Modified Pd Catalysts Research Articles

Integration of CO2capture, activation, and conversion with a ternary acetylglucosyl 2-methyl-imidazolium modified Pd catalyst

High-efficiency ternary acetylglucosyl 2-methyl-imidazolium modified Pd catalyst for integration of CO2 capture, activation, and conversion in carboxycyclization of propargyl amines and dilute CO2 with a record TOF of 1440 h−1has been developed.

Research on alkali metal-modified Pd catalyst for oxygen removal from propylene.

A series of alkali metal (Li, Na, and K)-modified Pd catalysts and Pd/Al2O3 were prepared and used to remove oxygen in a propylene flow with hydrogen's existence. The results showed that the alkali metals could enhance the performance of the Pd catalysts and the effect followed the order of K > Na > Li. X-Ray diffraction (XRD), N2-physisorption, transmission electron microscopy (TEM), hydrogen temperature programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS) were carried out to investigate the alkali metal-modified Pd catalysts and the promotional effect mechanism was explained. The results showed that alkali metal modification increased the electron density of Pd atoms to induce the negatively charged Pd species, which could enhance the adsorption of oxygen while weakening the adsorption of propylene, and then enhance the performance of the modified catalysts for oxygen removal from unsaturated hydrocarbon. The Pd-K/A catalyst performed the best on both oxygen removal and propylene hydrogenation inhibition.

High performance of metal modified Pd catalyst for hydrodechlorination of chlorophenols to cyclohexanone

High performance of metal modified Pd catalyst for hydrodechlorination of chlorophenols to cyclohexanone

Neutrophil-Membrane-Directed Bioorthogonal Synthesis of Inflammation-Targeting Chiral Drugs

Summary Targeted bioorthogonal catalysis holds great potential for localized prodrug activation. Although enantiomerically pure drugs are of vital importance in the clinic, chiral drug synthesis by bioorthogonal reactions in living systems is scarcely reported. Toward this goal, we constructed chirally modified Pd catalysts for the asymmetric transfer hydrogenation (ATH) reaction by using sodium formate as the biocompatible reductant. By combining the ATH reaction and chemotaxis of neutrophil membrane, we achieved inflammation site-selective chiral drug synthesis in living cells. As a proof of concept, we synthesized the chiral model drug ibuprofen in situ by a targeted ATH reaction to alleviate inflammation in the mouse paw as an in vivo model. Compared with controls, the neutrophil-membrane-coated chiral Pd catalysts exhibited inflammation-targeted capability and enantioselectivity simultaneously in the anti-inflammatory action. This study could offer a novel perspective for bioorthogonal catalysis in targeted prodrug activation.

Enhanced electrochemical glucose oxidation in alkaline solution over indium decorated carbon supported palladium nanoparticles

At present, carbon nanotube (CNT) supported In modified Pd catalysts are prepared at varying Pd:In ratios via NaBH4 reduction method to investigate the synergetic effect of Pd and In monometallic catalysts through glucose electrooxidation. These catalysts are characterized by advanced surface analytical techniques, namely, inductively coupled plasma-mass spectrometry (ICP-MS) with Agilent 7800 ICP-MS, N2 adsorption-desorption measurements (BET) with Micromeritics 3Flex equipment Tristar II 3020 equipped, PANalytical Empyrean device-ray diffractometer (XRD), Hitachi HighTech HT7700 high resolution-transmission electron microscope (HR-TEM), and scanning electron microscope (SEM). Electrochemical measurements are performed by using cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) by CHI660E potentiostat in a three electrode system. The characterization results show that all catalysts are successfully synthesized at desired molar composition. For PdIn (90:10)/CNT catalyst, the crystal size obtained from HR-TEM is 2.36 nm and BET surface area is 212.28 cm2g-1.5% PdIn(90:10)/CNT catalyst exhibits the best catalytic activity, lowest charge transfer resistance (Rct), and a long term stability compared to Pd, In, other Pd:In bimetallic catalysts. EIS and CA results are in a good agreement with CV results.

A Schiff Base Modified Pd Catalyst for Selective Hydrogenation of 2-Butyne-1,4-diol to 2-Butene-1,4-diol

Schiff-base modified Pd nanoparticles (NPs) supported on silica with an average size of ca. 2 nm have been synthesized via a one-pot aldimine condensation followed by impregnation-reduction of a palladium precursor, and the sample exhibits an excellent catalytic activity and selectivity in hydrogenation of 2-butyne-1,4-diol (BYD) to 2-butene-1,4-diol (BED). Under the mild reaction conditions (50 °C, 2 MPa H2, and 4 h) and additive-free, 95.2% BYD conversion has been achieved with ca. 100% BED selectivity over the Pd/SiO2–Schiff catalyst, and the Pd/SiO2–Schiff catalyst presents an excellent catalytic stability. The above results are much better than that of commercial Lindlar catalyst, and the improved catalytic performance is attributed to the strong metal–support interaction derived from the coordination of nitrogen sites (Schiff-base) to Pd NPs, based on catalyst characterization results. Featured by additive-free and high selectivity, hydrogenation of 2-butyne-1,4-diol to 2-butene-1,4-diol over the Pd/SiO2–Schiff catalyst has been developed, aiming for green production of fine chemicals.

Zirconia Modified Pd Electrocatalysts for DFAFCs

In order to enhance the Pd based anodic catalysts for direct formic acid fuel cells (DFAFCs), the research work includes increasing catalyst activity and preventing CO poison. In this study, various zirconium oxides-modified multi-walled carbon nanotubes (MWCNTs) were prepared as the supports of Pd catalysts for DFAFCs by adjusting the preparation parameters: metal adding, sintering temperature and atmospheres. The prepared pure zirconia has both monoclinic and tetragonal phases. The addition of MWCNTs depresses the growth of monoclinic phase. A small amount of Pd adding allows both monoclinic and tetragonal zirconia structures to appear again. Pd nanoparticles of 20 wt% synthesized on MWCNTs and tetragonal ZrO2/MWCNTs have similar particle size, while Pd/[Pd:ZrO2/AO-MWCNTs-300Air-900Ar] have more nanoparticles aggregation. The electrochemical surface area can be improved by adding zirconia which implies those zirconia modified Pd catalysts better electrocatalytic performance. By analyzing the maximum current density and the corresponding potential, Pd/AO-MWCNTs are inferred to undergo the formic acid direct oxidation initially. The Pd catalysts modified by tetragonal ZrO2 have higher current density. Those having both tetragonal and monoclinic ZrO2 modified Pd catalysts have lower potential of formic acid oxidation. All the Pd based catalysts with zirconia modification possess better CO resist ability and electrocatalytic activity. Pd/[ZrO2/AO-MWCNTs-300Air-900Ar] and Pd/[Pd:ZrO2/AO-MWCNTs-300Air-900Ar] which catalyze formic acid in direct oxidation path are the two best catalysts.

Selective Hydrogenation of Concentrated Vinyl Acetylene Mixed C4 by Modified Pd Catalysts: Effect of Cu

The Pd and Pd-Cu on alumina catalysts were tested for hydrogenation of vinyl acetylene in mixed C4 in a circulating tubular reactor. The results showed that adding proper amounts of Cu improved the reaction activity, but inhibited 1,3-butadiene selectivity. Moreover, the presence of Cu retarded the carbon deposition on catalysts during the reaction. Temperature programmed oxidation (TPO), Temperature programmed reduction (TPR), H2 chemisorption, and X-ray photoelectron spectroscopy (XPS) were utilized to characterize the catalysts. The characterization suggested both geometric and electronic modifications.

Asymmetric Hydrogenation of α-Amino Ester Probed by FTIR Spectroscopy

Asymmetric hydrogenation reaction of dehydro-α-amino acid (i.e., α-amino ester) over cinchonidine (CD) modified Pd catalyst has been studied by an array of in situ infrared spectroscopic methods, including transmission, diffuse reflectance (DR), and attenuated total reflectance (ATR). Transmission FTIR spectra probed the hydrogenation reaction process, revealed OH–O and NH–N hydrogen bonding interactions between the adsorbed CD and during the reaction. DR and ATR spectra of the hydrogenation reaction under different conditions, which are consistent with but slightly different from the transmission spectra, evidenced the successful hydrogenation of the compound. The incorporation of DR and microfluidics flow-through design allowed us to investigate the adsorption of CD on the Pd surface efficiently. The results revealed that the N-bonded CD on Pd surface in a tilted configuration had increased abundance on the Pd surface with high coverage. These valuable insights provided an image of the reaction pathway ...

Electronically modified Pd catalysts supported on N-doped carbon for the dehydrogenation of formic acid

In this study, an electronically modified Pd nanocatalyst supported on nitrogen-doped carbon (Pd/N–C) was synthesized by a facile, scalable synthetic method. The electronic interaction between the nitrogen atoms incorporated into the carbon support and Pd active sites, as evidenced by X-ray photoelectron spectroscopy (XPS), resulted in the formation of electron-rich Pd sites. The resulting Pd catalyst demonstrated enhancement in catalytic activity for the dehydrogenation of formic acid via the activation of C–H bonds in H–COOH. Finally, a hydrogen generation system fueled by formic acid was designed and further integrated with a polymer electrolyte membrane fuel cell (PEMFC) stack for the successful demonstration of stable, practical production of hydrogen, generating a fuel cell power of 180 W over 1 h without noticeable catalytic deactivation.

Tuning the catalytic selectivity in biomass-derived succinic acid hydrogenation on FeOx-modified Pd catalysts

Pd–FeOx/C catalysts were prepared and found to be efficient in succinic acid hydrogenation to produce 1,4-butanediol in one-pot.

Enantioselective hydrogenation of β-dehydroamino acids on a cinchonidine-modified palladium catalyst

Enantioselective hydrogenation of (Z)-β-dehydroamino acids on a cinchonidine-modified Pd/Al2O3 catalyst was explored. Comparative studies by using (Z)-β-dehydroamino acids and esters identified that the carboxylic group in dehydroamino acids was essentially important to get enantioselectivities (33% for aryl substituted and 46% for alkyl substituted β-dehydroamino acids). This result extended the range of enantioselective hydrogenation of α,β-unsaturated carboxylic acids on chirally modified Pd catalysts and offered a new approach to synthesize optically active β-amino acids.

MoOx Modified Pd Catalyst for Alcohol Electro-Oxidations in Alkaline Media

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Modified Pd catalysts for the selective hydrogenation of acetylene

This article reviews our previous studies to develop high performance catalysts for acetylene hydrogenation. Ethylene selectivity of Pd catalysts in acetylene hydrogenation was improved by adding Si, metal oxides showing SMSI behavior, and either Ag or Cu as promoters. The promoter effect was further enhanced by maximizing the interactions between Pd and added promoters. Chemical vapor deposition was used for the addition of Si, high-temperature reduction for the SMSI metal oxides, and a surface redox (SR) for Ag and Cu. Si modified the Pd surface geometrically, SMSI metal oxides modified Pd both electronically and geometrically, and Ag modified Pd largely electronically. Cu added by SR modified Pd electronically to a small extent, but preferentially decorated the low-coordination sites of Pd such that the ethylene selectivity of the optimum catalyst was significantly promoted from that of Pd, while its activity remained comparable to that of Pd. The sensitivity of ethylene selectivity to the surface structure of Pd was demonstrated using model catalysts containing uniform-sized Pd particles in either cubic or spherical shapes. The three stage deactivation of the Pd catalyst and the self-regenerative behavior in early stages of deactivation were also investigated.

The relationship between the structural properties of bimetallic Pd–Sn/SiO 2 catalysts and their performance for selective citral hydrogenation

The effect of Sn addition to Pd on the selective liquid-phase hydrogenation of citral to α,β-unsaturated alcohols (UA: nerol and geraniol) was examined. Pd–Sn/SiO 2 bimetallic catalysts were prepared by successive impregnation method and were characterized by transmission electronic microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDX), temperature-programmed reduction (TPR), Fourier transform infrared (FTIR) spectroscopy of adsorbed CO, and X-ray photoelectron spectroscopy (XPS). Sn addition to Pd/SiO 2 catalysts significantly modifies their properties for citral hydrogenation performed at 130 °C, under 7 MPa and in isopropanol solvent, inducing a promoting effect on the UA selectivity. This promoting effect is related to the existence of a Pd–Sn interaction highlighted by EDX analysis, TPR under hydrogen and FTIR of adsorbed CO. The latter technique suggested the presence of a geometric effect on catalytic activity. Maximum UA selectivities (>75% at 30% citral conversion) were obtained when an alloy of the Pd 3Sn type is formed in the bimetallic particles, as confirmed by TPR and XPS. Moreover, FTIR measurements of the adsorbed CO singleton frequency as well as XPS binding energy shifts strongly imply an electron transfer from Sn to Pd, which is proposed to be responsible for enhanced adsorption of citral C O bond on the surface of Pd–Sn/SiO 2 bimetallic catalysts. To our knowledge, it is the first time that modified Pd catalysts lead to such important UA selectivity values during α,β-unsaturated aldehyde hydrogenation.

Enantioselective hydrogenation of (E)-2-methyl-2-butenoic acid over cinchonidine modified Pd catalyst. Effect of the structure of achiral amine additives

The effect of the structure of the achiral primary amine additive on the enantioselective heterogeneous catalytic hydrogenation of (E)-2-methyl-2-butenoic acid over cinchonidine modified Pd/Al2O3 was studied. It was found that a variety of amines increase the enantioselectivity, which was always accompanied by decrease in the initial rate of the hydrogenations. Based on these results, the participation of the amine additive in the formation of the intermediate complex responsible for enantioselection was suggested. A decrease in the reaction temperature resulted in further increase in the optical purity of the product up to 67%, the highest value reported in the hydrogenation of unsaturated aliphatic acids in this heterogeneous catalytic system so far.

Enantioselective hydrogenation of propenoic acids bearing heteroaromatic substituents over cinchonidine modified Pd/alumina

Abstract The hydrogenation of two 2,3-diarylpropenoic acids bearing heteroaromatic substituents, i.e. ( E )-2-phenyl-3-(2-furyl)propenoic acid and ( E )-2-(3-pyridyl)-3-phenylpropenoic acid was studied over cinchonidine modified Pd catalyst for the first time. The 2-furyl substituted compound was selectively hydrogenated to 2-phenyl-3-(2-furyl)propionic acid in the presence of cinchonidine in up to 73% ee. The hydrogenation of the acid bearing 3-pyridyl substituent afforded lower ee as compared to ( E )-2,3-diphenylpropenoic acid, reaching up to 61% in presence of benzylamine additive. The differences in the results were assumed to be due to the different adsorption strengths and modes of these acids and deviations in their interactions with the adsorbed modifier.

Synthesis of carbon nanotubes, nanofibers and encapsulated nanoparticles by decomposition of acetylene on Ge modified Pd catalysts

Different carbon nanostructures were synthesized by decomposition of acetylene over alumina supported palladium-germanium catalysts. The addition of small amounts of Ge to the Pd(1%)/γ-Al 2 O 3 catalyst increases the yield of carbon nanotubes among other carbon products, in the decomposition of acetylene. The use of a higher Ge concentration (0.3%) in the catalyst induces the formation of carbon nanofibers. For larger Ge concentrations (0.5%) the bimetallic catalyst particles become encapsulated in a graphitic structure.

Heterogeneous enantioselective hydrogenation of isophorone over proline modified Pd catalysts

Enantioselective hydrogenation of isophorone (3,5,5-trimethyl-2-cyclohexenone) over (S)-proline modified Pd catalysts has been studied. Both the Pd particle size and the acid–base properties of the support influenced the hydrogenation reaction of isophorone and the subsequent kinetic resolution of 3,3,5-trimethylcyclohexanone (TMCH). This was explained by assuming the reaction pathway as a consequential process. The rapid hydrogenation of isophorone initially yielded racemic TMCH, and then the slow kinetic resolution consumed the (R)-TMCH, leaving (S)-TMCH in excess. Most promisingly, the Pd/MgO catalyst with enhanced adsorption of proline and moderate Pd particle sizes resulted in high enantioselectivity (ee of 95%) and 43% yield of TMCH.

Oxidative dehydrogenation catalyst

Reaction of dichlorodifluoromethane(CFC-12) and chlorodifluoromethane(HCFC-22) with H2 was carried out on modified Pd catalysts. On 5wt% Pd/C, hydrogenation of CFC-12 gave mainly difluoromethane(HCF-32) at 200°C and methane at 350°C, respectively. Zr and V modifiers promoted to increase in activity with no change in selectivity and, thus, to enhance the yield of HFC-32. From temperature programmed reduction (TPR) measurements, formation of Pd-Zr hydride, which desorbed hydrogen at ca. 200°C, was observed. This hydride may play a role to supply active hydrogen in the reaction at the reaction temperature.