In-Situ Investigation of Gas Phase Radical Chemistry in the Catalytic Partial Oxidation of Methane on Pt

The catalytic partial oxidation of methane on platinum was studied in situ under atmospheric pressure and temperatures between 1000 and 1300 °C. By combining radical measurements using a molecular beam mass spectrometer and threshold ionization with GC, GC-MS and temperature profile measurements it was demonstrated that a homogeneous reaction pathway is opened at temperatures above 1100 °C, in parallel to hetero-geneous reactions which start already at 600 °C. Before ignition of gas phase chemistry, only CO, H2, CO2 and H2O are formed at the catalyst surface. Upon ignition of gas chemistry, CH3⋅ radicals, C2 coupling products and traces of C3 and C4 hydrocarbons are observed. Because the formation of CH3⋅ radicals correlates with the formation of C2 products it can be concluded that C2 products are formed by coupling of methyl radicals in the gas phase followed by dehydrogenation reactions. This formation pathway was predicted by numerical simulations and this work presents an experimental confirmation under high temperature atmospheric pressure conditions

Climate variability and vulnerability to poverty in Nicaragua

This study considers the effect of climate variability on vulnerability to poverty in Nicaragua. It discusses how such vulnerability could be measured and which heterogeneous effects can be expected. A multilevel empirical framework is applied, linking per capita consumption to household, regional and climate characteristics. Results confirm a negative effect of climate variability on consumption per capita of Nicaraguan households. This suggests the need for stronger public policies and more resources in order to adapt to the effect of climate change. Furthermore, the poverty reduction attainments reached since the 1990s could be jeopardized if this vulnerability persists

Reactor for In-Situ Measurements of Spatially Resolved Kinetic Data in Heterogeneous Catalysis

The present work describes a reactor that allows in-situ measurements of spatially resolved kinetic data in heterogenous catalysis. The reactor design allows measurements up to temperatures of 1300 ±C and 45 bar pressure, i.e. conditions of industrial relevance. The reactor involves reactants flowing through a solid catalyst bed containing a sampling capillary with a side sampling orifice through which a small fraction of the reacting fluid (gas or liquid) is transferred into an analytical device (e.g. MS, GC, HPLC) for quantitative analysis. The sampling capillary can be moved with ¹m resolution in or against flow direction to measure species profiles through the catalyst bed. Rotation of the sampling capillary allows averaging over several scan lines. The position of the sampling orifice is such that the capillary channel through the catalyst bed remains always occupied by the capillary preventing flow disturbance and fluid bypassing. The second function of the sampling capillary is to provide a well which can accommodate temperature probes such as a thermocouple or a pyrometer fiber. If a thermocouple is inserted in the sampling capillary and aligned with the sampling orifice fluid temperature profiles can be measured. A pyrometer fiber can be used to measure the temperature profile of the solid catalyst bed. Spatial profile measurements are demonstrated for methane oxidation on Pt and methane oxidative coupling on Li/MgO, both catalysts supported on reticulated a-Al2O3 foam supports

Heterogeneous–Homogeneous Catalytic Partial Oxidations Investigated by Molecular Beam Mass Spectrometry

Heterogeneous catalytic reactions are often insufficiently described by surface reaction steps only; gas phase contributions are neglected. Surface and gas phase reaction steps can take place simultaneously and are coupled by exchange of energy and reaction intermediates. Catalytic partial oxidations are suspected to proceed via combined heterogeneous–homogeneous mechanisms because of high reaction temperatures and the diradical oxygen as reactant. Gas phase radicals are thought to be key intermediates, but there is little understanding of mechanistic details [1]. To study the mechanism of such reactions we have developed a Molecular Beam Mass Spectrometer (MBMS) equipped with a high temperature catalytic wall reactor