Umit S. Ozkan

Photostable p-Type Dye-Sensitized Photoelectrochemical Cells for Water Reduction

A photostable p-type NiO photocathode based on a bifunctional cyclometalated ruthenium sensitizer and a cobaloxime catalyst has been created for visible-light-driven water reduction to produce H2. The sensitizer is anchored firmly on the surface of NiO, and the binding is resistant to the hydrolytic cleavage. The bifunctional sensitizer can also immobilize the water reduction catalyst. The resultant photoelectrode exhibits superior stability in aqueous solutions. Stable photocurrents have been observed over a period of hours. This finding is useful for addressing the degradation issue in dye-sensitized photoelectrochemical cells caused by desorption of dyes and catalysts. The high stability of our photocathodes should be important for the practical application of these devices for solar fuel production.

Changing the oxygen mobility in Co/ceria catalysts by Ca incorporation: implications for ethanol steam reforming.

The effect of calcium doping on the performance of Co/CeO(2) catalysts in ethanol steam reforming was examined using various characterization techniques including CO temperature-programmed reduction, O(2) and CO pulse chemisorption, laser Raman spectroscopy, X-ray diffraction, isotopically labeled oxygen exchange, and diffuse reflectance infrared Fourier transform spectroscopy. Characterization results showed Ca incorporation to lead to oxygen vacancies and unit cell expansion in the ceria lattice. The creation of oxygen vacancies, in turn, enhanced the oxygen mobility in ceria-supported Co catalysts. Steady-state reaction studies showed increased TOF and higher H(2) yields over Co catalysts supported on Ca-doped ceria in ethanol steam reforming.

NiMoO4 selective oxidation catalysts containing excess MoO3 for the conversion of C4 hydrocarbons to maleic anhydride: I. Preparation and characterization

Abstract NiMoO 4 catalysts containing “excess” MoO 3 are active for the selective oxidation of C 4 hydrocarbons to maleic anhydride. The synthesis and characterization of the active component of this catalyst are reported. Synthesis techniques included precipitation, solid-state reaction, and impregnation. Extensive characterization of the catalyst has been performed using complementary instrumentation techniques, including laser Raman spectroscopy, Raman microprobe spectroscopy, X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, and scanning electron microscopy.

Effect of synthesis parameters on the catalytic activity of Co–ZrO2 for bio-ethanol steam reforming

The effects of synthesis parameters on the activity of Co–ZrO2 catalysts in bio-ethanol steam reforming (BESR) were investigated. The supported catalysts were prepared by incipient wetness impregnation (IWI) and characterized through N2 physisorption, H2 chemisorption, X-ray diffraction, X-ray photoelectron spectroscopy, temperature programmed calcination, temperature programmed reduction, temperature programmed oxidation, thermogravimetric analysis, ethanol pulse chemisorption, and temperature programmed reaction techniques. The synthesis parameters examined include calcination temperature, reduction temperature, and reduction time. The catalyst evolution at different stages of the synthesis process was investigated. The ethanol adsorption and temperature programmed reaction experiments indicated a strong correlation between the catalytic activity and metallic cobalt surface area for the 10 wt% Co–ZrO2 catalyst.

NiMoO4 selective oxidation catalysts containing excess MoO3 for the conversion of C4 hydrocarbons to maleic anhydride. II: Selective oxidation of 1-butene

Abstract The selective oxidation of 1-butene to maleic anhydride over NiMoO 4 catalysts containing “excess” MoO 3 was studied using a fixed-bed, integral reactor system. Activity and selectivity measurement were performed using catalysts which had been prepared by precipitation, impregnation, or solid-state reaction and which had previously undergone extensive characterization. The most selective component of the catalyst for maleic anhydride production was determined to be a MoO 3 phase which possessed a surface covering of NiMoO 4 . Postreaction characterization by laser Raman spectroscopy. Raman microprobe spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy revealed that the catalyst was stable for prolonged reaction times.

Effect of surface species on activity and selectivity of MoO3/SiO2 catalysts in partial oxidation of methane to formaldehyde

The effect of the nature of surface species on the activity and selectivity of MoO3/SiO2 catalysts has been investigated for the partial oxidation of methane to formaldehyde. Characterization techniques including BET surface area, ambient and in situ Raman spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed reduction were used in conjunction with steady-state reaction studies to relate the presence of different surface species to the activity and selectivity of the catalyst. Results of these experiments indicate the presence of a highly dispersed silicomolybdic species with terminal Mo=O sites appearing at lower MoO3 loadings. As the weight loading increases, these sites are transformed into polymolybdate species, forming more Mo-O-Mo bridging sites at the expense of Mo=O sites. At high weight loadings, crystalline MoO3 begins to form. The abundance of the Mo=O sites is believed to affect activity and selectivity in the partial oxidation of methane to formaldehyde.

Characterization and temperature-programmed studies over Pd/TiO2 catalysts for NO reduction with methane

Abstract Characterization and temperature-programmed studies were performed over Pd/titania catalysts to examine their activity in the reduction of NO with methane. The catalyst was prepared using a wet impregnation technique and Pd-acetate was used as a precursor for palladium. Techniques such as BET surface area measurements, X-ray diffraction, laser Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy were used for the characterization of the catalyst before and after the reaction. Temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) were also used to probe the surface to understand its adsorption/desorption characteristics and reducing capabilities. The results obtained from these studies together with the reaction investigations have given some important insight into the functionality of this catalyst.

Heteroatom-Doped Carbon Nanostructures as Oxygen Reduction Reaction Catalysts in Acidic Media: An Overview

This paper provides an overview of the studies that were conducted in our laboratories in the last decade on hetero-atom doped carbon structures as potential oxygen reduction reaction (ORR) catalysts for PEM fuel cells. These studies include evaluating the potential of nitrogen doped carbon nanostructures as cathode catalysts for proton exchange membrane and direct methanol fuel cells and examining the nature of the transition metal used as growth catalysts in synthesis of these materials, through activity and in situ and ex situ characterization experiments. These studies also shed some light on the ongoing debate about the differences and similarities between two classes of materials used for ORR, namely FeNC and CNx catalysts, through activity and stability tests, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, temperature-programmed techniques and selective poisoning experiments designed to probe the active sites.Graphical Abstract

Effect of crystal morphology in selective catalytic reduction of nitric oxide over V2O5 catalysts

Abstract Structural specificity of vanadium pentoxide catalysts was investigated in the selective catalytic reduction (SCR) of nitric oxide. Catalysts were prepared by different temperature-programmed methods to obtain particles having preferential exposure of different crystal planes. Catalyst samples were characterized using the BET surface area technique, X-ray diffraction, laser Raman spectroscopy. X-ray photoelectron spectroscopy, scanning electron microscopy and 3-D imaging techniques. A steady-state fixed-bed reactor system was used for activity and selectivity measurements. Identification and quantification of reaction effluents were achieved using an analytical scheme that combined gas chromatography, chemiluminescence, gas chromatography-mass spectroscopy and wet chemistry techniques. Samples that preferentially exposed the (010) basal planes were found to promote direct oxidation of ammonia more readily than nitric oxide reduction as evidenced by the differences in nitric oxide and ammonia conversions and in nitrogen and nitrous oxide yields. The difference in catalytic activity and selectivity was related to the relative abundance of V O sites exposed on the catalyst surface and the competing reactions that are involved in SCR and direct ammonia oxidation reaction schemes.

Isotopic Labeling Studies on Oxidative Coupling of Methane over Alkali Promoted Molybdate Catalysts

The addition of the alkali promoters Li, Na, and K to MnMoO 4 has been shown to increase the catalytic activity and selectivity for the oxidative coupling of methane at 700°C (1). This promoter effect has been further investigated through transient isotopic labeling technique using oxygen and methane isotopes under steady-state reaction conditions and by the addition of CO 2 to the feed stream.