Active Sites for Propane Oxidation: Some Generic Considerations

Based on experimental observations about structure and dynamics of the reactive surface of the M1 phase some considerations are made about the nature and size of active sites. In analyzing the stoichiometry of the reactions following activation of propane it occurs that for dehydrogenation small sites are desirable being just sufficient to re-activate oxygen without kinetic hindrance. For deeper oxidation to acrylic acid (AA) the sites should be larger to accommodate all redox equivalents and oxygen species required for one transformation. A qualitative model for size and composition of the active site is made. It is likely that the active site consists on a VxOy species of strictly 2-D nature. This follows the structural suggestion for the active site on the a–b-plane of the M1 structure. The role of Te in moderating the active site is discussed. The suggestions are discussed in comparing requirements for oxidative dehydrogenation of propane (ODP) with those for AA synthesis

Higher alcohol synthesis over Rh catalysts: conditioning of Rh/N-CNTs by Co and Mn entrapped in the support

Rh nanoparticles supported on commercial non-purified N-doped CNTs (NCNTs) containing residual CNT growth catalyst have been studied in hydrogenation of CO to higher alcohols. It has been found that Co and Mn residues in NCNTs are not inert, but change the catalyst under reaction conditions and efficiently promote the catalyst resulting in both increasing activity and selectivity to C2+ alcohols with time on stream.BMBF, 03X0204C, CarboKat - Einsatz von Carbon Nanotubes als Katalysator und Katalysatorträge

The impact of steam on the electronic structure of the selective propane oxidation catalyst MoVTeNb oxide (orthorhombic M1 phase)

The selective propane oxidation catalyst MoVTeNb oxide M1 was investigated by microwave conductivity, synchrotron X-ray photoelectron, soft X-ray absorption and resonant photoelectron spectroscopy under reaction conditions to identify the influence of steam on the electronic bulk and surface properties. Steam significantly increases both the conversion of propane and the selectivity to the target product acrylic acid. The increased catalytic performance comes along with a decreased conductivity, a modification of the surface chemical and electronic structure with an enrichment of covalently bonded V5+ species to the extent of Mo6+, a decreased work function and hence polarity of the surface and a modified valence band structure. The higher degree of covalency in metal oxide bonds affects the mobility of the free charge carriers, and hence explains the decrease of the conductivity with steam. Furthermore we could prove that a subsurface space charge region depleted in electrons and thus an upward bending of the electronic band structure are induced by the reaction mixture, which is however not dependent on the steam content

Information management functions in national economies. An analysis of the information sector in Austria

The information sector has been an area of research for more than 40 years and researchers still try to find different approaches to this topic. The project presented in this contribution approaches the information sector from an information science perspective. Information management functions (IMF) – i.e. all functions and processes related to information selection, acquisition, description, preservation, product creation and services – will serve as a starting point for analysis. The fundamental assumption is that these functions do not occur only in libraries but also in other contexts. Accordingly, economic costs associated with IMF, represented by labor and capital necessary for their performance can be measured in a wide range of contexts, including libraries but also industries of various kinds. One of the main goals of the project is to investigate the extent of IMF in knowledge industries of the Austrian national economy. Since the project uses a methodology developed by Robert M. Hayes, who has already conducted similar research in the U.S., it will be possible to position the project outcome in an international context

Preparation of Solid Solution and Layered IrO _x-Ni(OH)₂Oxygen Evolution Catalysts:Toward Optimizing Iridium Efficiency for OER

Minimizing iridium loading in oxygen evolution reaction (OER) catalysts, without impairing electrocatalytic activity and stability is crucial to reduce the cost of water electrolysis. In this work, two Ir0.5Ni0.5Ox mixed oxide catalysts with layered and solid solution morphologies were prepared by modifying a facile hydrothermal methodology. The catalytic OER activity and stability of the Ir-Ni catalyst with a homogeneous distribution (IrNi-HD) was seriously compromised compared to pure IrOx due to the high concentration of surface nickel prone to corrosion under reaction conditions. However, the design of layered IrOx-Ni(OH)x (IrNi-LY) with Ir at the exposed surface allowed a 50% reduction in the molar concentration of the precious metal on the electrode compared to IrOx without impairing the catalytic activity or stability. As a result, IrNi-LY outperformed IrOx in activity when normalized to the Ir mass. </p

High performance (VOx)(n)-( TiOx)(m)/SBA-15 catalysts for the oxidative dehydrogenation of propane

Grafted VxOy catalysts for oxidative dehydrogenation of propane (ODP) have been studied due to their potential high performance and as model catalysts in the past. We report on a positive synergetic effect capable of considerably enhancing the propene productivities above reported performances. The most productive catalysts were found at metal loadings (V + Ti) close to the monolayer coverage. The 4V/13Ti/SBA-15 catalyst presented a considerably high productivity (6–9 kgpropene kgcat−1 h−1). Moreover, with this catalyst, propene productivity only slightly decreased as a function of propane conversion, indicating that propene combustion toward COx occurs more slowly in comparison to other catalysts exhibiting high propene productivities. A detailed kinetic analysis of the 4V/13Ti/SBA-15 catalyst revealed that high vanadia and titania dispersions are required for high propene productivity.DFG, SFB 546, Struktur, Dynamik und Reaktivität von Übergangsmetalloxid-Aggregate

The mechanism of interfacial CO2 activation on Al doped Cu/ZnO

We report on a combined quantitative charge carrier and catalytic activity analysis of Cu/ZnO(:Al) model catalysts. The promoting effect of Al3+ on the ZnO support for CO2 activation via the reverse water–gas-shift reaction has been investigated. The contact-free and operando microwave Hall Effect technique is applied to measure charge carriers in Cu/ZnO(:Al) based model catalysts under reverse water–gas shift reaction conditions. This method allows us to monitor the electrical conductivity, charge carrier mobility, and absolute number of charge carriers. An increase in charge carrier concentration with increasing Al3+ content and its direct correlation with the catalytic activity for CO formation is found. We conclude that the increased availability of charge carriers plays a key role in CO2 activation and CO formation, which finds additional support in a concurrent decrease of the apparent activation energy and increase in the reaction order of CO2. In combination with comprehensive DFT calculations, the impact of the interfacial charge transfer, coupled to oxygen defect sites in ZnO and CO2 adsorption properties, is elucidated and highlighted. In conclusion, the results from this operando investigation combined with DFT calculations demonstrate the importance of charge transfer processes as decisive descriptors for understanding and explaining catalytic properties

Transition-Metal-Doping of CaO as Catalyst for the OCM Reaction, a Reality Check

In this study, first-row transition metal-doped calcium oxide materials (Mn, Ni, Cr, Co., and Zn) were synthesized, characterized, and tested for the OCM reaction. Doped carbonate precursors were prepared by a co-precipitation method. The synthesis parameters were optimized to yield materials with a pure calcite phase, which was verified by XRD. EPR measurements on the doped CaO materials indicate a successful substitution of Ca2+ with transition metal ions in the CaO lattice. The materials were tested for their performance in the OCM reaction, where a beneficial effect towards selectivity and activity effect could be observed for Mn, Ni, and Zn-doped samples, where the selectivity of Co- and Cr-doped CaO was strongly reduced. The optimum doping concentration could be identified in the range of 0.04-0.10 atom%, showing the strongest decrease in the apparent activation energy, as well as the maximum increase in selectivity