针对SAPO-34分子筛在MTO反应中烯烃选择性低和易于酸性积炭失活的问题,通过等体积浸渍法向SAPO-34分子筛孔道内引入金属Co,系统考察了Co的加入量对Co/SAPO-34催化剂在MTO反应中的催化性能和积炭行为的影响。结果表明金属Co可以作为脱氢反应中心位点,削弱氢离子转移作用,抑制烷烃的生成,进而有效提高反应烯烃选择性;同时Co金属的引入可以精密调控SAPO-34分子筛表面酸中心强度,提高弱酸/强酸比例,进而削弱强酸中心的积炭作用,抑制催化剂的积炭失活。结合NH3-TPD、H2-TPD、氮气物理吸脱附、TG、XPS、GC-MS等表征方法,深入探讨Co/SAPO-34催化剂在MTO反应中的积炭行为,发现多甲基苯类关键积炭前体优先沉积于微孔和强酸位点,并显著促进稠环芳烃的生成,而相对较大的孔体积以及适量的弱酸浓度可以协同促进积炭前体的分解转化,抑制稠环芳烃等硬积炭物种的形成。积炭速率计算表明,具有适量酸性和孔道结构的Co0.5/SAPO-34的甲醇转化率及低碳烯烃选择性最高,催化寿命最长。

SAPO-34 molecular sieve has the problems of low olefin selectivity and easy carbon deposition of acidic sites in MTO reaction.In this article, Metal Co was introduced into the pores of SAPO-34 through equal volume impregnation method, and the effect of Co addition on the catalytic performance and carbon deposition behavior of Co/ SAPO-34 catalyst in the MTO reaction was systematically investigated. The results indicate that metal Co can serve as a central site for dehydrogenation reactions, weaken hydrogen ion transfer, inhibitthe generation of alkanes, and effectively improve the selectivity of olefins in the reaction. At the same time, the introduction of Co metal can also precisely regulate the strength of acid centers on the surface of SAPO-34, increase the ratio of weak acid to strong acid, thereby weakening the carbon deposition effect of strong acid centers and inhibiting the deactivation of catalyst. By combining characterization methods such as NH3-TPD, H2-TPD, BET, TG, XPS, GC-MS, etc., this paper deeply explored the carbon deposition behavior ofCo/ SAPO-34 catalyst in MTO reaction. It is found that key carbon deposition precursors like polymethyl-substituted benzene are preferentially deposited on micropores and strong acid sites, and significantly promote the generation of polycyclic aromatic hydrocarbons. The relatively large pore volume and appropriate weak acid concentration can synergistically promote the decomposition and transformation of carbon deposition precursors, inhibiting the formation of hard coke. The calculation of carbon deposition rate shows that Co0.5 / SAPO-34 withappropriate acidity and pore structure has the highest methanol conversion rate, low-carbon olefin selectivity and the longest catalytic life.

0 引言

1 试验

   1.1 催化剂的制备

   1.2 MTO催化反应性能评价

   1.3 催化剂表征

2 结果与讨论

   2.1 Co/SAPO-34催化剂在MTO反应中的性能

   2.2 Co/SAPO-34催化剂的表征

   2.3 Co改性SAPO-34分子筛积炭分析

3 结论