Hydrotalcite-supported Palladium Research Articles

Dehydrogenative Coupling of Alkanes and Benzene Enhanced by Slurry-Phase Interparticle Hydrogen Transfer.

The dehydrogenative coupling reaction of alkanes and benzene has attracted attention as a method of direct conversion of alkanes to raw materials for useful chemical products. Here, we report the first combined catalyst system composed of hydrotalcite-supported palladium and solid acid aluminum-exchanged montmorillonite for the direct alkylation of benzene promoted by slurry-phase interparticle hydrogen transfer at 150 °C. The combination of the two catalytic particles showed excellent activity and achieved the maximum benzene conversion of 21% and target product selectivity of 84% in the reaction of n-heptane and benzene. Our results, thus, provide a feasible strategy to design efficient liquid-phase reaction systems employing simple physical mixing of two catalytic particles.

Biosynthesis of eco-friendly and recyclable Pd/LDHs catalyst using the withered leaves extract for Suzuki coupling reaction.

The hydrotalcite-supported palladium (Pd) catalyst is prepared with a green and environmentally friendly route, introducing the extract of withered leaves as a dispersant and reducing agent (Pd/LDHs-B). Compared with the as-prepared catalyst (Pd/LDHs-P with the average diameter of 4.3 nm) using a chemical synthesis method with polyvinylpyrrolidone as a dispersant and ascorbic acid (Vc) as a reductant, the results indicate that the size of Pd nanoparticles in Pd/LDHs-B is smaller (ca. 3.6 nm). The Pd-LHDs-B (0.5 mmol‰) exhibits higher activity (98.66%) than Pd/LDHs-P (98.19%) in the Suzuki reaction of 4-bromotoluene and phenylboronic acid at 60°C for 30 min. Also, the reusability of Pd/LDHs-B is confirmed by recycling tests without a significant decrease in activity.

Hydrotalcite-supported palladium nanoparticles as catalysts for the hydroarylation of carbon–carbon multiple bonds

Palladium nanoparticles supported on hydrotalcites catalyze the hydroarylation reaction of carbon–carbon multiple bonds.

Hydrotalcite-supported palladium nanoparticles as catalysts for the Suzuki reaction of aryl halides in water

A simple protocol for the Suzuki reaction of aryl halides with phenylboronic acid is proposed. The catalyst used consists of Pd(0) nanoparticles supported on an Mg/Al hydrotalcite. The catalyst was prepared and characterized in this work for the first time. Supported nanoparticles were obtained by depositing a Pd(II) salt onto the support and subsequently reducing it to Pd(0). The greatest novelties of the synthetic process are the use of a hydrogen donor (cyclohexene) to reduce the palladium precursor salt and that of water as solvent in the Suzuki reaction. Biphenyl conversions in the Suzuki reaction of phenylboronic acid with iodobenzene, bromobenzene and chlorobenzene were all excellent, and quantitative yields obtained within a very short time. Even fluorobenzene provided excellent results improving on many reported values for chelated Pd homogeneous catalysts. No homocoupling reaction was detected; also, although homogeneous and heterogeneous catalysis coexist, the catalyst can be recovered for reuse with no loss of activity.

Oxidant-Free Dehydrogenation of Alcohols over Hydrotalcite-Supported Palla-dium Catalysts

Pd catalysts supported on various supports have been studied for the oxidant-free dehydrogenation of alcohols.The Pd catalyst loaded on hydrotalcite (HT),which is an acid-base bifunctional support,demonstrates superior benzyl alcohol conversion and benzaldehyde selectivity.Detailed studies using the Pd/HT catalyst reveal that the best performance can be obtained over the catalyst with w(Pd)=0.32%-0.55%.The Pd/HT can be used repeatedly without significant deactivation and can efficiently catalyze the dehydrogenation of various alcohols including the substituted benzylic alcohols,2-thiophenemethanol,α,β-unsaturated alcohols,and cyclic aliphatic alcohols.The characterization results show that the Pd(II) species over the HT are transformed into Pd nanoparticles or nanoclusters with mean size of 2.0-2.5 nm during the reaction.The highly dispersed Pd(II) species in the catalyst precursors can lead to the formation of smaller Pd nanoparticles,favoring the catalytic performance.We speculate that the basicity of the catalyst may promote the activation of the O-H bond of alcohol to form a Pd-benzyl alcoholate intermediate,which undergoes β-H abstraction by Pd nanoparticles,and the Brnsted acid sites on the catalyst surface may facilitate the release of H2 by the interaction with the formed hydride species on Pd nanoparticles.

α-Alkylation of Nitriles Promoted by Hydrotalcite-Supported Catalysts

A ruthenium-grafted hydrotalcite (Ru/HT) and hydrotalcite-supported palladium nanoparticles (Pdnano/HT) were readily prepared by treatment of hydrotalcite [HT; Mg6Al2(OH)16CO3] with aqueous RuCl3·nH2O and K2PdCl4, respectively. Ru/HT promoted the α-alkylation of benzylic cyanides with primary alcohols under Ar atmosphere to give the corresponding α-alkylated nitriles in 37-99% yield while the α-alky­lation of malononitrile and ethyl cyanoacetate did not occur. Pdnano/HT promoted the α-alkylation of benzylic cyanides and ethyl cyanoacetate with benzylic aldehydes followed by hydrogenation to afford α-alkylated nitriles in 19-99% yield, whereas the reaction of acetophenone with malononitrile did not proceed.

Environmentally Friendly One‐Pot Synthesis of α‐Alkylated Nitriles Using Hydrotalcite‐Supported Metal Species as Multifunctional Solid Catalysts

A ruthenium-grafted hydrotalcite (Ru/HT) and hydrotalcite-supported palladium nanoparticles (Pd(nano)/HT) are easily prepared by treating basic layered double hydroxide, hydrotalcite (HT, Mg(6)Al(2)(OH)(16)CO(3)) with aqueous RuCl(3)n H(2)O and K(2)[PdCl(4)] solutions, respectively, using surface impregnation methods. Analysis by means of X-ray diffraction, and energy-dispersive X-ray, electron paramagnetic resonance, and X-ray absorption fine structure spectroscopies proves that a monomeric Ru(IV) species is grafted onto the surface of the HT. Meanwhile, after reduction of a surface-isolated Pd(II) species, highly dispersed Pd nanoclusters with a mean diameter of about 70 A is observed on the Pd(nano)/HT surface by transmission electron microscopy analysis. These hydrotalcite-supported metal catalysts can effectively promote alpha-alkylation reactions of various nitriles with primary alcohols or carbonyl compounds through tandem reactions consisting of metal-catalyzed oxidation and reduction, and an aldol reaction promoted by the base sites of the HT. In these catalytic alpha-alkylations, homogeneous bases are unnecessary and the only by-product is water. Additionally, these catalyst systems are applicable to one-pot syntheses of glutaronitrile derivatives.

One‐Pot Synthesis of α‐Alkylated Nitriles with Carbonyl Compounds Through Consecutive Aldol Reaction/Hydrogenation Using a Hydrotalcite‐Supported Palladium Nanoparticle as a Multifunctional Heterogeneous Catalyst.

AbstractFor Abstract see ChemInform Abstract in Full Text.

One-pot synthesis of α-alkylated nitriles with carbonyl compounds through consecutive aldol reaction/hydrogenation using a hydrotalcite-supported palladium nanoparticle as a multifunctional heterogeneous catalyst

α-Alkylation of various nitriles with carbonyl compounds successfully proceeded using a hydrotalcite-supported palladium nanoparticle as a multifunctional catalyst. The alkylated nitriles were formed through aldol reaction at base sites on the hydrotalcite surface followed by hydrogenation by molecular hydrogen on the palladium nanoparticle.

Hydrotalcite-supported palladium catalysts: Part II. Preparation, characterization of hydrotalcites and palladium hydrotalcites for CO chemisorption and phenol hydrogenation

Hydrotalcites and hydrotalcite-like compounds, having Zn 2+ and Li + as brucite layer cations are prepared. They are tested as supports to disperse palladium and for selective hydrogenation of phenol to cyclohexanone. The hydrotalcite materials and palladium catalysts are characterized by XRD, IR, DTA, BET surface area and CO uptake measurements. Calcination temperature and the aluminium content of the hydrotalcite were found to affect the palladium dispersion and deactivation in phenol hydrogenation. Hydrotalcite having Li +in the brucite-like layer was found to be a good support for dispersion of Pd and phenol hydrogenation activity. However, it is not selective for cyclohexanone.

Hydrotalcite-supported palladium catalysts: Part I: Preparation, characterization of hydrotalcites and palladium on uncalcined hydrotalcites for CO chemisorption and phenol hydrogenation

Hydrotalcites (HTs) are prepared by low supersaturation and high supersaturation methods, containing CO 2− 3, Cl −, SO 2− 4 interlayer anions and with different Al(III)/Al(III)+Mg(II) ( x=0.33 and 0.25) ratios. Palladium hydrotalcite catalysts are obtained by impregnation of PdCl 2 aqueous solution on HTs. Different precursors of palladium are used for loading the metal onto HT prepared at high supersaturation. HT and palladium HTs are well characterized by XRD, surface area, IR, SEM, DTA. CO chemisorption is used to estimate palladium dispersion and metal area. The activity is evaluated for phenol hydrogenation reaction. The selectivity to cyclohexanone is always ≥90% even though phenol conversion varies with metal area.

One-step synthesis of methyl isobutyl ketone from acetone with calcined Mg/Al hydrotalcite-supported palladium or nickel catalysts

Calcined Mg/Al hydrotalcites (CHT) with various atomic ratios of Mg/Al were prepared and used as support. One-step synthesis of methyl isobutyl ketone (MIBK) from acetone and hydrogen at atmospheric pressure was investigated over Pd/CHT and Ni/CHT catalysts. These catalysts showed high activities and high selectivities to MIBK, reaching 60–70% selectivity at 35–40% conversion in some experiments. A temperature of ca. 140°C was sufficiently high for the calcined hydrotalcite-supported catalyst to assume basic properties and good activities in MIBK synthesis. The loading of metal (or the density of metal sites) was an important factor for product distribution in MIBK synthesis. A strong metal–support interaction was exhibited in these catalysts. A higher reduction temperature (>500°C) was needed for Ni/CHT catalysts to assume considerable reactivity and selectivities. The reduction temperature played an important role in the behavior of the Ni/CHT catalysts.