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采用浸渍法和干混法制备了负载钼的层柱分子筛催化剂 ,利用 XRD分析了样品表面上钼的分散性。结果表明 ,通过浸渍或干混热处理 ,钼含量低的催化剂中 ,钼在层柱分子筛表面上自发分散而使晶相钼物种消失 ;而钼含量高时 ,催化剂表面上保留晶相钼物种。通过氨水处理 ,可以使低、中或高钼含量的催化剂上所有的晶相钼物种消失 ,并溶解掉一部分单层分散和全部多层分散的表面钼物种。通过噻吩加氢脱硫微反活性测定 ,发现中等钼含量的催化剂活性最佳 ,而且催化剂上不溶于氨水并呈单层分散的表面钼物种是加氢脱硫活性中心。用氨水处理能溶解掉部分非活性的表面钼物种及晶相钼物种 ,使得活性钼物种充分裸露 ,从而提高催化剂的活性。
Molybdenum-containing column-supported molecular sieve catalyst was prepared by impregnation method and dry blending method. The dispersibility of molybdenum on the sample surface was analyzed by XRD. The results show that molybdenum species disappear on the surface of pillared molecular sieve due to the spontaneous dispersion of molybdenum in the catalyst with low molybdenum content by impregnation or dry heat treatment. However, molybdenum species are retained on the surface of catalyst when molybdenum content is high. Through ammonia treatment, all the crystalline molybdenum species on the catalyst with low, medium or high molybdenum content can disappear and a part of the surface molybdenum species with single-layer dispersion and all multi-layer dispersion can be dissolved. Through the determination of thiophene hydrodesulfurization micro-activity, it was found that the catalyst with medium molybdenum content is the best, and the surface molybdenum species which is insoluble in ammonia and monolayer is the active center of hydrodesulfurization activity. Ammonia treatment can dissolve some of the inactive surface molybdenum species and crystalline molybdenum species, making the active molybdenum species fully exposed, thereby enhancing the activity of the catalyst.