Vladimir I. Kovalchuk

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.

Hydrodechlorination of 1,2-dichloroethane catalyzed by Pt-Cu/C: effect of catalyst pretreatment

Abstract The catalytic performance of Pt–Cu/C with Pt/Cu atomic ratios of 1:1 and 1:3 in the reaction of 1,2-dichloroethane dechlorination at 200°C and atmospheric pressure was investigated to understand the molecular phenomena governing the change in ethylene selectivity with time on stream (TOS). When the Pt1–Cu3/C catalyst is prereduced in H 2 at 220°C, ethane is the major product at early TOS, while ethylene is the major product at longer TOS. Pretreatment in flowing He at 220°C eliminates the transient behavior and significantly increases steady state selectivity toward ethylene for both Pt–Cu catalysts. The transient behavior is also eliminated after reduction at 220°C followed by treatment with HCl at the same temperature. Quite different behavior is observed with a Pt/C catalyst in that ethane is the major product regardless of the type of pretreatment. The results are interpreted via a molecular scheme including the formation of mixed PtCuCl x species during the non-reductive pretreatment. These PtCuCl x particles are converted into the corresponding alloy during subsequent reduction by H 2 or reaction mixture. The enrichment of the catalysts’ surface with Cu results from the pretreatment with HCl.

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

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.