Kinetika i kataliz

In this work, an experimental study of soot formation during pyrolysis of linear and cyclic hydrocarbons with different bond types between carbon atoms was carried out. Methane CH₄, acetylene C₂H₂, ethylene C₂H₄ and benzene C₆H₆; methyl, ethyl and butyl alcohols CH₃OH, C₂H₅OH, C₄H₉OH; linear esters dimethyl, diethyl and dimethoxymethane CH₃OCH₃, C₂H₅OC₂H₅, CH₃OCH₂OCH₃; cyclic esters furan and tetrahydrofuran C₄H₄O, C₄H₈O pyrolysis have been investigated. The laser extinction method was used to measure the soot volume fraction, and the laser induced incandescence method was used for in situ nanoparticle size measurements. The temperature dependences of the soot volume fraction and particles sizes, as well as the induction times of carbon nanoparticles inception and the effective activation energy values of the initial pyrolysis stage of selected hydrocarbons were obtained. The structure of carbon nanoparticles formed during acetylene C₂H₂, ethylene C₂H₄ and furan C₄H₄O pyrolysis was analyzed using microphotographs obtained on a transmission electron microscope. A kinetic modeling of soot formation during studied hydrocarbons pyrolysis has been carried out. In the case of methane CH₄, ethylene C₂H₄, furan C₄H₄O and tetrahydrofuran C₄H₈O the soot yield and the calculated effective activation energies of the initial pyrolysis reactions correlate with experimental data. In the case of acetylene C₂H₂ and benzene C₆H₆ pyrolysis, kinetic modeling greatly underestimates the soot yield. For benzene, the calculated effective activation energy value of the initial pyrolysis reactions does not agree with the experimental data. This fact may be related to the lack of polyyne path of soot growth in the considered kinetic mechanism that is especially important in case of acetylene and benzene pyrolysis. This hypothesis is justified by comparing the effective activation energy of the initial reactions during benzene pyrolysis obtained using experimental and calculated data.

The paper presents the results of the study of the differential selectivity patterns in the oxidative Mizoroki–Heck reaction under competition of two alkenes or of two arylboronic acids. It has been demonstrated that the loading and nature (soluble under the reaction conditions or insoluble deposited on a heterogeneous support) of the Pd catalyst precursor does not affect the differential selectivity of the products of competing reactions. The results obtained indicate that the nature of the catalytically active species remains unchanged when the nature and loading of the precursor is varied. In accordance with accepted view about the interconversions of dissolved and solid forms of palladium in cross-coupling reactions, such species are truly dissolved molecular Pd complexes.

The properties of Pd–P catalysts supported on ZSM-5 zeolite in H- and Na-forms in the hydrogenation of 2-ethyl-9,10-anthraquinone under mild conditions were studied. The size and phase composition of Pd–P particles were determined using transmission electron microscopy and X-ray powder diffraction analysis. The promoting effect of phosphorus on the dispersion of palladium catalysts and the yield of H₂O₂ has been established. The influence of the decationized form of the zeolite support on the properties of palladium catalysts in the hydrogenation of 2-ethyl-9,10-anthraquinone was considered. It was shown that the deposition of Pd on HZSM-5 zeolite increases the contribution of 2-ethyl-9,10-anthrahydroquinone hydrogenolysis, reducing the yield of H₂O₂. Modification of palladium catalysts with phosphorus significantly suppresses both side processes: saturation of aromatic rings and hydrogenolysis of the C–OH bond of 2-ethyl-9,10-anthrahydroquinone. With an increase in the P:Pd ratio from 0 to 1.0, the yield of H₂O₂ increases from 72–77 to 92–99%. The main reasons for the promoting effect of phosphorus are discussed.