Pd–Ag/SiO2 and Pd–Cu/SiO2 cogelled xerogel catalysts for selective hydrodechlorination of 1,2-dichloroethane into ethylene

Green Chemistry for the Transformation of Chlorinated Wastes: Catalytic Hydrodechlorination on Pd-Ni and Pd-Fe Bimetallic Catalysts Supported on SiO2

Monometallic catalysts based on Fe, Ni and Pd, as well as bimetallic catalysts based on Fe-Pd and based on Ni-Pd supported on silica, were synthesized using a sol–gel cogelation process. These catalysts were tested in chlorobenzene hydrodechlorination at low conversion to consider a differential reactor. In all samples, the cogelation method allowed very small metallic nanoparticles of 2–3 nm to be dispersed inside the silica matrix. Nevertheless, the presence of some large particles of pure Pd was noted. The catalysts had specific surface areas between 100 and 400 m2/g. In view of the catalytic results obtained, the Pd-Ni catalysts are less active than the monometallic Pd catalyst (<6% of conversion) except for catalysts with a low proportion of Ni (9% of conversion) and for reaction temperatures above 240 °C. In this series of catalysts, increasing the Ni content increases the activity but leads to an amplification of the catalyst deactivation phenomenon compared to Pd alone. On the other hand, Pd-Fe catalysts are more active with a double conversion value compared to a Pd monometallic catalyst (13% vs. 6%). The difference in the results obtained for each of the catalysts in the Pd-Fe series could be explained by the greater presence of the Fe-Pd alloy in the catalyst. Fe would have a cooperative effect when associated with Pd. Although Fe is inactive alone for chlorobenzene hydrodechlorination, when Fe is coupled to another metal from the group VIIIb, such as Pd, it allows the phenomenon of Pd poisoning by HCl to be reduced.

Applications of bimetallic PdCu catalysts

Bimetallic PdCu nanoparticles can be applied as catalysts in a wide range of chemical and electrochemical reactions.

A DFT study of chlorine coverage over late transition metals and its implication on 1,2-dichloroethane hydrodechlorination

Chlorine coverage and its impact on 1,2-dichloroethane hydrodechlorination over ten late transition metals, predicted using DFT-based phase diagrams.

In situ synthesis of Au–Pd bimetallic nanoparticles on amine-functionalized SiO2 for the aqueous-phase hydrodechlorination of chlorobenzene

The homogeneous Au–Pd NPs have been prepared through a facile in situ reduction method. The optimal AuPd_1.0/SiO₂ catalyst could complete the conversion of chlorobenzene due to the high dispersion and modified electronic properties of Pd.

Transport and activity of Desulfitobacterium dichloroeliminans strain DCA1 during bioaugmentation of 1,2-DCA-contaminated groundwater

The transport and activity of Desulfitobacterium dichloroeliminans strain DCA1 in 1,2-dichloroethane (1,2-DCA)-contaminated groundwater have been evaluated through an in situ bioaugmentation test at an industrial site (Belgium). The migration of strain DCA1 was monitored from an injection well toward a monitoring well, and the effect of the imposed groundwater flow on its distribution was assessed by means of transport model MOCDENS3D. The results of the real-time PCR (16S rRNA gene) quantification downstream from the injection point were used to evaluate the bacterial distribution pattern simulated by MOCDENS3D. In the injection well, the 1,2-DCA concentration in the groundwater decreased from 939.8 to 0.9 microM in a 35 day time interval and in the presence of a sodium lactate solution. Moreover, analyses from the monitoring well showed that the cells were still active after transport through the aquifer, although biodegradation occurred to a lesser extent. This study showed that strain DCA1 can be successfully applied for the removal of 1,2-DCA under field conditions and that its limited retardation offers perspectives for large-scale cleanup processes of industrial sites.

Assessment of the 3D localization of metallic nanoparticles in Pd/SiO2 cogelled catalysts by electron tomography

The purpose of this study is to analyze the localization of palladium nanoparticles within their silica support, in two heterogeneous catalysts synthesized by the sol-gel process, with different metal loadings. Electron tomography demonstrates that the palladium particles are localized deep inside the silica skeleton. The use of digital image analysis further shows that the dispersion of palladium is optimal in the sample with the lowest loading. The particles are regularly spaced in the middle of the silica skeleton, with a distance between them comparable to the diameter of the struts of silica.

Sulfate-Enhanced Catalytic Destruction of 1,1,1-Trichlorethane over Pt(111)

The catalytic destruction of 1,1,1-trichloroethane (TCA) over model sulfated Pt(111) surfaces has been investigated by fast X-ray photoelectron spectroscopy and mass spectrometry. TCA adsorbs molecularly over SO4 precovered Pt(111) at 100 K, with a saturation coverage of 0.4 monolayer (ML) comparable to that on the bare surface. Surface crowding perturbs both TCA and SO4 species within the mixed adlayer, evidenced by strong, coverage-dependent C 1s and Cl and S 2p core-level shifts. TCA undergoes complete dechlorination above 170 K, accompanied by C-C bond cleavage to form surface CH3, CO, and Cl moieties. These in turn react between 170 and 350 K to evolve gaseous CO2, C2H6, and H2O. Subsequent CH3 dehydrogenation and combustion occurs between 350 and 450 K, again liberating CO2 and water. Combustion is accompanied by SO4 reduction, with the coincident evolution of gas phase SO2 and CO2 suggesting the formation of a CO-SOx surface complex. Reactively formed HCl desorbs in a single state at 400 K. Only trace (<0.06 ML) residual atomic carbon and chlorine remain on the surface by 500 K.