Panpranot Joongjai, Kontapakdee Kunyaluck, Praserthdam Piyasan
Center of Excellence on Catalysis and Catalytic Reaction Engineering, Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand.
J Phys Chem B. 2006 Apr 20;110(15):8019-24. doi: 10.1021/jp057395z.
Pd/TiO(2) catalysts have been prepared using TiO(2) supports consisting of various rutile/anatase crystalline phase compositions. Increasing percentages of rutile phase in the TiO(2) resulted in a decrease in Brunauer-Emmett-Teller surface areas, fewer Ti(3+) sites, and lower Pd dispersion. While acetylene conversions were found to be merely dependent on Pd dispersion, ethylene selectivity appeared to be strongly affected by the presence of Ti(3+) in the TiO(2) samples. When TiO(2) samples with 0-44% rutile were used, high ethylene selectivities (58-93%) were obtained whereas ethylene losses occurred for those supported on TiO(2) with 85% or 100% rutile phase. X-ray photoelectron spectroscopy and electron spin resonance experiments revealed that a significant amount of Ti(3+) existed in the TiO(2) samples composed of 0-44% rutile. The presence of Ti(3+) in contact with Pd can probably lower the adsorption strength of ethylene resulting in an ethylene gain. Among the five catalysts used in this study, the results for Pd/TiO(2)-R44 suggest an optimum anatase/rutile composition of the TiO(2) used to obtain high selectivity of ethylene in selective acetylene hydrogenation.
已使用由各种金红石/锐钛矿晶相组成的TiO₂载体制备了Pd/TiO₂催化剂。TiO₂中金红石相百分比的增加导致布鲁诺尔-埃米特-特勒表面积减小、Ti³⁺位点减少以及Pd分散度降低。虽然发现乙炔转化率仅取决于Pd分散度，但乙烯选择性似乎受到TiO₂样品中Ti³⁺存在的强烈影响。当使用金红石含量为0 - 44%的TiO₂样品时，可获得高乙烯选择性（58 - 93%），而对于负载在金红石相含量为85%或100%的TiO₂上的样品则会出现乙烯损失。X射线光电子能谱和电子自旋共振实验表明，在金红石含量为0 - 44%的TiO₂样品中存在大量Ti³⁺。与Pd接触的Ti³⁺的存在可能会降低乙烯的吸附强度，从而导致乙烯增加。在本研究中使用的五种催化剂中，Pd/TiO₂ - R44的结果表明，用于在选择性乙炔加氢中获得高乙烯选择性的TiO₂的最佳锐钛矿/金红石组成。
