Tompos András, Margitfalvi József L, Hegedus Mihály, Szegedi Agnes, Fierro Jose Luis G, Rojas Sergio
Institute of Surface Chemistry and Catalysis, Chemical Research Center, Hungarian Academy of Sciences, 1525 Budapest, P.O. Box 17, Hungary.
Comb Chem High Throughput Screen. 2007 Jan;10(1):71-82. doi: 10.2174/138620707779802841.
In the present work, the role and the effect of platinum and gold on the catalytic performance of ceria supported tri-metallic Pt-Pd-Au catalysts have been studied. The optimum composition of these tri-metallic supported catalysts has been discovered using methods and tools of combinatorial catalyst library design. Detailed catalytic, spectroscopic and physico-chemical characterization of catalysts in the vicinity of the optimum in the given compositional space has been performed. The temperature-programmed oxidation of methane revealed that the addition of Pt and Au to Pd/CeO2 catalyst resulted in higher conversion values in the whole investigated temperature range compared to the monometallic Pd catalyst. The time-on-stream experiments provided further evidence for the high-stability of tri-metallic catalysts compared to the monometallic one. Kinetic studies revealed the stronger adsorption of methane on Pt-Pd/CeO2 catalysts than over Pd/CeO2. XPS analysis showed that Pt and Au stabilize Pd in a more reduced form even under condition of methane oxidation. FTIR spectroscopy of adsorbed CO and hydrogen TPD measurements provided indirect evidences for alloying of Pt and Au with Pd. CO chemisorption data indicated that tri-metallic catalysts have increased accessible metallic surface area. It is suggested that advantageous catalytic properties of tri-metallic Pt-Au-Pd/CeO2 catalysts compared to the monometallic one can be attributed to (i) suppression of the formation of ionic forms of Pd(II), (ii) reaching an optimum ratio between Pd0 and PdO species, and (iii) stabilization of Pd in high dispersion. The results also indicate that Pd0 - PdO ensemble sites are required for methane activation.
在本工作中，研究了铂和金对二氧化铈负载的三金属Pt-Pd-Au催化剂催化性能的作用和影响。利用组合催化剂库设计的方法和工具发现了这些三金属负载催化剂的最佳组成。对给定组成空间中最佳组成附近的催化剂进行了详细的催化、光谱和物理化学表征。甲烷程序升温氧化表明，与单金属Pd催化剂相比，在Pd/CeO2催化剂中添加Pt和Au在整个研究温度范围内具有更高的转化率。与单金属催化剂相比，三金属催化剂的稳定性更高，这一点在连续流动实验中得到了进一步证实。动力学研究表明，甲烷在Pt-Pd/CeO2催化剂上的吸附比在Pd/CeO2上更强。XPS分析表明，即使在甲烷氧化条件下，Pt和Au也能使Pd以更还原的形式稳定存在。吸附CO的FTIR光谱和氢气程序升温脱附测量为Pt和Au与Pd合金化提供了间接证据。CO化学吸附数据表明，三金属催化剂的可及金属表面积增加。有人认为，与单金属催化剂相比，三金属Pt-Au-Pd/CeO2催化剂具有有利的催化性能，这可归因于：（i）抑制Pd（II）离子形式的形成；（ii）使Pd0和PdO物种之间达到最佳比例；（iii）使Pd高度分散稳定。结果还表明，甲烷活化需要Pd0 - PdO组合位点。
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