Effect of active site distribution on liquid-phase olefin hydrogenation over polymer-supported palladium complex

Chloromethylated polystyrene beads with different distributions have been prepared and phosphinated. PdCl₂ was supported on the phosphinated supports to give polymer-supported Pd complex catalysts with different active site distributions. The effect of active site distribution on catalytic activity was investigated in the hydrogenation of olefins.     

Pd/polyaniline as the catalysts for 2‐ethylanthraquinone hydrogenation. The effect of palladium dispersion

By doping of polyaniline (PANI) in PdCl₂ aqueous and ethanol solutions the catalysts containing crystalline and colloidal Pd particles of different sizes were prepared. The size of palladium particles present in Pd/PANI catalysts (characterised by SEM and XRD methods) influenced the course of 2‐ethylanthraquinone (eAQ) hydrogenation, a key step in the industrial production of H₂O₂. The presence of large palladium particles promotes reactions leading to the formation of the so‐termed “degradation products” not capable of hydrogen peroxide formation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Metal dispersion and distribution in Pd-based PTA catalysts

The influence of the pH of the impregnating H₂PdCl₄ solution was studied in the preparation of Pd catalysts on granular active carbon. All catalysts were tested in the purification of crude terephthalic acid (4-CBA hydrogenation), in conditions strictly similar to those of industrial operation. The pH of the impregnating H₂PdCl₄ solution was found to strongly influence both Pd surface area and activity (best results with pH 1.5–2.0), while has a relatively small influence on Pd distribution. A linear relationship between catalytic activity for 4-CBA hydrogenation and Pd surface area was confirmed.     

Palladium Containing Catalysts Based on Hypercrosslinked Polystyrene for Selective Hydrogenation of Acetylene Alcohols

This paper reports palladium nanoparticle formation and stabilization by hypercrosslinked polystyrene and the catalytic properties of the nanocomposites obtained. The nanocomposites were characterized using low-temperature nitrogen physisorption, X-ray photoelectron spectroscopy and transmission electron microscopy. The inorganic nanoparticle size was found to depend on the Na₂PdCl₄ loading with the smallest nanoparticles formed at 0.1?wt% of Pd. The nanocomposites synthesized showed high activity [up to 27?mol/(mol Pd?s)] and selectivity (up to 98.5?% at 100?% conversion) in selective hydrogenation of acetylene alcohols.     

Catalysts with noble metals based on super-cross-linked polystyrene for the hydrogenation of aromatic hydrocarbons

A series of catalysts containing noble metals on a super-cross-linked polystyrene (SCP) support with a developed specific surface area (>1000 m²/g) and high thermal stability are prepared and studied to develop an effective catalyst for the low-temperature hydrogenation of aromatic hydrocarbons. A study of Pt- and Pd-containing catalysts based on SCP, carbon supports, and alumina in the hydrogenation of simple (benzene, toluene), branched (n-butylbenzene) and polycyclic (terphenyl) aromatic compounds is conducted. In the hydrogenation of aromatic hydrocarbons, the activity of the catalysts on SCP is comparable to or surpasses analogous catalysts based on Al₂O₃ and Sibunit in the content of noble metals; it is established that catalysts on SCP have greater selectivity in the hydrogenation of benzene in a benzene-toluene mixture. The electronic state of metals in the Pt(Pd)/SCP catalysts is studied by the IR spectroscopy of adsorbed CO. In testing the catalysts in the hydrogenation of terphenyl, it is found that Pt-containing catalyst on the SCP can operate in reversible hydrogenation-dehydrogenation cycles (terphenyl-tercyclohexane); this is promising for the use of such catalyst systems in creating composite materials for hydrogen storage.     

Effect of promotion with cobalt or zinc on the hydrogenating and oligomerizing activities of the Pd/Al2O3 catalyst in the hydrogenation of the BTX fraction

The promoter nature and content effects on the catalytic activity and stability of Pd-Co/δ-Al₂O₃ and Pd-Zn/δ-Al₂O₃ bimetallic catalysts in the hydrogenation of dienic and vinyl aromatic hydrocarbons in the BTX fraction have been investigated by IR spectroscopy and temperature-programmed reduction. The Pd : Co (Zn) molar ratio in the catalysts prepared is 1.0 : 0.5, 1.0 : 1.0, or 1.0 : 1.5, and their Pd content is 0.5 wt %. The support is δ-Al₂O₃ doped with sodium (0.5 wt %). Promotion of the palladium catalyst with zinc and cobalt causes the disappearance of cationic palladium species, thereby reducing the oligomerizing capacity of the active component, and, as was demonstrated by 100-h-long catalytic tests, enhances the stability of the catalyst. The Pd-Co/δ-Al₂O₃(Na) catalyst with Pd : Co = 1.0 : 1.0 mol/mol is recommended for the hydrogenation of the BTX fraction under industrial conditions. The expected service life of this catalyst between regenerations is 16 months.     

Preparation of bifunctional catalysts by solid-state ion exchange in zeolites

Bifunctional catalysts containing an acidic as well as a hydrogenation/dehydrogenation function were prepared by solid-state ion exchange. Preparation and properties of Pd-loaded H-ZSM-5 are described in detail. The catalytic behavior of the reduced catalysts was investigated using hydrogenation and hydroisomerisation of ethylbenzene as a test reaction. The catalytic performance of the catalysts could be significantly improved by concomitant incorporation of Ca²⁺. This was advantageously achieved in a two-step procedure, where first a solid-state ion exchange with CaCl₂ and subsequently a second solid-state ion exchange with PdCl₂ was carried out. A Ca, H-ZSM-5 with 1.5 wt-% Pd obtained via this two-step procedure and subsequent reduction in H₂ exhibited high activity, long life-time and good selectivity with respect to hydrogenation and hydroisomerisation of ethylbenzene to ethylcyclohexane and dimethylcyclohexanes, respectively. Electron micrographs of the reduced catalyst showed finely dispersed palladium with maximum size of about 2.0 nm.On leave from Central Research Institute of Chemistry of the Hungarian Academy of Sciences.     

“Click” Polymer‐Supported Palladium Nanoparticles as Highly Efficient Catalysts for Olefin Hydrogenation and Suzuki Coupling Reactions under Ambient Conditions

Complexation of palladium(II) acetate [Pd(OAc)₂] or dipotassium tetrachloropalladate [K₂PdCl₄] to “click” polymers functionalized with phenyl, ferrocenyl and sodium sulfonate groups gave polymeric palladium(II)‐triazolyl complexes that were reduced to “click” polymer‐stabilized palladium nanoparticles (PdNPs). Transmission electron microscopy (TEM) showed that reduction using sodium borohydride (NaBH₄) produced PdNPs in the 1–3 nm range of diameters depending on the nature of the functional group, whereas slow reduction using methanol yielded PdNPs in the 22–25 nm range. The most active of these PdNPs (0.01% mol Pd), stabilized by poly(ferrocenyltriazolylmethyl)styrene, catalyzed the hydrogenation of styrene at 25 °C and 1 atm hydrogen, with turnover numbers (TONs) of 200,000. When stabilized by the water‐soluble poly(sodium sulfonate‐triazolylmethyl)styrene, the PdNPs (0.01% mol Pd) catalyze the Suzuki–Miyaura coupling between iodobenzene (PhI) and phenylboronic acid [PhB(OH)₂] in water/ethanol (H₂O/EtOH) at 25 °C with TONs of 8,200. This high catalytic activity is comparable to that obtained with “click” dendrimer‐stabilized PdNPs under ambient conditions.     

Development of High-Efficiency,Magnetically Separable Palladium-Decorated Manganese-Ferrite Catalyst for Nitrobenzene Hydrogenation

Aniline (AN) is one of the most important compounds in the chemical industry and is prepared by the catalytic hydrogenation of nitrobenzene (NB). The development of novel, multifunctional catalysts which are easily recoverable from the reaction mixture is, therefore, of paramount importance. Compared to conventional filtration, magnetic separation is favored because it is cheaper and more facile. For satisfying these requirements, we developed manganese ferrite (MnFe₂O₄)–supported, magnetically separable palladium catalysts with high catalytic activity in the hydrogenation of nitrobenzene to aniline. In addition to high NB conversion and AN yield, remarkable aniline selectivity (above 96 n/n%) was achieved. Surprisingly, the magnetic support alone also shows moderate catalytic activity even without noble metals, and thus, up to 94 n/n% nitrobenzene conversion, along with 47 n/n% aniline yield, are attainable. After adding palladium nanoparticles to the support, the combined catalytic activity of the two nanomaterials yielded a fast, efficient, and highly selective catalyst. During the test of the Pd/MnFe₂O₄ catalyst in NB hydrogenation, no by-products were detected, and consequently, above 96 n/n% aniline yield and 96 n/n% selectivity were achieved. The activity of the Pd/MnFe₂O₄ catalyst was not particularly sensitive to the hydrogenation temperature, and reuse tests indicate its applicability in at least four cycles without regeneration. The remarkable catalytic activity and other favorable properties can make our catalyst potentially applicable to both NB hydrogenation and other similar or slightly different reactions.     

Effect of Water Vapor on Carbon Monoxide Oxidation over Promoted Platinum Catalysts

The catalytic behavior of the two kinds of Pd/SiO₂ catalysts prepared from dinitrodiamminepalladium and palladium nitrate are compared for ethene hydroformylation and carbon monoxide hydrogenation. The catalyst prepared from dinitrodiamminepalladium, on which very fine particles of Pd were observed, showed high activity for ethene hydroformylation. On the other hand, the catalyst prepared from palladium nitrate, on which relatively large particles of Pd were observed, showed high activity for CO hydrogenation.     

Homogenous catalysis in the reactions of olefinic substances. V. Hydrogenation of soybean oil methyl ester with triphenylphosphine and triphenylarsine palladium catalysts

Some palladium complexes containing coordinated triphenylphosphine or arsine have been found to be effective and selective catalysts in the homogeneous hydrogenation of soybean oil methyl ester. The characteristic features of the catalysis are 1) isomerization ofcis double bonds totrans double bonds, 2) migration of isolated double bonds to form conjugated dienes, 3) selective hydrogenation of poly olefines to mono olefines without hydrogenation of mono olefine, 4) ester exchange of methyl ester to butyl ester, 5) effective hydrogenation and isomerization by methanol in the absence of elemental hydrogen. The catalytic activity of a variety of palladium complexes decreases in the following order: (ϕ₃P)₂PdCl₂+SnCl₂·2H₂O>(ϕ₃P)₂PdCl₂+GeCl₂>(ϕ₃P)₂Pd(CN)₂> (ϕ₃As)₂Pd(CN)₂>(ϕ₃P)₂PdCl₂≫(ϕ₃As)₂PdCl₂. However, neither K₂PdCl₄ with SnCl₂·2H₂O nor (ϕ₃P)₂Pd(SCN)₂ was effective for hydrogenation. The hydrogenation and isomerization of soybean oil methyl ester have been examined under various conditions using a mixture of (ϕ₃P)₂PdCl₂ and SnCl₂·2H₂O. Under nitrogen pressure, in benzene and methanol as a solvent, both isomerization and hydrogenation of soybean oil methyl ester proceeded less effectively than under hydrogen pressure. This work was done under contract with the USDA. Earlier articles in the series are: I, Inorg. Chem.4, 1618 (1965): II, Proceedings of the Symposium on Coordination Chemistry (Tihany, Hungary, 1964), Edited by M. T. Beck, Budapest, 1965; III, JAOCS43, 337 (1966); IV, Advances in Chemistry Series, American Chemical Society, in press.     

Precious-Metal-Decorated Chromium(IV) Oxide Nanowires as Efficient Catalysts for 2,4-Toluenediamine Synthesis

The catalytic hydrogenation of 2,4-dinitrotoluene (DNT) to 2,4-toluenediamine (TDA) is a key step in the production of polyurethanes; therefore, the development of efficient hydrogenation catalysts for industrial use is of paramount importance. In the present study, chromium(IV) oxide nanowires were decorated by palladium and platinum nanoparticles in a one-step, simple, and fast preparation method to yield highly efficient hydrogenation catalysts for immediate use. The nanoparticles were deposited onto the surface of CrO₂ nanowires by using ultrasonic cavitation and ethanol as a reduction agent. Beneficially, the catalyst became catalytically active right at the end of the preparation and no further treatment was necessary. The activity of the Pd- and Pt-decorated CrO₂ catalysts were compared in the hydrogenation of 2,4-dinitrotoluene (DNT). Both catalysts have shown high activity in the hydrogenation tests. The DNT conversion exceeded 98% in both cases, whereas the 2,4-toluenediamine (TDA) yields were 99.7 n/n% and 98.8 n/n%, with the Pd/CrO₂ and Pt/CrO₂, respectively, at 333 K and 20 bar H₂ pressure. In the case of the Pt/CrO₂ catalyst, 304.08 mol of TDA formed with 1 mol Pt after 1 h hydrogenation. Activation energies were also calculated to be approximately 24 kJ∙mol⁻¹. Besides their immediate applicability, our catalysts were well dispersible in the reaction medium (methanolic solution of DNT). Moreover, because of their magnetic behavior, the catalysts were easy to handle and remove from the reaction media by using a magnetic field.     

Hydrogenation of olefins over palladium(II) complexes supported on a modified macroporous polymer bead

Gellular and macroporous polymer supports have been prepared. A modified polymer support has also been prepared by coating the internal pore wall of macroporous poly(styrene-co-divinylbenzene) with lightly crosslinked polymer containing functional groups. The supports were phosphinated and PdCl₂ was supported on them. The supports and catalysts were characterized using scanning electron microscopy and Fourier transform infrared spectroscopy. The polymer-supported Pd catalysts were used in the hydrogenation of olefins. The effects of the support structure and solvent were also studied. ©1997 SCI     

对甲基苯乙酮催化加氢用钯炭催化剂研究

对甲基-α-苯乙醇是一种重要的化工产品,作为化工原料及产品中间体,被广泛用于医药、食品和精细化工等领域。以对甲基苯乙酮为原料,钯炭为催化剂,研究钯炭催化加氢合成对甲基-α-苯乙醇的性能。通过对载体进行定向改性,丰富其物化性能,考察不同Pd、Cu质量比的钯炭催化剂在对甲基苯乙酮催化加氢中的反应性能,表明Cu的引入能够有效提高钯炭催化剂反应性能,4. 5Pd-0. 5Cu/C催化剂在对甲基苯乙酮催化加氢合成对甲基-α-苯乙醇的性能最佳。     

Total oxidation of volatile organic compounds by vanadium promoted palladium-titania catalysts: Comparison of aromatic and polyaromatic compounds

Vanadium oxide, palladium oxide and mixed Pd/V-supported on titania catalysts have been prepared and tested in the total oxidation of volatile organic compounds (VOCs). A comparative study with two different aromatic VOCs (benzene and naphthalene) has been carried out. For benzene, the mixed Pd/V-catalysts presented the highest catalytic activity. However, whilst studies with benzene led to the formation of CO₂ only, the total conversion of naphthalene to CO₂ was not achieved throughout the full temperature range for naphthalene conversion. A naphthalene conversion to CO₂ of 99% was obtained over Pd/TiO₂, V/TiO₂ and Pd/V/TiO₂ catalysts at 275, 325 and 300 °C, respectively. Therefore, the requirements for an effective benzene total oxidation catalyst cannot be readily extrapolated to larger polycyclic aromatic compounds, as in the naphthalene oxidation the most active catalyst from an environmental point of view is Pd supported on TiO₂.     

Characterization study of CeO2 supported Pd catalyst for low-temperature carbon monoxide oxidation

Catalysts consisting of palladium supported on cerium dioxide (Pd/CeO₂) were prepared and used for carbon monoxide oxidation in a stoichiometric mixture of carbon monoxide and oxygen. Pd/CeO₂ exhibits high catalytic activity for the oxidation of CO, showing markedly enhanced catalytic activities due to the combined effect of palladium and cerium dioxide. The Pd/CeO₂ catalyst is superior to Pd/ZrO₂, Pd/Al₂O₃, Pd/TiO₂, Pd/ZSM-5 and Pd/SiO₂ catalysts with regard to the activity under the conditions examined. The catalysts were characterized by means of XRD and TPR. The position of the H₂-TPR peak shifts to lower temperature with increasing Pd loading from 0.25 to 2.0%. CeO₂ inhibits the hydrogen reduction of PdO. CO-TPR measurements have shown the existence of three peaks. The low-temperature peak (α) is due to the Pd hydroxide species. The β peak has been attributed to finely dispersed PdO. The high-temperature peak (γ) has been attributed to crystal phase PdO. Crystal phase PdO is more difficult to reduce by CO than finely dispersed PdO. On the basis of the catalytic activity and CO-TPR results, we conclude α species (Pd hydroxide) mainly contribute to the catalytic activity for low-temperature CO oxidation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Vapour phase hydrogenation of phenol over Pd/C catalysts: A relationship between dispersion,metal area and hydrogenation activity

A series of palladium supported on activated carbon catalysts, with Pd varying from 0.5 to 6.0 wt%, were prepared via wet impregnation method using PdCl₂ · xH₂O as a precursor salt. The dried samples were further reduced at 573 K in hydrogen and characterized by CO adsorption at room temperature in order to determine the dispersion, metal area and particle size. The catalysts were tested for vapour phase phenol hydrogenation in a fixed-bed all glass micro-reactor at a reaction temperature of 453 K under normal atmospheric pressure. The decrease in metal surface area as well as dispersion with corresponding increase in turn-over frequency (TOF) against palladium loadings suggest the unusual inverse relationship that exist between Pd dispersion and phenol hydrogenation activity over Pd/carbon catalysts. The stability of TOF at larger crystallite size indicates that phenol hydrogenation is less sensitive reaction especially beyond 3 wt% of Pd content. It is evident from the results that structural properties of the catalysts strongly influence the availability of Pd atoms on the surface for CO chemisorption and hence for phenol hydrogenation. A comparison between selectivity and product yield of the reaction against overall phenol conversion indicates that changes in reaction selectivity for cyclohexanone or cyclohexanol is independent of phenol conversion level and either of the product is not formed at the cost of another. The stability of the catalysts with reaction time suggests that coke formation on the surface of the catalyst is less significant and the formation of cyclohexanone remains almost total even at higher reaction temperatures.     

Promotional SMSI Effect on Supported Palladium Catalysts for Methanol Synthesis

High-temperature reduction (HTR) of palladium catalysts supported on some reducible oxides, such as Pd/CeO₂, and Pd/TiO₂ catalysts, led to a strong metal-support interaction (SMSI), which was found to be the main reason for their high and stable activity for methanol synthesis from hydrogenation of carbon dioxide. But low-temperature-reduced (LTR) catalysts exhibited high methane selectivity and were oxidized to PdO quickly in the same reaction. Besides palladium, platinum exhibited similar behavior for this reaction when supported on these reducible oxides. Mechanistic studies of the Pd/CeO₂ catalyst clarified the promotional role of the SMSI effect, and the spillover effect on the HTR Pd/CeO₂ catalyst. Carbon dioxide was decomposed on Ce₂O₃, which was attached to Pd, to form CO and surface oxygen species. The carbon monoxide formed was hydrogenated to methanol successively on the palladium surface while the surface oxygen species was hydrogenated to water by spillover hydrogen from the gas phase. A reaction model for the hydrogenation of carbon dioxide was suggested for both HTR and LTR Pd/CeO₂ catalysts. Methanol synthesis from syngas on the LTR or HTR Pd/CeO₂ catalysts was also conducted. Both alcohol and hydrocarbons were formed significantly on the HTR catalyst from syngas while methanol formed predominantly on the LTR catalyst. Characterization of these two catalysts elucidated the reaction performances.     

Dependence of Synergetic Effect of Palladium–Manganese-Hexaaluminate Combustion Catalyst on Nature of Palladium Precursor

A synergetic effect in the methane oxidation activity of palladium and manganese hexaaluminate was studied over Pd-modified manganese-hexaaluminate catalysts, prepared by incipient wetness impregnation and calcined at 1,200?°C. The magnitude of the synergetic effect is found to be depends on the palladium precursor: it is higher for palladium nitrate and palladium acetate than for tetrachloropalladic acid. The Pd/MnLaAl₁₁O₁₉ catalysts were characterized by X-ray diffraction, X-ray microanalysis, transmission electron microscope and temperature-programmed reduction with hydrogen. These data were compared with the properties of Pd/Al₂O₃ catalysts. At variation of Pd-precursors, a minor trend to the decrease of the Pd particle size was observed at transition from the ex-chloride Pd/MnLaAl₁₁O₁₉ catalyst with uniform Pd-distribution profile to the ex-nitrate and ex-acetate catalysts with egg-shell Pd-distribution. Slightly smaller size of metal palladium particles in the ex-nitrate and ex-acetate catalysts leads to the formation of larger amount of PdO dispersed on their surface during oxygen-pretreatment in H₂-TPR experiments (Pd/PdO atomic ratio was 1/4) and under methane-oxidation mixture in comparison with ex-chloride catalysts (Pd/PdO?=?4/1). The palladium addition to manganese-hexaaluminate changes strongly its redox properties, as result Mn³⁺ reduction to Mn²⁺ take place about 100?°C below that of pure hexaalunimate. The latter indicate probably on the higher oxygen mobility in Pd-modified manganese-hexaaluminate. A higher PdO/Pd ratio formed in the ex-nitrate and ex-acetate Pd-modified manganese-hexaaluminate catalysts together with the high oxygen mobility provide the synergetic effect in methane oxidation activity at light-off temperature region. The high catalytic activity of manganese-hexaaluminate ensures methane combustion efficiency of the Pd-modified manganese-hexaaluminate catalysts at temperature above 700?°C.     

Characterisation and catalytic properties of MCM-41 and Pd/MCM-41 materials

Pure silica MCM-41 mesoporous molecular sieve material was synthesised and characterised by in situ synchrotron XRD, TEM, TGA/DTA and DRIFTS techniques. In situ energy dispersive XRD (EDXRD) confirmed the exact nature of the pore diameter of MCM-41 and the change in crystal structure on calcination. The IR band at 1057 cm^-1 of as-synthesised MCM-41 was shifted by 14 cm^-1 on heating to 673 K due to increased condensation of silanol groups to form Si-O-Si bridges. Calcined MCM-41 materials were used to support Pd, and the catalytic activities for 1-hexene and benzene selective hydrogenation were investigated. The Pd/MCM-41 catalyst showed high activity in hydrogenation of 1-hexene at an inlet reaction temperature of 298 K, but did not show any activity in hydrogenation for benzene. TEM results for the reduced Pd/MCM-41 catalysts revealed that the average Pd particle size was around 2-2.5 nm and these particles were located in the pores of MCM-41 and showed good distribution. TPR measurements showed that about 70% of palladium oxide (PdO) loading in the calcined catalysts was reduced at sub-ambient temperature. This revised version was published online in July 2006 with corrections to the Cover Date.