金屬覆載的鎳-鋁雙層狀氫氧化物用於CO2光催化還原

時至今日，工業發展蓬勃，導致過多的二氧化碳排放，全球暖化現象更顯惡化；過度的能量消耗，化石燃料不足將使人類未來面臨能源短缺。為同時解決此兩大問題，學界針對消除二氧化碳做了許多研究，而二氧化碳光催化還原最受到關注。其具有兩大特點：一、光還原的有機產物可作為能源再利用，減少碳排放及對於石化燃料的仰賴；二、觸媒以光能驅動還原反應，而太陽光是用之不盡、取之不竭的潔淨能源。本研究中以鎳-鋁層狀雙金屬氫氧化物(Ni-Al LDH, Ni/Al = 3)作為二氧化碳光催化還原的觸媒材料，並透過共沉澱法複合水熱處理合成。此外，藉由初濕含浸法與硼氫化鈉水溶液的還原，分別負載0.5 wt% Pt與Cu金屬於Ni-Al LDH表面作為共觸媒。三種Ni-Al LDH分別經過一系列的觸媒鑑定，深入了解其光學特性、外觀型態、晶體結構、元素價態等材料性質。光觸媒活性的測試分別於單一反應器和雙胞反應器中進行。單一反應器中，Ni-Al LDH觸媒皆散佈於水溶液中，於紫外光燈(λ = 254 nm，光照度~ 6.5 mW/cm2)照射下反應4小時。經比較，0.5 wt% Cu/Ni-Al LDH有最高的CO及CH4產量，分別達11.53 μmol/gcat及0.86 μmol/gcat。負載金屬些微提升了CO及CH4產量。另於Ni-Al LDH的氣相反應中，可發現其還原效率略有提升；引入氫氣作為氫源時，CO產量的增幅更為明顯。雙胞反應器中，改以兩盞300 W氙燈(光照度~ 90 mW/cm2)作為可見光源，照射雙邊反應端8小時。0.5 wt% Cu/Ni-Al LDH於液相反應系統中，還原物產量分別為CO (1.05 μmol/gcat)、CH4 (0.17 μmol/gcat)、CH3OH (2.90 μmol/gcat)、HCHO (0.20 μmol/gcat)及H2 (0.43 μmol/gcat)，紫外光(λ = 254 nm)量子使用效率1.8711%為三者中最高。

關鍵字

二氧化碳光催化還原；金屬負載LDH ；雙胞反應器

並列摘要

Nowadays, people are facing the threat of the worsening greenhouse effect, triggered by the emission of more CO2. Furthermore, the energy shortage may bring about the energy crisis. To deal with these two issues simultaneously, scientists have done a lot of studies to reduce CO2 emissions, especially by utilizing photocatalysts. On one hand, the products of this reaction are able to be reused as fuels again, and the carbon footprint can also be reduced. On the other, solar energy is inexhaustible, ubiquitous, and clean. In this study, we tried to use layered double hydroxides (LDH) as the photocatalyst of CO2 reduction. Nickel-aluminum LDH was the selected material, denoted as Ni-Al LDH. Ni-Al LDH was synthesized by coprecipitation and hydrothermal treatment. Besides, Pt and Cu were loaded on the surface of Ni-Al LDH by incipient wetness method and reduction of sodium borohydride (NaBH4) solution. The as-prepared Ni-Al LDHs were thoroughly characterized, in order to study their optical properties, surface morphology, crystal structure, chemical status, and thermal properties. The photocatalytic tests were conducted in a single photoreactor and a twin reactor system. In the single photoreactor, Ni-Al LDHs were dispered in aqueous phase after UV irradiation for four hours at room temperature. We investigated slight enhancement of CO and CH4 production, and 0.5 wt% Cu/Ni-Al LDH gave the highest yields of CO (11.53 μmol/gcat) and CH4 (0.86 μmol/gcat). From the result of another test, we found that Ni-Al LDHs would have higher activities in gaseous phase. The enhancement of CO2 photoreduction to CO from H2 addition was also comparably evident. In the twin reactor system, 300W xenon lamps were applied as the visible light source instead. Three Ni-Al LDHs acted as hydrogen evolution and CO2 reduction photocatalyst in aqueous phase. In the presence of 0.5 wt% Cu/Ni-Al LDH, the yields were CO (1.05 μmol/gcat), CH4 (0.17 μmol/gcat), CH3OH (2.90 μmol/gcat), HCHO (0.20 μmol/gcat) and H2 (0.43 μmol/gcat), respectively. Meanwhile, its quantum efficiency of UVC reached 1.8711%, the highest of three Ni-Al LDHs.

並列關鍵字

CO2 photocatalytic reduction ； metal-loaded LDH ； twin reactor

參考文獻

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[5] S.N. Habisreutinger, L. Schmidt-Mende, J.K. Stolarczyk, Photocatalytic reduction of CO2 on TiO2 and other semiconductors, Angewandte Chemie International Edition, 52 (2013) 7372-7408.

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金屬覆載的鎳-鋁雙層狀氫氧化物用於CO2光催化還原

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