PdZn/α-Al2O3 catalyst for liquid-phase alkyne hydrogenation: effect of the solid-state alloy transformation into intermetallics

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Gas Chromatography Columns Based on Functionalized Polymer for the Analysis of Catalytic Reaction Products

For the first time in this work, two methods of modification of poly(1-trimethylsilyl-1-propyne) (PTMSP) and the possibilities of its application for the determination of catalytic reaction products are described. Aging of PTMSP is determined by three mechanisms: physical, chemical and mechanical effects. Free volume decreases, texture characteristics change, and partial oxidation of the polymer takes place in the structure of PTMSP. The chromatographic behavior of PTMSP, which was used for 18 months, differs significantly from the properties of the freshly prepared polymer. Thermal stability and chemical inertness are the main requirements for chromatographic materials. Therefore, two methods were used to stabilize the aging process. The first method consisted of preparing a mixed phase by adding disubstituted polyacetylene poly(1-phenyl-1-propyne) (PPP) to PTMSP. The resulting sorbent Chromosorb Р NAW?+?10 wt% (97% PTMSP?+?3% PPP) is efficient for solving a wide range of chromatographic tasks such as simultaneous analysis of hydrocarbons and sulfur-containing inorganic gases, analysis of chlorine-substituted methanes in CCl₄ and thiophene in benzene, separation of hydrocarbons and aromatic compounds. It should be noted, the low selectivity of separation of oxygen-containing components on this sorbent. A second method of PTMSP modification, namely the oxidation treatment with nitrous oxide, is proposed. It was shown that the polymer is oxidized by means of its C=C double bond with the formation of ketone, carbonyl and hydroxyl groups. The increase in number of those groups in the polymer changed the polarity of PTMSP. The change in polarity of polymer led to the selectivity of separations, including oxygen-containing substances. Examples of separations of aliphatic and aromatic hydrocarbons, oxygen- and halogen-containing substances are presented. Chromatographic characteristics of the sorbent Chromosorb P NAW?+?10 wt% (97% PTMSP?+?3% PPP) and PTMSP oxidized by nitrous oxide are stable in the temperature range from 30 to 220 °C for at least 1.5 years of continuous operation.

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Pd–Cu/HOPG and Pd–Ag/HOPG Model Catalysts in CO and Methanol Oxidations at Submillibar Pressures

Kinetics and Catalysis - The regularities of formation of alloyed Pd–Cu bimetallic particles deposited on highly oriented pyrolytic graphite (HOPG) were studied by STM and...     

Tetranuclear, Oxygen Centered Copper(II) Clusters Linked Together with Guanidine-Guanidinate Ligands

The reaction of copper(I) chloride with Htbo (1,4,6-triazabicyclo[3.3.0]oct-4-ene) under reflux in THF with oxidation by oxygen, produces a neutral cluster comprising two oxo-tetra-copper(II) units connected by six tbo⁻ bridges three of them bind two and the other three bind four metals; each unit also contains three chlorine bridges and a Htbo terminal ligand. Two different X-ray crystal structures (1a, 1b) have been determined and the magnetic behavior has been studied. The molar magnetic susceptibility measurements indicate strong exchange interactions within an oxo cluster with coupling constants of J ₁ = −163 cm⁻¹ and J ₂ = −1.1 cm⁻¹, and a weak interaction across the guanidinate bridges of J ₃ = −5.2 cm⁻¹ of the octa-Cu^II cluster.     

The synthesis of liquid crystalline lanthanide complexes and their magnetic birefringence

Liquid crystalline complexes of the type [ML(LH)₂](NO₃)₂, where LH=C₇H₁₅O-C₆H₃(OH)CH=N-C₁₈H₃₇ and M=Gd, Dy, and La, have been obtained. All of them exhibit the S_A phase and have high magnetic birefringence constants due to the association of the complexes in solution. In the case of the dysprosium derivative, the effect is much stronger (four orders of magnitude greater than the usual value) because of the high magnetic anisotropy of the particles of the complex.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1003–1005, June, 1994.The authors are grateful to Prof. S. G. Vul'fson for helpful advice and discussions.     

In Situ Study of the Selective Oxidation of Methanol to Formaldehyde on Copper

Combined use of X-ray photoelectron spectroscopy (XPS) and in situ mass spectrometry made it possible to simultaneously obtain the O1s spectra and the mass spectrometric signal of formaldehyde (m/z = 30) in the course of heating (420–670 K) of polycrystalline foil in a flow of the reaction mixture of methanol and oxygen (with a total pressure of 0.1 mbar and a ratio of 3/1). It is shown that the O1s spectra contain two lines with E _b = 530.1 and 531.2 eV, whose relative intensities depend on the sample temperature. At a low temperature (420 K) the line with a lower binding energy dominates, whereas sample heating leads to a drastic decrease in its intensity and its replacement by a line with a higher value of E _b. A decrease in the intensity of the latter line occurs at T > 550 K, in the same temperature range as a drastic increase in the intensity of the formaldehyde signal. These lines were assigned on the basis of literature data and data obtained by the authors for the known forms of oxygen on copper and for the intermediate species of the reaction, such as methoxy and formate. The O1s line with E _b = 530.1 eV was assigned to methoxy groups, and the line with E _b = 531.2 eV was assigned to suboxide oxygen. The correlation of the intensity of the XPS signal of suboxide oxygen with the yield of formaldehyde was supported by stationary experiments using in situ XPS that prove its participation in the key step of the selective oxidation of methanol to formaldehyde.     

Electronic and chemical properties of nanostructured cerium dioxide doped with praseodymium

Nanostructured doped ceria is a prospective material for catalytic applications such as the construction of membranes with mixed electronic and ionic conductivity for effective syngas production. In this article, the surface properties of nanostructured ceria doped with praseodymium have been studied by X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and Fourier transform infrared spectroscopy of adsorbed carbon monoxide. The effects of supporting 1.4 wt % Pt as well as structural changes upon the reduction of the samples with methane have been investigated. While in samples without supported platinum, mainly praseodymium cations are reduced in a methane atmosphere; stronger reduction of cerium cations was found in the case of surface modification with Pt. The structural differences correlate with results from temperature-programmed reaction experiments with methane. Explanations are discussed in terms of different reaction mechanisms.