水滑石Ni基催化剂上甲烷干重整制氢的研究

Hydrogen production by dry reforming of methane on hydrotalcite Ni-based catalysts

  • 摘要: 层状双金属氢氧化物(Layered Double Hydroxides, LDHs)是一类具有典型水滑石结构的阴离子黏土材料,其可设计的组成与优异的结构可塑性为高性能催化剂的制备提供了理想前驱体.本研究以水滑石型LDHs为前驱体,采用共沉淀法制备了不同Ge/Ni摩尔比(0、0.10、0.30、0.50、1.0)的Ni-Ge/(Mg,Al)Ox催化剂,并在700 ℃、常压、GHSV=42 000 mL·h−1·g−1条件下考察其对甲烷干重整(DRM)制氢的活性与稳定性.通过N2吸附-脱附、FTIR、XRD、H2-TPR、TGA-DTA、TPO与拉曼光谱等手段对反应前后催化剂进行了系统表征.结果表明,Ge的引入未改变催化剂的介孔结构,但显著增强了金属-载体相互作用(H2-TPR测试中,Ge/Ni = 0.3催化剂的还原峰温度较未改性Ni/(Mg, Al)Ox提升10 ℃,总H2消耗量增至1.35 mmol·g−1,表明金属与载体结合更紧密),并形成Ni-Ge合金活性中心.在5种催化剂中,Ni-Ge/(Mg,Al)Ox(Ge/Ni = 0.3)表现出最优DRM性能:CH4和CO2初始转化率分别达65%和74%,连续反应20h无失活;积碳质量分数降至13%(未改性催化剂积碳质量分数约24%),且沉积碳石墨化程度最低(ID/IG = 1.80,未改性催化剂ID/IG仅0.93).性能提升主要归因于Ge促进的CO2吸附-活化与碳气化循环,有效抑制了烧结与石墨碳沉积.本研究为利用温室气体CH4和CO2高效制氢提供了高稳定性Ni-Ge水滑石型LDHs衍生催化剂的实验依据和设计思路.

     

    Abstract: Layered Double Hydroxides (LDHs), a class of anionic clay materials with typical hydrotalcite structure, are offer ideal precursors for preparation of high-performance catalysts, due to their designable composition and excellent structural flexibility Chem. Commun. 2010, 46, 5912; Chem. Sci. 2017, 8, 590. In this study, Ni-Ge/(Mg, Al)Ox catalysts with different Ge/Ni molar ratios (0, 0.10, 0.30, 0.50, 1.0) were prepared by co-precipitation using hydrotalcite-type LDHs as precursors. Their activity and stability for hydrogen production via dry reforming of methane (DRM) were evaluated at 700 ℃, under atmospheric pressure, and with GHSV = 42 000 mL h−1 g−1. Catalysts before and after the reaction were systematically characterized by N2 adsorption-desorption, FTIR, XRD, H2-TPR, TGA-DTA, TPO, and Raman spectroscopy. Introduction of Ge did not alter mesoporous structure of the catalyst, but significantly enhanced metal-support interaction, and formed Ni-Ge alloy active sites. Among the five catalysts used, Ni-Ge/(Mg, Al)Ox (Ge/Ni = 0.3) exhibited the best DRM performance: initial conversions of CH4 and CO2 reached 65% and 74%, respectively, with no deactivation after 20 hours of continuous reaction; carbon deposition was reduced to 13%, graphitization degree of deposited carbon was the lowest. Improved performance was mainly due to Ge-promoted CO2 adsorption-activation and carbon gasification cycle, which effectively inhibited sintering and graphitic carbon deposition.

     

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