Hydrogen absorption by intermetallics M2Fe (M = Zr,Hf, Ti) and their effect on the catalytic aromatization of ethane

The absorption properties of the hydride-forming intermetallics M₂Fe(M = Zr, Hf, Ti) and their effect on the aromatization of ethane over Pt,Ga/HCVM catalyst within the temperature range 400–450 °C are studied. The absorption capacity of the intermetallics under aromatization conditions and their efficiency as hydrogen acceptors are shown to decrease in the order Zr₂Fe > Ti₂Fe > Hf₂Fe.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1726–1729, October, 1994.     

The effect of an intermetallic hydrogen acceptor on catalytic aromatization of propane

The effect of the intermetallic compound Zr₂Fe as a hydrogen acceptor in the aromatization of propane in the presence of a zeolite catalyst has been investigated. High-silica, pentasil-type zeolite ZVM was modified by Zn, Ga, or Pt. The intermetallic compound was found to remove hydrogen formed during aromatization, resulting in a 2-to 5-fold increase in the yields of aromatics and in a marked increase in selectivity for aromatization. The magnitude of this effect is shown to be dependent on the catalyst composition.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 61–63, January, 1993.     

Influence of Metallic Modification on Ethylbenzene Dealkylation over ZSM‐5 Zeolites

A series of metal‐modified HZSM‐5 catalysts were prepared by impregnation and were used for ethylbenzene dealkylation of the mixed C8 aromatics (ethylbenzene, m‐xylene and o‐xylene). The effects of different supported metals (Pt, Pd, Ni, Mo) on catalytic performance, including reaction conditions, were investigated. The physicochemical properties of catalysts were characterized by means of XRD, BET, TEM and NH₃‐TPD. Experimental results showed that metallic modification obviously increased the ethylbenzene conversion and reduced the coke deposition, greatly improving the catalyst stability. The distinction of ethylbenzene conversion depended on the interaction between hydrogenation reactivity and acidic cracking of bifunctional metal‐modified zeolites. Compared with Pt and Ni, Pd and Mo were easier to disperse into HZSM‐5 micropores during loading metals. The acidic density of different metal‐modified HZSM‐5 declined in the following order: HZSM‐5>Pt/HZSM‐5>Pd/HZSM‐5>Ni/HZSM‐5>Mo/HZSM‐5. The activity of ethylene hydrogenation decreased with Pt/HZSM‐5>Pd/HZSM‐5>Ni/HZSM‐5>Mo/HZSM‐5. In comparison, Pd/HZSM‐5 showed the best catalytic performance with both high activity and high selectivity, with less cracking loss of m‐xylene and o‐xylene. Moreover, the following reaction conditions were found to be preferable for ethylbenzene dealkylation over Pd/HZSM‐5: 340°C, 1.5 MPa H₂, WHSV 4 h^?1, H₂/C8 4 mol/mol.     

IR spectra of catalysts and adsorbed molecules. 39. Acid and catalytic properties of pentasils modified with platinum,chromium, and zinc

It was shown that when platinum is incorporated in pentasil (HZSM), the concentration of L sites increases by 2 times with no change in the number of B sites; in Pt-Cr-containing catalysts, the concentration of L sites passes through a maximum with a 0.72% concentration of Cr, and the number of OH groups and B sites decreases. The concentration of B sites decreases and the concentration of L sites increases in samples simultaneously promoted with Pt, Cr, and Zn. In conditions of aromatization of lower alkanes on Pt-Cr-containing catalysts, the concentration of OH groups and B sites decreases, while the concentration of L sites increases. Incorporation of platinum in HZSM increases the aromatizing activity with respect to methane, and additional incorporation of chromium and zinc increases the yield of aromatic hydrocarbons from ethane and propane also.See [1] for communication 38.Deceased.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 1038–1042, May, 1992.     

Transformation of n-hexane on Al2O3and SiO2supported Pt, Pt+Ga and Ir+Pt+Ga catalysts prepared by anchoring methods

Summary Transformation of n-hexane over Al₂O₃and SiO₂supported Pt, Pt+Ga and Ir+Pt+Ga catalysts was studied in a continuous-flow reactor operated under slug-pulse mode at 520°C. Bimetallic catalysts were prepared by introducing first Ga(OEt)₃and then diallylplatinum as precursor compounds. Iridium was then introduced viadecomposition of Ir₄(CO)₁₂adsorbed onto Pt+Ga catalysts. The addition of Ga to Pt/SiO₂catalyst decreased hydrogenation, aromatization and hydrogenolysis selectivity. Over Pt/Al₂O₃catalyst Ga increased hydrogenolysis selectivity and decreased isomerization and C₅-cyclization. The main effect of Ir was to increase hydrogenolysis selectivity and the stability of catalysts.</o:p>     

Modified heterosilicates (Fe,B)-catalytic characteristics and IR spectra

The catalytic characteristics (in the aromatization of propane and propylene) and acidic characteristics (IR spectra in diffuse scattered light) of modified crystalline heterosilicates (Pt, Zn, Ga) were studied. It was shown that new centers, capable of substantially increasing (by 2–7 times) the yield of aromatic hydrocarbons from propane, are formed when Zn and Ga are introduced into ferri- and borosilicates. In the case of propylene the aromatizing characteristics of the modified heterosilicates show up particularly clearly in the region of relatively low temperatures.DeceasedN. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1291–1299, June, 1992.     

丙烷在无机膜反应器中的芳构化

研究了在固定床反应器和膜反应器中的丙烷芳构化，考察了ＨＺＳＭ－５担载的Ｇａ和Ｐｔ－Ｇａ催化剂对反应的影响。结果表明，采用无机膜反应器可以提高丙烷芳构化选择性，从而提高芳烃收率达１０％以上。在膜反应器中，低碳烷烃选择性降低，烯烃选择性增强。固定床相比，膜反应器在低温时对芳构化反应的促进作用最为显著，但是随着温度升高，其促进作用减弱。     

ZrO2?SiO2 mixed oxides as supports for platinum catalysts

Mixed ZrO₂–SiO₂ oxides were prepared by the sol-gel method and used as supports for platinum catalysts. Activity tests show that Pt/ZrO₂–SiO₂ catalysts can be used in the aromatization of n-heptane.     

Study of the properties of pentasil-containing catalysts in reactions of transformation of hydrocarbons 5. Kinetics and mechanism of aromatization of propane and propylene on Ga and H forms of pentasils

The kinetics of transformations of propane and propylene on Ga-modified pentasils and the H-form of zeolite were investigated in a wide range of conversions (20–95%). The selectivity of formation of aromatic hydrocarbons (ArH) on Ga-pentasils is significantly higher than on HTsVM. Quantitative data which demonstrate acceleration of aromatization of propane and propylene in modification of H-TsVM zeolite with gallium were obtained. An especially large increase in the reaction rate is observed in the case of the starting olefin: the rate constants on Ga/HTsVM and HTsVM are respectively equal to 9.21 and 1.44 sec^–1. The significant effect of H₂ on the selectivity of action of the Zn/HTsVM system in aromatization of propane was demonstrated. The effect of H₂ was virtually not manifested on Ga/HTsVM in the conditions studied. The data obtained in the study permitted introducing important corrections in the scheme of the mechanism of aromatization of lower alkanes examined in the literature.For communications 3 and 4, see [1, 10].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1250–1257, June, 1990.     

Catalytic aromatization of light alkanes

Experimental data on the application of pentasil-type zeolites in the aromatization of lowmolecular-weight alkanes are surveyed. Examples of the transformation of ethane and propane into aromatics over pentasils containing Zn, Ga, or Ga-Pt are given. An important role of Pt in the formation of active and selective Ga-Pt catalysts for light alkane aromatization is shown.     

Chemical reaction in chromatographic columns : Dehydrogenation of ethane over cadmium-exchanged zeolite 4A

Pulsed-flow techniques were used to detect considerable differences in the heats of adsorption of ethane and ethylene on various cadmium-exchanged zeolites 4A at temperatures up to 500°C. Higher values (about 10.0 kcal/mole) were observed for ethylene than for ethane (5.0 kcal/mole) at 300–400°C. Experimental verification is provided pertaining to the dehydrogenation of ethane in a gas chromatographic reactor. By appropriate choice of the reaction conditions, conversions up to 80% per pass could easily be obtained at temperatures (400–500°C) at which the thermodynamic equilibrium for a diluted ethane stream (Pc⁺₂ = 0.01-0.1 P_tot.) would not permit more than 25%.     

Cesium dimethyltetrachloroplatinate,a complex of dimethylplatinum(IV). Synthesis and some reductive elimination reactions involving the monomethylplatinum(II) complex as an intermediate

The reduction of Pt(IV) complexes followed by the oxidative addition of dimethyl sulfate to Pt(II) affords Cs₂PtMe₂Cl₄, a complex of dimethylplatinum(IV). On treatment with such nucleophiles as Cl^–, Br^–, I^–, and PtCl₄ ^2– in aqueous solutions at 368 K this complex undergoes reductive elimination to give MeX and Pt^IIMe as a transient species. The latter is further converted to methane upon protolysis, whereas in the presence of an oxidant (Na₂PtCl₆) it gives rise to the Pt^IVMe species. The kinetics of decomposition of Cs₂PtMe₂Cl₄ in aqueous HCl-KCl systems (2M or 3M in Cl^–; [Pt^IVMe₂][Cl^–]) were studied. The reaction takes place as anS _N 2 attack of X^– on the carbon atom of a methyl group located with thetrans position with respect to the aqua-ligand of the [PtMe₂Cl₃(H₂O)]^– complex.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 389–395, February, 1993.     

Time-on stream behavior of Pd-, Co-, and Mn-zeolite catalysts supported on metal blocks in high-temperature methane oxidation

Stability of the Pd-, Co-, and Mn-zeolite catalysts supported on metal blocks was studied in high-temperature methane oxidation. The temperature regions were found in which the starting catalysts exhibit stable performance. The temperature was determined at which a partial deactivation is followed by stabilization of catalysts in reaction environment. In terms of specific activity, the partially deactivated Pd-zeolite catalyst is several times more active than conventional oxidation catalysts Pd/Al₂O₃, Pt/Al₂O₃, and the most active oxide CeO·6Al₂O₃.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2075–2078, October, 2004.     

The nature of active sites in Pt promoted GaZSM-5 catalysts

Summary Activity and selectivity of Pt-promoted GaZSM-5 catalysts in the aromatization of ethane were studied. XRD indicated that high temperature treatment of the Pt promoted GaZSM-5 zeolites results in the formation of bimetallic GaPt clusters located on the inner surface of zeolites. Both experimental results and calculations suggest that the clusters containing Ga and Pt atoms stabilized in cationic positions are characterized by an increased activity and selectivity in the dehydrogenation of ethane.</o:p>     

Hydrolysis of cis- and trans-Diammineplatinum(II) Complexes: Hydration, Equilibrium, and Kinetics Properties

We have used a combination of ultrasound and density techniques to measure the hydration parameters, apparent molar volume, and apparent molar adiabatic compressibility, of the antitumor drug cis-dichlorodiammineplatinum(II), cis-[Pt(NH₃)₂Cl₂], and its inactive isomer trans-dichlorodiammineplatinum(II), trans-[Pt(NH₃)₂Cl₂], in 10 mM NaNO₃, pH 5.6 at 37°C. The data have been interpreted in terms of the overall hydration of each isomer, the actual hydration contribution to the adiabatic compressibility, K _h, ranges from –56.4 × 10^–4 to –20.3 × 10^–4 cm³-mol^–1-bar^–1, and the volume contribution, V _h, ranges from –16.3 to –6.4 cm³-mol^–1. The negative signs of these hydration contributions indicate that the volume and compressibility of the water immobilized by the platinum complexes is smaller than the volume and compressibility of bulk water. The V _h and K _h parameters for all platinum complexes investigated are linearly dependent on the relative amount of hydrolyzed chlorides. The values of each parameter become more negative with increasing hydrolysis, and show that the degree of hydration increases. The similar dependence of the amount of hydrolyzed chloride ligands reveals similar hydration properties for these two complexes. Thus, the symmetry of the complexes, which is of crucial importance for anticancer activity, has no influence on their hydration properties. Under our experimental conditions, the equilibrium constants for the hydrolysis of cis-[Pt(NH₃)₂Cl₂] are K ₁ = 2.52 mM and K ₂ = 0.04 mM. The equilibrium constant for the first step of hydrolysis of trans-[Pt(NH₃)₂Cl₂] is 0.03 mM, while the second chloride ligand cannot be substituted by water, even in the irreversible reaction with AgNO₃. Furthermore, continuous measurements of the ultrasonic velocity during hydrolysis permits the accurate evaluation of the pseudo-first-order rate constant k ₁ for the hydrolysis of the first chloride ligand of cis-[Pt(NH₃)₂Cl₂], which is 16±1×10^–5 s^–1.     

Metallosilicates as supports of Co catalysts for the synthesis of liquid hydrocarbons from CO and H2

The effect of the nature of the silicate support on the activity and selectivity of 10%. Co/M silicate catalysts (where M=Cu, Zn, Ce, Ti, Hf, La, Al, Zr, Co, Mg) in the synthesis of hydrocarbons from CO and H₂ has been established. Co and Zr catalysts have been shown to provide the highest catalytic efficiency. The yield of liquid hydrocarbons in their presence exceeds 120 g m^–3.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 480–482, March, 1993.     

Synthesis and characterization of the Pt/Al2O3 systems modified with group III (Ga) and Group IV (Ge,Ti, and Zr) elements in the combined conversion of propane and n-Heptane

Under the conditions of a joint reaction of propane and n-heptane at temperatures of 460–520°C and a pressure of 0.35 MPa, the conversion of propane and the concentration of C₇₊ aromatization products on platinum-containing catalysts modified by Group III (Ga) and Group IV (Ge, Ti, and Zr) elements were higher than those on an unmodified Pt/Al₂O₃ sample. This is explained by a change in the aprotic acidity of the catalysts as a result of the support modification. The sample with the addition of gallium was most active. A plausible reason for this is the conversion of hydrocarbons at active sites that consist of Pt and Ga, which were formed upon catalyst activation. It is believed that gallium adjacent to platinum in an ionic form on the support surface acts as an aprotic acid site.     

Cyclohexane transformations over metal oxide catalysts. 1. Effect of the nature of metal and support on the catalytic activity in cyclohexane ring opening

The activities of monometallic Pt-, Ru-, and Rh-containing catalysts supported on Al₂O₃, Al₂O₃—F, SiO₂, WO₃/ZrO₂, and La₂Î₃/ZrO₂, in cyclohexane ring opening to form n-hexane were studied. The most active catalyst is Rh/Al₂O₃. Cyclohexane hydrogenolysis to n-hexane also occurs over the Pt/Al_;>2O₃ and Pt/La₂Î₃/ZrO₂ catalysts. Ring opening over the Ru catalysts proceeds at significantly lower temperatures (210—230 °C) than over the Pt and Rh catalysts (350—400 °C), but the ruthenium systems are less selective for n-hexane formation than Rh/Al₂O₃ catalysts. The effects of acid-basic properties of the support and the reaction conditions on the activities of the catalytic systems in cyclohexane ring opening was studied.     

Correlation between acidic properties of nickel catalysts and catalytic activities for ethylene dimerization and butene isomerization

Catalytic activities of NiO–SiO₂ for ethylene dimerization and butene isomerization run parallel when the catalysts are activated by evacuation at elevated temperatures, giving two maxima in activities. The variations in catalytic activities are closely correlated to the acidity of NiO–SiO₂ catalysts. Catalytic activities of NiO–TiO₂ catalysts modified with H₂SO₄, H₃PO₄, H₃BO₃, and H₂SeO₄ for ethylene dimerization and butene isomerization were examined. The order of catalytic activities for both reactions was found to be NiO–TiO₂/SO₄^2- >> NiO–TiO₂/PO₄^3-NiO–TiO₂/BO₃^3- > NiO–TiO₂/SeO₄^2-> NiO–TiO₂, showing clear dependence of catalytic activity upon acid strength. The high catalytic activity of supported nickel sulfate for ethylene dimerization was related to the increase of acidity and acid strength due to the addition of NiSO₄. The asymmetric stretching frequency of the S=O bonds for supported NiSO₄ catalysts was related to the acidic properties and catalytic activity. That is, the higher the frequency, the larger both the acidity and catalytic activity. For NiSO₄/Al₂O₃–ZrO₂ catalyst, the addition of Al₂O₃ up to 5 mol% enhanced catalytic activity for ethylene dimerzation and strong acidity gradually due to the formation of Al–O–Zr bond. The active sites responsible for ethylene dimerization consist of a low-valent nickel, Ni⁺, and an acid, as evidenced by the IR spectra of CO adsorbed on NiSO₄/ -Al₂O₃ and Ni 2p XPS.     

Use of m-(mercaptoacetamido)phenol for the differentiation and separation of selenite,selenate, tellurite,and tellurate

Summary m-(Mercaptoacetamido)phenol (m-MAP) is used as a reductant for the distinction and separation of SeO₃ ^2–, SeO₄ ^2–, TeO₃ ^2–, and TeO₄ ^2–.

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Zusammenfassung m-(Merkaptoacetamido)-phenol wurde als Reduktionsmittel zur Unterscheidung und Trennung von SeO₃ ^2–, SeO₄ ^2–, TeO₃ ^2– und TeO₄ ^2– verwendet.