A novel bimetallic Rh-Ni/BN catalyst for methane reforming with CO2
|關鍵字:||鎳, 甲烷, 二氧化碳,雙金屬, 銠;BN, methane, CO2, bimetallic,Rh-Ni||公開日期:||2007||摘要:||甲烷-二氧化碳重組反應可利用溫室氣體(CH4、CO2)生成具有高價值的氫氣與一氧化碳。工業上多使用鎳觸媒，但會因為積碳與金屬燒結的關係造成觸媒失活，於是利用加入第二金屬或將金屬負載在特殊載體上，進而改善觸媒失活並提高活性。
氮化硼(Boron Nitride，BN)和傳統氧化物載體，如氧化鋁等比較，具有許多特有的性質。根據之前的研究由於BN為惰性物質不易與金屬產生交互作用，特別容易有合金產生，有助提升活性。我們利用共臨界沾濕法製備不同比例的Rh-Ni/BN 觸媒，並另外製備Rh-Ni/γ-Al2O3作為比較。將所製備的觸媒分為未經鍛燒及經不同溫度鍛燒後的新鮮觸媒作為比較，並在不同溫度氫氣還原後進行實驗。所使用的觸媒檢測方法有氮氣比表面積測定(BET)、氫氣化學吸附測定、TPR、XRD、XPS及TEM。
Methane and CO2, which are greenhouse gases, can be consumed by dry reforming with CO2 to form valuable products in the form of CO and H2. Ni catalyst has been widely used in industry, however it results in coking and sintering, which deactivates the catalyst. By adding an second metal, or loading it on the support, sintering can be reduced resulting in catalyst activity increased. Boron nitride(BN) has many unique properties compared with traditional supports. Previous studies shows that BN is an inert material, it does not interact readily with other metal compounds, as a result alloys are formed which increase the catalytic activity. The incipient wetness method was used to prepare different ratios of Rh-Ni/BN catalyst. This catalyst was also compared with Rh-Ni/γ-Al2O3. The prepared fresh catalysts are examined under non-calcinated and different calcination temperature conditions. The reaction of catalysts was preformed at different temperatures under hydrogen flow. The catalyst was characterized using BET, hydrogen chemisorption, TPR, XRD, XPS and TEM. BET results showed that the catalyst surface area did not change significantly before and after the reaction. Hydrogen chemisorption experiments showed that the addition of Rh increased metal dispersion. It was found from TPR results that when a second metal was added, the reduction temperature would shift between that of pure Ni and pure Rh catalyst, this may be due to the formation of an alloy or other compounds. The interaction is smaller between the metal particle and BN than with γ-Al2O3. Therefore on the BN support, metal particles move freely and form clusters. TEM results show that when a second metal is added on the BN support, a second kind of particle can be seen, this could be a bi-metal cluster or alloy formation. XPS results showed that after H2 reduction, the metal compounds loaded on the BN support became metallic elements, however on the γ-Al2O3 support, Ni remained same oxidation state before and after reduction. This suggests that there is no interaction between the two metals on the γ-Al2O3 support. Experiments show that the addition of Rh, increases the activity of Ni/BN as well as the catalyst life. At a reaction temperature of 700℃, the conversion of methane and CO2 reaches 90%, this is higher than that using Rh-Ni/γ-Al2O3 catalyst. The ratio of H2/CO product is about 0.7 and does not show signs of deactivation after 6 hours of reaction time. The optimum ratio of Rh/Ni is 0.01, under this condition, the largest yield of products are formed and methane conversion is highest.
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