改性Ag/TS-1上丙烯直接气相氧化合成环氧丙烷的研究

GAS-PHASE OXIDATION OF PROPYLENE TO PROPYLENE OXIDE OVER MODIFIED Ag/TS-1 CATALYSTS

在150℃、常压固定床石英反应器中,考察了Ag/TS 1催化剂上分别添加Cu、Pd、La,水汽处理,硅烷化处理及洗涤程度等处理方法对丙烯气相氧化性能的影响。采用UV Vis、TEM和ICP等分析方法对催化剂进行了表征。结果表明,少量Pd的存在有利于提高催化剂的稳定性;在催化剂的制备过程中,La沉淀于载体上再担载Ag与La浸渍于载体上再担载Ag相比,环氧丙烷(PO)的选择性由90%下降至64%。水汽处理会使催化剂性能大幅度下降。对载体进行适量的硅烷化处理,有利于提高催化剂的活性和选择性。TEM测试表明,过量的SiO2担载量使担载于催化剂表面的Ag颗粒增大,从而使环氧丙烷的选择性由98%下降至90%。当SiO2担载量为2%(质量分数)时,丙烯转化率和环氧丙烷选择性分别为2.1%和98%。在制备过程中未经洗涤的催化剂比经过洗涤的催化剂的Ag和K的含量略高,表现出较佳的催化性能,其活性和选择性分别为2.43%和86.97%。

The effects of incorporation of Cu, Pd and La, steam treatment, silylation treatment, as well as washing times of Ag/TS-1 catalyst on its catalytic properties of propylene oxidation using oxygen as an oxidant were investigated at 150℃ and atmospheric pressure in a fixed-bed quartz reactor. The catalysts were characterized by UV-Vis, TEM and ICP, respectively. The incorporation of small amount of palladium (Pd) would improve the catalyst stability. Compared with the catalyst of Ag loaded on La impregnated TS-1, the catalyst of Ag loaded on the La deposited TS-1 decreased drastically for its propylene oxide (PO) selectivity, from about 90% to 64%. Steam treatment resulted in detriment to catalyst activity. The silylation of support TS-1 led to the increase of catalyst activity and selectivity. Excessive loading of SiO_2 resulted in the decrease of PO selectivity from 98% to 90% as shown by the TEM photos that the Ag particles loaded on the surface of the support forming bigger aggregates. When 2% (mass fraction) SiO_2 was loaded, the propylene conversion and the selectivity to PO are 2.1% and 98%, respectively. During the preparation of Ag/TS-1 catalyst, the contents of Ag and K in the catalyst without washing showed the optimum catalytic properties; the propylene conversion and the selectivity to PO were 2.43% and 86.97%, respectively.