| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 95 === 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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