T. V. Yagodovskaya

The influence of plasma chemical treatment of a platinum catalyst on its activity in the dehydrogenation of cyclohexane

The influence of plasma chemical treatments on the catalytic activity of 0.64 wt % Pt/SiO2 and 1.0 wt % Pt/SiO2 platinum catalysts in the dehydrogenation of cyclohexane was studied. The state of the surface of the catalysts was examined using X-ray photoelectron spectroscopy. Temperature hysteresis caused by the formation of active carbon was observed in flow experiments. It was shown that the reaction on the initial catalysts occurred on neutral and positively charged Pt particles, and that the active centers contained carbon. After catalyst treatment with a high-frequency plasma in H2, its activity increased by many times because of the formation of a large number of low-activity centers on positively charged platinum particles also containing carbon. Glow discharge plasma in Ar sharply decreased catalytic activity, and the reaction then predominantly occurred on centers localized on neutral Pt particles, whereas centers on positive Pt particles were blocked. The state of the substrate (silica gel) did not change under the action of plasmas of both kinds.

Cyclohexane Dehydrogenation on a Copper-Platinum Catalyst

The reaction of the dehydrogenation of cyclohexane on a copper-platinum catalyst supported by silica gel (1 wt % Pt + 0.15 wt % Cu)/SiO2 was studied. The state of the catalyst surface was investigated using X-ray photoelectron spectroscopy. It was established that under both flow and static conditions, the activity of the copper-platinum catalyst is higher than the activity of a catalyst containing 1 wt % Pt/SiO2. The rise in activity as a result of the introduction of copper, due to a decrease in the activation energy, is explained by an increase in the fraction of carbon in the composition of active centers localized on particles of neutral (Ptm0) and positively charged (Ptn+δ) platinum, and by the formation of centers with increased activity as a result of the adsorption of Cu+δ on particles of Ptm0. It was demonstrated that treating the copper-platinum catalyst with the plasma of a glow discharge in argon and oxygen increases its activity, while treatment in high-frequency H2 plasma reduces it. The indicated changes in the activity are associated with the alteration of the activation energies and the number of active centers, revealed by X-ray photoelectron spectroscopy, that depend on changes in the catalyst surface composition.

The interaction of CH3Cl, CH2Cl2, CHCl3, and CCl4 with ozone on the surface of ice under stratospheric conditions

The interaction of ozone with chlorinated methanes adsorbed on a thin ice film was studied over the temperature range 77–292 K. Ozone was shown to oxidize chlorinated methanes starting with 210 K to produce chlorine oxides of various compositions. The products formed in the oxidation of chlorinated methanes with ozone over the temperature range 77–292 K were analyzed by IR Fourier transform spectroscopy. Along with carbon dioxide and water, chlorine oxides in high oxidation states were predominantly formed.

The influence of plasma chemical treatment of nickel and nickel-rhenium catalysts deposited on sibunite on their activity in dehydrogenation

The dehydrogenation of isopropanol was studied at 440–680 K to find that the activity of the Ni(1 wt %)/sibunite catalyst decreased after annealings and quenchings and was stabilized after subsequent treatment with an (I) O2 glow-discharge or (II) H2 high-frequency plasma. Treatments of both kinds decreased the activity of the catalyst below the Curie point (633 K) and increased it over the paramagnetic temperature range (635–680 K). The treatment of the (1 wt % Ni–1 wt %Re)/sibunite and (2 wt % Ni–2 wt % Re)/sibunite catalysts with plasma II weakly influenced their activity, whereas treatment with plasma I substantially increased it. The kinetic reaction parameters on the (2 wt % Ni–2 wt % Re)/sibunite catalyst were found to depend on the duration of treatment with plasma II. Treatment with plasma I much more effectively changed the state of the surface of all the catalysts studied than treatment with plasma II.

Experimental modeling of the processes of ozone hydrate clathrate formation

AbstractThe possible formation of ozone hydrates and their interaction with hydrogen chloride under near-stratospheric conditions were investigated. The low-temperature IR spectroscopic technique was used to demonstrate the in situ formation of ozone hydrates that were stable in the temperature range 77–220 K. It was found that HCl reacted with ozone hydrate to destruct clathrate at temperatures above 220 K. This process resulted in compositionally different chlorine oxides.

Modeling the interaction of ozone with chloroform and bromoform under conditions close to stratospheric

The reactions of ozone with chloroform and bromoform are studied using a flow gas discharge vacuum unit under conditions close to stratospheric (temperature range, 77-250 K; pressure, 10−3-0.1 Torr in the presence of nitrate ice). It is shown that the reaction with bromoform begins at 160 K; the reaction with chloroform, at 190 K. The reaction products are chlorine and bromine oxides of different composition, identified by low-temperature FTIR spectroscopy. The presence of nitrate ice raises the temperature of reaction onset to 210 K.

The desorption and reactivity of butanol adsorbed on lithium iron phosphate (LISICON) activated in a hydrogen plasma

The reactivity and desorption of butanol-2 adsorbed on Li3Fe2(PO4)3 not subjected and subjected to treatment in a glow discharge hydrogen plasma were studied under flow conditions with a gas chromatographic analysis of products. X-ray photoelectron spectroscopy data showed that the number of phosphate groups on the surface of the phosphate was two times larger than the stoichiometric number and increased after plasma chemical treatment. The strength of butanol-phosphate bonds also increased, and the selectivity of alcohol decomposition with the formation of an olefin (dehydration) and ketone (dehydrogenation) changed. After plasma treatment, dehydrogenation centers were deactivated. The selectivities of alcohol transformations in the adsorbed state and under vapor phase conditions were different. Ketone was formed from adsorbed alcohol because the activation energies of dehydrogenation were equal for the two reaction variants.

Dehydrogenation of isopropyl alcohol on modified cobalt catalyst

The effects of plasmochemical processing and of Ce, K, and Hf additives on the rate of dehydrogenation for isopropyl alcohol on a 5 wt % Co/SiO2 catalyst is studied under static and flow conditions. Glow discharge plasma in O2 and Ar and high-frequency electrodeless plasma in H2 (HF-H2) are used. Except for one sample containing Hf, an increase in catalytic activity is observed due to the formation of new active centers. The change in the composition of the initial catalyst’s surface after treatment with Ce and with oxygen, argon, and HF-H2 plasmas is determined by means of X-ray photoelectron spectroscopy. The change in the size and shape of Co particles after treating the catalyst with HF-H2 plasma and Ce is determined via X-ray phase analysis. It is suggested that the new catalytic centers formed after treatment in O2 and Ar plasma contain carbon atoms with C1s bond energies of 282.1 eV; after treatment with HF-H2 plasma, active centers contain hydrogen and carbon atoms with C1s bond energies of 282.5 eV; with cerium, the C1s bond energy is 297.7 eV.

The dehydrogenation of cyclohexane on an AP-64 industrial platinum catalyst subjected to plasma chemical treatments

The influence of glow discharge plasma in oxygen and argon and high-frequency discharge plasma in hydrogen on the activity of the AP-64 (Pt/γ-Al2O3) catalyst in the dehydrogenation of cyclohexane was studied. The catalytic experiments were performed in a flow unit and under static conditions in a vacuum. Under flow conditions, catalyst treatment with plasmas in O2 and Ar decreased the yield of benzene by ∼50% but strengthened temperature hysteresis because of the formation of active carbon on the surface of the catalyst. Under static conditions, argon plasma and high-frequency discharge H2 plasma multiply increased the rate of the reaction because of an increase in the number of active centers, whereas an oxygen plasma decreased the rate of the reaction by two times because of an increase in activation energy. The determination of the order of the reaction led us to suggest that the stage scheme of the reaction did not change after plasma chemical catalyst treatments.

The influence of plasma chemical treatments on the activity of the Li3Fe2(PO4)3 catalyst in butanol-2 transformations

The influence of plasma chemical treatments in oxygen, hydrogen, and argon on the catalytic activity of Li3Fe2(PO4)3 was studied for the example of butanol-2 transformations. Plasma chemical treatment was found to be an effective method for increasing catalyst activity and changing its selectivity. The character of activation depends on the selection of the plasma-forming gas. The highest activity in the dehydration of butanol-2 was observed after treating the catalyst in hydrogen under glow discharge conditions.