Liquid-phase Hydrogenation Of Diphenylacetylene Research Articles

Kinetics of liquid-phase diphenylacetylene hydrogenation on “single-atom alloy” Pd-Ag catalyst: Experimental study and kinetic analysis

• Pd 1 Ag 3 SAA catalyst demonstrates extremely high selectivity in diphenylethene (ca. 98 %). • Selectivity of Pd 1 Ag 3 does not depend on P(H 2 ) and DPA concentration. • Proposed kinetic model is capable to describe the experimental dependencies. Catalytic performance of Pd 1 Ag 3 /Al 2 O 3 single-atom alloy (SAA) catalyst was studied in liquid-phase hydrogenation of diphenylacetylene (DPA) and compared with the performance of the reference monometallic Pd/Al 2 O 3 . Formation of SAA structure in Pd 1 Ag 3 /Al 2 O 3 was confirmed by FTIR CO technique. It was found that Pd 1 Ag 3 /Al 2 O 3 single-atom alloy catalyst exhibits excellent selectivity in diphenylethene (stilbene) (ca. 98 %), which remains constant over a wide range of DPA conversions (0–95%), while over Pd/Al 2 O 3 selectivity decreases steadily with the increase in DPA conversion. It is remarkable that the selectivity of Pd 1 Ag 3 /Al 2 O 3 depends neither on hydrogen pressure (5–15 bar), nor on DPA concentration (0.0262 – 0.159 mol/l). In contrast, over the reference Pd/Al 2 O 3 selectivity tends to decrease with increasing P(H 2 ) and decreasing DPA concentration. The proposed reaction network comprises hydrogenation of DPA in a parallel formation of cis and trans -stilbene with following hydrogenation to bibenzyl and direct formation of the latter from the initial DPA. The calculations clearly shows the capability of the kinetic model to describe the experimental dependencies for Pd 1 Ag 3 single-atom catalyst in an excellent way with the degree of explanation equal to ca. 99 %.

Synthesis of Supported Heterogeneous Catalysts by Laser Ablation of Metallic Palladium in Supercritical Carbon Dioxide Medium.

To obtain a supported heterogeneous catalyst, laser ablation of metallic palladium in supercritical carbon dioxide was performed in the presence of a carrier, microparticles of γ-alumina. The influence of the ablation process conditions—including supercritical fluid density, ablation, mixing time of the mixture, and laser wavelength—on the completeness and efficiency of the deposition of palladium particles on the surface of the carrier was studied. The obtained composites were investigated by scanning and transmission electron microscopy using energy dispersive spectroscopy. We found that palladium particles were nanosized and had a narrow size distribution (2–8 nm). The synthesized composites revealed high activity as catalysts in the liquid-phase hydrogenation of diphenylacetylene.

Synthesis of Polymer–Metal Composites by the Impregnation of Hypercrosslinked Polystyrene with Palladium Compounds in Supercritical Carbon Dioxide and Their Catalytic Activity in the Liquid-Phase Hydrogenation of Diphenylacetylene

Composites—palladium metal particles in a polymer matrix—are obtained by impregnation of hypercrosslinked polystyrene with palladium compounds in supercritical carbon dioxide (SC-CO2) followed by molecular hydrogen reduction. The synthesized composites exhibit a high level of catalytic activity in the liquid-phase hydrogenation of diphenylacetylene (DPA). The turnover frequency (TOF) is 15–50 min–1 and the selectivity in the formation of diphenylethylene is 60–80% at ~90% conversion of the substrate.

Experimental and theoretical analysis of particle size effect in liquid-phase hydrogenation of diphenylacetylene

The liquid-phase hydrogenation of diphenylacetylene (DPA) over 1 wt% Pd/Al2O3 catalysts with the mean palladium cluster size varying from 1.9 to 20 nm was studied at 5 bar H2 pressure and 25 °C. Hydrogenation of the triple bond was found to be structure sensitive and turnover frequency increased as Pd cluster size increased, while TOF in hydrogenation of the intermediate stilbene was essentially independent on the cluster size. Selectivity to stilbene was rather high (90–94%) and tends to increase with an increasing of Pd particle size.A reaction network was proposed for diphenylacetylene hydrogenation involving formation of cis- and trans- stilbene and their subsequent hydrogenation. The effect of Pd nanoparticle size on the hydrogenation kinetics was analyzed and discussed using a geometric approach based on the respective contribution of low (edges, corners) and highly coordinated sites (terraces) for a cubooctahedral shape of metal clusters. A quantitative description of the concentration dependences was performed incorporating the Pd particle size in the rate equations through changes in dispersion and the ratio of sites of different coordination. An excellent correspondence between theory and experiments was demonstrated.

Tuning the surface structure and catalytic performance of PdIn/Al2O3 in selective liquid-phase hydrogenation by mild oxidative-reductive treatments

The in situ DRIFT-CO and XPS data demonstrated that the mild oxidation of PdIn intermetallic nanoparticles results in the partial oxidation of an In component and the trans-formation of isolated Pd1 sites to Pdn multiatomic ones thus enhancing PdIn activity in the liquid-phase hydrogenation of diphenylacetylene without sacrificing the alkene selectivity.

Highly Selective Pd–Cu/α-Al2O3 Catalysts for Liquid-Phase Hydrogenation: The Influence of the Pd: Cu Ratio on the Structure and Catalytic Characteristics

The structure and catalytic characteristics of a series of Pd–Cu/α-Al2O3 catalysts with Pd: Cu ratio varied from Pd1–Cu0.5 to Pd1–Cu4 were studied. The use of α-Al2O3 with a small surface area (Ssp = 8 m2/g) as a support made it possible to minimize the effect of diffusion on the catalytic characteristics and to study the structure of Pd–Cu nanoparticles by X-ray diffraction (XRD) analysis. The XRD analysis and transmission electron microscopy (TEM) data indicated the formation of uniform bimetallic Pd–Cu nanoparticles (d = 20–60 nm), whose composition corresponded to a ratio between the metals in the catalyst, and also the absence of monometallic Pd0 and Cu0 nanoparticles. The study of catalytic properties in the liquid-phase hydrogenation of diphenylacetylene (DPA) showed that the activity of the catalysts rapidly decreased with the Cu content increase; however, in this case, the yield of a desired alkene compound significantly increased. The selectivity of alkene formation on the catalysts with the ratios Pd: Cu = 1: 3 and 1: 4 was superior to the commercial Lindlar catalyst.

Adsorption-Induced Segregation as a Method for the Target-Oriented Modification of the Surface of a Bimetallic Pd–Ag Catalyst

The effect of palladium segregation was studied which resulted from the effect of CO and O2 on the surface structure and catalytic characteristics of the Pd–Ag2/Al2O3 catalyst. The IR-spectroscopic study of adsorbed CO showed that Pd1 centers isolated from each other by silver atoms predominated on the surface of reduced Pd–Ag2/Al2O3, as evidenced by the almost complete absence of absorption bands typical for the multicentred CO adsorption. In the course of catalyst treatment with CO and O2, the intensity of absorption bands characteristic of the multicenter CO adsorption considerably increased due to the transformation of a portion of monatomic Pd1 centers into multiatomic Pdn ones as a result of the surface segregation of Pd. In this case, a substantial increase in the catalyst activity in the liquid-phase hydrogenation of diphenylacetylene was observed. It was established that, after treatment with CO, the catalyst selectivity for the formation of a target olefin (stilbene) remained almost constant, whereas the treatment with O2 led to a decrease in the selectivity because of more considerable surface modification.

PdZn/α-Al2O3 catalyst for liquid-phase alkyne hydrogenation: effect of the solid-state alloy transformation into intermetallics

The complex characterization of a PdZn /Al2O3 catalyst by XPS, XRD, TEM and H2-TPD techniques revealed the route of solid-state alloy → intermetallics transformation. The influence of this transformation on the performance of PdZn /Al2O3 in the liquid-phase hydrogenation of diphenylacetylene was estimated.

Influence of the Support on the Catalytic Characteristics of the Deposited Palladium in the Liquid-Phase Hydrogenation of Diphenylacetylene

Palladium catalysts on various types of supports were studied in the liquid-phase hydrogenation of diphenylacetylene. Samples of Pd/SiO2–Al2O3, Pd/MgAl2O4, Pd/Al2O3, and Pd/TiO2 were characterized by the chemisorption of the CO and IR spectroscopy of adsorbed CO. The use of n-hexane as the solvent increases the reaction rate, which can be explained by the better solubility of hydrogen in the liquid phase. It is established that the acid–base properties of the support do not affect the activity and selectivity of the catalysts in the reaction under study. However, they alter the electronic state of palladium. According to the catalytic tests, Pd/TiO2 has the highest activity (turnover frequency) and selectivity to alkene. The comparison of the obtained catalytic data and the results of IR spectroscopy made it possible to conclude that this is due to the electron density redistribution between the palladium and TiO x particles, which is caused by the strong metal–support interaction.

Size effect of Pd nanoparticles in the selective liquid-phase hydrogenation of diphenylacetylene

The liquid-phase hydrogenation of diphenylacetylene over Pd catalysts supported on Al2O3 with different specific surface areas has been investigated. A decrease in the specific surface area of the support leads to a marked increase in the selectivity of the reaction. The observed increase in the selectivity is due to the increase in the size of Pd0 nanoparticles. As a result, the specific rate of triple bond hydrogenation increases over the rate of the undesired hydrogenation of the olefinic intermediate and the efficiency of kinetic control over the selectivity of the overall process is enhanced.

Novel catalysts for selective hydrogenation of C≡C bond based on Pd nanoparticles immobilized in phenylenecarboxylate frameworks (NH2)-MIL-53(Al)

Novel catalysts based on Pd nanoparticles encapsulated into microporous metal-organic framework MIL-53(Al) and NH2-MIL-53(Al) were synthesized. Their catalytic properties were studied in the model reaction of liquid-phase hydrogenation of diphenylacetylene (DPA) (293 K, \(P_{H_2 }\) = 5 atm). The activity and selectively of the palladium-containing materials Pd—MIL in DPA hydrogenation depend substantially on the nature of the organic linker.

Liquid-phase hydrogenation of diphenylacetylene on Pd-Au/Al2O3 bimetallic catalysts

The modification of the Pd/Al2O3 catalysts by gold considerably increases their catalytic activity in the liquid-phase hydrogenation of diphenylacetylene. The "turnover frequency" on the Pd-Au/Al2O3 bimetallic catalysts is 3–4 times higher than that of the monometallic samples. The increase in catalytic activity is more pronounced at the second step of diphenylethylene hydrogenation to diphenylethane. According to the data of IR spectroscopy of adsorbed CO, the observed effect is related to an increase in the electron density on the Pd atoms in the bimetallic samples.

Aminopolymer–Silica Composite-Supported Pd Catalysts for Selective Hydrogenation of Alkynes

A single-component, recyclable heterogeneous palladium nanoparticle catalyst is described for the selective hydrogenation of alkynes. The palladium nanoparticles are generated through reduction of Pd(II) species loaded into a mesoporous silica material functionalized with branched poly(ethyleneimine) polymers. An array of composite catalysts with similar polymer composition, palladium loading, and nanoparticle size (∼2 nm) are prepared to understand the importance of the polymer attachment method, the metal reduction method, the polymer molecular weight, and the oxide porosity. Each catalyst shows excellent activity in room temperature, liquid phase hydrogenation of diphenylacetylene to selectively produce cis-stilbene. Interestingly, it was found that the rate of over-hydrogenation could be significantly reduced by increasing the support porosity and using a high-molecular-weight polymer. These single-component catalysts are competitive with the best palladium catalysts known for the selective liquid phase hydrogenation of alkynes and can be easily recovered and recycled with no leaching of palladium detected, retaining high activities and selectivities over multiple cycles with a simple regeneration procedure.