Selective photooxidation of methane to C1 oxygenates by constructing heterojunction photocatalyst with mild oxidation ability  

异质结光催化剂选择性光氧化甲烷为C1含氧化合物

作　　者：Hantao Gong Caihao Deng Peipei He Mingjie Liu Yiliang Cai Yiwen Yang Qiwei Yang Zongbi Bao Qilong Ren Siyu Yao Zhiguo Zhang 龚汉涛;邓才豪;何佩佩;刘明杰;蔡翼亮;杨亦文;杨启炜;鲍宗必;任其龙;姚思宇;张治国(浙江大学化学与生物工程学院,生物质化工教育部重点实验室,浙江杭州310058;浙江大学衢州研究院,浙江衢州324000)

机构地区：[1]Key Laboratory of Biomass Chemical Engineering of Ministry of Education,College of Chemical and Biological Engineering,Zhejiang University,Hangzhou 310058,Zhejiang,China [2]Institute of Zhejiang University-Quzhou,Quzhou 324000,Zhejiang,China

出　　处：《Chinese Journal of Catalysis》2024年第12期61-70,共10页催化学报(英文)

基　　金：国家自然科学基金(22208290,22288102,22078288,22225802);浙江省重点研发计划(2021C03005).

摘　　要：Selective photocatalytic aerobic oxidation of methane to value-added chemicals offers a promising pathway for sustainable chemical industry,yet remains a huge challenge owing to the consecutive overoxidation of primary products.Here,a type II heterojunction were constructed in Ag-AgBr/ZnO to reduce the oxidation potential of stimulated holes and prevent the undesirable CH_(4) overoxidation side reactions.For photocatalytic oxidation of methane under ambient temperature,the products yield of 1499.6μmol gcat^(-1) h^(-1) with a primary products selectivity of 77.9%was achieved over Ag-AgBr/ZnO,which demonstrate remarkable improvement compared to Ag/ZnO(1089.9μmol gcat^(-1) h^(-1) ,40.1%).The superior activity and selectivity result from the promoted charge separation and the redox potential matching with methane activation after introducing AgBr species.Mechanism investigation elucidated that the photo-generated holes transferred from the valence band of ZnO to that of AgBr,which prevent H_(2)O oxidation and enhance the selective generation of•OOH radical.甲烷作为天然气等含碳资源的关键组分,除用作燃料外,将其直接催化转化为高附加值产物(如甲醇和甲基过氧化氢等),对实现甲烷的高效利用意义重大,在可持续化学工业中具有重要意义.然而,甲烷C‒H键具有高达439 kJ mol^(-1)的解离能,这使得转化条件极为苛刻,通常需在高温或强酸性环境下进行活化.光催化半导体材料被广泛应用于在温和条件下甲烷转化,但较宽的带隙和过正的氧化电位,易导致氧化产物过度氧化,从而使产物选择性较低.鉴于此,迫切需要开发一种能在温和条件下实现甲烷活化并有效抑制产物过氧化的方法.本文通过构建异质结催化剂,有效抑制了甲烷氧化产物的过氧化,为光催化甲烷选择性氧化催化剂的设计提供了新思路.通过组合两种半导体构建异质结是光催化领域的常见策略之一,不但能够防止单个光催化剂中光生载流子的复合,还可调节复合材料的氧化还原电位.针对ZnO过正的价带电位,以ZnO和AgX(AgBr,AgCl,AgI,Ag₂WO_(4),Ag₂MoO_(4)和Ag₃PO_(4))为基础,设计构建了一系列异质结催化剂,期望降低ZnO空穴的较强氧化性,进而抑制甲烷氧化产物的过度氧化.实验结果表明,构建的Ag-AgBr/ZnO光催化剂在甲烷选择性氧化反应中表现出较好的催化性能,在室温下光催化甲烷氧化获得了1499.6μmol gcat^(-1) h^(-1)的产物产率,初级氧化产物选择性高达77.9%,远高于Ag/ZnO和其他Ag-AgX/ZnO催化剂.能带结构表征结果表明,Ag-AgBr/ZnO催化剂中ZnO和AgBr间构成了II型异质结,其中ZnO价带中的光生空穴能够转移至AgBr,而AgBr导带中的光生电子则流向ZnO,说明该异质结的形成有利于载流子的迁移和分离.荧光发射光谱中较低的荧光发射峰以及瞬态光电流中更强的光电流强度,也证明了Ag-AgBr/ZnO相较于Ag/ZnO具有更强的光生载流子分离和迁移能力,这也是甲烷氧化产物产率得以提升的原因所在.值�

关 键 词：Selective methane oxidation Photocatalysis HETEROJUNCTION Ag-AgBr/ZnO catalyst 

分 类 号：O64[理学—物理化学]