Supported Pd Nanoparticles Research Articles

Amino-functionalized CuFe2O4 supported Pd nanoparticles as magnetically catalyst for H2 production from methanolysis of ammonia borane and hydrogenation of nitro aromatics

Small and equally distributed Pd nanoparticles (NPs) are tightly anchored on the surface of magnetic and amino (–NH2) functionalized CuFe2O4 to obtain magnetically separable CuFe2O4–NH2@Pd catalyst with core-shell structure. Compared to the inherent catalytic activity of CuFe2O4, the catalytic performance of CuFe2O4–NH2@Pd for dehydrogenation of ammonia-borane (AB) and concurrent hydrogenation of different nitro aromatics by H2 generated from AB methanolysis can be boosted more effectively than that of CuFe2O4@Pd, which is the control catalyst and is prepared by loading Pd NPs on pristine CuFe2O4. As electron donating groups, the –NH2 groups covalently bonded to the surface of CuFe2O4 play vital roles in stabilizing Pd NPs, providing strong metal-support interaction and rendering enhanced catalytic activity. However, we find that the catalytic performance of CuFe2O4, CuFe2O4@Pd and CuFe2O4–NH2@Pd for the hydrogenation reduction of mercapto-substituted nitro aromatics (p-nitrothiophenol, p-NTP) is far inferior to that for the reduction of nitroarenes that do not contain a sulfur substituent. Therefore, it is quite essential to research and develop the new-type catalysts with more excellent catalytic performance.

Sub-Millisecond Laser-Irradiation-Mediated Surface Restructure Boosts the CO Production Yield of Cobalt Oxide Supported Pd Nanoparticles.

The catalytic conversion of CO2 into valuable commodities has the potential to balance ongoing energy and environmental issues. To this end, the reverse water-gas shift (RWGS) reaction is a key process that converts CO2 into CO for various industrial processes. However, the competitive CO2 methanation reaction severely limits the CO production yield; therefore, a highly CO-selective catalyst is needed. To address this issue, we have developed a bimetallic nanocatalyst comprising Pd nanoparticles on the cobalt oxide support (denoted as CoPd) via a wet chemical reduction method. Furthermore, the as-prepared CoPd nanocatalyst was exposed to sub-millisecond laser irradiation with per-pulse energies of 1 mJ (denoted as CoPd-1) and 10 mJ (denoted as CoPd-10) for a fixed duration of 10 s to optimize the catalytic activity and selectivity. For the optimum case, the CoPd-10 nanocatalyst exhibited the highest CO production yield of ∼1667 μmol g-1catalyst, with a CO selectivity of ∼88% at a temperature of 573 K, which is a 41% improvement over pristine CoPd (~976 μmol g-1catalyst). The in-depth analysis of structural characterizations along with gas chromatography (GC) and electrochemical analysis suggested that such a high catalytic activity and selectivity of the CoPd-10 nanocatalyst originated from the sub-millisecond laser-irradiation-assisted facile surface restructure of cobalt oxide supported Pd nanoparticles, where atomic CoOx species were observed in the defect sites of the Pd nanoparticles. Such an atomic manipulation led to the formation of heteroatomic reaction sites, where atomic CoOx species and adjacent Pd domains, respectively, promoted the CO2 activation and H2 splitting steps. In addition, the cobalt oxide support helped to donate electrons to Pd, thereby enhancing its ability of H2 splitting. These results provide a strong foundation to use sub-millisecond laser irradiation for catalytic applications.

Pd/oCNT Monolithic Catalysts for Continuous-Flow Selective Hydrogenation of Cinnamaldehyde

Chemical engineering optimization from a batch process to continuous flow in liquid-phase hydrogenation brings a significant improvement in efficiency. However, its further application is limited due to the severe pressure drop and tube blockage problems in a powder-form catalyst fixed-bed reactor, especially for nanocarbon-supported catalysts. In this work, spherical monoliths containing oxygenated carbon nanotube (oCNT)-supported Pd nanoparticles (ca. average size of 2 mm) are fabricated via an in situ gelation method and applied for cinnamaldehyde (CAL) selective hydrogenation in a continuous-flow system. The simulated results by the computational fluid dynamics–discrete element method (CFD–DEM) coupled method show that the pressure drop of the monolith catalyst bed is maintained within 0.4 Pa. The Pd/oCNT monolithic catalyst exhibits excellent CAL conversion of 85.8% and hydrocinnamaldehyde (HCAL) selectivity of 93.5% within a high weight hourly space velocity (WHSV) of 0.012 s–1 at mild reaction conditions (30 °C, 3 bar). The catalyst maintains robust catalytic activity and HCAL selectivity (>93%) under varied reaction temperatures (30/60 °C), H2 partial pressures (3–10 bar), and WHSVs (0.012–0.184 s–1) and a stable reaction activity for more than 60 h time on stream, revealing the possibility in industrial hydrogenation reactions. The catalytic activity of the monolithic catalyst is determined by the surface properties of the carbon nanotubes and the chemical interactions between Pd nanoparticles and supports. The oxygenated functional groups and surface defects on oCNTs are beneficial for strong chemical interaction with Pd species, which forms abundant electron-deficient Pdδ+ species to facilitate C═C hydrogenation. This study puts forward insights into and perspectives for selective hydrogenation reactions in both electronic structure tuning of the active phase at the atomic scale and fabrication of monolithic catalysts at the macroscopic scale.

Pd nanoparticles supported on magnetic CoTiMgLDH with enhanced catalytic activity in Suzuki cross‐coupling and reductive degradation of dyes

With an aim to combine the catalytic properties of Pd nanoparticles (NPs) with the excellent characteristics of porous layered double hydroxides (LDH), in the present study, four different catalysts (Pd/Fe3O4‐CoTiMgAlLDH, Pd/Fe3O4‐CoTiMgLDH, Pd/Fe3O4‐CoTiAlLDH and Pd/Fe3O4‐CoTiLDH) were synthesized by supporting Pd NPs onto four different Fe3O4‐LDH supports, which were synthesized by varying the metals in LDH. The catalytic activity of these catalysts was studied for Suzuki coupling and reductive degradation of dyes. Pd/Fe3O4‐CoTiMgLDH outperformed the other catalysts in both reactions. The synthesized catalysts were examined via different characterization techniques like X‐ray diffraction (XRD), Brunauer–Emmett–Teller analysis (BET), X‐ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), high resolution transmission electron microscopy (HR‐TEM), field emission scanning electron microscopy (FE‐SEM), energy dispersive X‐ray (EDX), energy dispersive X‐ray mapping (SEM–EDX mapping), inductively coupled plasma atomic emission spectroscopy (ICP‐AES) and vibrating sample magnetometry (VSM). On the basis of results obtained from XPS and the experimental data, Fe3O4‐CoTiMgLDH was found to be the support of choice as it not only stabilized the Pd0 NPs but also increased the electron density on the anchored Pd0 species, which enhanced the catalytic activity of Pd/Fe3O4‐CoTiMgLDH for studied organic transformations.

Atomic Scaled Depth Correlation to the Oxygen Reduction Reaction Performance of Single Atom Ni Alloy to the NiO2 Supported Pd Nanocrystal.

This study demonstrates the intercalation of single-atom Ni (NiSA ) substantially reduces the reaction activity of Ni oxide supported Pd nanoparticle (NiO2 /Pd) in the oxygen reduction reaction (ORR). The results indicate the transition states kinetically consolidate the adsorption energy for the chemisorbed O and OH species on the ORR activity. Notably, the NiO2 /Ni1 /Pd performs the optimum ORR behavior with the lowest barrier of 0.49eV and moderate second-step barrier of 0.30eV consequently confirming its utmost ORR performance. Through the stepwise cross-level demonstrations, a structure-Eads -ΔE correspondence for the proposed NiO2 /Nin /Pd systems is established. Most importantly, such a correspondence reveals that the electronic structure of heterogeneous catalysts can be significantly differed by the segregation of atomic clusters in different dimensions and locations. Besides, the doping-depth effect exploration of the NiSA in the NiO2 /Pd structure intrinsically elucidates that the Ni atom doping in the subsurface induces the most fruitful NiSA /PdML synergy combining the electronic and strain effects to optimize the ORR, whereas this desired synergy diminishes at high Pd coverages. Overall, the results not only rationalize the variation in the redox properties but most importantly provides a precision evaluation of the process window for optimizing the configuration and composition of bimetallic catalysts in practical experiments.

Hydrogenation of CO2 into Formates by Ligand‐Capped Palladium Heterogeneous Catalysts

AbstractThe synthesis of two series of catalysts based on ligand‐capped supported Pd nanoparticles was carried out using a simple procedure and the resulting materials were tested in the formate synthesis. Within these series, PPh3 revealed the most appropriate stabilizing ligand while TiO2 was the most efficient support for these catalysts. The hydrogenation of CO2 was carried out under mild reaction conditions (1.8 MPa CO2, 1.8 MPa H2, 60 °C) using water as solvent and in the presence of a base, providing excellent selectivity towards formates with a TON of 1032 (TOF of 69 h−1, [HCOOK]=1.1 mol/l).

Heterogeneous Hydrogenation with Hydrogen Spillover Enabled by Nitrogen Vacancies on Boron Nitride-Supported Pd Nanoparticles.

Heterogeneous hydrogenation with hydrogen spillover has been demonstrated as an effective route to achieve high selectivity towards target products. More effort should be paid to understand the complicated correlation between the nature of supports and hydrogenation involving hydrogen spillover. Herein, we report the development of the hydrogenation system of hexagonal boron nitride (h-BN)-supported Pd nanoparticles for the hydrogenation of aldehyde/ketones to alcohols with hydrogen spillover. Nitrogen vacancies in h-BN determine the feasibility of hydrogen spillover from Pd to h-BN. The hydrogenation of aldehyde/ketones with hydrogen spillover from Pd proceeds on nitrogen vacancies on h-BN. The weak adsorption of alcohols to h-BN inhibits the deep hydrogenation of aldehyde/ketones, thus leading to high catalytic selectivity to alcohols. Moreover, the hydrogen spillover-based hydrogenation mechanism makes the catalyst system exhibit a high tolerance to CO poisoning.

Heterogeneous Hydrogenation with Hydrogen Spillover Enabled by Nitrogen Vacancies on Boron Nitride‐Supported Pd Nanoparticles

AbstractHeterogeneous hydrogenation with hydrogen spillover has been demonstrated as an effective route to achieve high selectivity towards target products. More effort should be paid to understand the complicated correlation between the nature of supports and hydrogenation involving hydrogen spillover. Herein, we report the development of the hydrogenation system of hexagonal boron nitride (h‐BN)‐supported Pd nanoparticles for the hydrogenation of aldehydes/ketones to alcohols with hydrogen spillover. Nitrogen vacancies in h‐BN determine the feasibility of hydrogen spillover from Pd to h‐BN. The hydrogenation of aldehydes/ketones with hydrogen spillover from Pd proceeds on nitrogen vacancies on h‐BN. The weak adsorption of alcohols to h‐BN inhibits the deep hydrogenation of aldehydes/ketones, thus leading to high catalytic selectivity to alcohols. Moreover, the hydrogen spillover‐based hydrogenation mechanism makes the catalyst system exhibit a high tolerance to CO poisoning.

Controlling the reactions of free radicals with metal-radical interaction

Radicals are key intermediates in numerous reactions. Their high reactivity enables various transformations to occur under mild conditions, however, also brings great challenges to control their reactions especially over heterogeneous catalysts. Here we propose to use metal nanoparticles to directly steer the conversion of free radical species. Results from photocatalytic reactions, in situ transient absorption spectroscopy, and theoretical simulation demonstrate that supported Pd nanoparticles can efficiently stabilize free radical species generated from photo-excited TiO2, and thus manipulate their conversion on catalyst surface, owing to the enhanced electronic interactions between metal and radical species. These understandings are crucial for the design of advanced heterogeneous catalytic systems with controllable radical reactions.

Distinct Roles of Additives in the Improved Sensitivity to CO of Ag- and Pd-Modified Nanosized LaFeO3

Perovskite-type mixed-metal oxides are of particular interest as semiconductor gas sensors due to the variability in the material composition and the stability of sensing parameters. LaFeO3 is a p-type semiconductor with relatively high conductivity and gas sensitivity. However, less is known about the sensitivity and sensing mechanisms of LaFeO3 modified by catalytic noble metals. In this work, we used a microwave-assisted sol–gel method to synthesize perovskite LaFeO3 nanoparticles with an average size of 20–30 nm and a specific surface area of 6–8 m2/g. LaFeO3 was modified by 2–5 wt.% Ag and Pd nanoparticles via the impregnation route. Using X-ray photoelectron spectroscopy, the additives were observed in the partially oxidized states Ag2O/Ag and PdO/Pd, respectively. Electric conduction and sensitivity to noxious gases were characterized by electrophysical measurements. It was shown that LaFeO3 modified by Ag and Pd had improved sensitivity and selectivity to CO, and the sensing behavior persisted in a wide range of relative humidity. Pristine and Ag-modified LaFeO3 had the maximum sensitivity to CO at a temperature of 200 °C, while modification with Pd resulted in a decreased optimal operating temperature of 150 °C. In situ infrared spectroscopy revealed that supported Pd nanoparticles specifically catalyzed CO oxidation at the surface of LaFeO3 at room temperature, which was the likely reason for the improved sensitivity and decreased optimal operating temperature of LaFeO3/Pd sensors. On the other hand, Ag nanoparticles were deduced to activate CO oxidation by lattice oxygen at the surface of LaFeO3, providing enhanced CO sensitivity at a higher temperature.

In situ study of catalytic CO oxidation on ultrathin MgO film supported Pd nanoparticles by sum frequency generation: size and site effects.

Controlling the reactive sites of nanoparticles (NPs) is crucial to improve catalyst efficiency. In this work, sum-frequency generation is used to probe CO vibrational spectra on MgO(100) ultrathin film/Ag(100) supported Pd nanoparticles ranging from 3 to 6 nm in diameter and compared to those of coalesced Pd NPs and Pd(100) single crystals. We aim to demonstrate in situ the role played by active adsorption sites in the catalytic CO oxidation reactivity trends varying with the NP size. From ultrahigh vacuum to the mbar range and temperatures from 293 K to 340 K, our observations suggest that bridge sites are the main active sites for CO adsorption and catalytic oxidation. On Pd(100) single crystals at 293 K, CO oxidation predominates over CO poisoning at a pressure ratio of O2/CO greater than 300; on Pd NPs, both the site coordination due to NP geometry and MgO-induced Pd-Pd interatomic distance change impact the reactivity trend varying with size in different ways. Edge sites with low coordination are more reactive than facet sites, while facet sites with a smaller Pd-Pd atomic length are more reactive than that with a larger length. The interplay of both site and size effects gives rise to a non-monotonic reactivity trend of CO on the MgO(100) ultrathin film supported Pd NPs: the reactivity of Pd NPs increases for the smaller NP size side due to a higher edge/facet ratio and meanwhile increases for the larger NP size side due to the terrace facet with a smaller Pd-Pd atomic length at the NP surface and a lower diffusion barrier.

A comparative study of palladium-gold and palladium-tin catalysts in the direct synthesis of H2O2

Supported PdSn catalysts are highly effective for the direct synthesis of hydrogen peroxide showing significantly higher selectivity to comparable PdAu catalysts.

Facile surface restructure by one-step sub-millisecond laser exposure promotes the CO2 methanation performance of cobalt oxide supported Pd nanoparticles with copper-oxide cluster decoration

The schematic representation for the atomic structures of pristine CPCu, CPCu-1 and CPCu-10 nanocatalysts.

One-pot synthesis of gamma-graphyne supported Pd nanoparticles with high catalytic activity.

As a unique member of the graphyne family, gamma-graphyne (γ-graphyne) is a novel kind of 2D carbon allotrope with potential high carrier mobility and large surface area. It remains a great challenge to synthesize graphynes with targeted topologies and good performance. Herein, a novel one-pot method was applied to the synthesis of γ-graphyne using hexabromobenzene and acetylenedicarboxylic acid via a Pd-catalyzed decarboxylative coupling reaction, which is easy to perform with mild reaction conditions, facilitating the possibility of mass production. As a result, the synthesized γ-graphyne reveals a two-dimensional γ-graphyne structure consisting of 1 : 1 sp/sp2 hybridized carbon atoms. Furthermore, γ-graphyne as a carrier for Pd (Pd/γ-graphyne) displayed a superior catalytic activity for the reduction of 4-nitrophenol with a short reaction time and high yields, even in aqueous media under aerobic conditions. Compared with Pd/GO, Pd/HGO, Pd/CNT, and commercial Pd/C, Pd/γ-graphyne showed more excellent catalytic performance with lower palladium loadings. Thus we expect that the novel approach for the synthesis of γ-graphyne will boost research on the design and application of graphyne-type functional materials for catalysis.

Synthesis, characterization and catalytic evaluation of supported catalysts (PdNPs/TiO2, PdNPs/Al2O3, PdNPs/SiO2) for esterification of levulinic acid to levulinate esters

• The manuscript describes the synthesis of supported (Silica, titania, and alumina) Pd nanoparticles via wet-impregnation method. • The size of supported Pd nanoparticles determines their catalytic activity. • Indicators such as induction period and kinetics of de/activation were used to determine the possibility of Pd surface atom rearrangement during catalytic reaction. • The alumina-supported Pd nanoparticles proved to be more robust and activate at later reaction cycles. • The manuscript contributes towards the development of sustainable and environmentally friendly biobased value-added chemicals. In this work, we report on the synthesis of supported-palladium nanoparticles (Pd NPS /TiO 2 , Pd NPS /SiO 2 , Pd NPS /Al 2 O 3 ) and their catalytic performance in the esterification of levulinic acid (LA). The N 2 physisorption technique (BET) was used to determine the surface properties of Pd NPS and gave surface areas ranging between 69.53 – 596.5 m 2 g -1 for the set of catalysts, and the high-resolution transmission electron microscopy (HRTEM) whose images were used to measure the average nanoparticle sizes (2.2 ± 0.2 – 8.0 ± 2.0 nm) of all supported Pd NPS . Metal loading ranged from 0.5 to 5 Pd wt.% as determined by the inductively coupled plasma-optical emission spectroscopy (ICP-OES). The highest LA conversion, 96% was achieved with Pd/Al 2 O 3 . An interesting observation for 0.5 – 5% Pd NPS /TiO 2 catalytic systems is that LA's turnover frequency (TOF) decreases with increasing metal loading and/or size of the Pd NPS on TiO 2 . The Pd NPS supported on TiO 2 exhibit an induction period during the first hour of the reaction and later reported 83% LA conversion with 98% selectivity towards isopropyl levulinate (IL). Therefore, we postulate a TiO 2 support-induced surface atom rearrangement of Pd NPS prior to the catalytic reaction that is responsible for the induction period observed.

Front Cover: Catechol‐Functionalized Carbon Nanotubes as Support for Pd Nanoparticles: a Recyclable System for the Heck Reaction (Eur. J. Org. Chem. 45/2022)

Front Cover: Catechol‐Functionalized Carbon Nanotubes as Support for Pd Nanoparticles: a Recyclable System for the Heck Reaction (Eur. J. Org. Chem. 45/2022)

Ti3C2@Pd nanocatalytic amplification-polypeptide SERS/RRS/Abs trimode biosensoring platformfor ultratrace trinitrotoluene

A new MXene supported Pd nanoparticles (Ti3C2@Pd) nanosol with good stability and strong catalysis was prepared by the two-step procedure. Experiment was found that Ti3C2@Pd could strongly catalyze the reduction of HAuCl4 by H2O2 to produce gold nanoparticles (AuNPs), with strong surface enhanced Raman scattering (SERS), resonance Rayleigh scattering (RRS) and surface plasmon resonance absorption (Abs). Coupled this new SERS/RRS/Abs trimode nanocatalytic indicator reaction with specific TNT polypeptide (PTTNT), a facile and selective trimode polypeptide biosensoring platform was established for the detection of ultratrace TNT, with a linear range of 1.1–66, 1.1–66 and 4.4–66 pmol/L TNT, and detection limit (DL) of 0.69, 0.97 and 3.36 pmol/L by SERS, RRS and Abs assay respectively. It has been used to detect TNT in wastewater and soil samples, with recovery of 98.7–106% and RSD of 6.22–8.77%. In addition, this biosensoring platform can be also used to assay glyphosate and estradiol, respectively.

MnCo-Layered double hydroxides nanosheets supported Pd nanoparticles for complete catalytic oxidation of formaldehyde at room temperature

Removal of gaseous formaldehyde by room-temperature catalytic oxidation has promising applications. The rational design of the structure of catalyst to improve the ability of activated key species (adsorbed oxygen and hydroxyl) through understanding the reaction mechanism can improve the catalytic activity. In this paper, Pd nanoparticles were deposited on pre-reduction uniform LDH nanosheets to prepare Pd-decorated sodium borohydride-reduced Mn/Co layered double hydroxides (Pd/LDH-NaBH4). The transition metal (Mn and Co) doping of Pd improved the catalyst's ability to activate oxygen and formaldehyde, and the support of LDHs increased the hydroxyl concentration of the catalyst. Pd/LDH-NaBH4 showed reduced valence of Pd, improved dispersion of Pd NPs, and retention of abundant hydroxyl groups on LDH. Characterizations revealed that the synergistic effect of the supported Pd NPs and LDH, as well as many oxygen vacancies, was responsible for the effective removal of HCHO by Pd/LDH-NaBH4 catalyst at ambient temperature. This study further developed a new catalyst for HCHO oxidation, which may provide a new idea for the removal mechanism of oxidized HCHO.

Catechol‐Functionalized Carbon Nanotubes as Support for Pd Nanoparticles: a Recyclable System for the Heck Reaction

AbstractCarbon nanotubes have been covalently functionalized with catechol moieties through the formation of the corresponding aryl radicals obtained by reacting 4‐aminocatechol with isoamyl nitrite. The functionalized multiwalled carbon nanotubes have been in turn used to immobilize Pd(II) ions on its surface forming catechol‐Pd complexes, which were reduced to Pd nanoparticles (NPs). The so‐obtained hybrid material has been characterized by means of thermogravimetric analysis coupled with differential scanning calorimetry (TGA‐DSC), X‐ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). This latter technique allowed to estimate the nanoparticle size (5.7±2.8 nm) whereas a palladium loading of 20.3 wt % has been found by inductively coupled plasma optical emission spectroscopy (ICP‐OES). The carbon nanotube‐catechol‐Pd hybrid was used as catalyst in two C−C coupling reactions, namely Suzuki and Heck reactions, resulting recyclable for at least 9 times in the latter process. During the reuse Pd nanoparticles increase their dimension to 19.3±11.7 nm.

Defective Layered Double Hydroxide Nanosheet Boosts Electrocatalytic Hydrodechlorination Reaction on Supported Palladium Nanoparticles

Electrocatalytic hydrodechlorination on Pd, utilizing the H+ of H2O as hydrogen sources, represents a promising technology to detoxify the chlorinated organic pollutants (COPs) in water bodies. However, Pd alone affords limited activity due to its low efficacy in H2O disassociation and the poor mass diffusion of COPs that are commonly of low concentrations in the environment. Herein, we demonstrate that arming Pd with OH– vacancy-bearing NiAl-layered double hydroxide nanosheets (Pd/NixAl100–x-LDH-OHv) can significantly improve its performance, benefiting from the enhanced H2O disassociation at OHv and the facilitated C–Cl cleavage on the supported Pd nanoparticles. Al3+ is also indispensable because it promotes the formation and regeneration of OHv, but an overload will reduce the number of accessible OHv and weaken its function. Pd/Ni67Al33-LDH-OHv with the optimal Ni/Al ratio delivers a peak specific activity of 0.53 min–1 m–2 and mass activity of 6.54 min–1 g–1Pd in treating 50.0 mg L–1 2,4-dichlorophenol (2,4-DCP, a probe COP) at −0.25 V versus RHE, outperforming most of the reported catalysts. To address the mass diffusion issue, Pd/Ni67Al33-LDH-OHv is integrated into a customized continuous-flow membrane cell. When fed a dilute wastewater (20.4 mg L–1), the system affords a 2,4-DCP removal rate of 3.75 g2,4-DCP gcatalyst–1 h–1 and faradaic current efficiency of 42.6%, which is 3.2 and 4.0 times that obtained in a traditional batch reaction system, respectively.