Catalyst Screening Studies Research Articles

Direct catalytic hydrodechlorination of toxic organics in wastewater

AbstractThe in‐situ catalytic hydrodechlorination of chlorinated hydrocarbons in waste‐water‐generating HCl and a hydrocarbon‐free chlorine is demonstrated as a viable wastewater remediation technique. Catalyst screening studies with a shaker‐type hydrogenation reactor have shown that the commercial Pd/C catalyst is highly effective in hydrochlorinating various chlorinated hydrocarbons in synthetic wastewater at room temperature and near atmospheric pressure. 1, 1, 2‐trichloroethane hydrodechlorination experiments in an autoclave reactor shows that initial rates are well correlated with first‐order dependence of the reactant hydrocarbon adsorbed on carbon. Initial rates are also independent of hydrogen pressure, and adsorption on the carbon support is Langmuir type. Activation energies calculated at different catalyst loadings varied from 29 to 38 MJ/mol.1,1,2‐trichloroethane hydrodechlorination activity is much lower for Pd/Al2O3 than Pd/C because the reactant hydrocarbon does not adsorb on alumina. When the carbon support does not readily adsorb the reactant hydrocarbon, the hydrodechlorination rates dropped significantly. These results confirm the role of the carbon support in providing the major path to reaction and thereby significantly increasing reaction rates compared to direct adsorption from solution onto the palladium.

Behaviour of calcium as a steam gasification catalyst

The catalytic coal gasification process for synthetic natural gas, which is being developed by the Exxon Research and Engineering Company, uses a potassium salt to catalyse the steam gasification of coal while it simultaneously catalyses methanation reactions in the same vessel. The catalyst is recovered from the gasifier residue and recycled, but some is lost. These relatively small, but inevitable, losses from the recovery process provide an incentive to find a lower-cost catalyst. Exploratory catalyst screening studies have shown that calcium compounds provide good catalytic activity under certain conditions. Essentially, the calcium must be atomically dispersed throughout the char to obtain good activity. Potassium compounds tend to be mobile and distribute themselves during gasification even when applied to the coal in a dry, mechanical mixture. Calcium, in contrast, is poorly active unless it is very well dispersed by chemical reaction with the organic matter. For example, it is an active catalyst when it is transferred to acid sites in coal by ion exchange. Sufficient sites occur naturally in lower-rank coals, and some of these coals have undergone ion-exchange with calcium naturally. Such coals show high reactivities during gasification for this reason. Higher-rank coals have fewer ion-exchangeable acid sites, but these can be created by a mild air-oxidation. This paper describes the experimental techniques used, to develop low-cost, calcium catalysts for the steam gasification of coal and presents the results obtained in this work.

Analysis of the reaction network for the vanadia-catalyzed oxidation of ortho-xylene

The oxidation of o-xylene over a vanadium oxide catalyst was studied using a recirculation reactor over the following ranges of conditions: 310 to 330 °C oxygen feed concentration (0.25 to 0.75) × 10 −2 g moles/liter, o-xylene feed concentration (0.5 to 3.0) × 10 −4 g moles/liter, conversion 8 to 75%. The combination of a recirculation reactor and a quantitative rate modeling approach was shown to provide an effective method for the characterization of reaction networks which should be useful for catalyst screening and optimization studies. The extended form of the steady-state adsorption model was shown to provide a satisfactory description of the vanadia-catalyzed oxidation of o-xylene at high conversions with significant secondary reactions.

Catalyst screening using a stone DTA apparatus: I. Oxidation of toluene over cobalt-metal-oxide catalysts

A method is presented for determining the activity of catalysts based on measurement of the temperature rise in a sample of the catalyst weighing a fraction of a gram. A Stone DTA apparatus was used in the experimental work. The reaction studied was the oxidation of toluene over 10 cobalt-metal-oxide catalysts. The activity of each catalyst was found to be directly proportional to the steady-state temperature rise in the sample, a fact which simplifies considerably the determination of activity. Activation energies were obtained for 9 of the 10 catalysts in the temperature range where the activity was stable. The determination of activity can be made without carrying out a product analysis, a fact which is useful for certain types of catalyst screening studies.