CAREER: Integrated CO2 Capture and Catalytic Conversion to Solar Fuels Using Hybrid Multifunctional Materials

【摘要】技术/科学价值利用太阳光与水光催化还原二氧化碳（CO2）是生产甲烷和甲醇等太阳能燃料的一种非常理想的方法。这项技术不仅减少了温室气体（如二氧化碳），而且为可持续能源提供了途径。然而，由于其稳定的热力学性质，二氧化碳的活化和转化是非常具有挑战性的。尽管近年来在这方面的努力越来越多，但光催化CO2还原的效率仍然很低。一些研究者认为，一些重要的问题还没有得到充分的探索，包括光催化剂表面活性位点的性质、其对CO2的吸附能力、反应产物解吸动力学以及催化剂的长期稳定性。在本次美国国家科学基金会教师早期职业发展（Career）计划奖中，威斯康星大学密尔沃基分校的李颖教授将解决这些问题。Li将探索一种集成二氧化碳捕获和催化转化（IC4）的新概念，利用新型多功能材料生产太阳能燃料，旨在实现显著提高、稳定的二氧化碳转化效率。提出的多功能材料将以混合金属氧化物、层状双氢氧化物（LDHs）及其混合物的形式利用相互作用的吸附剂/催化剂成分，这些混合物是金属氧化物纳米颗粒嵌入重建的LDHs上。将研究不同形态和纳米结构的吸附剂/催化剂组分，以最大限度地发挥两组分/功能之间的协同作用。提出的研究中另一个独特的想法是在100至200°C的高温下进行光催化CO2反应；而传统的光催化反应是在室温或近室温下进行的。在这些较高的温度下，反应中间体和产物从催化剂表面的解吸将得到加强，而杂化材料的吸附剂成分将起到保证CO2吸附的作用。这种稍微升高的温度可以通过在大规模应用中利用工业废热或阳光的红外部分来实现，因此期望更高的整体太阳能转换效率。这个CAREER项目也将促进对二氧化碳光还原机制的基本理解。二氧化碳吸附/解吸和光催化转化效率将通过先进的光谱方法，包括原位漫反射红外傅立叶变换光谱（DRIFTS）和x射线吸收光谱（XAS），与材料的综合表征相关联。这些综合方法将成为研究光反应过程中材料性质变化、表面吸附物相互作用、反应中间体命运、电荷转移途径以及影响催化剂活性和稳定性的因素的有力工具。更广泛的影响这项将二氧化碳等温室气体转化为燃料的拟议研究的结果将对可持续能源技术的发展产生重大影响。目前科学界对CO2捕集和CO2转化利用的研究是分开进行的。采用混合吸附剂/催化剂材料，在稍高的温度下实现二氧化碳捕集和催化转化，为以更综合、更有效的方式解决这一极具挑战性的问题提供了一条新途径。李教授在这项研究中的新材料设计和对催化剂稳定性的基本理解也将为其他光催化系统（如水裂解太阳能制氢）提供启示。与职业发展计划的预期一样，拟议的研究将纳入教学和课程发展。研究生将接受跨学科研究的培训；本科生和高中生，特别是那些代表性不足的群体，将被招募参加研究项目。与密尔沃基公立学校和密尔沃基城市地区的非营利教育组织（如城市生态中心）合作，计划开展外展项目，协助教师编写与太阳能和纳米技术相关的课程材料，从而增加学生人数。对全球气候变化的认识，同时促进对STEM领域的兴趣。

ABSTRACTTechnical/Scientific MeritPhotocatalytic reduction of carbon dioxide (CO2) with water by sunlight is a highly desirable process to produce solar fuels such as methane and methanol. This technology not only reduces greenhouse gases (e.g., CO2) but also provides pathways to sustainable energy. However, CO2 activation and conversion is very challenging because of its stable thermodynamic properties. Despite increasing efforts in this area in recent years, the efficiency of photocatalytic CO2 reduction remains low. Some investigators believe important problems have yet to receive adequate exploration, including the nature of the photocatalyst surface active sites, its capacity for CO2 adsorption, the kinetics of reaction product desorption, and the long-term stability of the catalyst. In this NSF Faculty Early Career Development (CAREER) Program Award, Prof. Ying Li of the University of Wisconsin-Milwaukee will address a number of these issues. Li will explore a new concept of integrated CO2 capture and catalytic conversion (IC4) to produce solar fuels using novel multifunctional materials, with the aim to achieve significantly improved, stable CO2 conversion efficiency. The proposed multifunctional materials will exploit interacting adsorbent/catalyst components in the form of mixed metal oxides, layered double hydroxides (LDHs), and their hybrids, which are metal oxide nanoparticles embedded on reconstructed LDHs. Different morphologies and nanostructures of the adsorbent/catalyst components will be investigated to maximize the synergy between the two components/functions. Another unique idea in the proposed research is to perform the photocatalytic CO2 reaction at elevated temperatures in the range of 100 to 200 °C; whereas, conventional photocatalytic reactions are conducted at room or near-room temperatures. At these higher temperatures, the desorption of reaction intermediates and products from the catalyst surface will be enhanced, while the adsorbent component of the hybrid material will function to ensure CO2 adsorption. This slightly elevated temperature can be achieved by utilizing industrial waste heat or the infrared portion of sunlight in large-scale applications, and thus a higher overall solar energy conversion efficiency is expected. This CAREER project will also advance fundamental understanding of the CO2 photoreduction mechanism. CO2 adsorption/desorption and the measured photocatalytic conversion efficiency will be correlated with comprehensive material characterization, through advanced spectroscopic methods including in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and x-ray absorption spectroscopy (XAS). These combined approaches will be powerful tools to investigate changes in material properties during photoreaction, interactions of adsorbates on the surface, fate of reaction intermediates, charge transfer pathways, and factors that affect catalyst activity and stability. Broader ImpactThe results of this proposed research in converting greenhouse gases like CO2 to fuels will have significant impact on the development of sustainable energy technology. The current research on CO2 capture and CO2 conversion/utilization are separately investigated in the scientific community. The proposed concept of integrated CO2 capture and catalytic conversion at slightly elevated temperatures using hybrid adsorbent/catalyst materials offers a new route to solve this very challenging problem in a more integrated, efficient way. The new material design and fundamental understanding in catalyst stability in this research by Prof. Li will also shed light on other photocatalytic systems such as solar hydrogen production from water splitting.As expected for CAREER projects, the proposed research will be integrated into teaching and curriculum development. Graduate students will be trained in this interdisciplinary research; undergraduate and high school students, particularly those in underrepresented groups, will be recruited to participate in the research project. Outreach programs are planned in collaboration with Milwaukee Public Schools and non-profit education organizations in Milwaukee urban areas such as the Urban Ecology Center, to assist teachers to build course materials related to solar energy and nanotechnology, thereby increasing the students? awareness in global climate change while promoting interests in the STEM fields.