A rational approach to the evaluation of supported metals and surface alloys as oxidation and reforming catalysts

该项目建立在美国国家科学基金会/NIRT资助下的塔夫茨大学当前工作中令人兴奋的新发现的基础上，我们收集了重要的证据，指出金和铂在铈中的原子分散，以及金在氧化铁中的原子分散，是水煤气转移反应（WGS）的催化位点。我们跟踪了氧化铈基质中金簇生长的活性损失，并确定了稳定金簇生长的条件。我们已经证明，添加少量的氧气可以用来稳定Au-或Pt-CeO2变换催化剂在所有温度下和在现实的燃料气流中循环启动/关闭操作。我们进一步证明了铈的形状/晶面/应变对Au/ceria的WGS活性有很强的影响，通过控制水热合成的纳米级单晶，可以在流动反应器系统中常压测试。此外，该项目建立在威斯康星大学新的重要理论发现的基础上，该发现表明，作为表面或近表面合金的某些金属对作为PEM阴极电催化剂具有更高的活性。Tufts co- pi之一的高分辨率STM/STS的独特能力将开辟一条新的研究途径，将这些模型催化剂的原子级组成和电子性质与表面化学联系起来。在本文中，我们将把对金属的原子分散的研究扩展到其他氧化物，如氧化锆和氧化锌，它们都是通过新的合成路线制备的纳米棒、立方体、多面体等，暴露出特定的晶体平面，在其上沉积和研究金属和金属合金。WGS和甲醇蒸汽重整（MSR）过程将是探测结构灵敏度的重要反应。金属和近表面金属合金组的Au， Cu， Pd和Pt，将被检查。提出了一种新的排列顺序合金金属反应性的组合方法，该方法将纳米合金尖端压在热电偶上的薄氧化结上，并将热电响应用于监测纳米合金上的吸附/反应。提出了一种合理的WGS和MSR新型催化剂的合成和评价方法，以补充和指导催化工作。因此，STM/STS研究和计算化学是该项目的中心。我们还将通过我们的合作者在布鲁克海文国家实验室（BNL）使用XAS功能。我们在该项目的总体目标是阐明金属-氧化物和金属-金属相互作用对氢燃料重整产生的氧化还原反应的影响，并为下一代WGS和MSR催化剂的设计铺平道路。更广泛的影响我们建议进行一项系统的，多学科的研究工作，以调查Au， Cu， Pt和Pd与铈，氧化锆或氧化锌的原子水平相互作用，以产生燃料电池用氢的两个感兴趣的反应；即水煤气变换和甲醇蒸汽重整反应。从这些系统中获得的知识对其他与清洁能源密切相关的重要反应具有机械和实际意义，包括来自化石燃料或生物质的其他含氧化合物的加工。来自塔夫茨大学化学工程和化学、威斯康星大学化学工程和BNL化学的跨学科专家团队已经为这个项目组装起来。在跨学科努力的最后，我们将回答有关原子分散金属，金属团簇和支撑表面合金在氧化铈，氧化锆或氧化锌纳米颗粒上的活性和选择性的关键问题，并能够为实际催化剂制备提供合理的设计。这些材料将用于燃料和生物燃料的加工，以及用作燃料电池的阳极催化剂和薄膜。因此，这些发现的影响将导致更好的电力系统设计。这里涉及的每个学科都有其他一些切实的好处：催化剂合成的新方法，对传感器、燃料电池组件和催化剂具有重要意义的纳米尺度的新材料特性；以及为低成本燃料和化学品生产设计新的催化剂。总体效益将成为合理设计来自项目跨学科活动的催化剂的模板。我们定期与业界同仁交换信息，这已成为我们实验室的传统。在这个项目中，我们计划让工业界的同事作为技术顾问，为科学和可能的技术转让提供咨询。该提案的跨学科性质显然影响了研究生和研究生研究员的教育。该项目还计划对BNL的年轻研究人员进行广泛培训。大量女学生将参与该项目，塔夫茨大学本科生暑期学者项目将用于招募其他代表性不足的群体。工作的传播将按照出版物、介绍和会议等正常渠道进行。为了实现真正广泛的传播，我们将创建一个网站，作为纳米催化和能源网站的一部分，作为教育资源和招聘工具来推广这项工作。

Intellectual Merit This project builds on exciting new findings from current work at Tufts University under an NSF/NIRT grant, in which we have collected significant evidence pointing to atomic dispersions of gold and platinum in ceria, and gold in iron oxide, as the catalytic sites for the water gas shift reaction (WGS). We followed activity loss with gold cluster growth in ceria matrices and identified conditions that stabilize gold growth. We have shown that addition of small amounts of oxygen can be used to stabilize Au- or Pt-CeO2 shift catalysts at all temperatures and in cyclic start up/ shutdown operation in realistic fuel gas streams. We have further demonstrated a strong shape/crystal face/strain effect of ceria on the WGS activity of Au/ceria by using single ceria crystals at the nanoscale prepared by controlled hydrothermal synthesis, which can be tested at normal pressures in flow reactor systems. Moreover, this project builds on new, important theoretical findings from the University of Wisconsin that certain pairs of metals examined as surface or near surface alloys possess much improved activity as PEM cathode electrocatalysts. The unique capability in high-resolution STM/STS of one of the Tufts co-PIs will open a new avenue of investigation that connects atomic-level composition and electronic properties with the surface chemistry of these model catalysts. In the proposed work, we will extend the study of atomic dispersions of metals to other oxides, such as zirconia and zinc oxide, both prepared by novel synthesis routes as nano rods, cubes, polyhedra, etc. exposing specific crystal planes on which to deposit and study metals and metal alloys. The WGS and methanol steam reforming (MSR) processes will be the reactions of interest to probe structure sensitivity with the support. Metals and near surface metal alloys from the group of Au, Cu, Pd, and Pt, will be examined. A new combinatorial approach to rank order alloy metal reactivity is proposed, whereby nanoalloy tips pressed on thin oxides-on-thermocouple junctions will be constructed in arrays and thermoelectric response will be used to monitor adsorption/reaction on the nanoalloys. A rational approach to the synthesis and evaluation of novel catalysts for WGS and MSR is proposed to complement and guide the catalysis work. Thus, STM/STS studies and computational chemistry are center-stage in the project. We will also make use of the XAS capabilities at Brookhaven National Lab (BNL) through our collaborators there. Our overall goal in the project is to elucidate the metal-oxide and the metal-metal interactions responsible for redox reactions of interest to fuel reforming for hydrogen generation and pave the way for the design of the next generation of WGS and MSR catalysts. Broader Impacts We propose to undertake a systematic, multidisciplinary research effort to investigate the atomic-level interaction of Au, Cu, Pt, and Pd with ceria, zirconia, or zinc oxide for two reactions of interest to the production of hydrogen for fuel cells; namely, the water-gas shift and methanol steam reforming reactions. Knowledge garnered from these systems has both mechanistic and practical implications for other closely related reactions of importance to clean energy, including the processing of other oxygenates derived from fossil fuels or biomass. An interdisciplinary team of experts from Chemical Engineering and Chemistry at Tufts, Chemical Engineering at the Wisconsin, and Chemistry at BNL, has been assembled for this project. At the end of the interdisciplinary effort, we will have answered key questions on the activity and selectivity of atomically dispersed metals, metal clusters, and supported surface alloys on nanoparticles of ceria, zirconia, or zinc oxide, and be in a position to provide rational designs for practical catalyst preparation. These materials will be used in fuel and biofuel processing, and as anode catalysts and films for fuel cell applications. Thus, the impact of these findings will lead to better power systems design. There are several other tangible benefits for each of the disciplines involved here: new methods for catalyst synthesis, new materials properties specific to the nanoscale of importance to sensors, fuel cell components, and to catalysts; and new catalyst designs for low-cost fuels and chemicals production. An overall benefit will be a template for the rational design of catalysts derived from the interdisciplinary activities of the project. In what has become a tradition in our laboratories, we regularly exchange information with industrial colleagues. In this project, we plan to involve industrial colleagues as technical advisors, both for science and possibly for technology transfer. The interdisciplinary nature of the proposal clearly impacts the education of graduate students and postgraduate fellows. Extensive training of young researchers at BNL is also planned in the project. A significant number of women students will be involved in the project, and the Tufts Summer Scholars program for undergraduates will be used to recruit other under represented groups. The dissemination of the work will follow the normal channels of publications, presentations and meetings. To achieve really broad dissemination, a website will be created as part of the nano catalysis and energy site to promote this work both as an educational resource and a recruiting tool.