摘要
运用TPD、XRD、XPS、Mossbauer谱,比表面和孔径分布等测定方法,结合催化剂的活性考察,对丁烯氧化脱氢制丁二烯的Zn-Mg-Fe-O催化剂的表面性质和失活机理进行了研究。实验表明,在Zn-Mg-Fe-O催化剂表面上存在着三种不同的氧吸附中心,在不同温度范围内,通过不同方式形成晶格氧的选择性氧化部位,使吸附的丁烯生成丁二烯。导致催化剂在长期使用过程中失活的主要原因是积炭,经烧炭后能恢复大部分的活性,由于高温等原因造成催化剂结构上的变化,如α-Fe_2O_3的消失、Fe和Zn离子价态的变化、晶粒烧结等,使烧炭再生后的催化剂活性有一定的损失。避免现有绝热反应器高温段的出现,控制反应温度小于500℃是延长催化剂寿命的重要措施。
The deactivation and the surface properties of Zn-Mg-Fe-O catalysts for oxidative dehydrogenation of butene to butadiene were studied by TPD (Temperature Programmed Desorption), XRD(X-ray Powder Diffraction), XPS (X-ray Photoelectron Spectroscopy), Mossbauer spectra, measurement of specific surface, and determination of pore structure. The catalytic activities were also investigated.The TPD study showed that there were three distinct types of adsorption centers for oxygen on the catalyst surface as identified by the peak (1) at 140℃, the peak (2) at 267℃, and the peak (3) at 600℃. Subsequently, the selective oxidation sites of httice oxygen were formedin various ways at different temperatures. Butene can be converted to butadiene on the sites.The measurements of specific surface and pore structure showed that the main cause for deactivation of the catalyst was the coke deposition during the reaction. The regeneration of the catalyst was carried out by burning off the carbonaceous deposit of coke in the pores. The activity and selectivity of the regenerated catalyst could be substantially recovered.The XRD, XPS, and Mossbauer spectra indicated that the activity of the regenerated catalyst decreased as compared with the fresh catalyst. The damage involved the disappearance of α-Fe_2O_3, the unreversible change in valent state of the ions, the change in chemical environment, and the sintering of catalyst.
基金
国家自然科学基金
关键词
丁烯
氧化脱氢
催化剂
失活
catalyst
butene
butadiene
oxidative dehydrogenation
deactivation
