Magdalena Bonarowska

Hydrodechlorination of CCl2F2 (CFC-12) over silica-supported palladium–gold catalysts

Abstract Two series of well-mixed Pd–Au/SiO 2 catalysts prepared by direct redox method were tested in the reaction of CCl 2 F 2 (CFC-12) hydrodechlorination. A moderate selectivity for CH 2 F 2 exhibited by monometallic Pd/SiO 2 (∼40%) is significantly increased, up to ∼95%, with Au addition. Proper Pd–Au alloying is essential to obtain such a selectivity enhancement. Poorly mixed Pd–Au/SiO 2 catalysts show the catalytic behaviour not very much different from that of Pd/SiO 2 , producing a lot of methane. Changes in the apparent activation energy are also associated with the degree of Pd–Au alloying. After reaction, the Pd/SiO 2 and Pd–Au/SiO 2 catalysts contain dissolved carbon. Hydrogen treatment of carbonized Pd–Au/SiO 2 catalysts removes this carbon. XRD study of the regenerated samples shows no change in the structure and composition of Pd–Au phase, compared to freshly prereduced bimetallic catalysts.

Hydrodechlorination of CCl2F2 (CFC-12) over Pd-Au/C catalysts

Abstract A series of carbon-supported palladium-gold (Pd-Au) catalysts prepared by direct redox reaction method and characterized by various techniques were investigated in the reaction of dichlorodifluoromethane (CFC-12) with dihydrogen. The selectivity towards difluoromethane (desired reaction product) was increased upon introducing gold to palladium, from ∼72 to ∼86%, at 180°C. Such a selectivity enhancement was not observed in our previous studies when Pd-Au/C catalysts prepared by incipient wetness impregnation showed inadequate extent of Pd-Au alloying. Conditions of preparation of Pd-Au/C catalysts by the direct redox reaction method are found to affect the amount of deposited metals and the degree of Pd-Au mixing. The latter factor is essential in determining hydrodehalogenation behavior of the catalysts.

Supported ruthenium catalysts in hydrodechlorination of CCl2F2 (CFC-12)

Active carbon-and MgF2-supported ruthenium catalysts characterized by a comparable metal dispersion were investigated in CCl2F2 hydrodechlorination. Ruthenium, especially when supported on carbon, exhibits a considerable selectivity to CHClF2. This propensity and a noticeable activity towards C2-products differentiate ruthenium from palladium catalysts.

Multi-Wall Carbon Nanotubes as a Support for Platinum Catalysts for the Hydrodechlorination of Carbon Tetrachloride and Dichlorodifluoromethane

Multi-wall carbon nanotubes (MWCNTs) were used as a support for the deposition of highly dispersed platinum. After characterization by several physical techniques, the catalyst was studied in reactions for: hydrodechlorination of carbon tetrachloride and the hydrodechlorination of dichlorodifluoromethane. For the first reaction Pt/MWCNTs were very effective catalysts in terms of both the overall activity and the selectivity to CHCl3; both quantities appeared high and stable. For CCl2F2 hydrodechlorination the catalyst was rather moderate, although very stable, activity and product selectivities were established at a constant level in a relatively short time-on-stream. The MWCNTs-supported Pt particles do not undergo great changes during the reactions, i.e. neither substantial metal sintering occurred nor extensive surface carbonization/chloriding took place.

Hydrodechlorination of tetrachloromethane over silica-supported palladium-gold alloys

Abstract Compared with the monometallic palladium, bimetallic Pd-Au/SiO2 catalysts show much higher activity and better stability in the reaction of hydrodechlorination of tetrachloromethane, also providing higher selectivity to longer than methane hydrocarbon products. Reasonably mixed Pd-Au particles show better catalytic performance during ~60 h operation, whereas the monometallic palladium and very rich in palladium catalysts suffer rapid deactivation. Smaller amounts of carbon- and chlorine-containing deposits found after reaction on Pd-Au catalysts correspond to their superior catalytic behavior.

Tetrachloromethane as an Effective Agent to Transform Nanoparticles of Palladium and Gold in Supported Catalysts

The use of CCl4 as an effective medium to generate important phase changes in supported Pd and Au catalysts is presented. The dissolution of carbon that originates from CCl4 to form a PdC0.13 solid solution is more complete for the lowest temperature of the CCl4+H2 reaction (30–50 °C). At higher temperatures, the bulk carbiding competes with the hydrogenative removal of bare carbon species to contribute to an enhanced CH4 and C2H6 formation.

Hydrodechlorination of Tetrachloromethane Over Supported Platinum Catalysts. Effects of Hydrogen Partial Pressure and Catalyst’s Screening Protocol on the Catalytic Performance

Two series of silica- and alumina-supported platinum catalysts were investigated in the hydrodechlorination (HdCl) of tetrachloromethane. During an initial period of reaction carried out at a lower H2/CCl4 ratio the catalysts, especially those characterized by high metal dispersion, deactivated with time-on-stream. Two catalyst screening protocols were used. The first one concerned a gradually increased hydrogen partial pressure, whereas during the second one the H2 pressure was decreased. Although, in general, the hydrogen-rich reaction conditions resulted in improved catalyst performance (higher overall activity and selectivity to CHCl3), the second protocol led to even better results. Reasons for such a behaviour are suggested. Because of very high activity of a few tested samples, changes in CCl4 conversion with the hydrogen partial pressure do not reflect real reaction orders in hydrogen. The same reason may lead to falsification of apparent activation energies. In certain cases the relation between conversion and hydrogen pressure showed a maximum, suggesting that HdCl undergoes via a Langmuir–Hinshelwood mechanism, when hydrogen and CCl4 compete for metal surface sites. Both carbon- and chlorine-containing deposits were found in the post-reaction catalyst samples.

Hydrodechlorination of Tetrachloromethane over Palladium Catalysts Supported on Mixed MgF2-MgO Carriers

Pd/MgO, Pd/MgF2 and Pd/MgO-MgF2 catalysts were investigated in the reaction of CCl4 hydrodechlorination. All the catalysts deactivated in time on stream, but the degree of deactivation varied from catalyst to catalyst. The MgF2-supported palladium with relatively large metal particles appeared the best catalyst, characterized by good activity and selectivity to C2-C5 hydrocarbons. Investigation of post-reaction catalyst samples allowed to find several details associated with the working state of hydrodechlorination catalysts. The role of support acidity was quite complex. On the one hand, a definite, although not very high Lewis acidity of MgF2 is beneficial for shaping high activity of palladium catalysts. The MgO-MgF2 support characterized by stronger Lewis acidity than MgF2 contributes to very good catalytic activity for a relatively long reaction period (~5 h) but subsequent neutralization of stronger acid centers (by coking) eliminates them from the catalyst. On the other hand, the role of acidity evolution, which takes place when basic supports (like MgO) are chlorided during HdCl reactions, is difficult to assess because different events associated with distribution of chlorided support species, leading to partial or even full blocking of the surface of palladium, which plays the role of active component in HdCl reactions.

Hydrodechlorination Using Pd–Au Nanoparticles to Convert Chloro-Containing Compounds to Useful Chemicals

Organo-chlorinated compounds, including tetrachloromethane, remain important intermediates and products of the chemical process industries; their adverse impact on the environment has motivated the development of methods to detoxify unwanted chlorocarbons and chlorohydrocarbons. The last decades also saw a paradoxical change on the way we see waste, from simple removal to recycling and nowadays upcycling. Upcycling relates to the use of waste to produce something with a higher value. This article reports on the recent developments in the field of catalytic dehydrochlorination with palladium-based supported catalysts, which were alloyed with gold. The modification led to a significant improvement of catalytic performance and stability. State-of-the-art characterization techniques were used to unveil reasons behind these catalysts remarkable catalytic abilities.

Synergistic effects in hydrodechlorination of organic compounds catalyzed by metals

Synergistic effects in hydrodechlorination of organic compounds catalyzed by metals The search for the most suitable hydrodechlorination catalysts should consider both the C-Cl bond strength in a molecule subjected to reaction and the metal-chlorine bond, which should be neither too strong nor too weak. An improvement of Pd- and Pt-based catalysts can be achieved by alloying with metals which bind chlorine even less strongly, e.g. with gold. Addition of platinum to palladium would also be beneficial because of metal-chloride bond energy considerations. Analogous effects occur in the hydrodechlorination of dichlorodifluoromethane and 1,2-dichloroethane, the molecules characterized by stronger carbon-chlorine bonds.