摘要
Photo-thermal CO_(2) reduction with methane(CRM)is beneficial for solar energy harvesting and energy storage.The search for efficient photo-thermal catalysts is of great significance.Here,we reveal that group Ⅷ metal catalysts supported by optical material WO_(3) are more effective for photo-thermal CRM,giving catalytic activities with visible light assistance that are 1.4-2.4 times higher than that achieved under thermal conditions.The activity enhancement(1.4-2.4 times)was comparable to that achieved with plasmonic-Au-promoted catalysts(1.7 times).Characterization results indicated that WO_(3) was partially reduced to WO_(3-x) in situ under the reductive CRM reaction atmosphere,and that WO_(3-x) rather than WO_(3) enhanced the activities with visible light assistance.Our method provides a promising approach for improving the activity of catalysts under light irradiation.
将廉价的碳源(CO_(2))转化为化石燃料可缓解由于温室气体引起的气候问题.CH_(4)/CO_(2)重整(CRM)是CO_(2)转化利用的有效途径之一,要实现这个过程的关键是研制高效的光响应催化剂.本文采用WO_(3)负载的第Ⅷ族金属催化剂、引入光照能量来活化CO_(2),利用光热协同催化CRM.研究结果表明,光学材料WO_(3)负载的第Ⅷ族金属催化剂在可见光辅助下的催化活性是热驱动条件下的1.4~2.4倍,与等离子体金催化剂的活性增强率(1.7倍)相当.进一步以不同波段的可见光为光源,对WO_(3)负载的第Ⅷ族金属催化剂上催化活性提高的原因进行了研究.结果表明,活性增强率与WO_(3)在可见光区域的吸光趋势并不吻合,说明并非WO_(3)提高了其负载的第Ⅷ族金属催化剂上CRM活性.除WO_(3)外,WO_(3−x)亦可作为光催化剂吸收可见光,因此,本文通过X射线光电子能谱、X射线衍射及紫外-可见分光光度法等进行表征.结果表明,在还原型CRM反应气氛下,WO_(3)部分原位还原为WO_(3−x),并且活性增强率与WO_(3−x)在可见光区域的吸光趋势相吻合,说明导致可见光辅助下活性增强的是WO_(3−x)而不是WO_(3).热力学分析及原位电子顺磁共振波谱法结果表明,CO_(2)的活化是CRM的速控步,该步骤吸热,在500 ℃时不能自发进行.在可见光的辅助下,CO_(2)可以被WO_(3)−x通过Mars-van Krevelen机理进行活化,提高速控步的反应速率,进而提高了催化活性.综上,本文为提高光催化活性提供了一条有效途径.
基金
国家自然科学基金(21902116).
