催化学报

催化学报 ›› 2016, Vol. 37 ›› Issue (2): 273-280.DOI: 10.1016/S1872-2067(15)61014-2

• 论文 • 上一篇    下一篇

Co掺杂SAPO-5分子筛制备及其催化氧气氧化环己烷反应性能

校准, 詹望成, 郭耘, 郭杨龙, 龚学庆, 卢冠忠   

  1. 华东理工大学结构可控先进功能材料及其制备教育部重点实验室和工业催化研究所, 上海 200237
  • 收稿日期:2015-08-25 修回日期:2015-11-10 出版日期:2016-01-30 发布日期:2016-01-31
  • 通讯作者: 詹望成, 卢冠忠
  • 基金资助:

    国家重点基础研究发展计划(2010CB732300); 国家自然科学基金(21103048).

The synthesis of Co-doped SAPO-5 molecular sieve and its performance in the oxidation of cyclohexane with molecular oxygen

Zhun Xiao, Wangcheng Zhan, Yun Guo, Yanglong Guo, Xueqing Gong, Guanzhong Lu   

  1. Key Laboratory for Advanced Materials and Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237, China
  • Received:2015-08-25 Revised:2015-11-10 Online:2016-01-30 Published:2016-01-31
  • Supported by:

    This work was supported by the National Basic Research Program of China (2010CB732300) and the National Natural Science Foundation of China (21103048).

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698

被引次数

2

摘要：

环己醇和环己酮(KA油)是制备尼龙所需材料己二酸和己内酰胺的重要中间体, 也可用作油漆、农药和染料等的溶剂以及染色和褪光丝的均化剂等. 工业上制取KA油的方法主要为苯酚加氢法、环己烯水合法和环己烷氧化法, 其中环己烷氧化法最为普遍, 是非常重要的工业过程. 为获得适宜的KA油选择性, 工业上普遍采用Co盐为催化剂, 将环己烷氧化单程转化率控制在5.0%以下, 从而使得产物选择性达到70%以上. 该环己烷氧化制KA油过程不仅生产效率较低, 而且所用均相催化剂因分离困难而不能重复使用. 因此, 当前关于环己烷氧化反应催化剂的研究均是围绕多相催化剂进行.
氧气选择性氧化环己烷反应因具有更高的原子经济性而逐渐成为环己烷氧化法制KA油研究中最具挑战性的课题. 该反应是自由基机理, 而Co2+, Cr3+, Mn2+和Ce2+等金属离子可以促进自由基链反应, 因此含有这些金属的多相催化剂被广泛用于该反应. 另一方面, AlPO-n系列分子筛由于具有特殊的孔结构和一定的表面酸性, 在催化反应中显示出较大的应用潜力. 如果进行杂原子掺杂, 通过改变分子筛骨架的电荷平衡, 可以有效提高其表面酸性. 例如磷酸硅铝分子筛(SAPO-5)具有中等强度的酸性和良好的择形性, 因而作为固体酸催化剂广泛用于乙醇脱水、甲醇制烯烃、丙烯聚合和苯乙烯环氧化等反应, 表现出较高的选择性和良好的稳定性.
本文以传统均相Co盐催化剂的多相化为出发点, 制备了Co掺杂SAPO-5与分子筛催化剂(Co-SAPO-5), 考察了Co掺杂量对催化剂结构、表面性质以及氧气选择性氧化环己烷反应性能的影响. 结果表明, 一部分Co进入分子筛骨架, 同时有少量Co以氧化钴形式高度分散在SAPO-5表面. Co掺杂对SAOP-5催化剂比表面积没有显著影响, 但可使其孔体积减小. 相反, Co掺杂可以提高SAOP-5分子筛表面B酸性位数量和总酸量. 活性测试结果表明, 环己烷转化率随着Co-SAPO-5催化剂中Co含量的增加而增加, 但KA油选择性在转化率高于6.3%时急剧下降. 还考察了反应温度、反应时间、初始氧气压力和催化剂用量对Co-SAPO-5分子筛催化剂性能的影响, 得到了最优反应条件. 以Co-SAPO-5-0.2 (Co/Si摩尔比为0.2)分子筛为催化剂时, KA油总收率最高可达7.8%. 另外, Co-SAPO-5催化剂在环己烷氧化反应中显示出很好的稳定性, Co-SAPO-5-0.2催化剂套用6次后活性几乎没有变化.

关键词: SAPO-5分子筛, 钴, 环己烷, 选择氧化, 氧气

Abstract:

Silicoaluminophosphate (SAPO) molecular sieves doped with cobalt (Co-SAPO-5) were synthesized hydrothermally with different concentrations of Co. Each sample was characterized by X-ray diffraction, N2 adsorption-desorption, scanning electron microscopy, ultraviolet-visible spectroscopy, temperature-programmed desorption of NH3 (NH3-TPD), and infrared spectrascopy of adsorbed pyridine (Py-IR). The results showed that Co was highly dispersed in the Co-SAPO-5 samples. In addition, a part of the Co content had been incorporated into the SAPO-5 framework, while the remainder existed on the surface as extra-framework Co. The surface areas of the Co-SAOP-5 samples were similar to the SAPO-5 sample. However, the pore volumes of the Co-SAOP-5 samples were lower than that of the SAOP-5 sample. As the concentration of Co increased, the pore volume gradually decreased because extra-framework cobalt oxide was present on the catalyst surface. NH3-TPD and Py-IR results revealed that the amount of Brønsted acid and the total amount of acid for the Co-SAPO-5 samples were higher than that for the SAPO-5 sample. These values were also higher for samples with higher Co content. The catalytic activity of the Co-SAPO-5 samples was evaluated for the oxidation of cyclohexane with molecular oxygen. When Co was added to the SAPO-5 catalyst, the catalytic activity of the Co-SAPO-5 catalysts improved. In addition, the conversion of cyclohexane increased as the Co content in the Co-SAPO-5 catalysts increased. However, with a high conversion of cyclohexane (>6.30%), the total selectivity of cyclohexanone (K) and cyclohexanol (A) decreased sharply. The K/A ratio ranged from 1.15 to 2.47. The effects of reaction conditions (i.e., reaction temperature, reaction time, initial oxygen pressure, and the catalyst amount) on the performance of the Co-SAPO-5 catalysts have also been measured. Furthermore, the stability of the Co-SAPO-5 catalyst was explored and found to be good for the selective oxidation of cyclohexane by molecular oxygen.

Key words: SAPO-5 molecular sieve, Cobalt, Cyclohexane, Selective oxidation, Oxygen