摘要
采用蒸汽脱铝法对HZSM-5分子筛进行预处理,利用XRD、N2物理吸附及NH3微分量热吸附对分子筛的结构和酸性质进行表征,在关联催化剂的活性评价结果的基础上,研究了分子筛的结构、酸性质对Mo/HZSM-5催化剂反应性能的影响。结果表明,市售的母本HZSM-5分子筛上,少量的强B酸中心的存在,促使了反应中间物种的深度脱氢,造成催化剂在反应过程中发生严重积炭;水蒸汽处理的HZSM-5分子筛,其骨架结构和酸性质随处理温度的不同而改变。923K蒸汽处理的分子筛,结晶度显著降低,骨架结构的严重受损导致了微孔的阻塞和B酸中心的大量减少,不利于C2中间物种的芳构化;823K处理的HZSM-5分子筛,骨架铝脱出相对缓和,在有效地消除了母本分子筛原有的强B酸中心的同时,又保持着较高的结晶度,改善了分子筛的抗积碳能力,因此其Mo基催化剂的甲烷芳构化反应性能较传统制备的Mo/HZSM-5催化剂有显著提高。
A streaming-dealuminated treatment was used to modify HZSM-5, and the structure and acidity of the zeolites were investigated by XRD, N2 physical adsorption and Microcalorimetry of NH3 adsorption techniques. It was found that the catalytic performance of Mo/HZSM-5 catalyst in methane dehydroaromatization was related to the acidity of the HZSM-5 zeolites. On the parent HZSM-5 zeolite with a Si/A1 atomic ratio of 25, the existence of some Broensted acid sites with strong acidic strength promoted the formation of coke deposited on its corresponding Mo/HZSM-5 catalyst. After undergoing the streaming treatment, the framework compositions and acidity of the ZSM-5 zeolite would be significantly altered with the treatment temperatures. At 923 K, the occurrence of a severe extraction of framework aluminum during the treatment led to a significant reduction in both the crystallinity and the microspores volume of the zeolite as well as the amount of Brfinsted acid sites, and thus restricted the C2 intermediates being further transformed into aromatics. At 823 K, the streaming treatment induced a mild dealumination of the zeolite and as a result, destroyed the origin strong Broensted acidic sites while kept a higher crystallinity. Accordingly, a remarkable improvement in catalytic durability and selectivity to aromatics was achieved on the moderated dealuminated Mo/HZSM-5 catalyst compared with the conventional Mo-based catalysts, mainly due to the effective suppression of coke formation during the aromatization reaction.
出处
《天然气化工—C1化学与化工》
CAS
CSCD
北大核心
2007年第2期10-14,共5页
Natural Gas Chemical Industry
