以半導體材料做為二氧化碳可見光還原反應之觸媒

Photocatalytic Reduction of Carbon Dioxide on Semiconductor Photocatalyst under Visible Light Irradiation

潘姵彣(Pei-Wen Pan)

指導教授 ： 陳郁文

國立中央大學/工學院/化學工程與材料工程學系/碩士(2006年)

摘要

不同光觸媒材料研究，近年來受到一些學者的討論。發展可以將太陽光能轉換成電能或是化學能的光觸媒系統，則是近年來各界研究的重點。半導體光觸媒材料：InTaO4，InNbO4 以及 InVO4等，已經廣泛的用於可見光下分解水製氫氧之反應，且此系列之光觸媒在水分解的反應中具有相當高的活性。由 InTaO4，InNbO4 以及 InVO4等光觸媒之能帶結構可以知道，其可利用於二氧化碳光還原反應，然而，此應用研究並未在國內外文獻中發表，為一創新的發現。

我們探討 InTaO4，InNbO4 以及 InVO4一系列光觸媒作為可見光之二氧化碳還原反應的研究，改變不同的製備條件(例如：加入不同種類、不同量的助觸媒，氧化還原前處理程序及不同的水溶液)探討對二氧化碳還原反應活性之影響。這一系列之光觸媒使用金屬氧化物當作起始材料，以固態反應法製備而成。觸媒之物化特性，以下列方法鑑定：X-光繞射分析，掃瞄式電子顯微鏡，X-光射線電子譜和UV-Vis吸收光譜。

由X-光繞射分析，InTaO4，InNbO4 以及 InVO4一系列光觸媒均具有良好晶相。在SEM圖中，當加入氧化鎳或氧化鈷等助觸媒於 InTaO4，InNbO4 以及 InVO4一系列光觸媒上時，可以觀察到有許多的小球在InTaO4，InNbO4之觸媒表面以及許多的小洞在InVO4觸媒表面。由UV-Vis吸收光譜可以計算出InTaO4，InNbO4 以及 InVO4等觸媒，其能帶間隙分別為2.7電子伏特，2.6電子伏特以及1.8電子伏特，此數據顯示InTaO4，InNbO4 以及 InVO4一系列光觸媒可應用於二氧化碳還原成甲醇之反應。

光還原反應在一透明的Pyrex反應器中進行，其裝載碳酸氫鉀或氫氧化鈉水溶液，以高純度之二氧化碳通入溶液中，使二氧化碳飽和於溶液中，並在可見光下連續照射20小時。InTaO4觸媒，其甲醇之產量隨著助觸媒增加的量而增加，而觸媒經過氧化還原之前處理之後，也對活性有助益，另外將觸媒置於碳酸氫鉀水溶液中進行反應，也會增加甲醇的產量。總結上述結果，InTaO4觸媒添加1.0 wt.%的氧化鎳助觸媒，經過氧化還原前處理之後，在碳酸氫鉀水溶液中具有最高之活性，其甲醇產量為1.394

關鍵字

二氧化碳還原 ； 光還原反應 ； 光觸媒

並列摘要

Developing a photocatalytic system for solar energy conversion to electric energy or chemical energy is a topic of great interest with fundamental and practical importance. Semiconductor photocatalysts such as InTaO4, InNbO4 and InVO4, have been extensively used for water splitting under visible light irradiation and demonstrated very high activity. According to the band structures of InTaO4, InNbO4 and InVO4, the photoreduction of carbon dioxide on InTaO4, InNbO4 and InVO4 catalysts should be feasible. However, they have not been applied for photoreduction of carbon dioxide.

The photocatalysts were synthesized by solid-state reaction method using metal oxide as the starting materials. The catalysts were characterized by powder X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Ultraviolet-Visible Spectroscope (UV-Vis) and X-ray Photoelectron Spectroscope (XPS). The photocatalytic reduction was carried out in a Pyrex reactor with KHCO3 or NaOH aqueous solution bubbled with ultra pure CO2 gas under visible light illumination (500W halogen light as the light source). All the catalysts were fully characterized. SEM micrographs showed the appearance of many pellets on InTaO4 and InNbO4 particles, whereas many pinholes were observed on the InVO4 particles with NiO and CoO cocatalysts. The band gap of InTaO4, InNbO4 and InVO4 were observed to be 2.7 eV, 2.6 eV and 1.8 eV, respectively, showing that these catalysts have the ability to reduce CO2 into methanol.

In this study, photocatalytic activity of InTaO4, InNbO4 and InVO4 catalysts for carbon dioxide reduction under visible light irradiation was investigated. The effect of adding different species and various amounts of cocatalysts, pretreatment process and diverse aqueous solutions on the photocatalytic reduction was a top priority to investigate. InTaO4 catalysts were tested by varying several conditions such as different species and various amounts of cocatalysts and diverse aqueous solutions. The methanol yield was increasing with the amount of cocatalysts. Also, the pretreatment method has a good effect on the catalyst. The activity of the photocatalyst performs better in KHCO3 aqueous solution. It was found that the reaction of InTaO4 catalyst with 1.0 wt. % NiO cocatalyst after pretreatment in KHCO3 aqueous solution gave the highest activity and the yield of methanol was 1.394

並列關鍵字

photoreduction ； photocatalyst ； InMO4(M=Ta ； Nb ； V) ； reduction of carbon dioxide

參考文獻

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