基于纳米金催化甲酸分解的高选择性低温制氢反应研究

Formic acid (FA), an important chemical intermediate, has recently been identified as a promising renewable energy carrier suitable for hydrogen-powered micro fuel cells. Catalytic decomposition of FA offers great advantages over conventional methanol steam reforming that can produce high purity hydrogen (H2) in terms of excellent selectivity and very mild conditions. Based on our latest discovery that gold nanoparticles (NPs) highly dispersed on acid-tolerant zirconia can catalyze selective decomposition of concentrated aqueous FA to produce H2 under highly acidic hydrothermal conditions, the primary objective of the current proposal is to explore and develop new advanced processes that can deliver selective FA decomposition at low temperature by screening and fabricating new generation of Au-based FA decomposition catalysts, with the aim to overcome the inherent low efficiency, limited selectivity and poor stability associated with the state-of- the-art heterogeneous nobel metal-based catalyst systems. To gain an insight into the key aspects (nature of the support, size and micro-structure of Au NPs, solvent etc.) that influence the activity, selectivity and stability of the Au catalysts, special efforts will be focused on an extensive physicochemical characterization of the Au-based catalysts active and selective for FA decomposition. Besides seeking and advocating an innovative clean and sustained hydrogen production system based on selective FA decomposition at temperatures lower than 60 oC, efforts will also be directed to a thorough understanding of the structure-activity relationship as well as the mechanistic pathways involved in the Au-catalyzed FA decomposition process, exploiting and improving relevant concepts, thus providing fundamental data, models and guidance for developing new viable FA-based hydrogen production technologies for portable electronic applications.

甲酸是重要的化学中间体和可再生能源载体，其低温催化选择分解是新近发现的一类在微型氢燃料电池领域具有重要应用前景的供氢反应体系，较传统甲醇重整在条件温和及制氢选择性高等方面独具优势。基于我们有关耐酸氧化锆负载纳米金在水热条件下催化高浓度甲酸选择分解制氢的最新发现，针对现有多相贵金属催化液相甲酸分解制氢体系中存在的反应效率和选择性偏低以及稳定性严重不足等关键基础问题，本项目以探索和开发甲酸低温制氢新工艺为目标，筛选并创制高性能甲酸分解纳米金催化剂；结合多种理化表征手段和反应评价，系统认识甲酸选择分解反应的关键因素（载体特性、纳米金尺寸/微结构、溶剂等）对活性、选择性和稳定性的影响；发现并确立可在低于60 oC 条件下实现甲酸持续选择分解的新型高效洁净制氢体系，明确相关反应与催化剂组成和结构的关系，揭示相关催化作用机理，拓展并完善相关理念，为发展相应的便携式制氢工艺提供基础数据、模型和理论指导。

本项目针对多相金属催化剂在液体甲酸低温活化及选择分解制氢反应中金属-载体协同作用机制及催化剂性能调控规律等关键问题开展了基础性研究工作。在氧化物及纳米碳基材料负载高分散金属催化甲酸低温分解制氢的反应机理、性能调控规律和相关高效催化剂体系设计等方面进行了探索。针对碱性介质中氧化物负载纳米金催化甲酸低温分解制氢，发展了以二甲基乙醇胺等高沸点有机胺为反应介质、单斜相氧化锆负载亚纳米Au 为催化剂的高效复合催化体系，在进一步较大幅度提高甲酸制氢活性的同时可有效避免传统反应介质极易显著挥发流失的问题，60 oC反应条件下可获得高达1166 h-1 的转换频率。发展了基于金属铜及氧化锆的甲酸高效活化分解非贵金属催化剂，通过高分散金属铜催化甲酸脱氢活化与生物基乙酰丙酸还原的匹配，实现了无外源气体H2条件下生物基乙酰丙酸/甲酸体系到戊内酯的一步高值转化。针对碳基负载纳米金属钯催化甲酸低温分解制氢，设计合成了高效的氮杂碳纳米片负载Pd双功能催化剂，载体的碱性质及耐Pd与氮杂碳纳米片的协同催化作用在酸性水相介质中可有效活化甲酸分子，在无碱性助剂添加下即可显著加快反应速率，进一步通过调控碳纳米片载体表面吡啶氮物种相对含量及结合XRD、TEM、XPS等多种谱学表征，实现了室温下高达5530h-1的甲酸制氢效率，催化剂可多次连续使用不失活，具有较好的稳定性。针对金属钯催化甲酸盐低温脱氢分解及碳酸氢盐水相选择加氢，设计合成了高效的氧化石墨烯负载纳米Pd催化剂，通过氧化石墨烯载体对Pd活性组分微结构的调控，成功构建出基于水相甲酸盐-碳酸氢盐循环转化的“类电池”可逆制/储氢Pd基多相体系。在上述研究基础上，进一步实现了低温甲酸选择制氢体系与炔烃选择半还原、喹啉选择还原及甘油等生物基平台化合物的可控还原转化的反应集成，为发展相应的便携式制氢及基于甲酸活化的绿色选择还原工艺提供了新思路和理论指导。