Xianqin Wang

In situ time-resolved characterization of Au-CeO2 and AuOx-CeO2 catalysts during the water-gas shift reaction: presence of Au and O vacancies in the active phase.

Synchrotron-based in situ time-resolved x-ray diffraction and x-ray absorption spectroscopies were used to study the behavior of nanostructured {Au+AuO(x)}-CeO(2) catalysts under the water-gas shift (WGS) reaction. At temperatures above 250 degrees C, a complete AuO(x)-->Au transformation was observed with high catalytic activity. Photoemission results for the oxidation and reduction of Au nanoparticles supported on rough ceria films or a CeO(2)(111) single crystal corroborate that cationic Au(delta+) species cannot be the key sites responsible for the WGS activity at high temperatures. The rate determining steps for the WGS seem to occur at the gold-ceria interface, with the active sites involving small gold clusters (<2 nm) and O vacancies.

The behavior of mixed-metal oxides: Physical and chemical properties of bulk Ce1−xTbxO2 and nanoparticles of Ce1−xTbxOy

The physical and chemical properties of bulk Ce(1-x)Tb(x)O(2) and Ce(1-x)Tb(x)O(y) nanoparticles (x<or =0.5) were investigated using synchrotron-based x-ray diffraction (XRD), x-ray adsorption near edge spectroscopy (XANES), Raman spectroscopy (RS), and first-principles density-functional (DF) calculations. DF results and Raman spectra point to a small tetragonal distortion after introducing terbium in ceria. The results of XRD show a small contraction (< or = 0.08 A) in the cell dimensions. The presence of Tb generates strain in the lattice through the variation of the ionic radii and creation of crystal imperfections and O vacancies. The strain increases with the content of Tb and affects the chemical reactivity of the Ce(1-x)Tb(x)O(y) nanoparticles towards hydrogen, SO(2), and NO(2). DF calculations for bulk Ce(1-x)Tb(x)O(2) and Ce(8-n)Tb(n)O(16) (n=0, 1, 2, or 4) clusters show oxide systems that are not fully ionic. The theoretical results and XANES spectra indicate that neither a Ce<-->Tb exchange nor the introduction of oxygen vacancies in Ce(1-x)Tb(x)O(y) significantly affect the charge on the Ce cations. In contrast, the O K-edge and Tb L(III)-edge XANES spectra for Ce(1-x)Tb(x)O(y) nanoparticles show substantial changes with respect to the corresponding spectra of Ce and Tb single oxide references. The Ce(0.5)Tb(0.5)O(y) compounds exhibit a much larger Tb(3+)/Tb(4+) ratio than TbO(1.7). A comparison with the properties of Ce(1-x)Zr(x)O(y) and Ce(1-x)Ca(x)O(y) shows important differences in the charge distribution, the magnitude of the dopant induced strain in the oxide lattice, and a superior behavior in the case of the Ce(1-x)Tb(x)O(y) systems. The Tb-containing oxides combine stability at high temperature against phase segregation and a reasonable concentration of O vacancies, making them attractive for chemical and catalytic applications.

The behavior of mixed-metal oxides: Structural and electronic properties of Ce1−xCaxO2 and Ce1−xCaxO2−x

Synchrotron-based time-resolved x-ray diffraction (TR-XRD), x-ray absorption near edge spectroscopy (XANES), Raman spectroscopy (RS), and first-principles density functional (DF) calculations were used to study the structural and electronic properties of Ce–Ca mixed-metal oxides. The XRD results and DF calculations show that doping with calcium induces relatively minor variations (<0.05 A) in the cell dimensions of ceria. However, the presence of Ca leads to slightly distorted tetragonal structures, a substantial strain in the lattice of the oxide and a tendency to form O vacancies in an ideal Ce1−xCaxO2 solid solution. The two latter effects can be a consequence of the large number of oxygen neighbors that Ca is forced to have in Ce1−xCaxO2 and differences in the electronic charges of calcium and cerium cations. The Ce1−xCaxO2−x systems are not fully ionic. Cation charges derived from the DF calculations indicate that these systems obey the Barr model for charge redistribution in mixed-metal oxides. The ...

The structural and electronic properties of nanostructured Ce1-x-yZrxTbyO2 ternary oxides: unusual concentration of Tb3+ and metal oxygen metal interactions.

Ceria-based ternary oxides are widely used in many areas of chemistry, physics, and materials science. Synchrotron-based time-resolved x-ray diffraction, x-ray absorption near-edge spectroscopy (XANES), Raman spectroscopy, and density-functional calculations were used to study the structural and electronic properties of Ce-Zr-Tb oxide nanoparticles. The nanoparticles were synthesized following a novel microemulsion method and had sizes in the range of 4-7 nm. The Ce1-x-yZrxTbyO2 ternary systems exhibit a complex behavior that cannot be predicted as a simple extrapolation of the properties of Ce1-xZrxO2, Ce1-xTbxO2, or the individual oxides (CeO2, ZrO2, and TbO2). The doping of ceria with Zr and Tb induces a decrease in the unit cell, but there are large positive deviations with respect to the cell parameters predicted by Vegards rule for ideal solid solutions. The presence of Zr and Tb generates strain in the ceria lattice through the creation of crystal imperfections and O vacancies. The O K-edge and Tb LIII-edge XANES spectra for the Ce1-x-yZrxTbyO2 nanoparticles point to the existence of distinctive electronic properties. In Ce1-x-yZrxTbyO2 there is an unexpected high concentration of Tb3+, which is not seen in TbO2 or Ce1-xTbxO2 and enhances the chemical reactivity of the ternary oxide. Tb<-->O<-->Zr interactions produce a stabilization of the Tb(4f,5d) states that is responsible for the high concentration of Tb(3+) cations. The behavior of Ce1-x-yZrxTbyO2 illustrates how important can be metal<-->oxygen<-->metal interactions for determining the structural, electronic, and chemical properties of a ternary oxide.

Recovering Magnetic Fe3O4–ZnO Nanocomposites from Algal Biomass Based on Hydrophobicity Shift under UV Irradiation

Magnetic separation, one of the promising bioseparation technologies, faces the challenges in recovery and reuse of magnetic agents during algal harvesting for biofuel extraction. This study synthesized a steric acid (SA)-coated Fe3O4-ZnO nanocomposite that could shift hydrophobicity under UV365 irradiation. Our results showed that with the transition of surface hydrophobicity under UV365 irradiation, magnetic nanocomposites detached from the concentrated algal biomass. The detachment was partially induced by the oxidation of SA coating layers due to the generation of radicals (e.g., •OH) by ZnO under UV365 illumination. Consequently, the nanocomposite surface shifted from hydrophobic to hydrophilic, which significantly reduced the adhesion between magnetic particles and algae as predicted by the extended Derjaguin and Landau, Verwey, and Overbeek (EDLVO) theory. Such unique hydrophobicity shift may also find many other potential applications that require recovery, recycle, and reuse of valuable nanomaterials to increase sustainability and economically viability.

Water-induced morphology changes in BaO/γ-Al2O3 NOx storage materials

Exposure of NO2-saturated BaO/γ-Al2O3 NOx storage materials to H2O vapour results in the conversion of surface nitrates to Ba(NO3)2 crystallites, causing dramatic morphological changes in the Ba-containing phase, demonstrating a role for water in affecting the NOx storage/reduction properties of these materials.

Enhancement of Nitrite Reduction Kinetics on Electrospun Pd-Carbon Nanomaterial Catalysts for Water Purification

We report a facile synthesis method for carbon nanofiber (CNF) supported Pd catalysts via one-pot electrospinning and their application for nitrite hydrogenation. A mixture of Pd acetylacetonate (Pd(acac)2), polyacrylonitrile (PAN), and nonfunctionalized multiwalled carbon nanotubes (MWCNTs) was electrospun and thermally treated to produce Pd/CNF-MWCNT catalysts. The addition of MWCNTs with a mass loading of 1.0-2.5 wt % (to PAN) significantly improved nitrite reduction activity compared to the catalyst without MWCNT addition. The results of CO chemisorption confirmed that the addition of MWCNTs increased Pd exposure on CNFs and hence improved catalytic activity.

Catalytic reduction for water treatment

AbstractTreating water contaminants via heterogeneously catalyzed reduction reaction is a subject of growing interest due to its good activity and superior selectivity compared to conventional technology, yielding products that are non-toxic or substantially less toxic. This article reviews the application of catalytic reduction as a progressive approach to treat different types of contaminants in water, which covers hydrodehalogenation for wastewater treatment and hydrogenation of nitrate/nitrite for groundwater remediation. For hydrodehalogenation, an overview of the existing treatment technologies is provided with an assessment of the advantages of catalytic reduction over the conventional methodologies. Catalyst design for feasible catalytic reactions is considered with a critical analysis of the pertinent literature. For hydrogenation, hydrogenation of nitrate/nitrite contaminants in water is mainly focused. Several important nitrate reduction catalysts are discussed relating to their preparation method and catalytic performance. In addition, novel approach of catalytic reduction using in situ synthesized H2 evolved from water splitting reaction is illustrated. Finally, the challenges and perspective for the extensive application of catalytic reduction technology in water treatment are discussed. This review provides key information to our community to apply catalytic reduction approach for water treatment.

H2 PRODUCTION AND FUEL CELLS.

Oxide nanosystems play a key role as components of catalysts used for the production of H{sub 2} via the steam reforming or the partial oxidation of hydrocarbons, and for the water-gas shift reaction. The behavior seen for Cu-ceria and Au-ceria WGS catalysts indicates that the oxide is much more than a simple support. The special chemical properties of the oxide nanoparticles (defect rich, high mobility of oxygen) favor interactions with the reactants or other catalyst components. More in-situ characterization and mechanistic studies are necessary for the optimization of these nanocatalysts. The use of oxide nanomaterials for the fabrication of PEMFCs and SOFCs can lead to devices with a high practical impact. One objective is to build electrodes with low cost conducting oxide nanoarrays. The electron and oxygen-ion conducting capabilities of many oxides improve when going from the bulk to the nanoscale. Furthermore, one can get a more homogeneous surface morphology and an increase of the effective reaction area. Much more fundamental and practical research needs to be done in this area.

Special Issue in Honor of Professor S. Ted Oyama: 2014 ACS Distinguished Researcher Award in Petroleum Chemistry and Storch Award in Fuel Science

This special issue of Topics in Catalysis honors Professor S. Ted Oyama for his Awards in Petroleum Chemistry and Fuel Science Research. These awards were celebrated at two American Chemical Society (ACS) symposia in 2014. The first one, the ACS’s Distinguished Research Award in Petroleum Chemistry Symposium, took place at the 247th ACS National Meeting in Dallas, TX, during March 17-19, 2014 and the second one, the ACS’s Storch Award in Fuel Science Symposium, took place at the 248th ACS National Meeting in San Francisco, CA, during August 10-12, 2014. Professor Oyama received the 2014 ACS Distinguished Research Award in Petroleum Chemistry ‘‘for his substantial contributions to the field of heterogeneous catalysis’’ including the discovery of highly active transition metal phosphide catalysts for hydrotreatment of petroleum and coal-derived feedstocks and biomass refining, the development of new compositions, and the understanding of their reaction mechanisms by in situ spectroscopic techniques at high temperatures and pressures of reaction. Following this recognition, Professor Oyama was also awarded the 2014 ACS Storch Award in Fuel Science ‘‘for his broad contributions to the field of fuel science’’ including the production of hydrogen by catalytic reforming, selective oxidation of hydrocarbons, biomass conversion, their reaction kinetics and mechanisms, and spectrokinetic methods to study catalysts in situ at reaction conditions and theory and application of inorganic membranes for separation of hydrogen and fuel-relevant gases. This special issue consists of contributions by catalysis researchers who participated in the two ACS symposia honoring Professor Oyama’s Awards. Currently, Professor S. Ted Oyama holds dual appointments in the Chemical Systems Engineering Department at the University of Tokyo and the Chemical Engineering Department at Virginia Polytechnic Institute & State University (Virginia Tech). He earned his PhD degree in Chemical Engineering at Stanford University in 1981, after which he has held positions in industry and academia: Research Engineer/Project Leader at Catalytica Associates, Inc. (1981–1986), Visiting Scholar at the University of California, Berkeley (1986–1988), Associate Professor at Clarkson University (1988–1993), Associate Professor (1993–1996), Professor (1996-Present), and Fred W. Bull Professor (1999–2009) at Virginia Polytechnic Institute & State University, Professor at the University of Tokyo (2010-Present), and Visiting Professor at University of Rio de Janeiro (1992), University Pierre and Marie Curie, Paris J. J. Bravo-Suárez (&) Chemical & Petroleum Engineering Department, The University of Kansas, Lawrence, KS 66045, USA e-mail: jjbravo@ku.edu