酸处理对CuY催化剂孔结构及氧化羰基化性能的影响

Effects of Acid Treatment on Pore Structure and Oxidation Carbonylation Performance of CuY Catalysts

对NaY分子筛(nSi/nAl=2.65)进行了草酸脱铝处理并作为载体采用液相离子交换法制备CuY催化剂,应用于常压甲醇氧化羰基化合成碳酸二甲酯(DMC)反应。NaY分子筛及其CuY催化剂通过N_2低温吸附-脱附、透射电子显微镜、X射线衍射、29Si固体核磁共振、NH3吸附程序升温脱附、吡啶吸附红外光谱、H_2程序升温还原、原子吸收等方法进行表征。研究结果表明,酸处理NaY分子筛后,骨架铝被脱除,导致骨架nSi/nAl比增加、相对结晶度降低并产生介孔,有利于产物分子的扩散,从而影响催化活性。采用4 h、2 mol·L^(-1)草酸处理NaY分子筛作为载体制备的CuY催化剂显示出较高的催化性能,DMC时空收率和甲醇转化率分别从103.6 mg·g^(-1)·h^(-1)和6.3%增加到184.9 mg·g^(-1)·h^(-1)和10.2%。产生的介孔能够促进催化剂中铜活性位的可接近性及反应物分子和产物分子的扩散。

The NaY zeolite with nSi/nAl=2.65 was treated by oxalic acid aqueous solutions and used as supports to prepare CuY catalysts by liquid ion exchange for oxidative carbonylation of methanol to dimethyl carbonate（DMC） in atmospheres condition. The NaY zeolites and their corresponding CuY catalysts were characterized intensively by N_2adsorption-desorption, TEM, XRD,29 Si MAS NMR, NH3-TPD, Py-FTIR and H_2-TPR. The results revealed that framework aluminum was leached out by acid, resulting in increase of the framework nSi/nAlratio,decrease of the relative crystallinity, and formation of mesopores which are favor for diffusion of the products molecules and significantly affect the catalytic activity. Compared with the untreated sample, CuY catalysts treated by 4 h, 0.2 mol·L^（-1）oxalic acid exhibited higher catalytic performance with the increased space-time yield to DMC and conversion of methanol of 184.9 mg·g^（-1）·h^（-1）and 10.2% from 103.6 mg·g^（-1）·h^（-1）and 6.3%respectively. It is found the formed mesopores in CuY catalyst enhance the accessibility of Cu active sites by reactants and the diffusion of reactants and products molecules.