Pd(0)-<Emphasis Type="Italic">S</Emphasis>-methylisothiourea grafted onto mesoporous MCM-41 and its application as heterogeneous and reusable nanocatalyst for the Suzuki,Stille and Heck cross coupling reactions

In this project palladium (0) S-methylisothiourea was grafted into MCM-41 mesoporous silica. Palladium (0) S-methylisothiourea complex supported on MCM-41 (Pd(0)-SMT-MCM-41), as heterogeneous and reusable catalyst, was used in C–C bond formation between various aryl halides with sodium tetraphenylborate or phenylboronic acid (Suzuki reaction), aryl halides with triphenyltin chloride (Stille reaction), and aryl halides with styrene or n-butyl acrylate (Heck reaction). This catalyst was characterized by various physico-chemical techniques such as X-ray diffraction, transmission electron microscopy, scanning electron microscopy (SEM/EDX), thermal gravimetric analysis (TGA/DTA), fourier transform infrared spectroscopy and inductively coupled plasma. The results indicated that Pd(0)-SMT-MCM-41 catalyst could be easily recovered from reaction mixture for several consequence runs without significant loss of its catalytic activities.     

Microwave-assisted Sonogashira cross-coupling reaction catalyzed by Pd-MCM-41 under solvent-free conditions

In this paper microwave-assisted Sonogashira reactions of phenyl acetylene with aryl iodide using palladium modified Pd-MCM-41, Pd-Y, Pd-VSB-5 and Pd-SBA-15 under solvent-free conditions were described. The results of microwave-assisted Sonogashira reaction using Pd-MCM-41 or Pd-Y in aqueous conditions were also discussed. The microwave-assisted reaction of phenyl acetylene with phenyl iodide using Pd-Y or Pd-MCM-41 and DBU as a base under solvent-free conditions resulted in yields of 85% and 93%, respectively. The reaction with Pd-Y or Pd-MCM-41 using DBU in DMF:H₂O (4:1) solution reduced yields to 64% and 76%, respectively.     

Mesoporous silicas containing carboxylic acid: Preparation,thermal degradation,and catalytic performance

The calcination and thermal degradation behaviors of surfactants in mesoporous silicas SBA-15 and MCM-41 were investigated by FT-IR, ¹³C CP/MAS NMR, TG/DTA, and GPC. It was found that carboxylic acid-containing products were generated as active components in the mesopores of SBA-15 and MCM-41 from the triblock copolymer (PEO)₂₀(PPO)₇₀(PEO)₂₀ and cetyltrimethylammonium bromide (CTAB), respectively; the latter materials were used as templates. The carboxylic acid-containing mesoporous silica obtained showed a catalytic activity for hydrolysis of sucrose. The acidity was evaluated by means of NaOH titration. The acidity sensitively depended on both the calcination temperature and the atmosphere; the maximum appeared at 150 °C in air for SBA-15 where the highest activity was observed. However, the product in MCM-41 showed a lower catalytic activity than that in SBA-15. The SBA-15 product was easily leached from the mesopores of SBA-15 into the solution, but the degree of leaching for MCM-41 was considerably smaller than that for SBA-15.     

Highly efficient palladium catalysts supported on nitrogen contained polymers for Suzuki-Miyaura reaction

Through Pd catalyzed CN coupling reaction, Pd nanoparticles and diadamantylphosphine ligand were immobilized in situ into the formed N contained polymers as heterogeneous Pd catalysts for Suzuki-Miyaura reaction. The Pd@NPad₂-1.0 catalyst was found to be highly efficient and only 4 ppm of Pd (Pd@NPad₂-1.0) was required for the coupling of aryl bromides with phenylboronic acid, and the corresponding products were obtained in good to excellent yields with high TON and TOF as 250,000 and 41,666 h^− 1 respectively. Moreover, the coupling of various aryl chlorides with phenylboronic acids gave the corresponding products in high yields also. And the Pd@NPad₂-1.0 catalyst is reusable at least 5 times with only slight deactivation.     

Short channeled Zr-Ce-SBA-15 supported palladium catalysts for toluene catalytic oxidation

Short channeled Zr-Ce-SBA-15 (ZCS) mesoporous materials were synthesized through hydrothermal routes without addition of mineral acids. 0.5 wt.% palladium was loaded on ZCS and SBA-15 via an ethanol reduction approach. Pd/ZCS possesses unique hexagonal platelet morphologies with short channels running parallel to the thickness in the range of 400–500 nm, while Pd/SBA-15 has a fibrous macrostructure with channels at the micrometer scale. Palladium species present in supports as well dispersed PdO nanocrystals with diameter of ca. 5–6 nm. Comparing with Pd/SBA-15, Pd/ZCS shows enhanced catalytic activity for toluene oxidation, which is ascribed to short channeled supports facilitating the molecular diffusion.     

Hydrodeoxygenation of phenol over Pd catalysts by in-situ generated hydrogen from aqueous reforming of formic acid

Hydrodeoxygenation of phenol, as model compound of bio-oil, was investigated over Pd catalysts, using formic acid as a hydrogen donor. The order of activity for deoxygenation of phenol with Pd catalysts was found to be: Pd/SiO₂ > Pd/MCM-41 > Pd/CA > Pd/Al₂O₃ > Pd/HY ≈ Pd/ZrO₂ ≈ Pd/CW > Pd/HSAPO-34 > Pd/HZSM-5. The good performance of Pd/SiO₂ is owing to its proper pore structure and large specific surface area. The high level of Brønsted acid sites in SiO₂ also favors the deoxygenation of phenol.     

Carboncarbon bond forming reactions: Application of covalently anchored 2,4,6-triallyloxy-1,3,5-triazine (TAT) Pd(II) complex over modified surface of SBA-15 to Heck,Suzuki, Sonogashira and Hiyama cross coupling reactions

A highly active SBA-15-TAT-Pd(II) catalyst was synthesized from organofunctionalized SBA-15 and 2,4,6-triallyloxy-1,3,5-triazine. The catalyst was employed in carrying out Heck, “copper-free” Sonogashira, Suzuki and Hiyama cross coupling reactions. Under the optimized conditions the catalyst displays excellent catalytic activity in delivering the desired products in good to excellent yields. The catalytic system exhibited superior activity regarding the time taken for the completion of reaction, isolation, Pd loading (0.62 mmol%) and yields of products as compared to the earlier reported heterogeneous SBA-15 anchored Pd catalysts. The catalyst could be recycled and reused for five times without any appreciable loss of catalytic activity.     

Pd Functionalized MCM-41 Catalysts for Suzuki Reactions

Palladium (II) containing siliceous-MCM-41 has been prepared according to an original pathway by the reaction between silica precursors (imeo) and MCM-41. The resulting materials have been characterized by chemical analysis, X-ray powder diffraction, nitrogen sorption isotherms, and SEM and catalysis tests. Catalysis tests show that the very dispersive structure of the Pd-MCM-41 promotes the generation of fairly active catalysts for Suzuki cross-coupling of aryl chlorides and phenyl boronic acid under specific conditions, where the leaching of redox-active species has been minimized (less than 2 ppm).     

Size dependence in solvent-free aerobic oxidation of alcohols catalyzed by zeolite-supported palladium nanoparticles

The size dependence in the palladium nanoparticle-catalyzed solvent-free aerobic oxidation of alcohols was studied. Palladium nanoparticles with tunable mean sizes in a range of 2.0–10.5 nm were prepared over NaX zeolite by ion exchange of Na⁺ with an ionic Pd precursor followed by calcination and H₂ reduction. The calcination temperature was found to be a crucial factor in determining the mean size of Pd nanoparticles. Pd/NaX catalysts with proper mean sizes of Pd could catalyze the solvent-free aerobic oxidation of various alcohols, and were particularly efficient for the oxidation of benzylic alcohols without substituents in benzene ring. Detailed studies using the Pd/NaX catalysts with different mean sizes of Pd revealed that the solvent-free aerobic oxidation of benzyl alcohol was structure-sensitive, and the intrinsic turnover frequency (TOF) reached a maximum at a medium mean size of Pd (2.8 nm). On the other hand, for the oxidation of geraniol or 2-octanol without delocalized π-ring, the reaction was structure-insensitive, and the intrinsic TOF did not change significantly with the mean size of Pd particles.     

A porous metal–organic framework as active catalyst for multiple C–N/C–C bond formation reactions

A 3D porous metal–organic framework {[Cu(4-tba)₂](solvent)}_n (1⋅S) is assembled via 4-(1H-1,2,4-triazol-1-yl)benzoic acid (Htba) and Cu(II) nodes, which shows the [2 + 2] roto-translational interpenetrating network. Interestingly, 1 displays high CO₂ adsorption selectivity over CH₄/H₂/O₂/Ar/N₂ gases, and acts an efficient catalyst precursor in some C–N/C–C bond formation reactions, including Chan–Lam coupling reaction of phenylboronic acid with imidazole, Suzuki–Miyoura coupling reaction of phenylboronic acids with aryl halides, and Heck coupling reaction of styrene with aryl halides.     

Cu-ZSM5 as reusable catalyst for the one-pot,odorless and ligand-free C-S bond formation

Cu^I-ZSM5 and Cu^II-ZSM5 as reusable and heterogeneous nanocatalysts were synthesized and characterized using various techniques. The catalysts have been applied for the practical synthesis of various phenyl aryl/benzyl sulfides via one-pot and odorless processes from the reaction of triphenyltin chloride or phenylboronic acid as phenyl source with different aryl/benzyl halides in the presence of S₈ as sulfur source and KF or KOH as S₈ activator in DMF at 80 °C.     

MCM-41 catalyzed rapid and efficient one-pot synthesis of polyhydroquinolines via the Hantzsch reaction under solvent-free conditions

A one-pot four-component reaction of aldehydes, 5,5-dimethyl-1,3-cyclohexanedione, ethyl acetoacetate and ammonium acetate has efficiently been carried out in the presence of 1 mol% of MCM-41 as a heterogeneous catalyst in a solvent-free media at 90 °C to form the corresponding polyhydroquinoline derivatives via the Hantzsch reaction. The present methodology offers several advantages such as excellent yields, simple procedure, short reaction time (15–25 min), milder conditions and the remarkable reusability of the catalyst, MCM-41.     

Diesel-like hydrocarbons obtained by direct hydrodeoxygenation of sunflower oil over Pd/Al-SBA-15 catalysts

Hydrodeoxygenation of sunflower oil was performed in an autoclave over 5.0 wt.% Pd/Al-SBA-15 (Si/Al molar ratios from 22 to 300) and Pd/HZSM-5(22). The effects of acidity of the catalysts and the reaction temperatures on the activity of the catalysts were investigated. Pd/Al-SBA-15(Si/Al = 300) showed a high activity as 74.4% liquid yield and 72.9% C15–C18 diesel-like hydrocarbons yield at 250 °C. At 300 °C, the higher activity over Pd/Al-SBA-15(Si/Al = 50, 100 and 300) catalysts compared with that over Pd/Al-SBA-15(22) and Pd/HZSM-5(22) indicated that strong acidity of the catalysts was not favorable for converting sunflower oil into C15–C18 diesel-like hydrocarbons at a high temperature.     

The effect of TiO2 particle size on the characteristics of Au–Pd/TiO2 catalysts

The nanocrystalline TiO₂ materials with average crystallite sizes of 9 and 15 nm were synthesized by the solvothermal method and employed as the supports for preparation of bimetallic Au/Pd/TiO₂ catalysts. The average size of Au–Pd alloy particles increased slightly from sub-nano (< 1 nm) to 2–3 nm with increasing TiO₂ crystallite size from 9 to 15 nm. The catalyst performances were evaluated in the liquid-phase selective hydrogenation of 1-heptyne under mild reaction conditions (H₂ 1 bar, 30 °C). The exertion of electronic modification of Pd by Au–Pd alloy formation depended on the TiO₂ crystallite size in which it was more pronounced for Au/Pd on the larger TiO₂ (15 nm) than on the smaller one (9 nm), resulting in higher hydrogenation activity and lower selectivity to 1-heptene on the former catalyst.     

Suzuki–Miyaura reaction catalyzed by graphene oxide supported palladium nanoparticles

Pd supported on polyamine modified graphene oxide (GO-NH₂-Pd^2 +) was fabricated for the first time. The prepared catalyst was characterized by transmission electron microscopy, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy and infrared spectroscopy. The catalytic activity of the prepared catalyst was investigated by employing Suzuki–Miyaura coupling reaction as a model reaction. A series of biphenyl compounds were synthesized through the Suzuki–Miyaura reaction using GO-NH₂-Pd^2 + as catalyst. The yields of the products were in the range from 71% to 95%. The catalyst can be readily recovered and reused at least 10 consecutive cycles without significant loss its catalytic activity.     

Self-oscillations of methane oxidation rate over Pd/Al2O3 catalysts: Role of Pd particle size

Oscillations of the methane oxidation rate were studied under methane-rich conditions on Pd/Al₂O₃ catalysts differing in Pd particle size. It was demonstrated that the temperature interval where oscillations occur narrows from 300–360 °C for the catalyst with Pd particle aggregates from 50–100 nm to 345–355 °C for the catalyst with isolated Pd particles of ~ 5 nm in size. At the same time, the period of oscillations showed ~ 6-fold increase. Structural transformations of Pd in the oscillation cycle were similar to those observed on bulk Pd used as a catalyst in the same reaction.     

Sunflower oil hydrogenation on Pd in supercritical solvents: Kinetics and selectivities

The partial hydrogenation of sunflower oil on a few supported Pd catalysts in supercritical (SC) dimethyl ether (DME) as reaction solvent was studied to obtain hydrogenates with low trans C 18:1 and stearic contents.The kinetics was determined on eggshell 0.5% Pd/Al₂O₃ and uniform 2% Pd/C catalysts using a sequential experimental design in a continuous, radial-flow, internal recycle reactor. The operating variables were temperature (456–513 K), pressure (18–23 MPa) and the space-velocity (WHSV = 41–975 h⁻¹). The rotation frequency and the molar feed concentration (oil:H₂:DME) were held constant at 157 rad/s and 1:4:95 mol%, respectively. Kinetic scheme was based on that published before. Some reactor runs were simulated using mixed-flow assumption and the kinetics data for both systems with good results. A comparison was established between the eggshell 0.5% Pd/Al₂O₃ in DME and the data for 2% Pd/C in propane with respect to trans production and stearic formation. trans seems to be lower using 2% Pd/C in propane, while the undesired stearic formation is less on the eggshell 0.5% Pd/Al₂O₃ catalyst in DME. An overview is presented on the merits of the catalysts available for the SCF process in terms of linoleic selectivity and trans yield on a few vegetable fats.     

Promoting effect of Pd on H2 production from cellulose pyrolysis over mesocellular-foam-supported Ni catalysts

Noble-metal promoters have been added to catalysts for reactions such as steam-methane reforming, but have rarely been applied to systems that produce H₂ from larger, biomass-derived molecules, such as polyols or cellulose. We have previously found that nickel catalysts supported on mesocellular-foam-(MCF)-type silica catalyze H₂ formation during cellulose pyrolysis, and sought to increase their activity. Thus, palladium-promoted nickel catalysts supported on MCF were prepared, and their activities were tested in cellulose pyrolysis (RT → 800 °C, 40 °C/min) under dry argon. A thermogravimetric analyzer–mass spectrometer (TG–MS) was used to semi-quantitatively monitor the gases, especially H₂, that were released during pyrolysis over catalysts with and without Pd promoters. Although the Pd promoters had little impact on the fraction of H₂ in the product gas, adding ≥ 0.4 wt.% Pd enhanced the H₂ yield from cellulose pyrolysis by increasing the total gas yield from the reaction. Thus the promoter improved H₂ yield by enhancing the tar-cracking activity of the catalyst. A 5%Ni/MCF catalyst that was doped with 0.7 wt.% Pd yielded 85 cm³ H₂/g cellulose, which was 15% more H₂ than was obtained when the catalyst was 5%Ni/MCF.     

A facile preparation of palladium Schiff base complex supported into MCM-41 mesoporous and its catalytic application in Suzuki and Heck reactions

A simple and efficient method for phosphine-free C–C coupling reactions such as Heck and Suzuki reactions in the presence of pyrrole Schiff base complex of palladium immobilized on mesoporous mesoporous of MCM-41 (Pd-Py-MCM-41) has been reported. The Suzuki reaction was carried out in PEG-400 using phenylboronic acid (PhB(OH)₂). Pd-Py-MCM-41 has been found as a promising catalyst for Heck reaction of butyl acrylate with aryl halides (including Cl, Br and I). The catalyst was characterized by FT-IR, TEM, XRD, SEM, BET and ICP-OES techniques. The protocol proves to be efficient and environmentally benign in terms of high yield, easy of recovery and reusability of catalyst.     

Epoxidation of propene on vanadium species supported on silica supports of different structure

Silica supports such as mesoporous materials (SBA-3, SBA-15 and MCM-41), silicalite and amorphous silica were used for accommodation of vanadium species introduced on the support surface by means of impregnation, with vanadium concentration from 1 to 7 wt.%. Catalysts were characterised by means of XRD, low temperature adsorption/desorption of nitrogen, DR UV–vis and Raman spectra and also H₂-TPR measurements. Isolated vanadium species dispersed in the channels of mesoporous SBA-3 with pores diameter related to micropores range, seems to be the most active for propene epoxidation.