the pore or occupy the pore mouth. The results of catalyst recycle experiment demonstrated that the catalyst remained stable without significant loss of its catalytic activity after five successive cycles. This work will provide some new insights into catalyst design for the hydrogenation reaction of 1,8-DNN into 1,8-DAN at a large scale.