新型鎳系混成式奈米觸媒技術作為甲烷能源技術之相關應用

Synthesis of Nickel-based Hybrid Nanocatalyst for Methane-based Energy Applications

梁騰云(Teng-Yun Liang)

指導教授 ： 蔡德豪

國立清華大學/工學院/化學工程學系/碩士(2020年)

摘要

本研究工作的目的是希望開發出新型的材料製備技術用以生成鎳系混成式奈米觸媒，並將此觸媒應用在甲烷相關的能源科技當中，此觸媒需擁有非常良好的材料性質及催化活性，藉此提升甲烷的應用價值。
在第一部份的研究工作中，我們希望開發一種氣相合成方法用於製備混成式奈米粒子團簇(Ni-CeO2-Al2O3 NPC)，並將其作為甲烷乾式重組的催化劑。在材料合成方面，我們利用實驗室現有的氣相奈米粒子合成系統以製備此混成式奈米粒子團簇，方法上結合了氣溶膠相的蒸發誘導自組裝原理以及氧化鋁奈米顆粒在噴霧後液滴內的膠體穩定化原理。本階段結果顯示，以氣相合成的奈米粒子團簇具有高分散性，同時藉由改變前驅物溶液的濃度及種類，可改變產物的組成、團簇大小及表面形態。與相關文獻的結果相比，本研究實現了更卓越的催化性能：較低的起始反應溫度、較高的活性和反應選擇性，以及長達8小時反應的操作穩定性，而在添加二氧化鈰後可在低溫環境操作下有較高的反應活性及操作穩定性，並且操作穩定性會隨著二氧化碳的濃度進一步地增加。
在第二部份的研究工作中，我們從鎳鈷雙金屬的金屬有機框架材料(M-MOF/Al2O3)中成功製備出了M@C/Al2O3混成式奈米結構，將其作為甲烷乾式重組的催化劑，能擁有較高的催化性能，在低溫環境下達到了較高的轉換頻率及產物選擇率，而鎳金屬觸媒在摻入鈷之後可以提高操作的穩定性。本階段結果顯示，MOF衍生的混成式奈米結構具有殼狀的碳包覆，然而此碳殼層並不會阻隔反應氣體的通過，因此對於甲烷乾式重組反應來說，可以在穩定操作的同時有效地降低積碳的生成，此研究將為催化劑的設計開闢了新的視野。
第三部份的研究工作我們用一新式氣溶膠合成概念，該方法可製備Ni-Ce-O混成式多孔奈米粒子，用於結合甲烷乾式重組與甲烷部分氧化的複合式甲烷重組反應(DRM+POM)。該合成方法是結合氣相蒸發誘導的聚乙二醇(PEG)在噴霧液滴中會聚集的原理，可利用PEG作為軟物質模板，接著對自組裝前驅物進行氣相的熱分解，並在其中形成中孔與微孔結構。結果表明，在氣相合成的過程中，透過使用PEG軟物質模板，會增加Ni-Ce-O混成式奈米結構中的比表面積和活性金屬表面積，並對複合式甲烷重組反應有很高的催化活性，而通過調整進料中的O2濃度，可調節H2/CO比例，從而實現較高的產物選擇性，並且藉由氧氣的添加能夠顯著地減少積碳的形成，使在100小時的反應中具有較高的操作穩定性。這項工作開發了一種氣相合成混成式奈米多孔結構的方法，可用於有效地催化複合式甲烷重組反應。

關鍵字

鎳 ； 甲烷 ； 能源 ； 觸媒 ； 奈米粒子

並列摘要

We aim to develop a new synthetic route for the fabrication of nickel-based hybrid nanocatalyst used for methane-based energy applications. The syngas, consisting of CO and H2, is an important feedstock for large-scale productions of a wide range of commodity chemicals including aldehyde, methanol, ammonia, and other oxygenated chemicals.
In the first part, a gas-phase approach is demonstrated for controlled synthesis of Ni-CeO2 nanocrystallites decorated on Al2O3 nanoparticle clusters (NPC) as the catalysts of dry reforming of methane with CO2 (DRM). The method combines the principles of aerosol-phase evaporation-induced self-assembly with colloid-phase stabilization of Al2O3 nanoparticles in sprayed aqueous droplets. Hybrid NPC was successfully created with ultrafine Ni crystallites, tunable chemical composition, cluster size and surface state. A superior high catalytic performance achieved in comparison to the results reported in the literatures: low starting temperature, high turnover frequency, high selectivity and high stability over 8-h reaction. Hybridization with Al2O3 NPC and CeO2 nanoparticle significantly improved operation stability of Ni catalyst. The work demonstrates a facile route for gas-phase synthesis of hybrid nanocatalysts using Al2O3 NPC as support matrix for effective low-temperature operations of DRM.
In the second part, we developed NiCo@C nanocomposites from corresponding NiCo-based bimetallic metal-organic framework (MOF) to serve as high performance catalysts for the DRM process, achieving high turnover frequencies (TOF) at low temperatures and high product selectivities. Incorporation of Co in Ni catalysts improves the operation stability and light-off stability. The present development for MOF-derived nanocomposites opens a new horizon for design of DRM catalysts.
In the third part, a refined gas-phase controlled synthesis method was demonstrated to prepare Ni-Ce-O hybrid nanoporous particle for synergistic catalysis of dry reforming of methane (DRM) coupled with partial oxidation of methane (POM). The method combines the principles of aerosol-phase evaporation-induced aggregation of polyethylene glycol (PEG) as soft template in sprayed aqueous droplets, followed by a direct gas-phase thermal decomposition of the self-assembled precursor crystallites for the creation of mesopores in the hybrid nanostructure. The results show increases of specific surface area and metal surface area in the Ni-Ce-O hybrid nanostructure by using the PEG template during the gas-phase synthesis. A high catalytic activity in term of turnover frequency of methane achieved, and the ratio of H2/CO was tunable through the adjustment of O2 concentration in the feed to accomplish high selectivity for syngas production. High light-off stability was observed, and high operation stability over 100-h reaction achieved through a remarkable reduction of coke formation. The work demonstrates a facile route for gas-phase synthesis of hybrid nanoporous catalyst useful for effective methane-based combined reactions.

並列關鍵字

Nickel ； Methane ； Energy ； catalyst ； nanoparticle

參考文獻

[1] C. Papadopoulou, H. Matralis, X. Verykios, Utilization of Biogas as a Renewable Carbon Source: Dry Reforming of Methane, in: Catalysis for Alternative Energy Generation, 2012, pp. 57-127.

[2] D. Pakhare, J. Spivey, A Review of Dry (CO2) Reforming of Methane over Noble Metal Catalysts, Chemical Society Reviews, 43 (2014) 7813-7837.

[3] J.R. Rostrup-Nielsen, J.H.B. Hansen, CO2-Reforming of Methane over Transition Metals, Journal of Catalysis, 144 (1993) 38-49.

[4] J.R. Rostrup-Nielsen, J. Sehested, J.K. Nørskov, Hydrogen and Synthesis Gas by Steam and CO2 Reforming, in: Advances in Catalysis, Academic Press, 2002, pp. 65-139.

[5] M. Aresta, Carbon Dioxide as Chemical Feedstock, Wiley-VCH, Weinheim, 2010.