溶胶-凝胶法制备钯催化剂的织构与性能

采用溶胶-凝胶法制备了Pd/Al2O3催化剂，用LLS(激光光散射)、XRD和BET等技术考察了溶液pH值对所成胶体粒子流体力学半径、相应催化剂产品孔径分布及热稳定性的影响.研究发现，由pH=4.1的胶体制备的催化剂具有良好的热稳定性和CO、C3H6的氧化活性.氧化镧添加剂可抑制Al2O3载体在高温下由γ相向α相的转化，同时也促进了催化剂上Pd粒子的生长. La2O3可提高新鲜Pd催化剂的氧化活性，但对老化后催化剂活性的提高无促进作用.

The Properties of Pd Catalysts Prepared by Sol-gel Method

Highly thermostable palladium catalysts have been prepared by sol-gel method. The possible effects of pH of alumina gel precursor on the final structure and thermal stability of catalyst have been investigated by the wide-angle X-ray diffraction, laser light scattering (LLS) and BET techniques. The results indicated that pore size distributions of catalyst are related with the gel particle size distributions, which were strongly dependent on the pH of the system. It was found that the Pd particles could be anchored within the relatively stable alumina host structure by sol-gel method and resulted in elevation of hydrothermal stability, as well as the enhancement of catalytic activity for CO and C3H6 oxidation over aged catalysts. In addition, it was found that the La2O3 additive could elevate the phase transfer temperature of alumina remarkably, whereas it promoted the sintering of Pd to form bigger particle size at high temperature. The experimental results showed the La2O3 additive could promote the catalytic activities for oxidation of CO and C3H6 over fresh Pd catalysts. However, the activities were a little lower than that of unmodified catalyst after aged at 1050 ℃ for 24 h due to more serious sintering of Pd metal on the surface.