Some constructions of almost para-hyperhermitian structures on manifolds and tangent bundles

In this paper we give some examples of almost para-hyperhermitian structures on the tangent bundle of an almost product manifold, on the product manifold $M\times\mathbb{R}$, where $M$ is a manifold endowed with a mixed 3-structure and on the circle bundle over a manifold with a mixed 3-structure.Comment: 10 pages; This paper has been presented in the "4th German-Romanian Seminar on Geometry" Dortmund, Germany, 15-18 July 200

Combined spatially resolved operando spectroscopy: New insights into kinetic oscillations of CO oxidation on Pd/γ-Al 2O3

Spatially resolved, combined energy dispersive EXAFS (EDE) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements have been performed over a fixed catalyst bed of Pd/γ-Al 2 O 3 during kinetic oscillations of CO oxidation. The kinetic oscillations of CO oxidation over Pd (or for that matter Pt or Rh) catalysts are a complicated phenomenon that require characterisation techniques with high time resolution and spatial resolution in order to make links between catalyst structure and surface reactivity. By measuring the extent of Pd oxidation at the nanoparticle surface, from Pd K-edge EDE, and matching this with the CO coverage, from DRIFTS spectra, at multiple positions of the fixed bed reactor it is found that the majority of the catalyst undergoes a sharp transition from the CO poisoned catalyst to the highly active, oxidised Pd surface. This transition occurs initially at the end of the catalyst bed, nearest the outlet, and propagates upstream with increasing temperature of the reactor. The oscillations in Pd surface oxide formation and CO coverage are observed only in the first ∼1 mm of the bed, which gives rise to oscillations in CO 2 and O 2 concentrations observed by end-pipe mass spectrometry after the light-off temperature. The catalyst initially exists as less active, CO poisoned metallic Pd nanoparticles before light-off which transition to a highly active state after light-off when the Pd nanoparticle surface becomes dominated by chemisorbed oxygen. Kinetic oscillations only occur at the front of the catalyst bed where there is sufficient concentration of CO in the gas phase to compete with O 2 for adsorption sites at the catalyst surface. We demonstrate the complex nature of the evolving catalyst structure and surface reactivity during catalytic operation and the need for spatially resolved operando methods for understanding and optimising catalyst technologies

Unraveling the H-2 Promotional Effect on Palladium-Catalyzed CO Oxidation Using a Combination of Temporally and Spatially Resolved Investigations

The promotional effect of H2 on the oxidation of CO is of topical interest, and there is debate over whether this promotion is due to either thermal or chemical effects. As yet there is no definitive consensus in the literature. Combining spatially resolved mass spectrometry and X-ray absorption spectroscopy (XAS), we observe a specific environment of the active catalyst during CO oxidation, having the same specific local coordination of the Pd in both the absence and presence of H2. In combination with Temporal Analysis of Products (TAP), performed under isothermal conditions, a mechanistic insight into the promotional effect of H2 was found, providing clear evidence of nonthermal effects in the hydrogen-promoted oxidation of carbon monoxide. We have identified that H2 promotes the Langmuir–Hinshelwood mechanism, and we propose this is linked to the increased interaction of O with the Pd surface in the presence of H2. This combination of spatially resolved MS and XAS and TAP studies has provided previously unobserved insights into the nature of this promotional effect

Combined spatially resolved operando spectroscopy: new insights into kinetic oscillations of CO oxidation on Pd/γ-Al2O3

Spatially resolved, combined energy dispersive EXAFS (EDE) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements have been performed over a fixed catalyst bed of Pd/γ-Al2O3 during kinetic oscillations of CO oxidation. The kinetic oscillations of CO oxidation over Pd (or for that matter Pt or Rh) catalysts are a complicated phenomenon that require characterisation techniques with high time resolution and spatial resolution in order to make links between catalyst structure and surface reactivity. By measuring the extent of Pd oxidation at the nanoparticle surface, from Pd K-edge EDE, and matching this with the CO coverage, from DRIFTS spectra, at multiple positions of the fixed bed reactor it is found that the majority of the catalyst undergoes a sharp transition from the CO poisoned catalyst to the highly active, oxidised Pd surface. This transition occurs initially at the end of the catalyst bed, nearest the outlet, and propagates upstream with increasing temperature of the reactor. The oscillations in Pd surface oxide formation and CO coverage are observed only in the first ∼1 mm of the bed, which gives rise to oscillations in CO2 and O2 concentrations observed by end-pipe mass spectrometry after the light-off temperature. The catalyst initially exists as less active, CO poisoned metallic Pd nanoparticles before light-off which transition to a highly active state after light-off when the Pd nanoparticle surface becomes dominated by chemisorbed oxygen. Kinetic oscillations only occur at the front of the catalyst bed where there is sufficient concentration of CO in the gas phase to compete with O2 for adsorption sites at the catalyst surface. We demonstrate the complex nature of the evolving catalyst structure and surface reactivity during catalytic operation and the need for spatially resolved operando methods for understanding and optimising catalyst technologies