Palladium supported on bacterial biomass as a novel heterogeneous catalyst: A comparison of Pd/Al2O3 and bio-Pd in the hydrogenation of 2-pentyne

Nanoparticles of palladium supported on bacterial biomass, bio-Pd, were tested for their catalytic activity in the hydrogenation of 2-pentyne in a stirred tank reactor. The rates of reaction and the selectivity obtained using the novel materials were compared to those obtained with a conventional heterogeneous catalyst, palladium on alumina, under various reaction conditions. Under the same conditions, the initial rate of reaction over a 5 wt% bio-Pd catalyst in isopropanol was only 30% of that for a 5 wt% Pd/Al₂O₃ catalyst. However, the biomass-supported showed a high selectivity, displaying quantitative conversions of alkyne after 5 h with maximum product ratios of pentene/pentane in the range of 8–14 and cis/trans product ratios in the range of 6–14. Although the conventional 5% Pd/Al₂O₃ catalyst gave very high initial pentene/pentane and cis/trans ratios (26 and 10), these values fell rapidly over the course of the reaction and became slightly lower than those observed with bio-Pd at alkyne conversions greater than 70%. For example, at 92% alkyne conversion, the bio-Pd catalyst gave a cis/trans ratio of 2.5 and pentene/pentane ratio of 3.3, as opposed to respective values of 2.0 and 2.0 with 5% Pd/Al₂O₃. This is the first time that selectivity has been demonstrated for the bio-Pd in a multi-product reaction, thus showing promise of this material for use in catalytic syntheses where it is desirable to maximise yield of a specific component. The type of bacteria used as support in the 2-pentyne hydrogenation experiments was Desulfovibrio desulfuricans. The metal particles grow within the cell envelope, are regularly dispersed and are of uniform particle size, of ～1.7 nm as determined by chemisorption. The bio-Pd is also easily separated from the product mixture and remained active and selective when reused in a subsequent hydrogenation.     

Influence of ligands of palladium complexes on palladium/Nafion composite membranes for direct methanol fuel cells by supercritical CO2 impregnation method

Palladium/Nafion composite membranes were synthesized by supercritical impregnation method to reduce methanol crossover in direct methanol fuel cells. The palladium complexes used in this study were palladium(II) acetylacetonate, palladium(II) hexafluoroacetylacetonate, and palladium (II) bis(2,2,6,6-tetramethyl-3,5-heptane-dionato). The palladium complexes with various loading amounts from 0.010 to 0.050 g in a high-pressure vessel were dissolved in supercritical CO₂, and impregnated into Nafion membranes.The SEM images indicated that the palladium complexes were successfully deposited into Nafion membrane, and there were no problems such as cracking and pinhole. The EDX analysis showed that the palladium particles were distributed both at the membrane surface and also extended deeper into the membrane. The TEM images indicated that thin dense band of agglomerated Pd particles can be observed near the membrane surface, and a significant number of isolated Pd particles can be seen deeper into the membrane, when Pd(II) acetylacetonate was used as palladium complex. When palladium(II) hexafluoroacetylacetonate and palladium (II) bis(2,2,6,6-tetramethyl-3,5-heptane-dionato) were used, dense band of agglomerated Pd particles cannot be observed near the membrane surface, and small Pd particles were observed inside the membranes.The XRD analysis indicated that the crystalline peak of Nafion membrane at 2θ = 17° increased with the supercritical CO₂ treatment. It means that the degree of crystallinity for Nafion membrane increased by supercritical CO₂. The metal Pd peak at 2θ = 40° was observed for the Pd/Nafion membranes.The methanol crossover was reduced and the DMFC performance was improved for the Pd/Nafion membranes compared with Nafion membrane at 40 °C. The successful preparation of Pd/Nafion membranes by supercritical CO₂ demonstrated an effective alternative way for modifying membranes and for depositing electrode catalytic nanoparticles onto electrolyte.     

Synergy between tungsten and palladium supported on titania for the catalytic total oxidation of propane

Titania-supported palladium catalysts modified by tungsten have been tested for the total oxidation of propane. The addition of tungsten significantly enhanced the catalytic activity. Highly active catalysts were prepared containing a low loading of 0.5 wt.% palladium, and activity increased as the tungsten loading was increased up to 6 wt.%. Catalysts were characterised using a variety of techniques, including powder X-ray diffraction, laser Raman spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction and aberration-corrected scanning transmission electron microscopy. Highly dispersed palladium nanoparticles were present on the catalyst with and without the addition of WO_x. However, the addition of WO_x slightly increases the average palladium particle size, and there was some evidence for the Pd forming epitaxial islands on the support in the tungsten-doped samples. Surface analysis identified a combination of Pd⁰ and Pd²⁺ on a Pd/TiO₂ catalyst, whereas all of the Pd loading was found in the form of Pd²⁺ with the addition of tungsten into the catalysts. At low tungsten loadings, isolated monotungstate and some polytungstate species were highly dispersed over the titania support. The concentration of polytungstate species increased as the loading was increased, and it was also promoted by the presence of palladium. The coverage of the highly dispersed tungstate species over the titania also increased as the tungsten loading increased. Some tungstate species were also found to be associated with the palladium oxide particles, and there was an enrichment of oxidised tungsten species at the peripheral interface of the palladium oxide nanoparticles and the titania. Sub-ambient temperature–programmed reduction experiments identified an increased concentration of highly reactive species on catalysts with palladium and tungsten present together, and we propose that the new WO_x-decorated interface between PdO_x and TiO₂ particles may be responsible for the enhanced catalytic activity in the co-impregnated catalysts.     

A method for coating a polymer inclusion membrane with palladium nanoparticles

The preparation of palladium nanoparticles on the surface of a polymer inclusion membrane (PIM) consisting of 30 wt% di-(2-ethylhexyl)phosphoric acid and 70 wt% poly(vinyl chloride) is described. The Pd(II) ion was firstly extracted into the membrane via cation-exchange and then subsequently reduced to form clusters of palladium nanoparticles on the membrane surface. The reducing agents investigated were NaBH₄, trisodium citrate, sodium formate, and l-ascorbic acid. Best results were obtained with l-ascorbic acid which at pH 2.0 formed a uniform layer of palladium nanoparticle clusters on the surface of the PIM with an average nanoparticle size of 38 nm.Factors such as pH, temperature and intensity of mixing of the l-ascorbic acid solution, reduction time and Pd(II) loading of the PIM were found to have a significant influence on the surface coverage and size of the palladium nanoparticles.     

Room-temperature Suzuki–Miyaura coupling of aryl bromides with phenylboronic acid catalyzed by a palladium complex with an inexpensive nitrogen-containing bis(phosphinite) ligand

A palladium(II) complex with a known inexpensive and very easily synthesized nitrogen-containing bis(phosphinite) ligand has been prepared and characterized by spectroscopic and crystallographic studies. The ligand is bound to the metal in a P,P-bidentate coordination mode with a bite angle of 98.90°. This complex was found to be an efficient catalyst for room-temperature Suzuki–Miyaura coupling of a variety of aryl bromides with phenylboronic acid. At 0.1 mol% of palladium in DMF/K₃PO₄ for 24 h, the corresponding biaryls were obtained with 75–92% yields. Activated substrates displayed high yields even within minutes.     

Characterisation of BN-supported palladium oxide catalyst used for hydrocarbon oxidation

Hexagonal boron nitride (BN), with a graphite-type structure and with surface area of 184 m²/g was used as a support for palladium oxide (PdO/BN). About 1 wt% of palladium was deposited on BN by incipient wetness method by using palladium nitrate as precursor. The support and the catalyst were characterized by BET, TEM, XRD, XPS, ICP, TG, TPD, in situ ac electrical conductivity and by ammonia adsorption microcalorimetry. Oxidation of propylene and methane were used as model reactions to study the catalytic properties of the PdO/BN catalyst. The BN support was practically inactive in propylene oxidation up to 400 °C, while the onset of the oxidation was detected around 200 °C on PdO/BN, which points out the role of the palladium in adsorption of the reactive hydrocarbon species. At the same time, this temperature is coincident with the increase of the electronic conductivity on both BN and PdO/BN samples, which is important for oxygen adsorption/activation as electrophilic species. The catalyst was inactive in methane oxidation below 400 °C. Only about 2% CH₄ conversion was observed at 400 °C, increasing sharply up to 87% at 550 °C with methane transformation only to CO₂ and water.     

Highly efficient non-noble metal based nanostructured catalysts for selective CO methanation

Highly efficient non-noble metal based catalysts (Zr_1 − xNi_xO₂) showed outstanding catalytic performance at lower temperature for selective CO methanation. The characterization techniques revealed that Zr_1 − xNi_xO₂ catalyst contained uniformly dispersed Ni particles with strong interaction between Ni and ZrO₂.     

Free formic acid by hydrogenation of carbon dioxide in sodium formate solutions

Free formic acid was produced in hydrogenation of carbon dioxide dissolved in aqueous sodium formate solutions under H₂ and CO₂ pressure with the water-soluble rhodium–phosphine complex, [RhCl(mtppms)₃] (mtppms = monosulfonated triphenylphosphine) as catalyst. Concentration of sodium formate, total gas pressure and the pressure ratio of H₂ to CO₂ were the most important factors for production of HCOOH. Up to 0.13 M concentration of HCOOH was achieved, while there was negligible formic acid production in the absence of sodium formate.     

Photocatalytic decolorization of methyl green using Fe(II)-o-phenanthroline as supported onto zeolite Y

The potential of Fe(II)-orthophenantroline photocatalyst, doped on zeolite Na-Y via complexation process, was studied in decolorization of methyl green. The characterization of samples was studied using XRD, FT-IR, TG/DTG and SEM methods. The best photodecolorization efficiency was obtained at: 1 g L⁻¹ catalyst, 40 ppm MG, pH: 9 using catalyst containing 7 mg per gram catalyst. The degradation process obeyed first-order kinetics. The reusability of the intended catalyst was also investigated. Homogeneous photodecolorization using unsupported complex does not significant role in photodecolorization of the dye, which confirms the importance of zeolitic support to prevent the aggregation of complex particles.     

Cationic palladium(II)–acetylacetonate complexes bearing α-diimine ligands as catalysts in norbornene polymerization

A variety of palladium(II)–acetylacetonate complexes bearing α-diimine ligands were synthesized by the reaction of [Pd(acac)(MeCN)₂]BF₄ with N⁀N ligands. When activated with BF₃·OEt₂, these complexes provide access to a new class of alkylating agent free Pd–diimine catalyst systems. Catalyst screening for the vinyl addition polymerization of norbornene showed their high activities of 10²–10⁴ kg_pol mol_cat^− 1 h^− 1.     

Growth of nitrogen-doped carbon nanotubes and fibers over a gold-on-alumina catalyst

Nitrogen-doped carbon nanotubes (N-CNTs) were synthesized by chemical vapor decomposition of a N,C-precursor over a supported Au catalyst. Large quantities of carbon nanotubes with a compartmentalized structure containing ca. 5 at.% N were produced over a 1.5% Au/δ-Al₂O₃ catalyst with a mean diameter of Au particles equal to 2.8 nm under continuous flow conditions at 800 °С and 1 bar of the reaction gas mixture containing pyridine (Py) vapor (5 vol.%), Н₂ (10–20 vol.%) and Ar (balance). The majority of the N-CNTs obtained after 10 min have outer diameters (ODs) of 13–45 nm and closed tips without any encapsulated gold particles of the catalyst which indicates the “base-growth” mechanism of N-CNT formation. Carbon deposits synthesized for 30–135 min contain carbon fibers with OD values up to several micrometers, formed by self-assembling of N-CNTs, and individual N-CNTs. X-ray photoelectron spectra provide evidence for various chemical states of nitrogen (pyridinic, “quaternary” (graphitic) and pyrrolic nitrogen) in the N-CNTs, and these are discussed.     

A green approach for efficient p-nitrophenol hydrogenation catalyzed by a Pd-based nanocatalyst

A magnetically recyclable nanocatalyst, Pd–Fe₃O₄, has been synthesized through a simple one-pot, cost effective method. The electrostatic interaction between the catalyst and the support in the synthesis led to the formation of highly dispersed ultra-fine Pd clusters supported on magnetite. The Pd-based catalyst shows a turnover frequency of 476 h^− 1, which is eight times higher in the efficiency for p-nitrophenol (PNP) hydrogenation than that of the commercial Pd/C (62 h^− 1) under ambient conditions in water. This efficient and green chemical transformation system for the PNP hydrogenation shows promising perspective.     

A phosphine-free heterogeneous formylation of aryl halides catalyzed by a thioether-functionalized MCM-41-immobilized palladium complex

Thioether-functionalized MCM-41-immobilized palladium(II) complex [MCM-41-S-PdCl₂] was found to be a highly efficient catalyst for the formylation of aryl iodides or bromides with CO (1 atm) using HCO₂Na as a hydrogen source. This phosphine-free heterogeneous palladium complex can be easily recovered by simple filtration and reused for at least 10 consecutive trials without any decreases in activity.     

Palladium(II)-catalyzed addition polymerizations of nadimides with linear alkyl and alicyclic pendant groups

Two series of polynadimides with pendant linear alkyl and alicyclic groups have been prepared by addition polymerization of N-alkyl-exo-norbornene dicarboximides (nadimides; alkyl = propyl, butyl, pentyl, hexyl, cyclopropyl, cyclopentyl, cyclohexyl, and cycloheptyl) in the presence of palladium(II) catalyst. The catalytic reactivity of the nadimides strongly depends on the nature and the steric bulk of the pendant groups. Nadimides with alicyclic groups (except for N-cyclopropyl nadimides) exhibit higher reactivity than the nadimides with linear alkyl groups and substituents with the same number of carbons. The polynadimides with alicyclic groups present lower dielectric constants than those with linear alkyl groups. All resulting polynadimides exhibit better thermal stability than the unsubsitituted polynorbornenes.     

Ultrasound assisted production of daunorubicin: Process intensification approach

The present endeavor encompasses process intensification approach for daunorubicin fermentation from Streptomyces peucetius MTCC 4332 using ultrasonic stimulus. One factor at a time design was employed to illustrate the effect of various process parameters of ultrasonic irradiation (irradiation at various growth phases, power, irradiation time and duty cycle) on enhancement of daunorubicin productivity. Ultrasonic irradiation on 4th day of bacterial culture growth at 25 kHz frequency with 160 W power and 40% duty cycle for 5 min shows 1.62 fold increase in daunorubicin production (from 46.96 to 76.42 mg/l) as compared to non-sonicated batch fermentation. Higher duty cycle imparts detrimental effect on bacterial cell and decreases viability of cells. Environmental scanning electron microscopic analysis depicted structural integrity of bacterial cell after irradiation of optimized ultrasonic dose. Moreover, declined glucose concentration after ultrasonication from 1.16 to 0.46 mg/l after 7 days of incubation, implies that cellular uptake of substrate was increased and productivity of cell was also enhanced. Hence, proposed process intensification approach will be very useful to boost up the fermentation of various therapeutic molecules.     

Carbon nanotubes and carbon nanofibers fabricated on tubular porous Al2O3 substrates

Carbon nanotubes and carbon nanofibers were grown at different temperatures on porous ceramic Al₂O₃ substrates with single channel geometry by means of a chemical vapor deposition technique using methane as carbon source and palladium as catalyst. Time-resolved in-situ Fourier transformed infrared spectroscopy was used for the investigation of methane decomposition for characterizing the catalyst’s performance. With increasing synthesis temperature, a structural transition from carbon nanofibers to carbon nanotubes was observed. At a synthesis temperature of 700 °C, solely carbon nanofibers were found, whereas at 800 °C a mixture of two types of bamboo-shaped carbon nanofibers were obtained, suggesting a structural transition. A synthesis temperature to 850 °C results in bamboo-shaped multi-walled carbon nanofibers and multi-walled carbon nanotubes. The carbon products and the observed structural transition were characterized by means of field emission scanning electron microscopy, high-resolution transmission electron microscopy, thermal gravimetric analysis, and Raman spectroscopy.     

Hydrogenation activity and selectivity behavior of supported palladium nanoparticles

Enhancement in activity and selectivity of catalytic hydrogenation using supported nanosize palladium catalyst has been investigated. Pd/C catalyst prepared in the presence of polyvinyl pyrrolidone (PVP) as a stabilizer gave Pd particle size in a narrow range of 3–5 nm. While, evaluating for hydrogenation of 2-butyne-1,4-diol, the rate enhancement was found to be 10 times higher as compared to the conventional (bulk) Pd catalysts. A proper choice of stabilizer (PVP) giving small particle size as well as highly dispersed nature of nano particles were the major factors for such a dramatic enhancement of activity.     

A wall-coated catalytic capillary microreactor for the direct formation of hydrogen peroxide

The direct formation of hydrogen peroxide from H₂ and O₂ was successfully carried out in a capillary microreactor at room temperature and atmospheric pressure. A key element in sustaining the activity of the catalyst is the incarceration of the palladium nanoparticles in a cross-linkable amphiphilic polystyrene-based polymer, prepared following the protocol of Kobayashi [R. Akiyama, S. Kobayashi, J. Am. Chem. Soc. 125 (2003) 3412–3413]. The immobilization effectively reduced the leaching of palladium under acidic conditions. Applying the catalyst as a coating on the inner walls of a capillary enabled the sustained production of 1.1% hydrogen peroxide over at least 11 days. The highest catalyst utilization in a 2 mm capillary reactor was 0.54 mol_H2O2/h g_Pd. When the inner diameter of the reactor capillary was reduced to 530 μm, the rate was enhanced fourfold to 2.28 mol_H2O2/h g_Pd corresponding to a turnover frequency of 0.067 s^?1.     

A novel low-temperature methanol synthesis method from CO/H2/CO2 based on the synergistic effect between solid catalyst and homogeneous catalyst

The activity of a binary catalyst in alcoholic solvents for methanol synthesis from CO/H₂/CO₂ at low temperature was investigated in a concurrent synthesis course. Experiment results showed that the combination of homogeneous potassium formate catalyst and solid copper–magnesia catalyst enhanced the conversion of CO₂-containing syngas to methanol at temperature of 423–443 K and pressure of 3–5 MPa. Under a contact time of 100 g h/mol, the maximum conversion of total carbon approached the reaction equilibrium and the selectivity of methanol was 99%. A reaction pathway involving esterification and hydrogenolysis of esters was postulated based on the integrative and separate activity tests, along with the structural characterization of the catalysts. Both potassium formate for the esterification as well as Cu/MgO for the hydrogenolysis were found to be crucial to this homogeneous and heterogeneous synergistically catalytic system. CO and H₂ were involved in the recycling of potassium formate.     

Preparation of a highly dispersed Ni2P/Al2O3 catalyst using Ni–Al–CO32 − layered double hydroxide as a nickel precursor

We now report a novel method for the synthesis of a Ni₂P/Al₂O₃-LW catalyst using Ni–Al–CO₃^2 − layered double hydroxide (Ni–Al–CO₃^2 −-LDH) as a nickel precursor and ammonium dihydrogen phosphate as a phosphorous precursor under microwave–hydrothermal (MWH) treatment for 20 min at 363 K. The catalysts were characterized by XRD, TPR, BET, CO uptake and XPS. MWH treatment can promote the formation of smaller and highly dispersed Ni₂P particles and a higher surface area of the catalyst. The Ni₂P/Al₂O₃-LW shows hydrodesulfurization activity of 99.3%, which was much higher than that found for the Ni₂P/Al₂O₃ catalyst obtained via an impregnation method.