低Pd负载量结构化邻二甲苯燃烧催化剂的设计

为了在极短的时间内制备具有超低贵金属含量的结构化催化剂，并将其应用于邻二甲苯的催化燃烧体系，在阴极极化技术的基础上采用电解法制备具有不同载体的Pd基结构化催化剂，通过SEM（扫描电子显微镜）、EDS（能谱仪）、XRD（X射线衍射）、CO-Pulse（一氧化碳脉冲化学吸附）等表征手段分析不同催化剂上Pd的分散行为对催化活性的影响，并利用交流阻抗试验解释Pd在不同载体上的负载机理.结果表明:①阴极极化技术有效地减薄了AAO/Al（CP-AAO/Al、CP-AlOOH/Al和CP-γ-Al₂O₃/Al 3种载体的前驱体）的阻挡层，从而提高了载体的导电性，2.5 min内AAO/Al的表面电阻从7.23×108 Ω降至1.21×108 Ω.②当w（Pd）为0.1%时，采用电解法在3种载体上负载Pd的时间在5 min以内.③3种载体中CP-γ-Al₂O₃/Al（阴极极化后的γ-Al₂O₃载体）的阻抗最小，其电荷转移能力最好，更有利于Pd的负载及分散.④Pd/CP-AAO/Al、Pd/CP-AlOOH/Al和Pd/CP-γ-Al₂O₃/Al催化剂上Pd的分散度分别为11.24%、10.90%、17.42%，对应的T₅₀（转化率为50%时的温度）分别为170、172、160℃.研究显示，电解法可有效地将催化剂制备时间由传统的数十小时缩短为数分钟，同时邻二甲苯催化活性结果表明，催化剂活性与Pd的分散度呈正相关，即Pd的分散度越高，催化剂的催化活性越好. 

Design of Structured Catalysts with Low Pd Loading for o-Xylene Combustion

In order to prepare structured catalysts with ultralow Pd loading in a very short time and use it for o-xylene combustion, Pd-based structured catalysts with different carriers were prepared by electrolysis method on the basis of cathodic polarization technology. The effects of Pd dispersion on the catalytic activity of the catalysts were analyzed by SEM (Scanning Electron Microscope), EDS (Energy Dispersive X-Ray Spectroscopy), XRD (X-Ray Diffractomer) and CO-Pulse (Carbon Monoxide Pulse Chemisorption). Meanwhile, the mechanism of Pd loaded on different carriers was studied through AC impedance experiment. The results showed that: (1) The barrier layer of AAO/Al (the precursor of CP-AAO/Al, CP-AlOOH/Al and CP-γ-Al₂O₃/Al carriers) was effectively reduced by cathodic polarization technology, therefore improving the conductivity of the carriers. The surface resistance of AAO/Al was reduced from 7.23×108 Ω to 1.21×108 Ω within 2.5 min. (2) The time to load Pd on the three carriers by electrolysis method was not more than 5 min when w (Pd) was 0.1%. (3) The CP-γ-Al₂O₃/Al (gamma alumina after cathodic polarization) carrier was easier to load and disperse Pd because of its better ability to transfer charge. (4) The dispersion of Pd on Pd/CP-AAO/Al, Pd/CP-AlOOH/Al and Pd/CP-γ-Al₂O₃/Al catalysts was 11.24%, 10.90% and 17.42%, respectively, and the corresponding T₅₀ (the temperature at the conversion of 50%) was 170, 172 and 160 ℃, respectively. The study showed that the preparation time of catalysts was effectively reduced from traditional tens of hours to a few minutes. The catalytic activity of the catalysts for o-xylene combustion was positively related to the dispersion of Pd, that is the higher the dispersion of Pd, the better the catalytic activity of the catalyst.