Effect of thermal treatments and palladium loading an hydrogen sorption characteristics of single-walled carbon nanotubes

WOS: 000255322400008The effects of thermal treatments and palladium loading on sorption characteristics of single-walled carbon nanotube (SWCNT) samples were investigated. The thermal treatment experiments were carried out in a temperature range of 300-800 degrees C. The sorption characteristics of nitrogen and hydrogen on the original, heat treated and the palladium loaded samples were investigated. Analyzing the nitrogen adsorption isotherms on these samples at 77.4 K, the highest specific surface area of 2230 m(2)/g was obtained at 575 degrees C, while the original samples had a specific surface area of 230 m(2)/g. The highest surface area samples obtained at 575 degrees C were loaded by 3.3, 6.3 and 10.1 wt% palladium and hydrogen adsorption isotherms on these samples were obtained at 77.4 K. The hydrogen sorption capacities of the original and the 10.1 wt% palladium loaded samples were found to be 0.76 and 1.66 wt%, respectively. it was shown that by controlling the temperature of heat treatment, the specific surface area of the samples could be increased and the spillover effect of palladium could enhance the hydrogen sorption. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved

A GRAIN MODEL FOR CATALYST TORTUOSITY

A simple model was proposed for the prediction of tortuosity factor of porous solids with mono or bidispersed pore size distributions. Model predictions were presented in graphical form for quick estimation of tortuosity. The experimental tortuosity factors reported in the literature for porous solids of different pore structures and the corresponding predicted values showed good agreement

Selective oxidation of H2S to elemental sulfur over Ce-V mixed oxide and CeO2 catalysts prepared by the complexation technique

Selective oxidation of H2S to elemental sulfur was investigated in a fixed bed reactor using Ce-V mixed oxides and cerium oxide (CeO2) catalytic materials prepared by the complexation technique. The Ce-V mixed oxide with a V/Ce atomic ratio of one and with the CeVO4 crystal structure gave very high sulfur selectivity values (close to one) at almost complete conversion of H2S, for O-2/H2S mote ratios close to 0.5. Best operation temperature was found as 250 degrees C with this catalyst. CeO2 gave lower selectivities, causing the formation of some SO2, even at substoichiometric O-2/H2S feed ratios. It also showed a fast deactivation due to the partial sulfidation of the catalyst surface during the reaction. XPS analysis of the fresh and the used catalysts containing different V/Ce ratios strongly indicated that the selective oxidation of H2S to elemental sulfur over the Ce-V mixed oxides involved a redox cycle of cerium, rather than a redox cycle of vanadium

Ethylene and diethyl-ether production by dehydration reaction of ethanol over different heteropolyacid catalysts

Dehydration reaction of ethanol was investigated in a temperature range of 140-250 degrees C with three different heteropolyacid catalysts, namely tungstophosphoricacid (TPA), silicotungsticacid (STA) and molybdophosphoricacid (NIPA). Very high ethylene yields over 0.75 obtained at 250 degrees C with TPA was highly promising. At temperatures lower than 180 degrees C the main product was diethyl-ether. Presence of water vapor was shown to cause some decrease of catalyst activity. Results showing that product selectivities did not change much with the space time in the reactor indicated two parallel routes for the production of ethylene and DEE. Among the three HPA catalysts, the activity trend was obtained as STA > TPA > MPA

Single pellet reactor for the dynamic analysis of gas-solid reactions ''reaction of SO2 with activated soda''

Single-pellet moment technique which was initially proposed for the measurement of effective diffusivities in porous catalysts and adsorption rate and equilibrium constants was modified for the analysis of gas-solid reactions. In this technique dynamic version of the Wicke-Kallenbach single-pellet cell was used A pulse of a tracer gas was introduced into stream flowing over one end face of the pellet. In the modified pulse-double response procedure, experimental moments of the response peaks of both reactant and product Bases measured in both top and bottom outlet streams of the single-pellet reader wee used for the evaluation of intrapellet rate and equilibrium parameters. Application of the technique to the reaction of SO2 with activated soda indicated that the value of while modulus decreased from 6.74 to 0.33 by the increase of fractional conversion of Na2CO3 to Na2SO3 from zero to 0.63. In this range of conversion values a significant variation in pore structure and also a decrease of effective diffusivity of SO2 from 0.045 cm(2)/s to 0.025 cm(2)/s was observed. A cell model which considered the changes in pore length and radius with reaction extent and variations in product lays diffusion resistance was shown to be successfully used in the analysis of experimental observations. A review of single-pellet dynamic reader studies for catalytic and noncatalytic gas-solid reactions was also given