奈米鈀觸媒之改質與甲苯完全氧化反應之應用; Toluene oxidation over supported palladium catalysts

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Title:	奈米鈀觸媒之改質與甲苯完全氧化反應之應用;Toluene oxidation over supported palladium catalysts
Authors:	蔡逸霆;Yi-Ting Tsai
Contributors:	化學工程與材料工程研究所
Keywords:	觸媒焚化;金;氧化鈰;金-鈀雙金屬觸媒;二氧化鈦;甲苯;Toluene;TiO2;CeO2;Bimetallic Au-Pd catalysts;Palladium;Gold;Catalytic combustion
Date:	2011-06-16
Issue Date:	2012-01-05 11:15:51 (UTC+8)
Abstract:	本實驗室先前的研究指出，奈米金/氧化鈰及奈米鈀/氧化鈰觸媒對於甲苯完全氧化反應有很高的活性。因此，吾人製備金–鈀雙金屬觸媒以期達到更佳的反應活性。在本研究中，製備一系列不同金比例的金–鈀/氧化鈰與金–鈀/二氧化鈦觸媒。先以初濕含浸法製備0.5 wt. %之鈀觸媒，再以沉積沉澱法製備金含量介於0.1 wt. %到1 wt. %之金–鈀雙金屬觸媒。使用高表面積且具有特殊微孔結構的氧化鈰(來自Nikki公司)以及二氧化鈦(來自Evonik Degussa公司)作為擔體。觸媒鑑定方面，主要是以X光繞射儀(XRD)，穿透式電子顯微鏡(TEM)，高解析度穿透式電子顯微鏡(HRTEM)與X光電子能譜儀(XPS)，進行鑑定與分析。並使用甲苯作為本研究觸媒焚化之指標物。反應物甲苯之進料濃度為8.564 g/m3 (2085 ppm)，空間流速為10,000 h-1。 TEM與HRTEM圖中顯示金與鈀的顆粒大小約為3到5奈米，且均勻分布於擔體上，其結果與XRD結果一致。由XPS中可發現在奈米鈀觸媒上加入適量的金，有助於鈀元素態的比例增加，同時也增進其反應活性。然而過量的引入金，會導致觸媒活性下降，原因為在觸媒表面上之金顆粒與鈀顆粒重疊，而金活性又比鈀活性差，因而造成反應活性下降。從活性測試中，金–鈀雙金屬觸媒之反應活性優於金、鈀物理混合觸媒，證明金與鈀之間有好的交互作用，與XPS結果相符。從實驗結果顯示出金–鈀雙金屬觸媒之反應活性優於單一活性金屬之觸媒，是因為金原子簇與鈀原子簇間有協同作用使得反應活性佳。對於甲苯完全氧化反應，金–鈀雙金屬觸媒是非常好的。 Au/CeO2 and Pd/CeO2 were reported to be very active to destruct toluene from this lab. Therefore, combination of gold and palladium is an interesting candidate to achieve a catalyst with higher activity. In this study, a series of Au–Pd/CeO2 and Au–Pd/TiO2 bimetallic catalysts with various Au loadings were prepared. Pd was loaded by incipient-wetness impregnation method and Au was loaded by deposition-precipitation method. The Pd loadings in all samples were fixed at 0.5 wt. %, and the content of gold was between 0.1 and 1 wt. %. High surface area CeO2 with unique microstructure from Nikki Company and TiO2 (P-25) from Evonik Degussa Company were used as the support. The catalysts were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). The catalysts were tested for total oxidation of toluene. The feed concentration of toluene was 8.564 g/m3 (2085 ppm), with GHSV= 10,000 h-1. The TEM and HRTEM images showed that both of Au and Pd particle sizes were 3–5 nm and well-dispersed on the support. This result is consistent with the XRD studies. XPS study indicated that the addition of suitable amount of gold to Pd-based catalyst increased the proportion of metallic palladium and the catalytic activity. However, the overdoes of Au decreased the activity because the Au metal overlapped with the Pd metal and Au was less active than Pd. In activity test, Au–Pd bimetallic catalyst is better than a physically-mixed Au-based and Pd-based catalyst, which indicates there is a good interaction between gold and palladium. In conclusion, Au–Pd bimetallic catalysts were superior to Au and Pd monometallic catalysts due to the synergetic effect between Au and Pd nanocluster. Au–Pd bimetallic catalysts are very promising for toluene destruction.
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