Qiyuan Wu

Electrochemical reduction of CO2 to synthesis gas with controlled CO/H2 ratios

The electrochemical carbon dioxide reduction reaction (CO2RR) to simultaneously produce carbon monoxide (CO) and hydrogen (H2) has been achieved on carbon supported palladium (Pd/C) nanoparticles in an aqueous electrolyte. The synthesis gas product has a CO to H2 ratio between 0.5 and 1, which is in the desirable range for thermochemical synthesis of methanol and Fischer–Tropsch reactions using existing industrial processes. In situ X-ray absorption spectroscopy in both near-edge (XANES) and extended regions (EXAFS) and in situ X-ray diffraction show that Pd has transformed into β-phase palladium hydride (β-PdH) during the CO2RR. Density functional theory (DFT) calculations demonstrate that the binding energies of both adsorbed CO and H are significantly weakened on PdH than on Pd surfaces, and that these energies are potential descriptors to facilitate the search for more efficient electrocatalysts for syngas production through the CO2RR.

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.

Understanding the Interactions of CO2 with Doped and Undoped SrTiO3.

SrTiO3 and doped SrTiO3 have a wide range of applications in different fields. For example, Rh-doped SrTiO3 has been shown to have photocatalytic activity for both hydrogen production and CO2 conversion. In this study, both undoped and Rh-doped SrTiO3 were synthesized by hydrothermal and polymerizable complex methods. Different characterizations techniques including X-ray photoelectron spectroscopy (XPS), XRD, Raman, and UV/Vis spectroscopy were utilized to establish correlations between the preparation methods and the electronic/structural properties of Rh-doped SrTiO3 . The presence of dopants and oxygen vacancies substantially influenced the CO2 interactions with the surface, as revealed by the in situ infrared spectroscopic study. The presence of distinctly different adsorption sites was correlated to oxygen vacancies and oxidation states of Ti and Rh.

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.

Unexpected visible light driven photocatalytic activity without cocatalysts and sacrificial reagents from a (GaN)1–x(ZnO)x solid solution synthesized at high pressure over the entire composition range

Optical and photocatalytic properties were determined for the solid solution series (GaN)1–x(ZnO)x synthesized at high pressure over the entire compositional range (x = 0.07 to 0.9). We report for the first time photocatalytic H2 evolution activity from water for (GaN)1–x(ZnO)x without cocatalysts, pH modifiers and sacrificial reagents. Syntheses were carried out by reacting GaN and ZnO in appropriate amounts at temperatures ranging from 1150 to 1200 °C, and at a pressure of 1 GPa. ZnGa2O4 was observed as a second phase, with the amount decreasing from 12.8 wt% at x = 0.07 to ∼0.5 wt% at x = 0.9. The smallest band gap of 2.65 eV and the largest average photocatalytic H2 evolution rate of 2.31 μmol h−1 were observed at x = 0.51. Samples with x = 0.07, 0.24 and 0.76 have band gaps of 2.89 eV, 2.78 eV and 2.83 eV, and average hydrogen evolution rates of 1.8 μmol h−1, 0.55 μmol h−1 and 0.48 μmol h−1, respectively. The sample with x = 0.9 has a band gap of 2.82 eV, but did not evolve hydrogen. An extended photocatalytic test showed considerable reduction of activity over 20 hours.

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

Active sites for tandem reactions of CO2 reduction and ethane dehydrogenation

Significance Catalytic activity or selectivity of a supported metal catalyst is predominantly determined by its active site structure. Rational optimization of supported metal catalysts requires fundamental insights into active sites and structure–function relationships. Here, we convincingly identify two types of metal–oxide active sites and successfully correlate them with the corresponding catalytic performance for CO2-assisted dehydrogenation of ethane. Controlled synthesis of the two distinct active sites enables rational manipulation of the activity and selectivity, offering an opportunity to efficiently convert the underutilized ethane from shale gas to value-added products while mitigating anthropogenic CO2 emissions. Ethylene (C2H4) is one of the most important raw materials for chemical industry. The tandem reactions of CO2-assisted dehydrogenation of ethane (C2H6) to ethylene creates an opportunity to effectively use the underutilized ethane from shale gas while mitigating anthropogenic CO2 emissions. Here we identify the most likely active sites over CeO2-supported NiFe catalysts by using combined in situ characterization with density-functional theory (DFT) calculations. The experimental and theoretical results reveal that the Ni–FeOx interfacial sites can selectively break the C–H bonds and preserve the C–C bond of C2H6 to produce ethylene, while the Ni–CeOx interfacial sites efficiently cleave all of the C–H and C–C bonds to produce synthesis gas. Controlled synthesis of the two distinct active sites enables rational enhancement of the ethylene selectivity for the CO2-assisted dehydrogenation of ethane.

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.