改性Ag/α-Al_2O_3催化丙烯气相环氧化反应

制备了以分子氧为氧化剂,对丙烯气相环氧化具有较好催化性能的改性负载银催化剂,并利用氧气程序升温脱附(O2-TPD)技术研究了氧在其表面上的脱附行为.实验结果表明:Ag/α-Al2O3催化剂只能使丙烯完全氧化成二氧化碳和水;当该催化剂用K2O改性后,可获得少量的环氧丙烷;Y2O3改性的Ag/α-Al2O3催化剂,可获得极少量的丙醛和丙酮;将0.1%(w)Y2O3添加到Ag-K2O/α-Al2O3后,可以显著提高催化剂的丙烯环氧化性能.在0.1MPa、245℃、20%C3H6/8%O2/72%N2和气体空速2000h-1的反应条件下,通过20%(w)Ag-0.1%Y2O3-0.1%K2O/α-Al2O3催化剂时,丙烯转化率为4.0%,环氧丙烷的选择性为46.8%.O2-TPD研究表明,少量的Y2O3、K2O或Y2O3-K2O作为助剂添加到20%Ag/α-Al2O3催化剂中时,减少了高温区与丙烯完全氧化有关的吸附氧物种的量,低温区余下的吸附氧物种量不变,有利于丙烯环氧化反应,提高了环氧丙烷的选择性.

Gas Phase Epoxidation of Propylene over a Modified Ag/a-Al2O3 Catalyst

Modified Ag/α-Al2O3 catalysts were prepared for the gas phase epoxidation of propylene by molecular oxygen. We used temperature-programmed desorption of oxygen (O2-TPD) to study the desorption behavior of oxygen from the catalyst's surface. Results showed that over the Ag/α-Al2O3 catalyst propylene was completely oxidized to CO2 and H2O. When the catalyst was modified with K2O, a small amount of propylene oxide (PO) was obtained. When the catalyst was modified with Y2O3, a very small amount of propanal and acetone was obtained. Adding 0.1% (w) Y2O3 to the Ag-K2O/α-Al2O3 catalyst significantly improved its catalytic performance for the gas phase epoxidation of propylene. Under reaction conditions of 0.1 MPa, 245 ℃, a feed gas of 20%C3H6/8%O2/72%N2 and gas hourly space velocity (GHSV) of 2000 h-1, the conversion of propylene was 4.0%and the selectivity to PO was 46.8%over the 20% (w)Ag-0.1%Y2O3-0.1%K2O/α-Al2O3 catalyst. O2-TPD showed that when the 20%Ag/α-Al2O3 catalyst was modified with Y2O3, K2O or Y2O3-K2O, the amount of adsorbed oxygen in the higher temperature region for the total oxidation of propylene decreased and the amount of adsorbed oxygen in the lower temperature region for the gas phase epoxidation of propylene was unchanged, which improves the selectivity to PO.