Effect of External Acidity of Mordenite-Supported Catalysts on the 2,2-Dimethylbutane Content in Hydroisomerization Products of n-Hexane

We have used potentiometric titration with tetrabutylammonium hydroxide to determine the acid center content on the outer surface of dealuminated natural and synthetic mordenites. We have established a symbatic relationship between the 2,2-dimethylbutane content in the hydroisomerization products of n-hexane on dealuminated palladium-containing mordenites and the number of their external acid centers. We have studied the possibility of partial deactivation of such centers during ion-exchange deposition of palladium on the catalysts, using a tetraammine palladium solution.     

High‐temperature catalysts for the production of α‐olefins based on iron(II) and iron(III) tridentate bis(imino)pyridine complexes modified by nitrilo group

Series of Fe(II) and Fe(III) tridentate bis(imino)pyridine complexes without nitrilo groups 2–6 and with nitrilo groups 7–13 were synthesized. According to X‐ray analysis, the introduction of nitrilo groups in para‐ and ortho‐positions tends to result in shorter axial Fe? N bonds. Both types of complexes, 2–6 and 9–13 , afforded very productive catalysts for the production of α‐olefins with higher K values and better linearity of Schultz–Flory distribution α‐olefins than the parent methyl substituted Fe(II) complex 1 . Noticeably, the complexes functionalized with a para‐nitrilo group 9–13 tend to make α‐olefins with higher K values of the Schultz–Flory distribution, more ideal distributions, and less of the heavier insoluble fractions of α‐olefins than corresponding nonsymmetrically substituted complexes without para‐nitrilo groups 2–6 . Statistically significant correlations were obtained between % solids of total α‐olefins and the blocked solid angle fraction in the +z hemisphere ( = 51.3%, p = 0.012) and between catalyst productivity and total blocked solid angle fraction ( = 43.5%, p = 0.023). The modest values of show that, while steric effects are significant, they are not the sole factor determining catalyst performance. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 585–611, 2008     

Increased n-Hexane Hydroconversion upon Poisoning of External Acid Sites of the Catalyst PdHZSM-5

Substitution of protons on external acid sites of the bifunctional catalyst PdHZSM-5 by tetrabutylammonium cations is accompanied by a substantial increase in n-hexane hydroconversion at T = 498 to 548 K. Based on analysis of the distribution of the catalytic reaction products, we suggest an explanation for this effect.     

Features of the Distribution of Aluminum in Mordeniteclinoptilolite Catalysts for the Hydroisomerization of n-Hexane

The content of tetrahedral, extraskeletal, and ion-exchanged aluminum in zeolites consisting of natural and decationized forms of mordeniteclinoptilolite rocks after acidic activation were studied. The results were compared with acidity and catalytic activity properties of modified samples of rocks and synthetic mordenite in the hydroisomerization of n-hexane.     

Effect of External Acid Site Content in PdHZSM-5 Catalyst on Its Activity and Selectivity in Hydroisomerization of n-Hexane

We have studied the relationship between the external acidity and the catalytic properties of zeolite PdHZSM-5 (Si/Al = 21) in hydroconversion of n-hexane. We have established that decreasing the external H-site content by 5-9 mol/g at 548 K leads to an increase in conversion by 18-19% and a decrease in the selectivity of the catalyst with respect to the isomerization products by 47-70%. We suggest an explanation for this substantial effect of the external H-sites on the activity and selectivity of the catalyst.     

Connections between neutron monitor count rate and solar modulation strength

We suggest a new approach to the normalisation of neutron monitor response to galactic cosmic rays. The reference normalisation count rate is the neutron monitor response to the model unmodulated flux of galactic cosmic rays. A comparison of the actually recorded neutron monitor count rate with the calculated normalisation count rate can provide one with an observationally obtained true-of-date integral measure of the current level of solar modulation of galactic cosmic rays. The Slovak VEGA grant agency is acknowledged for the grant 2-5137.     

High-performance liquid chromatographic analysis of norepinephrine and alpha-methylnorepinephrine in microdissected noradrenergic cell groups of the rabbit brain

A high-performance liquid chromatographic method with electrochemical detection has been developed to measure norepinephrine (NE) and alpha-methylnorepinephrine (alpha-MeNE) in microdissected noradrenergic cell groups of the rabbit brain stem. The method is shown to be specific, accurate and precise and has a sensitivity of 0.5 pmol per sample. The method has been applied to the measurement of NE and alpha-MeNE levels in the A1, A2, A5, A6 and A7 noradrenergic cell groups after administration of the antihypertensive drug alpha-methyldopa (alpha-MD), so that the sites of action of alpha-MD within the central nervous system may be localised.     

Molecular species in liquid carboxylic acids

Measurements of dielectric permittivity and electric conductance are presented for mixtures of carboxylic acids — formic, trifluoroacetic, acetic and propionic — and non-polar liquids. For the dielectric and associative behavior of carboxylic acids a knowledge of the cis—trans conformational equilibria of the monomeric acid molecules seems to be essential. Therefore the cis and trans conformations of these molecules have been calculated by the CNDO/2 and PCILO methods. Appreciable rotational barriers for their interconversion have been obtained.