Julie L. d'Itri

Dechlorination of 1,2‐dichloroethane catalyzed by Pt–Cu/C: unraveling the role of each metal

The effect of Pt–Cu/C catalyst composition on the activity and selectivity in the reaction of 1,2‐dichloroethane dechlorination in a H2‐containing atmosphere has been investigated. For monometallic Pt catalysts and those with Cu/Pt atomic ratio ⩽1, the reaction products are almost entirely ethane and monochloroethane. However, increasing the Cu/Pt ratio increases the selectivity towards ethylene. Approximately 90% selectivity towards ethylene is obtained for catalysts with Cu/Pt ratio ⩾9. Monometallic Cu/C produce only ethylene, but the activity is two orders of magnitude lower than that of other catalysts studied. With time on stream during the initial 2–30 h there is a continuous increase in selectivity towards ethylene at the expense of ethane. This behavior was rationalized in terms of equilibration of bimetallic particle surface composition exposed to the reaction mixture.

Hydrodechlorination of dichlorodifluoromethane on carbon-supported Group VIII noble metal catalysts

Activated carbon‐supported Group VIII noble metals formed CF2Cl2 oligomerization products under hydrodechlorination conditions. All the catalysts underwent deactivation during first 15–20 h on stream at 250°C independent of the H2 partial pressure, with steady‐state activity following the order: Pt > Pd ≫ Ir > Ru ≈Os ≈ Rh. The Pd/C catalyst exhibited high selectivity toward C2–C3 hydrocarbons (∼75% at CF2Cl2/H2 = 1). For the other catalysts except Pt, CF2=CF2 and CH2=CF2 were the main C2+ products.

Transient kinetics investigations of reaction intermediates involved in CF2Cl2 hydrodechlorination

Abstract The reaction intermediates formed during hydrodechlorination of CF2Cl2 catalyzed by Pd supported on AlF3 have been investigated using steady state and transient kinetics experiments. The formation of the coupling product C2H6 and its dependence on H2 partial pressure have been used to investigate the pathways by which possible surface carbene species react. Reactions of surface species formed during the CF2Cl2 hydrodechlorination with scavenging agent C2H4 yielded addition products typical of metal-carbenes. Information from these experiments suggests that for carbene and fluorocarbene species formed on the surface of a Pd/AlF3 catalyst the rates of hydrogenation vs. coupling reactions are different.

Olefins from chlorocarbons: Reactions of 1,2-dichloroethane catalyzed by Pt-Cu

The effect of (Pt+Cu)/SiO2 catalyst composition on the activity and selectivity in the reaction of 1,2-dichloroethane dechlorination in a H2 containing atmosphere has been investigated. For monometallic Pt catalysts and those with Pt/Cu atomic ratio ≥1, the reaction products are primarily ethane and monochloroethane. However, decreasing the Pt/Cu ratio increases the selectivity towards ethylene. A selectivity toward ethylene of nearly 90% is obtained for catalysts with Pt/Cu ratio

Hydrodechlorination of 1,1-Dichlorotetrafluoroethane on Supported Palladium Catalysts. A Static-Circulation Reactor Study

Supported palladium catalysts were studied in CF3CFCl2 hydrodechlorination at 100°C using a static-circulation system. In order to minimize catalysts deactivation a large excess of hydrogen was employed (H2/CF3CFCl2 ratio 54/1). In spite of this precaution significant inhibition of the process occurred, associated with blocking palladium surface by hydrogen chloride species. Differences in the catalytic behavior of alumina-supported and unsupported palladium are discussed. A mild dependence between the catalytic activity and Pd dispersion was found. The Pd/Al2O3 catalyst characterized by low metal dispersion was more active than highly dispersed catalysts, showing the overall activity and selectivity to CF3CFH2 comparable with those observed by other authors for palladium single crystals. It is speculated that the most active sites for hydrodechlorination are plane atoms, whereas low coordination sites (on edges and corners of metal crystallites) are less suitable.

On the role of free radicals NO2 and O2 in the selective catalytic reduction (SCR) of NOx with CH4 over CoZSM-5 and HZSM-5 zeolites

The reactions of CH 4 over CoZSM-5 and HZSM-5 zeolites with the mixtures of NO+O 2 and NO 2 +O 2 and with three oxidizing components separately were studied. Differential reaction rates were determined. Comparison of the “light-off” temperatures as well as the activation energies of these reactions led to the conclusion that the SCR of NO x into N 2 and, consequently, CH 4 oxidation into CO x are initiated by the reaction of CH 4 with NO 2 . At low temperatures (300–400°C) O 2 does not compete with NO x for CH 4 , and its role is limited to the oxidation of NO into NO 2 . However, at higher temperatures a strong competition between NO x and O 2 for CH 4 results in a decrease in the selectivity of the SCR process. It is shown that this competition is stronger with CoZSM-5 catalyst than with HZSM-5, and this explains the higher selectivity observed with the latter catalyst. Based on these observations the formation of the CH 3 • free radical is postulated and possible pathways of the SCR of NO x into N 2 are discussed.

Interaction of CH4 with NO and NO2 over Pt-ZSM-5 in the absence of O2

The reduction of NO and NO2 with CH4 to form N2 catalyzed by Pt-ZSM-5 has been investigated. For both reactions the dependence of conversion on temperature is similar to that of CH4 combustion catalyzed by Pt. The conversion increases slowly before a sharp increase at the ignition temperature (∼300 °C for NO + CH4 and ∼475 ○C for NO2 + CH4). Based on results in which the mole ratios and partial pressures of NOx and CH4 were varied, it is suggested that the oxygen surface coverage determines the catalytic activity of Pt-ZSM-5. It is postulated that NO2 rapidly dissociates on Pt, covering the surface with oxygen adatoms. The interaction of oxygen adatoms with the Pt surface is sufficiently strong that CH4 cannot compete for adsorption sites. Thus, the catalytic activity is low at temperatures less than 475 °C, where oxygen desorption from the surface is unfavorable. However, NO has a lower sticking probability, and the slower rate of N–O bond dissociation results in a lower steady state oxygen coverage and, in turn, a higher activity in the NO + CH4 reaction. Experiments in which the CH4 + NO2 reaction temperature was cycled from 350 to 500 °C and back to 350 °C provides evidence that overstoichiometric CH4 dissociation on the Pt surface can occur, and the surface carbon that is formed enhances NO2 reduction to N2.