Shen Zhao

Complex structural dynamics of nanocatalysts revealed in Operando conditions by correlated imaging and spectroscopy probes

Understanding how heterogeneous catalysts change size, shape and structure during chemical reactions is limited by the paucity of methods for studying catalytic ensembles in working state, that is, in operando conditions. Here by a correlated use of synchrotron X-ray absorption spectroscopy and scanning transmission electron microscopy in operando conditions, we quantitatively describe the complex structural dynamics of supported Pt catalysts exhibited during an exemplary catalytic reaction—ethylene hydrogenation. This work exploits a microfabricated catalytic reactor compatible with both probes. The results demonstrate dynamic transformations of the ensemble of Pt clusters that spans a broad size range throughout changing reaction conditions. This method is generalizable to quantitative operando studies of complex systems using a wide variety of X-ray and electron-based experimental probes.

Exceptional activity of sub-nm Pt clusters on CdS for photocatalytic hydrogen production: a combined experimental and first-principles study

In this work we have explored a new concept of substantially increasing photocatalytic activity for H2 production of conventional semiconductors by modifying them with sub-nm Pt particles. By combining both experimental and theoretical approaches, we have also developed new mechanistic insights into the 17 times increase in photocatalytic activity of Pt modified CdS catalysts.

Operando Characterization of Catalysts through use of a Portable Microreactor

In order to more deeply understand the mechanisms of catalytic reactions, improved methods are needed to monitor changes that occur in the electronic, structural, and chemical properties of catalytic systems under the conditions in which they work. We describe here a microreactor‐based approach that integrates the capabilities of advanced X‐ray, electron, optical, and gas‐phase compositional analysis techniques under operando conditions. For several exemplary catalytic systems, we demonstrate how this approach enables the characterization of three of the major factors that contribute to structure–property correlations in heterogeneous catalysis. Specifically, we describe how this approach can be used to better understand the atomic structure and elemental composition of nanocatalysts, the physiochemical properties of the support and catalyst/support interfaces, and the gas‐ and surface‐phase chemistry that occurs under operando conditions. We highlight the generality of the approach, as well as opportunities for future developments.

Development of a New Generation of Stable, Tunable, and Catalytically Active Nanoparticles Produced by the Helium Nanodroplet Deposition Method

Nanoparticles (NPs) are revolutionizing many areas of science and technology, often delivering unprecedented improvements to properties of the conventional materials. However, despite important advances in NPs synthesis and applications, numerous challenges still remain. Development of alternative synthetic method capable of producing very uniform, extremely clean and very stable NPs is urgently needed. If successful, such method can potentially transform several areas of nanoscience, including environmental and energy related catalysis. Here we present the first experimental demonstration of catalytically active NPs synthesis achieved by the helium nanodroplet isolation method. This alternative method of NPs fabrication and deposition produces narrowly distributed, clean, and remarkably stable NPs. The fabrication is achieved inside ultralow temperature, superfluid helium nanodroplets, which can be subsequently deposited onto any substrate. This technique is universal enough to be applied to nearly any element, while achieving high deposition rates for single element as well as composite core-shell NPs.

Characterizing Working Catalysts with Correlated Electron and Photon Probes

1. Center for Functional Nanomaterials, Brookhaven National Laboratory, New York, NY 11973 2. Department of Physics, Yeshiva University, New York, NY 10016 3. Department of Chemistry, University of Illinois at Urbana-Champaign, Illinois 61820 4. National Synchrotron Light Source II, Brookhaven National Laboratory, New York, NY 11973 5. Materials Science and Engineering Department, Stony Brook University, Stony Brook 11794 6. Department of Chemical Engineering, Columbia University, New York, NY 10027

Operando and multimodal studies of speciation and activity of Pt catalysts during the hydrogenation of ethylene

The creation of fuels and large volume chemicals (such as olefins) from crude oil feedstocks involves the hydrogenation of unsaturated hydrocarbons. These processes involve numerous catalytic reforming and hydrogenation/dehydrogenation processes, and are generally mediated by supported metal nanoparticle catalysts. These catalysts are generally chosen for their high activity, long term stability and the ease with which they can be regenerated and recovered. However, despite the extensive use of these materials, there are many questions that remain about how specific attributes of the structure and composition of the catalysts are affected by the gases with which they interact. Furthermore, it is critically important to understand how these structural changes affect selectivity, as well as how deactivation occurs because of the conversion process.