半导体表面阵列分布型双贵金属团簇催化材料可控制备及其CO2光催化还原协同增强机理研究

Due to the high catalytic activity and selectivity, alloy structured noble metal clustercatalysts are widely used in chemical industry, environmental protection and new energy area. Noble metal cluster catalysts show enhanced ability to reduce the activation energy of the CO2 to COOHads intermediate step through the low-coordinated noble metal surface atoms. So, highly dispersed noble metal on the support with fully explored active sites can improve the catalytic activity and optimize the atom utilization of noble metal supported catalysts. Especially, double noble metals catalyst shows better selectivity and catalytic activity, but double noble metals catalyst nearly single-atom scale is unstable due to the aggregation and hard alloy bond formation. Therefore, we proposed a new method to acquire the uniform three-dimensional distribution of the double novel metal clusters at nearly single-atom scale throughout the MOFs channel. This research plans to epitaxial grow ordered metal-organic frameworks (MOFs) layer on a semiconductor nanosheets. On the one hand, the Z-scheme photocatalyst was developed. On the other hand, using the channel array and the confined effect of MOFs, nearly single-atom noble metal clusters array are located and quantitative loaded on the channels of MOFs by a light reduction method. Followed the noble metal clusters will be partly replaced by other kinds of noble metal using a galvanic replacement reaction, and then the well-distribution arrayed double noble metals clusters supported catalysts will be prepared. Postsynthetic modification of MOFs is applied to enhance the selectivity and adsorbability of CO2. Utilizing the photo-reduction of CO2 reaction as a probe, the structure-function relationship of the arrayed double noble metals cluster-semiconductor catalysts can be revealed among structure, size and catalytic activity. Further, the synergistic enhancing effect will be explored among the high selectivity, adsorbability of MOFs and the high catalytic activity of double noble metals clusters.

贵金属合金化与团簇化是调节催化剂与中间产物的吸附能力和提高反应活性与选择性的有效方法。然而高催化性能的双贵金属团簇在近单原子尺度上难以键合或极易团聚。因此，如何在近单原子尺度获得均匀分散且活性位点充分暴露的双贵金属负载型催化剂成为极具挑战性的研究课题之一。本课题拟在半导体纳米片表面定向外延生长超薄MOFs层，获得有序MOFs孔道和定容的限域反应空间，通过光还原法在MOFs限域孔道内定量负载贵金属团簇，进一步对贵金属团簇进行置换反应，获得阵列分布式双贵金属团簇负载型催化剂。该催化剂同时具备双贵金属材料的高选择性、MOFs不饱和配位金属位点和选择吸附特征、半导体MOFs复合的Z型光催化体系及负载型催化剂的高催化活性等特征。以光催化CO2还原为探针反应，研究半导体表面阵列分布式双贵金属团簇催化剂的结构、尺寸与催化性能间的构效关系，揭示催化剂高催化活性、高吸附性和高选择性的催化协同增强机制。

针对当前高催化性能的双贵金属团簇在近单原子尺度上难以键合或极易团聚的问题，本研究从调控和构筑半导体材料的形貌和表面缺陷出发，以氧化物/硫化物半导体为研究对象，在材料表面构筑金属有机骨架(MOFs)/双金属位团簇，对其制备、形成和催化机理进行深入探索，具体研究如下：首先通过硬模板法和水热合成等方式制备得到不同形貌的二氧化钛和硫化物超薄结构，通过改变反应条件和前驱体成分等实验参数实现对材料表面的缺陷构筑，随后通过在半导体材料表面构筑多孔MOFs/金属位团簇，形成均匀分散且结构稳定的团簇位点，得到半导体表面阵列分布型双金属团簇催化材料。本研究通过对材料的形貌调控提高材料的比表面积并提供大量的活性反应位点，进一步通过缺陷构筑以改善半导体材料的能带结构，促进光生载流子的分离，同时对材料形貌调控及缺陷构筑机理进行探究，为光催化材料制备和优化提供了理论依据。通过构筑均匀分散且结构稳定的团簇位点能够获得更优异的光催化活性及特定的反应产物选择性，双金属团簇合金化效应促使金属原子表面电荷重排，改变费米能级附近态密度，改善对反应产物的吸脱附性能与键合方式，提高光生载流子迁移率，促进了二氧化碳及其他反应产物的生成，进一步通过密度泛函理论阐述光催化性能增强机理，为新型复合光催化材料的应用推广提供了数据支持。.此外，我们还对光热转换/导热复合材料进行了结构调控与性能增强的研究，拓展了一类兼具高储能能力、高光热转换率、高热导率和高可靠性的新型复合材料，为新型功能性复合光催化材料在太阳能领域的应用开发提供了技术拓展。