Effect of support on activity of palladium catalysts in nitrobenzene hydrogenation

The effect of two types of catalysts on the activity of the catalytic hydrogenation of nitrobenzene was studied. Catalysts were prepared by the surface deposition of palladium hydroxide with a simultaneous reduction with formaldehyde in a basic environment and were characterised by X-ray powder diffraction, transmission electron microscopy, adsorption-desorption, and catalytic tests — hydrogenation of nitrobenzene in methanol. The influence of the supports’ (activated carbon and a mixture of activated carbon and multi-walled carbon nanotubes) surface area is discussed. Despite having a size comparable (4–5 nm) to crystallites of metallic palladium, the catalyst prepared on a mixture of activated carbon and nanotubes (Pd/C/CNT) was significantly less active than the catalyst prepared on pure activated carbon (Pd/C); the rate of this reaction was approximately 30 % lower than the initial reaction rate. This feature could be attributed to the lower specific surface area of the Pd/C/CNT (531 m² g^?1) in comparison with the Pd/C (692 m² g^?1).     

The composition of transformation products of 2,4,6-trinitrobenzoic acid in the aqueous-phase hydrogenation over Pd/C catalysts

Due to a detailed analysis of NMR spectra of the reaction solutions with different composition obtained by the aqueous-phase catalytic (Pd/C) hydrogenation of 2,4,6-trinitrobenzoic acid, the intermediate compounds were identified and a more substantiated mechanism was proposed for the formation of the main reaction products—1,3,5-triaminobenzene and cyclohexane-1,3,5-trione trioxime. The condensation of the 1,3,5-triaminobenzene molecules produced by a complete hydrogenation of 2,4,6-trinitrobenzoic acid was shown to result in the formation of a paramagnetic heterocyclic compound.     

On the mechanism of auto-oscillations in CO hydrogenation on supported palladium catalysts

A mechanism accounting for the occurrence of auto-oscillations in the formation rates of CH₃Cl and (CH₃)₂O during CO hydrogenation on chlorine-containing supported palladium catalysts is proposed.

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, CH₃Cl (CH₃)₂O CO .

     

Polymer-modified supported palladium catalysts for the hydrogenation of acetylene compounds

Palladium catalysts supported on zinc oxide modified with polyethylene glycol or pectin were synthesized and investigated in the hydrogenation of acetylene compounds. It was established that the polymercontaining catalysts reduce acetylene hyrbons to olefins with high activity, selectivity, and stability. The composition and structure of the obtained composites were studied by elemental analysis, transmission electron microscopy, and XPS spectroscopy. It was found that the nanosized particles of palladium uniformly immobilized on the surface of zinc oxide were formed in the course of the synthesis of a supported polymer/oxide complex.     

Deactivation of silica supported Pd catalysts during liquid-phase hydrogenation

Summary Large pore MCM-41 was found to provide a better stabilization of Pd particles than amorphous SiO₂ during liquid phase hydrogenation. Pd/large pore MCM-41 exhibited higher hydrogenation activities as well as lower amount of metal loss by Pd leaching.     

Effect of Pt additives on the properties of Pd/C catalysts in the liquid-phase hydrogenation ofo-nitrophenol

The addition of platinum to Pd/C catalysts results in a synergetic increase in the activity of the catalysts in the hydrogenation ofo-nitrophenol. The synergetic effect depends on the method of preparation of the bimetallic catalysts.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, p. 804, April, 1993.     

An unusual reduction route of 2,4,6-trinitrobenzoic acid under conditions of aqueous-phase hydrogenation over Pd/Sibunit catalyst

For the first time it was established that the catalytic hydrogenation of 2,4,6-trinitrobenzoic acid to 1,3,5-triaminobenzene can proceed via the formation of aromatic hydroxyamines and cyclohexane-1,3,5-trione trioxime. As a result of aqueous-phase hydrogenation of sodium salt of 2,4,6-trinitrobenzoic acid in the presence of 5%Pd/Sibunit catalyst at a temperature of 323 K and pressure of 0.5 MPa, a trioxime in high yield (about 70 %) was obtained. Due to high selectivity to cyclohexane-1,3,5-trione trioxime the catalytic hydrogenation of sodium salt of 2,4,6-trinitrobenzoic acid can be considered as a new method for its synthesis.     

Graphyne-oxide supported Pd catalyst with ten times higher nitrobenzenes reduction activity than Pd/C

Research on Chemical Intermediates - Upon oxidation, a graphyne-like porous carbon-rich network (GYLPC), which is a two-dimensional carbon material consisting of sp- and sp2-hybridized carbon atoms...     

Influence of oxygen on catalytic properties of supported palladium catalysts in CO hydrogenation

It has been established that the addition of oxygen to synthesis gas has a positive effect of the activity and selectivity of supported palladium catalysts in methanol synthesis. The degree of the effect of oxygen depends on the chemical nature of the support and the conditions of catalysis, preceding the addition of oxygen to the reaction mixture. The probable causes for the influence of oxygen on the catalytic properties of palladium, supported on oxide supports, have been discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 5, pp. 557–563, September–October, 1989.     

Effect of reduction temperature and support on the surface electronic state of supported Pd catalysts

The effect of metal precursor, support and reduction temperature on the surface reduction of Pd on -Al₂O₃ and SiO₂ has been studied. For catalysts prepared from PdCl₂, temperatures as high as 450 °C are necessary to obtain surface Pd⁰.

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, Pd -Al₂O₃ SiO₂. , , PdCl₂, Pd^o - 450°C.

     

硫存在下Beta沸石负载钯催化剂上的芳烃加氢性能研究

采用浸渍和离子交换方法，制备了一系列H-Beta沸石负载钯催化剂，并用XRD，N2吸附和氨程序升温脱附进行了表征。采用连续流动固定床反应器，在总压4 MPa，270 ℃，液体空速为16 h－1和硫的质量分数为100×10－6的条件下进行了四氢萘的加氢反应。实验结果表明，钯催化剂的催化性能与催化剂制备方法及载体的硅铝比有关系。对Pd/Beta25(25是硅铝比，下同)来说,离子交换(IE)催化剂的加氢活性高于对应的初湿浸渍(IWI)样品。对于所有离子交换催化剂，Pd/Beta80(IE)在整个反应期间催化活性及抗硫性最好。Pd/Beta25(IE)四氢萘的初始转化率高达77％，失活最快，8 h降到10％；Pd/Beta60(IE)初始转化率为60％，8 h后为16％；Beta80负载催化剂最稳定，起始和8 h后转化率分别为75％和55％。离子交换的Beta80负载Pd催化剂的优良催化活性可以归结为催化剂中有较高比例的中强和强酸性位的存在，尤其中强酸比例较高，同时较多中孔的存在也是其中的影响因素之一。少量Al2O3的添加可以改善催化剂的活性。     

Nox reduction with CO over supported Pd catalysts under simulated post Euro-IV diesel exhaust conditions

The catalytic reduction of NO_x with CO over Pd/Al₂O₃ and Pd/TiO₂/Al₂O₃ under simulated post Euro-IV diesel exhaust conditions was studied. The catalytic activities obtained by using various Pd and TiO₂ loadings and total amounts of reductant and the influence of H₂ and H₂O was investigated.     

Pd/C catalysts. Deactivation and behavior of supported Pd particles upon heating

Deactivation of Pd/C catalysts upon heating in H₂ has been studied as a function of support surface composition. The behavior of Pd particles on a chosen part of surface upon sample heating in an electron microscope chamber has been investigated.     

Efficient and chemoselective reduction of carbonyl compounds with supported gold catalysts under transfer hydrogenation conditions

A new heterogeneous catalytic transfer hydrogenation (CTH) system, consisting of a non-flammable supported Au catalyst along with 2-propanol as the hydrogen donor, was proven to be effective for chemoselective reduction of a wide range of aromatic ketones and aldehydes to the corresponding alcohols.     

Activity of some crystal faces of supported palladium catalysts for benzene hydrogenation

Using known coverages of preadsorbed carbon monoxide as a specific poison on supported polycrystalline Pd, the degree of benzene conversion into cyclohexane was measured and compared with the conversion over a CO-free catalyst surface. Palladium crystal faces adsorbing carbon monoxide in various manners are uniformly active for benzene hydrogenation, which appears to be a structure insensitive reaction.

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. . , , . , .

     

Development of magnetic,ferrite supported palladium catalysts for 2,4-dinitrotoluene hydrogenation

Cobalt, copper, and nickel ferrite spinel nanoparticles have been synthesized by using a combination of sonochemical treatment and combustion. The magnetic nanoparticles have been used as supports to prepare ~4 wt% palladium catalysts. The ferrites were dispersed in an ethanolic solution of Pd(II) nitrate by ultrasonication. The palladium ions were reduced to metallic Pd nanoparticles, which were then attached to the surface of the different metal oxide supports. Thus, three different catalysts (Pd/CoFe₂O₄, Pd/CuFe₂O₄, Pd/NiFe₂O₄) were made and tested in the hydrogenation of 2,4-dinitrotoluene (DNT). A possible reaction mechanism, including the detected species, has been envisaged based on the results. The highest 2,4-diaminotoluene (TDA) yield (99 n/n%) has been achieved by using the Pd/NiFe₂O₄ catalyst. Furthermore, the TDA yield was also reasonable (84.2 n/n%) when the Pd/CoFe₂O₄ catalyst was used. In this case, complete and easy recovery of the catalyst from the reaction medium is ensured, as the ferrite support is fully magnetic. Thus, the catalyst is very well suited for applicationy in the hydrogenation of DNT or other aromatic nitro compounds.     

Effect of high-temperature reduction on Co/SiO2 catalysts activity in the hydrogenation of benzene

The influence of the high reduction temperature on the activity of Co/SiO₂ catalysts in benzene hydrogenation has been studied. The decrease of activity is caused by strong metal-support interaction.     

Determination of the degree of palladium reduction in supported catalysts based on anion exchangers

A procedure is suggested for determining the degree of palladium reduction in fibrous anion exchangers from data on the quantitative recovery of Pd(II) from samples with a hydrochloric acid solution of thiourea before and after the reduction stage.