Coulomb plasmas in outer envelopes of neutron stars

Outer envelopes of neutron stars consist mostly of fully ionized, strongly coupled Coulomb plasmas characterized by typical densities about 10^4-10^{11} g/cc and temperatures about 10^4-10^9 K. Many neutron stars possess magnetic fields about 10^{11}-10^{14} G. Here we briefly review recent theoretical advances which allow one to calculate thermodynamic functions and electron transport coefficients for such plasmas with an accuracy required for theoretical interpretation of observations.Comment: 4 pages, 2 figures, latex2e using cpp2e.cls (included). Proc. PNP-10 Workshop, Greifswald, Germany, 4-9 Sept. 2000. Accepted for publication in Contrib. Plasma Phys. 41 (2001) no. 2-

Catalytic cracking of naphtha: The effect of Fe and Cr impregnated ZSM-5 on olefin selectivity

This study focuses on the modification of ZSM-5 in order to enhance the catalytic cracking of refinery naphtha to produce light olefins. ZSM-5 was metal modified using different loadings (0.5–5 wt%) of Fe and Cr via the impregnation method. The metal modified ZSM-5 samples are compared and the effect of metal loading on the physicochemical properties and catalytic performance is investigated. Fe and Cr modification had an effect on both the physicochemical properties of the catalysts as well as catalytic activity and selectivity. Metal loading caused a decrease in the specific surface area which decreased further with increased metal loading. Fe had a greater effect on the total acidity in particular strong acid sites when compared to Cr. The optimum Fe loading was established which promoted selectivity to olefins, in particular propylene. Fe also had a dominant effect on the P/E ratio of which a remarkable ratio of five was achieved as well as enhanced the stability of the catalyst. Cr was found to be a good promoter for selectivity to BTX products with a two-fold increase observed when compared to Fe-modified catalysts

Surface characteristics and activity of chromia/alumina catalysts prepared by atomic layer epitaxy

A series of CrOx/¿-Al2O3catalysts was prepared by atomic layer epitaxy (ALE) from the vapor phase, with use of sequential saturating reactions of Cr(acac)3vapor and air. The loading was varied from 1.3 to 8.8 wt% of Cr. Lower loadings were achieved by partially blocking the alumina surface with acetylacetone or dipivaloylmethane before introducing Cr(acac)3. The catalytically active material was found to be evenly distributed through the catalyst particles. Low energy ion scattering measurements showed that, up to 7.4 wt% of Cr, the Cr species was dispersed in a monolayer. XPS and UV-vis spectrophotometry revealed that, even at the low loadings, both Cr3+and Cr6+species were present. This was attributed to a stabilization of Cr3+on the alumina support during the ALE process. Loading beyond monolayer coverage was not reflected in the dehydrogenation ofi-butane toi-butene: the activity continued to increase