Spray Jet Flames for Supported Gold Catalysts: New Catalysts by Intelligent Design

论文题目：用于负载金催化剂的喷射火焰：智能设计的新型催化剂知识优点：火焰为纳米颗粒的生长提供了独特的环境，因为它们含有高度的超饱和、极高的温度和快速的淬火条件，并锁定在动力学结构中。喷射火焰为纳米颗粒的形成提供了最通用和可控的热解条件。喷射的有机金属液体喷雾可以被点燃，以产生大量的纳米材料与惊人的控制形态。这种喷射火焰工艺（SFP）在纳米材料，特别是氧化物和负载金属的大规模生产中具有很大的潜力。由于光发射、高温（2000℃）、接近声速的流速和总生长时间仅为几毫秒，观察这种纳米材料的生长是困难的。在这种快速生长条件下研究粒子生长动力学需要能够快速检测并且对极高温度、明亮光学发射和高噪声不敏感的原位技术。本提案旨在通过理解这种复杂的“共沉淀”反应中结构成核和生长的基础来设计负载金纳米催化剂的SFP合成。由于利用原位x射线散射表征纳米颗粒在火焰中的成核、生长和聚集的最新进展，现在可以进行这样的设计。在本文提出的工作中，利用异常散射（ASAXS）通过对比匹配将金的贡献与支撑的贡献分离出来。这类似于TEM中的暗场成像，除了ASAXS具有元素分辨率而不是晶体分辨率。这项工作将是ASAXS首次在多相气溶胶纳米粉末的原位使用。原位ASAXS可以在50微米的空间分辨率和20 ms的曝光时间下，独立测量Au和载体（TiO2）的Sauter平均直径、尺寸分布、体积分数、数量浓度和聚集质量的分形维数、每聚集一次颗粒的大小和数量以及支含量在火焰中的演变。在与ETHZ的合作中，液滴速度将通过2d相位多普勒风速仪（PDA）测量，气体温度将通过傅里叶变换红外（FTIR）发射/透射光谱测量。在之前对单组分喷雾火焰、液滴蒸发、纳米材料成核和聚集的测量中，包括颗粒生长速率、聚集和分支的细节都是直接观察到的。更广泛的影响：该项目将支持一名博士候选人和两名本科生。计划继续与ETHZ（苏黎世）的研究人员互动。该提案包括在加州大学继续开发纳米粉末网络课程。该项目还将涉及开发一门新的纳米级催化技术共享课程，重点关注支撑金属催化剂和纳米尺寸/形状效应，瑞士合作者将为此做出贡献。本课程将由UC和ETHZ联合开设。自2000年以来，网络课程已成为向社区传播信息的有效手段，课程套件的独立IP点击量超过13万次（每天约60次）。

ABSTRACTProposal Number: 0626063Principal Investigator: Beaucage, GregoryAffiliation: University of Cincinnati Main CampusProposal Title: Spray Jet Flames for Supported Gold Catalysts: New Catalysts by Intelligent DesignIntellectual Merit:Flames offer a unique environment for nano-particle growth since they contain high degrees of super-saturation, extremely high temperatures and rapid quench conditions, locking in kinetic structures. Spray jets flames offer the most versatile and controllable of pyrolytic conditions for nano-particle formation. A jet of organometallic liquid spray can be ignited to produce copious quantities of nano-materials with surprisingly controlled morphologies. This spray flame process (SFP) is of great potential for mass production of nano-materials, especially oxides and supported metals. Observation of the growth of such nano-materials is difficult due to light emission, high temperature ( 2000 C), flow rates approaching the speed of sound with the total growth spanning a few milliseconds. The study of the dynamics of particle growth under such rapid growth conditions requires in situ techniques capable of rapid detection and being insensitive to extremely high temperatures, brilliant optical emission, and high noise. This proposal seeks to design SFP synthesis of supported gold nano-catalysts by understanding the basis of structural nucleation and growth in this complex "co-precipitation"- like reaction. Such design can now be made due to recent advances in characterization of nanoparticle nucleation, growth and aggregation in flames using in situ x-ray scattering. In the proposed work, anomalous scattering (ASAXS) is used to isolate the contribution due to gold from that of the support through contrast matching. This is similar to dark field imaging in TEM except that ASAXS has elemental resolution rather than crystallographic resolution. The proposed work will be the first in situ use of ASAXS for multiphase aerosol nano-powders. In situ ASAXS can measure independently the evolution of Au and support (TiO2) Sauter mean diameters, size distribution, volume fraction, number concentration, and aggregate mass fractal dimension, size and number of primary particles per aggregate as well as branch content in the flame with 50 micron spatial resolution and 20 ms exposure time. In collaboration with ETHZ, droplet velocities will be measured by 2D-Phase Doppler Anemometry (PDA) and gas temperature by Fourier transform infrared (FTIR) emission/transmission spectroscopy. In previous measurements on single component spray flames, droplet evaporation, nano-material nucleation and aggregation including details on the rate of particle growth, aggregation and branching have been directly observed.Broader Impacts:The project will support a PhD candidate and 2 undergraduates in this effort. Continued interaction with researchers at ETHZ (Zurich) are planned. The proposal includes continued development of a web course on Nano-powders at UC. The project will also involve development of a new shared course on Nano-Scale Catalytic Technology focusing on supported metal catalysts and nano-size/shape effects that will involve contributions from the Swiss collaborators. This course will be jointly offered at UC and ETHZ. The web course has been an effective means to disseminate information to the community with over 130,000 independent IP hits to the course suite since 2000 (~60/day).