二氧化钛改性α-氧化铝载体对银催化剂催化乙烯环氧化反应性能的影响

为了排除载体孔结构变化对催化性能的影响，研究了二氧化钛改性α-氧化铝载体对银催化剂催化乙烯环氧化反应性能的影响。研究结果表明，二氧化钛表面改性α-氧化铝载体对载体的比表面积、孔结构无明显影响；载体表面改性导致催化活性组分银在载体表面均匀分散，分散状况明显改善；经二氧化钛改性后载体表面与银的相互作用增强；对单负载银催化剂，由改性载体制备的银催化剂的活性和选择性均下降，改性对催化性能明显不利；对于共浸渍法制备的多组分银催化剂，低温焙烧对催化性能不利，而由经1000℃高温焙烧的二氧化钛改性载体制备的银催化剂的催化活性明显提高。研究表明，载体表面等电点降低及其与银的强相互作用是造成催化剂上金属银良好分散的主要原因；此外，银催化剂助剂的存在减弱了二氧化钛改性载体与银之间的强相互作用、抑制了环氧乙烷（EO）深度反应的活性，两者协同作用提升了多组分银催化剂的催化反应性能。

Effect of modification of α-alumina carrier with titania on catalyticperformance of silver catalyst for ethylene selective oxidation

In order to exclude the effect of pore structure of carrier, effect of modification of α-alumina with titania on catalytic performance of silver catalyst for ethylene selective oxidation reaction was studied carefully. Experimental results showed that the specific surface area and the pore structure of the carriers were almost unchanged after modification with titania, but silver was dispersed more evenly on the modified carrier than on the α-alumina and the interaction discovered stronger between the modified carrier and silver than between α-alumina and silver. Modification of alumina with titania deteriorates the catalytic performance and was unfavorable to the performance of non-promoted silver catalysts. But it was beneficial to the catalytic performance of the promoted silver catalysts prepared by co-impregnation method. Research results revealed that decrease of IEP (isoelectric point) for the modified carrier and the strong interaction between the carrier and silver are responsible for the even and good dispersion of silver on the modified carrier. In presence of promoters, the interaction between the carrier and silver is weakened and the oxidation and isomerization side-reactions of ethylene oxide are abated, which jointly improve the catalytic performance of the promoted silver catalyst.