還原時間、鎳(Ni)的摻入及載體(CeO2, BZDy)對於鈷(Co)催化劑在乙醇氧化蒸氣重組反應之影響與反應機構探討

The Mechanistic Study and Effects of Reduction Time and Ni-Dopant and Support for Cobalt-Based catalysts on Oxidation Steam Reforming of Ethanol (OSRE)

郭伯揚(Kuo Po-Yang)

指導教授 ： 王禎翰

國立臺灣師範大學/理學院/化學系/碩士(2018年)

https://doi.org/10.6345/THE.NTNU.DC.006.2018.B05

摘要

本實驗以含浸法來合成10%金屬鈷(Co)與鈷鎳合金分別附載於氧流動性之氧化鈰(CeO2)與親水性之鋯酸鋇摻雜鏑(BZDy)之催化劑，在進行乙醇氧化蒸汽重組反應(OSRE)前，催化劑分別在氫氣下進行還原0小時、還原1.5小時及還原4小時的前處理。催化劑鑑定方面使用能量散射光譜儀(EDS)、X-ray粉末繞射分析儀(XRD)、X-ray光電子能譜儀(XPS)、程序升溫還原反應(TPR)進行催化劑的特性鑑定。透過氣相層析儀GC分析產物選擇率、轉換效率及氫氣產率的催化性能。以原位漫反射傅立葉轉換紅外光譜儀(in situ DRIFTS IR)來推測乙醇氧化蒸汽重組之反應路徑。實驗結果顯示Co附載於親氧性之CeO2上時在OSRE反應過程中能很容易被氧化或還原，但Co在親水性之BZDy上則較難。兩者在氫氣還原4小時前處理下的反應性相似，但Co/CeO2表面活性氧較多，因此CO2選擇率較高，Co/BZDy表面活性氧較少，則CO選擇率較高。Ni摻入Co/CeO2後會使斷C－C鍵能力增強，也會使CO進行WGS反應而導致、H2產率及CO2選擇率提高，但同時也造成CH4選擇率較高及積碳失活的問題。在situ DRIFTS 實驗中，Co/CeO2的表面較具氧流動性，易使乙醛氧化成CH3COO-，而Co/BZDy的氧流動性較差，較易形成CH3CO-。氧氣的加入會促使CH3COO-及CH3CO-在200OC時就能斷C－C鍵而形成CH3 + CO2與CH3 + CO以及促使CH3和CO的氧化。Ni摻入Co/CeO2後會使得acetate的訊號較小，代表Ni對於斷C－C鍵有很高的活性。

關鍵字

乙醇氧化蒸汽重組 ； 產氫 ； 鈷 ； 氧化態 ； 氧化鈰 ； 鋯酸鋇摻鏑 ； in situ DRIFT ； XPS

並列摘要

Co and Co-Ni bimetallic catalysts on oxophilic CeO2 and hydrophilic Dy-doped BaZrO3 (BZDy) were synthesized by impregnation method and treated with H2 reduction for 0, 1.5 and 4 hours before proceeding the oxidation steam reforming of ethanol reaction (OSRE). The catalysts were characterized by Energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR). The catalytic performance of product selectivity, conversion efficiency and H2 yield was analyzed by gas chromatography. The catalytic mechanism was investigated by in situ DRIFTS IR. The experimental results found that Co can be easily reduced/oxidized on the oxophilic CeO2, but hard on the hydrophilic BZDy in OSRE. Both of the catalysts showed similar reactivity after 4-hour H2 pretreatment, but Co/CeO2 with more surface active oxygen showed higher, CO2 selectivity. Introducing Ni in the formation of Ni-Co bimetal can assist C-C bond cleavage and enhance the H2 yield as well as CO2 selectivity due to the water-gas-shift reaction (WGSR); however, it also results in a higher CH4 selectivity and carbon inactivation problems. The In situ DRIFT result showed that Co/CeO2 has better oxygen mobility and can easily to oxidize acetaldehyde to CH3COO-, while Co/BZDy with the poor oxygen mobility easily form CH3CO- instead. The addition of oxygen would assist the C-C bond cleavage of CH3COO- and CH3CO- at 200 OC to form CH3 + CO2 and CH3 + CO, respectively, as well as to promote the following oxidation of CH3 and CO. The doping Ni could reduce acetate signal, indicating its assistance for the C-C bond cleavage.

並列關鍵字

oxidation steam reforming of ethanol ； hydrogen production ； oxidation state ； cobalt ； CeO2 ； BZDy ； in situ DRIFT ； XPS

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