山西芮城永乐宫元代天花、藻井研究*

采用不同方法制备了一系列Ni/Al_2O_3催化剂,在无NH_3、无碱条件下对其己二腈催化加氢制1,6-己二胺的反应性能进行研究.通过XRD、 BET、 TEM、 XPS及程序升温实验等结果表明,采用沉淀剂有利于细小Ni纳米颗粒在催化剂介孔内的分散。然而较强的Ni与载体间相互作用不利于氢气的吸附活化,还原处理后催化剂中仍存在较高含量的氧化态Ni物种.采用浸渍法制备的Ni/Al_2O_3-I催化剂中颗粒的平均尺寸为18.5 nm, Ni颗粒暴露在载体表面,生成较高含量的还原态Ni0物种及有利于反应物吸附的中等强度酸性位点.该Ni/Al_2O_3-I催化剂表现出优良的低温活性,在60℃时,己二腈转化频率(TOF)可达39.7 h~(-1);80℃时转化率为100%, 1,6-己二胺收率可达73.0%.然而,由于Ni/Al_2O_3-I催化剂中Ni与Al_2O_3间相互作用较弱,经过3次循环性能测试,催化剂活性明显下降.进一步以少量Cu元素修饰低含量Ni/Al_2O_3-I催化剂, Cu助剂的引入有效改善了Ni纳米颗粒的分散性,并与部分Ni组分形成双金属纳米颗粒.Ni_(15)Cu_3/Al_2O_3催化剂经5次循环反应后无明显失活现象,催化剂的形貌及化学结构亦无明显变化, Cu的引入在保持Ni基催化剂低温活性的同时有效提升了催化剂的循环稳定性,催化剂的TOF为52.1 h~(-1).

The Tianhua and Zaojing Ceilings of the Yongle Taoist Temple in Ruicheng, Shanxi Province

A series of Ni/Al2O3 catalysts were prepared by different methods, and the reactivity for the catalytic hydrogenation of adiponitrile to 1,6-hexamethylenediamine was investigated under NH3/alkali-free conditions. The results of XRD, BET, TEM, XPS and temperature-programmed experiments suggested that the precipitant helped the formation of fine-sized Ni particles dispersed in the mesoporous of support. However, the as-formed strong interaction between Ni and alumina hindered the adsorption/activation of H2, and large amounts of Ni species in oxidative states still existed in the pre-reduced catalysts. On the contrary, average size of Ni particles in Ni/Al2O3-I was as large as 18.5 nm. However, the Ni particles were fully-exposed on the surface of alumina, the higher content of reduced Ni0 species and moderate acidic sites that were conducive to adsorb reactants have been formed easily in Ni/Al2O3-I. The much better low-temperature activity was observed by Ni/Al2O3-I with complete conversion of adiponitrile with 72% selectivity of hexamethylenediamine at only 80 oC. The TOF was calculated to be 39.7 h-1. Unfortunately, due to the weak interaction between Ni and Al2O3 in the Ni/Al2O3-I catalyst, the catalyst activity is significantly reduced after three reaction cycles. Cu species was thus doped in the Ni/Al2O3-I catalyst. The results showed that the doped Cu species effectively improves the dispersion of Ni nanoparticles and Cu-Ni alloy was formed. There was not deactivation of the catalytic performance by Ni15Cu3/Al2O3 catalyst during the stability test. The doping of copper species effectively improved the stability while maintaining the low-temperature activity of the Ni-based catalyst. Using a lower content of Ni-based catalyst, the adiponitrile could completely transformed with the TOF as 52.1 h-1 at 70 oC.