Bifunctional Pd Research Articles

Base-free aqueous Suzuki–Miyaura coupling reaction using recoverable bi-functional Pd supported nanocatalyst

A solid base catalyst comprising pyridine-palladium polyorganosiloxane framework was synthesized via a grafting method. The resulting organic–inorganic hybrid palladium nanomaterial was characterized by 13C CP-MAS NMR, 29Si CP-MAS NMR, XRD, EDX, TEM, TGA, and the BET measurements. The hybrid palladium nanomaterial exhibited high catalytic activity for the Suzuki–Miyaura cross-coupling reaction between aryl chlorides and phenylboronic acid under base-free and aerobic conditions. A maximum turnover number (TON) of 3150, with a 0.2 mol% Pd loading and a reaction temperature of 80 °C in aqueous solution. The catalyst demonstrated remarkable stability, maintaining its activity even after six cycles of reuse without significant loss of activity. TEM images showed that the catalyst retained its structure and high-order mesostructure after several uses. ICP-AES also confirmed the absence of palladium contamination in the final products. Leaching test studies further confirmed the true heterogeneous nature of the developed catalytic system.

Pd Nanoparticles Supported on N-Incorporated Hybrid Organosilica as an Active and Selective Low-Temperature Phenol Hydrogenation Catalyst

A heterogeneous Pd-NPMO hybrid-silica catalyst is synthesized and its application for aqueous phase selective hydrogenation of phenol to cyclohexanone at near ambient temperature (40 °C) and under atmospheric hydrogen pressure is demonstrated. The homogeneously distributed Pd nanoparticles on N-bridged hybrid mesoporous organosilica showed remarkable activity and selectivity for cyclohexanone compared to the unmodified Pd-SBA-15 catalyst. Control experiments strongly claim the role of nitrogen domains in the organic framework of hybrid silica support in stabilizing small Pd nanoparticles and possibly modifying the Pd sites responsible for catalysis to activate the substrate molecules in water. The hybrid silica catalyst was stable and reused several times without any significant drop-in activity, proving the heterogeneity of the bifunctional Pd catalyst. Based on the density functional theory study and experimental interventions, a possible reaction mechanism for the low-temperature phenol hydrogenation explaining the role of organic domains in the hybrid-silica framework is proposed.

Construction of a Bifunctional Pd(0)‐CALB@SiO2 Hybrid Catalyst for the Synthesis and Arylation of Imidazo[1,2‐a]pyridine in One Pot

AbstractHerein, we describe an efficient strategy for the construction of enzyme‐metal biohybrid catalyst [Pd(0)‐CALB@SiO2] via encapsulation of Candida antarctica lipase B and Pd(0) within silica. Next, the applicability of the newly constructed biohybrid was demonstrated by catalyzing the sequence of Groebke‐Blackburn‐Bienayme (GBB) multicomponent reaction and Suzuki‐Miyaura coupling in a single‐pot to produce clinically significant imidazo[1,2‐a]pyridine derivatives. Interestingly, both entities, i.e., CALB enzyme and Pd(0)‐metal of hybrid catalyst, exhibited good catalytic activity during this approach. Further, the generality of this protocol was explored by using differently substituted boronic acid, which gave related products in 49–87 % isolated yield. Next, the synthetic utility was proved by set‐up a gram scale reaction which provided the complementary product in 81 % yield. Also, the developed biohybrid was found to be reusable up to five catalytic cycles.

Rationally Engineering a CuO/Pd@SiO2 Core-Shell Catalyst with Isolated Bifunctional Pd and Cu Active Sites for n-Butylamine Controllable Decomposition.

Volatile organic amines are a category of typical volatile organic compounds (VOCs) extensively presented in industrial exhausts causing serious harm to the atmospheric environment and human health. Monometallic Pd and Cu-based catalysts are commonly adopted for catalytic destruction of hazardous organic amines, but their applications are greatly limited by the inevitable production of toxic amide and NOx byproducts and inferior low-temperature activity. Here, a CuO/Pd@SiO2 core-shell-structured catalyst with diverse functionalized active sites was creatively developed, which realized the total decomposition of n-butylamine at 260 °C with a CO2 yield and N2 selectivity reaching up to 100% and 98.3%, respectively (obviously better than those of Pd@SiO2 and CuO/SiO2), owing to the synergy of isolated Pd and Cu sites in independent mineralization of n-butylamine and generation of N2, respectively. The formation of amide and short-chain aliphatic hydrocarbon intermediates via C-C bond cleavage tended to occur over Pd sites, while the C-N bond was prone to breakage over Cu sites, generating NH2· species and long free-N chain intermediates at low temperatures, avoiding the production of hazardous amide and NOx. The SiO2 channel collapse and H+ site production resulted in the formation of N2O via suppressing NH2· diffusion. This work provides critical guidance for a rational fabrication of catalysts with high activity and N2 selectivity for environmentally friendly destruction of nitrogen-containing VOCs.

Selective upgrading of biomass-derived benzylic ketones by (formic acid)–Pd/HPC–NH2 system with high efficiency under ambient conditions

Selective upgrading of biomass-derived benzylic ketones by (formic acid)–Pd/HPC–NH2 system with high efficiency under ambient conditions

Formic Acid-Assisted Selective Hydrogenolysis of 5-Hydroxymethylfurfural to 2,5-Dimethylfuran over Bifunctional Pd Nanoparticles Supported on N-Doped Mesoporous Carbon.

Biomass‐derived 5‐hydroxymethylfurfural (HMF) is regarded as one of the most promising platform chemicals to produce 2,5‐dimethylfuran (DMF) as a potential liquid transportation fuel. Pd nanoparticles supported on N‐containing and N‐free mesoporous carbon materials were prepared, characterized, and applied in the hydrogenolysis of HMF to DMF under mild reaction conditions. Quantitative conversion of HMF to DMF was achieved in the presence of formic acid (FA) and H2 over Pd/NMC within 2 h. The reaction mechanism, especially the multiple roles of FA, was explored through a detailed comparative study by varying hydrogen source, additive, and substrate as well as by applying in situ ATR‐IR spectroscopy. The major role of FA is to shift the dominant reaction pathway from the hydrogenation of the aldehyde group to the hydrogenolysis of the hydroxymethyl group via the protonation by FA at the C‐OH group, lowering the activation barrier of the C−O bond cleavage and thus significantly enhancing the reaction rate. XPS results and DFT calculations revealed that Pd2+ species interacting with pyridine‐like N atoms significantly enhance the selective hydrogenolysis of the C−OH bond in the presence of FA due to their high ability for the activation of FA and the stabilization of H−.

Mechanistic aspects of n-paraffins hydrocracking: Influence of zeolite morphology and acidity of Pd(Pt)/ZSM-5 catalysts

The influence of zeolite domain size, acidity, and metal type on n-decane and n-nonadecane hydroconversion was investigated for bifunctional Pd(Pt)/ZSM-5 zeolite (bulk, desilicated, thin and thick nanosheets). Decreasing the size of zeolitic domains to a few nanometers results in lower overall activity, higher skeletal isomerization yield, and an imbalance between metal and acid functions. These changes are attributed to a lower pore occupancy of olefinic intermediates due to the substantially larger external surface of nanosheets and higher desorption rates. Well-balanced bifunctional behavior and higher activity of nanosheet ZSM-5 can be achieved by strengthening the metal function or lowering the acidity. The influence on the isomerized and cracked product fractions is also discussed. Hydroconversion of n-nonadecane gave low yields of skeletal isomers over all Pd-loaded ZSM-5 catalysts and led to significant over-cracking due to the long intracrystalline residence times of the long hydrocarbon reactant.

Reversible Aqueous Zinc-CO2 Batteries Based on CO2 -HCOOH Interconversion.

As a promising technique for CO2 fixation/utilization and energy conversion/storage, the metal-CO2 battery has been studied to improve its interconversion between CO2 and carbonates/oxalates. Herein, we propose and realize a reversible aqueous Zn-CO2 battery based on the reversible conversion between CO2 and liquid HCOOH on a bifunctional Pd cathode. The 3D porous Pd interconnected nanosheet with enriched edge and pore structure, has a highly electrochemical active surface to facilitate simultaneous selective CO2 reduction and HCOOH oxidation at low overpotentials. The resulting battery has a 1 V charge voltage, a cycling durability over 100 cycles, and a high energy efficiency of 81.2 %. The battery mechanism is proposed as Zn+CO2 +2 H+ +2 OH- ↔ ZnO+HCOOH+H2 O, through which the reversible conversion between CO2 and liquid HCOOH was realized.

Reversible Aqueous Zinc–CO2 Batteries Based on CO2–HCOOH Interconversion

AbstractAs a promising technique for CO2 fixation/utilization and energy conversion/storage, the metal–CO2 battery has been studied to improve its interconversion between CO2 and carbonates/oxalates. Herein, we propose and realize a reversible aqueous Zn–CO2 battery based on the reversible conversion between CO2 and liquid HCOOH on a bifunctional Pd cathode. The 3D porous Pd interconnected nanosheet with enriched edge and pore structure, has a highly electrochemical active surface to facilitate simultaneous selective CO2 reduction and HCOOH oxidation at low overpotentials. The resulting battery has a 1 V charge voltage, a cycling durability over 100 cycles, and a high energy efficiency of 81.2 %. The battery mechanism is proposed as Zn+CO2+2 H++2 OH−↔ ZnO+HCOOH+H2O, through which the reversible conversion between CO2 and liquid HCOOH was realized.

A novel bifunctional Pd–ZIF-8/rGO catalyst with spatially separated active sites for the tandem Knoevenagel condensation–reduction reaction

A novel bifunctional catalyst for the Knoevenagel condensation–reduction tandem reaction was prepared by immobilizing ZIF-8 and Pd on GO, respectively.

Substitution reactions of [Pd(bipy)(malonate)] explored with a different set of ligands: Kinetic and mechanistic interpretation in aqueous medium and at pH 7.4

A brief overview of mechanistic studies of the reactions of Pd(II)-bipy-malonate complex with different set of ligands, viz., (N, S), (S, O) and (S) donor molecules is reported here. The kinetics of complex-formation reactions of three sulphur containing bio-relevant ligands thioglycolic acid[L1],thiourea[L2] and thiosemicarbazide [L3] were studied with innermetallic [Pd(bipy)(malonate)] complex at physiological condition. The effect of the nucleophilicity of the chosen nucleophiles was studied for the reactant complex under pseudo-first order conditions as a function of nucleophile concentration and temperature using stopped-flow technique. This article describes the results obtained for substitution reactions of bi-functional Pd(II) complex with different biomolecules, under varying experimental conditions. The kinetic studies showed that the malonate ring departs from the coordination zone of palladium centre via two-step mechanism. The first step depends on the concentration of the incoming ligand for all the ligands. But in the second step thiourea is ligand dependent where as other two are independent of the ligand concentration. Hence, it can be concluded that the second step is the chelation step for L1 and L3. The mechanism for the substitution of the coordinated malonate molecule is associative, as demonstrated by the negative values of ΔS ≠. Such type of complexes are less toxic than chloro-, which in turn hydrolyses to aqua or aqua complexes as they are prevented from oligomer formation at physiological pH. Studies of kinetic and mechanistic pathways for the reactions of Pd(II)-bipy-malonate complex with thioglycolic acid, thiourea and thiosemicarbazide have been carried out. Innermetallic [Pd(bipy)(malonate)] complex reacts with above mentioned sulphur containing ligands at physiological condition and these substitution reactions are associative in nature.

One-pot two-step process for direct propylene oxide production catalyzed by bi-functional Pd(Au)@TS-1 materials

Different bi-functional materials (Pd(Au)@TS-1) based on metallic nanoparticles supported onto active nanocrystalline titanium silicalite (TS-1) zeolites were synthesized, characterized and used as recyclable heterogeneous catalysts for direct propylene oxide production from hydrogen, oxygen and propylene through one-pot two-step consecutive process. These catalysts allowed carrying out the combined reaction where metallic nanoparticles catalyzed the formation of in situ H2O2 that was the necessary intermediate for propylene epoxidation catalyzed by active TS-1 nanocrystalline support. Several variables were considered such as use of supercritical CO2 conditions, modifiable content of metallic species, and presence of additional co-solvents, surface acidity inhibitors and H2O2 stabilizers. Reusability and stability of the bi-functional catalyst was showed through consecutive catalytic cycles.

Inkjet Printing of a Highly Loaded Palladium Ink for Integrated, Low‐Cost pH Sensors

An inkjet printing process for depositing palladium (Pd) thin films from a highly loaded ink (>14 wt%) is reported. The viscosity and surface tension of a Pd‐organic precursor solution is adjusted using toluene to form a printable and stable ink. A two‐step thermolysis process is developed to convert the printed ink to continuous and uniform Pd films with good adhesion to different substrates. Using only one printing pass, a low electrical resistivity of 2.6 μΩ m of the Pd film is obtained. To demonstrate the electrochemical pH sensing application, the surfaces of the printed Pd films are oxidized for ion‐to‐electron transduction and the underlying layer is left for electron conduction. Then, solid‐state reference electrodes are integrated beside the bifunctional Pd electrodes by inkjet printing. These potentiometric sensors have sensitivities of 60.6 ± 0.1 and 57 ± 0.6 mV pH−1 on glass and polyimide substrates, and short response times of 11 and 6 s, respectively. Also, accurate pH values of real water samples are obtained by using the printed sensors with a low‐cost multimeter. These results indicate that the facile and cost‐effective inkjet printing and integration techniques may be applied in fabricating future electrochemical monitoring systems for environmental parameters and human health conditions.

One-step hydrogenation–esterification of furfural and acetic acid over bifunctional Pd catalysts for bio-oil upgrading

This contribution focuses on one-step hydrogenation–esterification (OHE) of furfural and acetic acid, which are difficult to treat and typically present in crude bio-oil, as a model reaction for bio-oil upgrading. A bifunctional catalyst is needed for OHE reaction. Among tested bifunctional catalysts, the 5%Pd/Al2(SiO3)3 shows the best catalytic performance. Compared to the physical mixture of 5%Pd/C+Al2(SiO3)3, there is a synergistic effect between metal sites and acid sites over 5%Pd/Al2(SiO3)3 for the OHE reaction. A moderate reaction condition would be required to obtain high yields of alcohol and ester along with lower byproduct yields. In this work, the optimum selectivity to desired products (alcohol and ester) of 66.4% is obtained, where the conversion of furfural is 56.9%. Other components, typically present in bio-oils, have little effects on the OHE of FAL and HAc. This OHE method is a promising route for efficient upgrading of bio-oil.

Performance of bifunctional Pd/M xN yO (M = Mg, Ca; N = Zr, Al) catalysts for aldolization–hydrogenation of furfural–acetone mixtures

The performance of different bi-functional Pd catalysts (supported on Mg–Zr, Mg–Al and Ca–Zr mixed oxides) for the aqueous-phase aldol-condensation of acetone and furfural was studied in this work. Experiments were carried out in a batch slurry reactor at 323–393 K. Activity trends, as well as selectivity for the formation of the different adducts (C 8 and C 13), were correlated with the physico-chemical properties of the materials, mainly with the distribution of acid and basic sites. In general, it was observed that the catalyst with the lowest concentration of basic sites (Pd/Ca–Zr) presents the poorest performance. By contrast, the presence of medium-strength acid sites (as the observed in the case of one the Pd/Mg–Al catalyst) seems to enhance the catalytic activity of the material. Although selectivities trends were similar for the catalysts supported on Mg–Zr and Mg–Al catalysts, the ability of the materials for catalyzing the formation of the heaviest adducts depends mainly on the total concentration of basic sites.

Synthesis of cyclohexylcyclohexanone on bifunctional Pd faujasites: Influence of the balance between the acidity and the metallic function

The transformation of cyclohexanone was carried out on a series of bifunctional PdHFAU catalysts with Pd contents between 0.1 and 0.5 wt.% and framework Si/Al ratios equal to 5, 20, 40 and 100, under the following conditions: flow reactor, 473 K, pressures of cyclohexanone and hydrogen equal to 0.17 and 0.83 bar, respectively. With all the catalysts, cyclohexylcyclohexanone, the formation of which requires successive steps of aldolization, dehydration and hydrogenation, is directly formed. The effect of the balance between the hydrogenating and acid functions of the catalysts (taken as the ratio between their activity for toluene hydrogenation and their number of protonic acid sites, A H/ B) on their activity, stability and selectivity is the one expected from a bifunctional catalytic process. The activity per protonic site first increases with A H/ B, then remains constant above a certain value of A H/ B (0.4 h −1), the limiting step of cyclohexylcyclohexanone formation being then cyclohexanone aldolization. The selectivity to cyclohexylcyclohexanone as well as the stability increase with A H/ B remaining constant for A H/ B>1 h −1. While a high selectivity to cyclohexylcyclohexanone is obtained, the catalyst stability is relatively poor due to the retention inside the zeolite micropores of polar tricyclic C 18 compounds.

Transformation of acetophenone over Pd aluminosilicate catalysts. Influence of acidity and pore structure

The gas phase transformation of acetophenone under hydrogen was investigated in a fixed-bed reactor over series of bifunctional Pd molecular sieves (HFAU, HBEA, MCM41). On all the catalysts, the desired product: 1,3-diphenylbutan-1-one (DPBO) which results from three successive steps: aldolisation then dehydration on the acid sites and hydrogenation over Pd sites, can be obtained directly. Benzoic acid, isopropenylbenzene and its transformation products formed by acid cracking of intermediates of DPBO production are the main secondary products. As expected from a bifunctional mechanism, the rate of DPBO formation over Pd zeolite samples of identical acidities increases firstly with the number of accessible Pd atoms (nPd) then remains constant above a certain value of nPd. On the other hand, nPd has a negative effect on the formation of the main secondary products. However, the main parameter determining the rate and selectivity of the Pd catalysts is their porosity, the most active and selective catalysts being large pore zeolites with a large mesopore volume (Pd HFAU and Pd HBEA) or mesoporous aluminosilicates (Pd HMCM41). This large effect of porosity can be related to limitation in the desorption of the bulky and polar molecules of DPBO (and olefinic intermediate) from the micropores.

Sequence-selective metal ion binding to DNA oligomers.

Sequence-selective interactions between DNA oligonucleotides and Pt(II) and Pd(II) complexes have been studied by 1D and 2D NMR spectroscopy. Titration of DNA oligomers with diamagnetic metal ion complexes induces chemical shifts of proton resonances close to the site of interaction. Conformational changes in the helical structure were monitored by measuring cross-peak intensities in 2D NOESY maps. Two duplex deoxynucleotides were studied, [d(CGCGCG)]2 and [d(CGCGAATTCGCG)]2, respectively. The hexamer was titrated in the duplex form with cis-[Pt(NH3)2Cl2]2+ (cis-DDP or cisplatin). The dodecamer was titrated with NO(3-)-salts of Pd(aq)2+, [Pd(en)(H2O)2]2+ and [Pd(dien)(H2O)]+, respectively. The reaction between cis-DDP and the hexamer at conditions where the duplex form is retained proceeded exceedingly slowly. In the initial phase of the titration the NOESY map indicates conformational changes induced by noncovalent adduct formation between the intact hexamer and cis-DDP. The more reactive Pd compounds show a tendency towards sequence-selective binding to the duplex dodecamer. The 'naked' Pd ion is very reactive and exhibits selectivity towards the thymine T8 imino proton and N7 on G4. At a Pd(II)/dodecamer ratio of 4:1 the metal ions induce helix-->coil transition. The mono- and bifunctional Pd complexes with 'bulky' ligands attack the dodecamer at the terminal GC base pairs, leaving the central Watson-Crick base pairs intact.