液相二氧化碳光催化還原效能提升研究:還原劑、光觸媒複合材料與選擇性之探討

Abstract

溫室CO2 氣體捕獲與儲存技術(CCS)已被IPCC 評估為可行之技術，而CO2 在捕獲後若能還原成具經濟價值之新能源或化學物質，將使CCS 技術更具可行 性。CO2 光催化還原受還原劑及光觸媒種類影響甚巨，水為最理想之還原劑， 但CO2 不易溶於水中且水之還原能力不佳，因此一般之研究多會改以氣相方式 還原，或利用如NaOH 等為吸收液，再加入如異丙醇等為還原劑。然而目前最 具商業化潛能的CO2 捕獲技術應屬醇胺與氨水吸收捕獲技術，因此若能直接以 其做為吸收液兼CO2 還原劑，將可有效整合捕獲-還原兩個CO2 處理流程。而只 有在太陽光下具備光催化還原CO2 之光觸媒，方可避免為了還原CO2 卻消耗更 多能源、產生更多CO2 之迷思。 因此本研究三年計畫即擬探討還原劑與光觸媒種類對於CO2 還原之影響， 並掌握其產物選擇性。在第一年研究中將先探討以醇胺與氨水為CO2 吸收液兼 還原劑之可行性，並與文獻常用吸收液與還原劑之CO2 還原效率進行比較。第 二年計畫將研究改良可見光觸媒複合材料，並擬直接利用太陽光為光源，進行 影響CO2 還原產物之選擇性機制探討。第三年計畫將探討光觸媒複合材料之中 孔洞基材特性，藉由孔洞大小與材料本身特性之調控掌握，以及將可見光觸媒 複合材料製備成金屬嵌入式單一材料之方式，來減少複合材料之剝落且增強其 可見光催化效應。

The CO2 capture and storage (CCS) has been evaluated by the IPCC as a feasible CO2 mitigation option. The reduction of CO2 could provide another alternative other than the storage of CO2 in underground or deep ocean by producing economical chemicals or new energy sources. The photocatalytic reduction of CO2 is mostly affected by the photocatalyst and the reducing agent. Water is the ideal reductant, however, CO2 is not very soluble in water and the redcing ability of water is poor. Therefore other absorbents and reducing agents such as NaOH and 2-propanol were employed in many studies to facilitate the CO2 reduction reaction. However the CO2 reduction process from flue gas could become economical only by combining it with the CO2 capture technology and by the use of photocatalyst which can make full use of solar energy. In this three-year project, we intend to evaluate effects of reducing agents and the photocatalysts on the CO2 reduction ability and the selectivity of the reduction products as well. During the first year study, the possibility of using the most readily available CO2 absorbents of amines and ammonia as the reducing agents will be evaluated. And for the second year project the main objective is to modify the metal-TiO2 photocatalysts which can maximize the usage of field solar light. The mechanisms that govern the selectivity of the prodcut is also studied. At the end of the third year, we expect to make the composite of visible light photocatalyst into single photocatalytic material which pore sizes can be manipulated and the selectivity of the product can be well controlled.