CO2綠色轉化

歐陽述昕, 王文中

CO2綠色轉化

歐陽述昕1, 王文中2

(1. 華中師范大學 化學學院, 武漢 430079；2. 中國科學院 上海硅酸鹽研究所, 上海 200050)

歐陽述昕, 博士, 華中師范大學教授。天津市海外高層次引進人才, 華中師范大學“桂子學者”特聘教授。長期從事新型光催化、光熱催化、電催化能源材料的開發及其反應機理研究。科技部973計劃“基于半導體人工光合成的二氧化碳能源化基礎研究”主要參與人。

E-mail: oysx@mail.ccnu.edu.cn

王文中, 博士, 中科院上海硅酸鹽研究所研究員, 中科院百人計劃。主要從事光催化機理、光催化材料的組分設計、合成和微結構調控, 以及光催化在環境凈化和太陽燃料方面的應用探索。承擔基金委、中科院和上海科委的多項研究項目。

E-mail: wzwang@mail.sic.ac.cn

全球工業化水平的持續提升加速了煤、石油、天然氣等化石燃料的消耗, 大量二氧化碳(CO2)被排放進大氣, 導致全球變暖和生態失衡, 削減CO2排放、將CO2資源化成為亟需解決的問題。2010年前后, 美國、歐洲、日本相繼開啟以“人工光合成”為題的國家級科研項目, 投入經費均在1億美元以上。2011年起, 我國國家自然科學基金委、科技部相繼資助了相關項目。2020年9月, 我國政府進一步提出力爭在2030年前實現“碳達峰”、2060年前實現“碳中和”的目標。

綠色植物或部分微生物通過“光合作用”將CO2和H2O轉化為有機物, 而通過催化劑在光能驅動下將CO2與H2O/H2轉化為燃料或化工原料, 正是模擬了自然界的“光合作用”, 被稱為“人工光合成”。當然, CO2的轉化并不局限于太陽能驅動, 利用非化石燃料產生的電能(如太陽能、風能、水能等)高效率驅動電催化、熱催化CO2還原也是可行途徑之一。目前, 基礎研究的熱點是光催化、光熱催化以及電催化CO2還原, 這類具有能耗低、環境負荷小、反應效率高等至少一個特點的技術途徑均屬于“CO2綠色轉化”的范疇, 在未來工業化應用中具有較強的競爭力。

近年來, 有關CO2轉化的研究突飛猛進, 但是仍面臨一些關鍵性問題亟待解決。光催化途徑利用最為溫和的方式(常溫、常壓)將CO2轉化為燃料或者化工原料, 但是在反應效率和穩定性等方面還面臨著巨大挑戰。光熱催化途徑于2014年被報道之后, 引起了廣泛關注, 它利用金屬納米粒子或窄帶隙半導體材料進行光能到熱能的轉換進而驅動熱催化反應。相比光催化, 光熱催化CO2還原的效率和穩定性得到顯著提升, 但是需要消耗氫氣(H2)提供氫源, 應用中會造成生產成本上升。相比前兩種方式, 電催化CO2還原也比較溫和, 其能量利用效率最高, 但是由于其反應環境為水溶液, CO2還原與質子還原的競爭不可避免, 提升產物的選擇性面臨瓶頸, 液相或者氣相產物的分離在一定程度上會增加生產成本。CO2轉化的經濟性還需要考慮產物的附加值, 光催化、電催化的產物主要集中在C1產物(主要包括一氧化碳、甲烷、甲醇、甲酸鹽等), 也有少數研究報道能夠產出乙烷。光熱催化途徑則較有優勢, 以CO2和H2為原料的費托合成可以生成C2～C7產物。可見, 各種技術途徑各具優勢, 但又面臨不同的科學或技術困難, 在未來應用中可能互為補充，在不同應用領域各展所長。

盡管CO2轉化的研究取得了長足進步, 但是仍面臨較多的挑戰。在我國提出“碳達峰”、“碳中和”的目標后不久, 《無機材料學報》編輯部即著手策劃“CO2綠色轉化”專欄。期待我國更多的科研工作者能夠投入這項研究并加強合作, 推動其從基礎研究快速步入應用研究, 并最終實現工業應用, 使我國由碳排放大國轉變為CO2資源化利用的強國！

Green Conversion of CO2

OUYANG Shuxin1, WANG Wenzhong2

(1. College of Chemistry, Central China Normal University, Wuhan 430079, China; 2. Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China)

With the continuous progress of global industrialization, fossil fuels have been over-consumed, which results in a large amount of CO2discharged into the atmosphere and therefore causes negative effects such as global warming and ecological imbalance. Reducing CO2emissions and converting recycled CO2to value added chemicals have become important tasks. Around 2010, led by the United States of America, followed by Europe and Japan, tens of countries started their national scientific research projects entitled “artificial photosynthesis”, with an investment as much as 100 million USDs. Since 2011, China has also funded similar projects by the National Natural Science Foundation of China and the Ministry of Science and Technology. In September of 2020, the Chinese government even put forward the goal of “carbon emission peak” by 2030 and “carbon neutrality” by 2060.

Green plants or microorganisms make organics fromCO2and H2O through “photosynthesis”. The photocatalysts can convert CO2and H2O/H2into fuels or chemicals under light irradiation, which simulates the natural “photosynthesis” and is entitled as “artificial photosynthesis”. Nevertheless, the conversion of CO2is not limited to be driven by solar energy; alternatively, the electricity generated by non-fossil fuels to drive efficient electrocatalytic or thermocatalytic CO2reduction is also a feasible way. At present, the hot spots in basic research are photocatalysis, photothermocatalysis and electrocatalysis for CO2reduction. “Green conversion of CO2” defines the technological approaches with at least one of the features of low energy consumption, low environmental load and high efficiency, which enables them competitive in future industrial applications.

In recent years, the study on CO2conversion has made rapid progresses, but some key problems are still to be solved. Photocatalysis provides the mildest way to convert CO2into fuels or chemicals, which means the lowest cost in the future application, but currently faces great challenge in efficiency and stability. Not until photothermocatalytic CO2reduction was reported in 2014, it has attracted extensive attention.The catalysts realize light-to-thermal conversion and subsequently drive thermocatalysis.Compared with photocatalysis, the efficiency and stability of photothermocatalytic CO2reduction are significantly increased, but the consumptionof H2asfeedstock will result in additional cost.Electrocatalytic CO2reduction is also a mild process, and its energy utilization efficiency is the highest among the three methods. However, due to the reaction environment of aqueous solution, there inevitably occurs the competition of CO2reduction and proton reduction;therefore, the improvement of product selectivity is still faced with a bottleneck. Moreover, the separation of liquid or gas phase products somewhat increases production cost. Importantly, the economy of CO2conversion should take account of the yield of value-added product. The products of photocatalysis and electrocatalysis mainly concentrated in C1 chemicals (mainly including carbon monoxide, methane, methanol, formic acid salt,.), and a few studies reported the production of ethane. However,the photothermocatalysisexhibitssuperior advantage in this aspect; for instance,the Fischer-Tropsch synthesis with CO2and H2as feedstocks to produce C2-C7 products has been reported.Each technological approach has its own advantages but faces different scientific or technical difficulties, which may complement each other and show its strengths in different application fields in the future.

Shortly after China put forward the goal of “carbon emission peak” and “carbon neutrality”, the editorial board oforganizes the special issue on “Green Conversion of CO2”. Although the investigation on CO2conversion has made great progress, but still faces various challenges.Looking forward to thatmore researchers devote to this study to promote it from the basic research to the industrial application,our continuous effort will make our country reverse the disadvantage of terrible carbon emission to the advantage of converting recycled CO2to resources effectively.

1000-324X(2022)01-0001-02

10.15541/jim20211001