UNS:High Surface Free Energy Anchoring of Bimetallic Core Shell Particles

当今应用的金属催化剂必须能够在原料组成和温度的极端条件下稳定运行。因此，催化剂的设计和合成变得越来越重要，以确保催化剂颗粒有效地利用贵金属，如铂族金属，并在高温和非典型进料成分下保持活性表面。所提出的工作将产生分散在碳催化剂载体上的双金属催化剂颗粒，与仅有活性金属组分相比，在反应条件下具有更好的抗颗粒粗化能力。颗粒稳定是通过将活性(金，金)催化剂的表面壳沉积在较高表面自由能核心材料(铂(铂)或各种富含地球的过渡金属)的核心上来实现的。这一概念将在金催化的乙炔与气相盐酸的选择性盐氯化反应中得到检验，以生产氯乙烯(大宗化工生产中的重要中间体)。初步工作表明，通过在原子层沉积制备的小铂团簇上沉积Au，Au粒子显著稳定。在这项研究中，铂(核)-金(壳)双金属颗粒将进一步优化，并将评估成本较低的富含稀土的铜(铜)、镍(镍)和钴(Co)作为稳定核心材料。这是一个假设驱动的建议，基于一个简单的想法，即在小的核-壳颗粒中具有较高的表面自由能核心材料可以稳定低表面能的壳材料，否则在反应条件下会迅速烧结。PI已经获得的数据表明，这一概念适用于表面包覆Au(通过原子层沉积制备)的两纳米铂(核)粒子(通过强静电吸附制备)。进一步的工作将比较均匀的合金和相同标称组成的核壳催化剂，还将考察壳层厚度和核颗粒尺寸对乙炔盐化活性和耐久性的影响。纳米多金属颗粒在提高催化性能和选择性方面的潜力，以及对这类催化剂的工作组成和结构的了解，是催化领域中一个日益感兴趣的领域。这一建议在优化反应条件下的双金属催化剂颗粒结构方面迈出了重要的一步，着眼于确保催化剂在现实高温反应环境中的长期稳定性。虽然人们对制备含有活性金属纳米团簇的负载型催化剂的新方法非常关注，但除了最初的合成和测试之外，很少有人研究在反应条件下的长期稳定性。因此，本提案对这一领域的研究是一个值得欢迎的补充，其预期结果可能会影响除这里所述的具体催化剂系统之外的广泛范围的催化剂系统。此外，该提案还提供了一条通过利用铜、镍和钴等低成本核心组分来节约使用昂贵的贵金属或贵重活性金属组分的低成本催化剂的途径。这项研究将为研究生和本科生提供机会，利用先进的合成技术参与针对工业应用的研究，这些技术可能会增强广泛的催化过程。

Metallic catalysts for today's applications must be capable of stable operation at extreme conditions of feed compositions and temperatures. Thus, catalyst design and synthesis have become increasingly important to ensure catalyst particles which efficiently use expensive metals such as platinum group metals, and maintain an active surface at high temperatures and atypical feed compositions.The proposed work will create bimetallic catalyst particles dispersed on a carbon catalyst support that have improved resistance to particle coarsening under reaction conditions compared to the active metal component alone. The particle stabilization is achieved by depositing a surface shell of the active (gold, Au) catalyst on a core of a higher surface free energy core material (platinum (Pt), or various earth-abundant transition metals). The concept will be tested in the Au-catalyzed selective hydrochlorination of acetylene with gas-phase hydrochloric acid to produce vinyl chloride (an important intermediate in bulk chemical production). Preliminary work has shown dramatic stabilization of Au particles by depositing the Au on small Pt clusters prepared by atomic layer deposition. In this study, the Pt(core)-Au(shell) bimetallic particles will be further optimized and lower-cost earth-abundant copper (Cu), nickel (Ni), and cobalt (Co) will be evaluated as stabilizing core materials.This is a hypothesis driven proposal based on the simple idea that a higher surface free energy core material in a small core-shell particle can stabilize a lower surface energy shell material that otherwise would sinter rapidly under reaction conditions. The PIs have already obtained data indicating the concept works for two-nanometer Pt(core) particles (prepared by strong electrostatic adsorption) surface-coated with Au (prepared by atomic layer deposition). The further work will compare homogeneous alloys to core-shell catalysts of the same nominal composition, and will also examine the effects of shell thickness and core particle size on acetylene hydrochlorination activity and durability. The potential of nano-scale multi-metallic particles for improved catalytic performance and selectivity is a growing area of interest in catalysis, as is understanding of the working composition and structure of such catalysts. This proposal takes important steps toward optimizing the structure of bimetallic catalyst particles under reaction conditions with an eye toward ensuring long-term catalyst stability in realistic high-temperature reaction environments. Although much attention is being directed towards novel ways of creating supported catalysts containing active metal nano-clusters, few studies have gone beyond initial synthesis and testing to examine long-term stability under reaction conditions. Thus, the present proposal is a welcome addition to research in this area, with expected results that could impact a broad range of catalyst systems beyond the specific ones addressed here. In addition, the proposal offers a route to lower-cost catalysts based on sparing utilization of expensive precious, or noble, active metal components by utilizing core components that are low in cost such as Cu, Ni, and Co. The research will provide opportunities for both graduate and undergraduate students to participate in research directed towards industrial applications utilizing advanced synthesis techniques that can potentially enhance a broad range of catalytic processes.