催化裂化催化剂有机硫氮转化机理量子化学分析

Quantum Chemical Analysis of Transformation Mechanism of Organic Sulfur and Organic Nitrogen in Catalytic Cracking Catalysts

国家环保法规的日益严格使得对催化裂化(FCC)再生烟气提出了更高的管控要求,再生烟气中污染物组成复杂且转化机制尚不清楚,迫切需要深入理解FCC待生催化剂中污染物的转化机理。对待生催化剂中有机硫和有机氮进行合理简化,选取合适的模型化合物,采用Gassian09软件在B3LYP/def2-TZVP水平下对模型化合物进行几何优化得到最稳定构型,并进行振动分析。利用Multiwfn多功能波函数分析仪对优化后模型化合物进行Laplacian键级(LBO)分析,通过LBO计算结果,得到自由基在再生过程中的详细转化机理。结果表明,含氮化合物中C—N键和含硫化合物中C—S键与C—C键相比均较弱,在催化剂再生过程中会优先发生断裂,生成不同的含氮(NH_(3)、HCN)、含硫(H_(2)S、COS)中间体,随后进一步与氧气反应生成相应的NO_(x)、SO_(x)。

Increasingly stringent national environmental protection regulations have put forward higher control requirements for fluid catalytic cracking(FCC) regenerated flue gas. The composition of pollutants in the regenerated flue gas is complicated and the transformation mechanism is unclear. It is urgent to understand the transformation mechanism of pollutants in FCC spent catalysts. The organic sulfur and organic nitrogen in the spent catalysts were reasonably simplified, and the most stable configuration was obtained by selecting the appropriate model compounds and using the Gassian09 software to optimize their geometry at the B3 LYP/def2-TZVP level. The vibration analysis was also carried out. Laplacian bond order analysis(LBO) of the optimized model compounds was performed by the multifunctional wave function analyzer(Multiwfn), and the detailed transformation mechanism of free radicals in the regeneration process was obtained through the calculation of the LBO. The results showed that both the C—N bond in the nitrogen-containing compounds and the C—S bond in the sulfur-containing compounds were weaker than C—C bond, and will preferentially break during the catalyst regeneration process to generate different nitrogen-containing intermediates(NH_(3), HCN) and sulfur-containing intermediates(H_(2)S, COS), which then further reacted with oxygen to generate corresponding NO_(x)and SO_(x).