双金属改性ZSM-5-USY复合分子筛催化裂解正己烷制备低碳烯烃

为了获得催化裂解制备低碳烯烃的高效催化剂，以等体积浸渍法制备了系列单金属(Ce, Y, Zr, Mn, Cu)及双金属(Zr-Ce, Mn-Ce, Y-Ce, Cu-Ce)改性ZSM-5-USY复合分子筛催化剂，通过XRD, NH3-TPD, BET等方法表征了其物理化学性质，并将所制备催化剂用于催化裂解正己烷。结果表明，催化剂的弱酸量越多，正己烷转化率及C2~C4烯烃选择性越高，Zr-Ce共改性分子筛的催化活性较优。水蒸气处理对Zr-Ce/ZSM-5-USY催化剂的酸性及催化裂解产物分布有较大影响，经水蒸气处理的催化剂性能更稳定，可将裂解产物中低碳烯烃的选择性由20.02% (催化剂未经水蒸气处理)提高到57.55% (催化剂经水蒸气处理4 h)。研究了0.25% Zr-0.5% Ce/ZSM-5-USY催化体系的裂解反应动力学，正己烷裂解为一级反应，裂解活化能为88.93 kJ/mol。

Catalytic cracking of n-hexane to light olefins by bimetallic modified ZSM-5-USY composite molecular sieves

Compared with steaming cracking, catalytic cracking is more appealing with much lower reaction temperature and adjustable distribution of the product (by changing the catalyst composition). In order to obtain efficient catalysts with high selectivity to light olefins for petroleum catalytic cracking, composite ZSM-5-USY zeolites were modified with single metal (e. g., cerium, yttrium, zirconium, manganese, and copper) or bimetals (e. g., zirconium-cerium, manganese-cerium, yttrium-cerium, and copper-cerium) by incipient impregnation. The physicochemical properties, including crystal structure, acidity, surface area, of the catalysts were characterized by XRD, NH3-TPD and BET. Catalytic activity of the prepared catalysts in cracking were evaluated by using n-hexane as a model compound for petroleum on a fix-bed reactor. The composition of the product was detected online by gas chromatography. The results showed that the composite molecular sieves modified by various metals exhibited quite different catalytic behaviors in n-hexane cracking, and the performance had close relationship with acidity content of the catalyts. Catalysts with higher weak acidity amount exhibited higher conversion of n-hexane and selectivity of C2~C4 olefins. The Ce-Zr co-modified molecular sieve showed excellent catalytic activity and high selectivity of C2~C4 olefins (57%) at 550℃. Steam treatment had significant influence on the acidity of Ce-Zr/ZSM-5-USY and distribution of the cracking products. After steam treatment, stability of the catalyst was significantly improved, and selectivity of C2~C4 olefins increased from 20.02% (when there was no steam treatment) to 57.55% (when the catalyst was steam treated for 4 h), but the n-hexane conversion rate decreased. Kinetics study of cracking of n-hexane over 0.25% Zr-0.5% Ce/ZSM-5-USY showed that this reaction was a first order reaction, and the activation energy was 88.93 kJ/mol.