摘要/Abstract

光热催化是一种高效利用太阳光, 将二氧化碳转化为高价值产物的方法. 本工作以石墨相氮化碳为载体, 通过水热-浸渍两步法制备了负载铂、铁氧化物的石墨相氮化碳催化剂. 该催化剂具备优异的光热转换性能, 可实现7.36 mmol•h^-1•g_cat^-1的二氧化碳还原活性和97%的一氧化碳选择性. 使用X射线晶体衍射(XRD)、配备能量色散X射线谱(EDS)的球差校正扫描透射电子显微镜(Cs-S/TEM)、X射线光电子能谱(XPS)、紫外可见漫反射光谱(DRS)等表征手段从催化剂物相、微观结构、表面状态、光学性能等方面对催化剂进行了表征. 结果显示, 催化剂能吸收全谱太阳光, 且具备较高的载流子分离效率. 基于原位傅里叶变换红外光谱(DRIFTS)表征结果, 提出了二氧化碳在催化剂表面的可能的反应机理, 并对铂在铁氧化物表面的氢溢流效应进行了表征. 结果表明二氧化碳和氢气分别在铁氧化物、铂位点被活化, 参与催化反应. 本工作对后续光热二氧化碳还原催化剂的设计、合成与机理研究具有一定的参考作用.
关键词: 石墨相氮化碳, 光热催化, 二氧化碳还原, 原位傅里叶变换红外光谱
Converting CO₂ into value-added compounds via photothermal catalysis is a promising strategy to reduce CO₂ emission and might be a sustainable alternative to traditional fossil fuels. Here, we report nano-structured a Pt_0.01Fe_0.05-g-C₃N₄ hybrid catalyst synthesized via hydrothermal-method and further reduced under reaction condition for the reverse water gas shift (RWGS) reaction. Taking advantage of the photo-thermal effect caused by the near-infrared (NIR) and visible light responsive, the hybrid catalyst produces a remarkable activity (7.36 mmol•h^-1•g_cat^-1) for CO₂ reduction with CO selectivity (97%) under 300 W Xe lamp irradiation and CO₂/H₂ (V/V, 1/1) feed gas. The apparent activation energy of reaction decreases from 238.59 kJ/mol to 48.88 kJ/mol calculated by Arrhenius formula. In order to comprehend the good catalytic activity of Pt_0.01Fe_0.05-g-C₃N₄in the RWGS reaction, the catalyst is characterized with powder X-ray diffraction (XRD), spherical-aberration-corrected scanning transmission electron microscopy (Cs-S/TEM) integrated with X-ray energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), UV-vis-NIR diffuse reflectance spectroscopy (DRS),etc. for investigating the structural information, surface state, optical properties and so on. Results show that the presence of FeO _x and Pt exhibits strong absorption in a wide range from UV to NIR regions. Low photoluminescence (PL) intensity at about 460 nm shows the suppressed photogenerated carrier recombination process of Pt_0.01Fe_0.05-g-C₃N₄ due to the heterojunction between FeO _x and g-C₃N₄. Operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) under different reaction conditions is employed to investigate surface species and their evolution during the conversion of CO₂ into CO and a broad IR absorption is observed due to hydrogen spillover from Pt to Fe₃O₄. Therefore, we propose a possible mechanism of photothermal catalytic CO₂ reduction, involving separate activation of CO₂ and H₂ over Fe and Pt acitve sites. Our work present a high-performance Pt_0.01Fe_0.05-g-C₃N₄ catalyst for RWGS reaction and open a new vista of the design, synthesis and mechanism research of photothermal catalytic CO₂ conversion in the future.
Key words: g-C₃N₄, photothermal catalysis, CO₂ reduction reaction, operando diffuse reflectance infrared Fourier transform spectroscopy


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