Supported Palladium Catalysts Research Articles

Pd Catalysts Supported on Bamboo-Like Nitrogen-Doped Carbon Nanotubes for Hydrogen Production

Bamboo-like nitrogen-doped carbon nanotubes (N-CNTs) were used to synthesize supported palladium catalysts (0.2–2 wt.%) for hydrogen production via gas phase formic acid decomposition. The beneficial role of nitrogen centers of N-CNTs in the formation of active isolated palladium ions and dispersed palladium nanoparticles was demonstrated. It was shown that although the surface layers of N-CNTs are enriched with graphitic nitrogen, palladium first interacts with accessible pyridinic centers of N-CNTs to form stable isolated palladium ions. The activity of Pd/N-CNTs catalysts is determined by the ionic capacity of N-CNTs and dispersion of metallic nanoparticles stabilized on the nitrogen centers. The maximum activity was observed for the 0.2% Pd/N-CNTs catalyst consisting of isolated palladium ions. A ten-fold increase in the concentration of supported palladium increased the contribution of metallic nanoparticles with a mean size of 1.3 nm and decreased the reaction rate by only a factor of 1.4.

Synthesis of C21H38ClN Assisted Si Pillared Clays and the Effects of CeO2 Addition on Its Supported Palladium Catalyst for Benzene Oxidation

Mesoporous silica-pillared clays (SPC) were prepared with C21H38ClN cationic surfactant as template and supported PdOx catalysts were prepared by impregnation method. The influence of addition of CeO2 on benzene combustion was evaluated. The samples were characterized by N2 adsorption–desorption, XRD, XPS, HRTEM and TPSR. Compared with the raw montmorillonite, the d001 value of SPC increased from 0.96 to 3.45 nm. Furthermore, the surface area was increased from 30 to 835 m2/g and the pore volume was increased from 0.11 to 1.30 cm3/g, respectively. The addition of CeO2 increased oxygen vacancies and improved the dispersion of PdOx on SPC, and the optimal addition of CeO2 was 10%. Therefore, of all the catalysts, 0.3%Pd/10%Ce/SPC could completely oxidize benzene at 280 °C, showing the highest catalytic activity. This catalyst showed high activity for benzene oxidation in wet conditions with or without Cl− displaying good durability, which should be related to the presence of Ce3+ on the surface of catalyst after reaction. The excellent pore structure of SPC, improved dispersion of PdOx and high concentration of Ce3+ on the catalyst surface were the key factors for the high catalytic activity of 0.3%Pd/10%Ce/SPC. Mesoporous silica-pillared clays (SPC) were synthesized and SPC supported CeO2 and PdO catalysts were prepared by impregnation method. The 0.3% Pd/10% Ce/SPC catalyst displayed the highest activity for benzene combustion.

Continuous-flow hydrogenation over resin supported palladium catalyst for the synthesis of industrially relevant chemicals

Herein, the catalytic performance of palladium nanoparticles grafted on the polymeric TSNH2 (Tentagel-S-NH2) resin was investigated for continuous-flow liquid-phase hydrogenation of two industrially relevant chemicals: 2-methyl-3-butyn-2-ol and nitrocyclohexane. We investigated the effect of process parameters such as temperature and pressure on PdTSNH2 activity and selectivity. Depending on the reaction conditions, well-dispersed PdNPs with average size of about 2 nm have shown very high flexibility in terms selectivity toward the desired products: 2-methyl-3-buten-2-ol or 2-methyl-2-butanol in the case of 2-methyl-3-butyn-2-ol hydrogenation and cyclohexanone oxime or cyclohexylamine as the main product in the case of nitrocyclohexane conversion. The optimal reaction conditions for 2-methyl-3-buten-2-ol formation were estimated at 25 °C and 5 bar, and in the case of cyclohexanone oxime formation at 40 °C and 10 bar. We demonstrated the general trend in the catalytic performance of 2.2 wt% Pd grafted on Tentagel-S-NH2. Independently of the hydrogenated substrate, the increase in conversion leads to decreased selectivity to 2-methyl-3-buten-2-ol and cyclohexanone oxime at the expense of increasing the selectivity to 2-methyl-2-butanol or cyclohexylamine.Graphic abstract

Ni/Cu/Ag promoted Pd/Al2O3 catalysts prepared by electroless co-deposition for enhanced butane dehydrogenation

In this study, performance of Ni, Cu and Ag promoted palladium catalysts supported on alumina was investigated for butane dehydrogenation. The activity, selectivity, yield and stability were studied in temperature range of 100–600 °C under atmospheric pressure. The catalysts were prepared by modified electroless co-deposition of metals on alumina support. The co-deposition of 10 mol% promoters along with palladium, increased activity, selectivity and yield of butene, depending on the nature of promoter. The addition of copper increased the activity more significantly while, silver increased the selectivity. Addition of nickel proved to be least effective in improving performance of supported palladium catalyst. At 550 °C, the conversion order was Pd–Cu/Al (34.4%) > Pd–Ag/Al (25.6%) > Pd–Ni/Al (21.4%) > Pd/Al (17.9%) and the total butene selectivity order was Pd–Ag/Al (91.9%) > Pd/Al (90.5%) > Pd–Cu/Al (85%) > Pd–Ni/Al (61.5%). The overall yield of butene was highest for Pd–Cu/Al, in the order of Pd–Cu/Al (29%) > Pd–Ag/Al (23%) > Pd/Al (16%) > Pd–Ni/Al (13%) at 550 °C. Further, increase in copper content increased the yield of butene and highest yield of 32% was observed for Pd–Cu20/Al with 20 mol% copper. The palladium metal was in strong interaction with the promoter metals, forming alloys. Higher activity of these alloys enhanced performance of the promoted catalysts. The stability of the catalysts was also enhanced by addition of promoters. The stability order was Pd–Ag/Al (30%) > Pd–Cu/Al (50%) > Pd–Ni/Al (61%) > Pd/Al (76%) over 10 h on stream study. The silver promoted catalyst showed the lowest deactivation of 30%.

Investigating the effect of carbon support on palladium-based catalyst towards electro-oxidation of ethylene glycol

Palladium-based catalysts serve as promising electrocatalysts for the oxidation of ethylene glycol to produce electrical energy that can be used to address the continuous worldwide energy demand increments along with the depletion of fossil fuels which serve as the main energy source. For optimal catalysts performance, carbon nanotubes and carbon nanodots were investigated as palladium catalyst support materials to address difficulties in oxidizing and breaking the C–C bonds in ethylene glycol, cost of electrocatalyst, and complex reaction mechanism that is restraining rapid development and applications of direct ethylene glycol fuel cells (DEGFC). Utilization of palladium catalysts supported on carbon nanotubes (CNT) and carbon nanodots (CND) as support materials resulted in spontaneous ethylene glycol oxidation. The Pd/CNT catalyst showed greater stability compared to Pd/CND during the oxidation of ethylene glycol, and it is not easily poisoned by carbon monoxide intermediates formed during ethylene glycol oxidation as shown by a slow current decay on chronoamperometry.

Highly selective oxidation of monosaccharides to sugar acids at room temperature over palladium supported on surface functionalized carbon nanotubes

A surface functionalized carbon nanotube supported palladium catalyst exhibits high catalytic activity for the selective oxidation of monosaccharides into sugar acids at room temperature.

Supported Palladium Catalysts: A Facile Preparation Method and Implications to Reductive Catalysis Technology for Water Treatment

Supported palladium (Pd) catalysts have been extensively studied for water purification applications. However, this technology is primarily challenged by the high cost of Pd and the lack of optimiz...

Dual Metal–Acid Pd-Br Catalyst for Selective Hydrodeoxygenation of 5-Hydroxymethylfurfural (HMF) to 2,5-Dimethylfuran at Ambient Temperature

Supported metal catalysts have found broad applications in heterogeneous catalysis. In the conventional bifunctional catalyst, the active metal sites are associated with the metal nanoparticles, while the acid sites are usually localized over the oxide support. Herein, we report a novel type of supported metal bifunctional catalyst, which combined the advantages of the promotion and bifunctionality. The catalyst was designed by the pretreatment of supported palladium catalysts with bromobenzene. The promotion with bromine creates Bronsted acid sites, which are localized directly on the surface of metal nanoparticles. An intimacy between metal and acid functions in this bifunctional catalyst generates unique catalytic properties in hydrodeoxygenation of 5-hydroxymethylfurfural to dimethylfuran, occurring with the yield up to 96% at ambient temperature under 5 bar of H-2. The catalyst exhibits stable catalytic performance.

Cellular Carbon Foam as a New Type of Supports for Palladium Catalysts

The applicability of a new carbon material—carbon foam with a cellular structure synthesized from the pyrolysis products of hydrocarbon gases—as a catalyst support was demonstrated. The modification of the carbon foam by the deposition of nanoglobular carbon particles on its surface made it possible to obtain a nonporous material with a specific surface area of <1 m2/g and an open-cell structure. Dispersed palladium particles uniformly distributed over the support surface were formed using a hydrolytic deposition method. It was found that the resulting catalyst with palladium immobilized on cellular carbon is promising for the selective hydrogenation of acetylene to ethylene.

Heterogeneous Supported Palladium Catalysts for Liquid-Phase Allylation of Nucleophiles.

In recent years, palladium-catalyzed allylation has become the focus of much research. However, conventional homogeneous Pd catalysts face problems regarding their recovery, reuse, and cost, especially with respect to green chemistry principles. Herein, we present an overview of the development of catalytic allylation with various heterogeneous Pd catalysts, because they can be easily and conveniently recovered and reused. We also emphasize the use of different solid supports such as polymers, silica, and other hybrid supports to inspire future research in this promising field. Moreover, the unique effects of support surfaces for enhancing catalysis by immobilized heterogeneous Pd species are introduced.

Synergy of ionic liquid and confinement in the design of supported palladium catalyst for efficient selective hydrogenation of acetylene

We present here a novel fabrication of highly effective supported Pd catalysts (Pd@S-1@IL) derived from Pd@S-1 core–shell material coated with ionic liquids (ILs), [Prmim][Cl], for the selective hydrogenation of acetylene. Catalytic testing on Pd@S-1@IL catalyst illustrated a remarkable selectivity towards semi-hydrogenation (over 90% for ethylene, irrespective of conversion level). Moreover, no indications of deactivation were observed after 800h on stream even under relatively severe conditions. Detailed characterization indicated that the selectivity enhancement was ascribed to the filter effect along with electronic effect on the adsorption/desorption processes arising from the ionic liquids layer. The stability, which has ranked the top reported values over advanced Pd-based catalysts, is attributed to the confinement effect of Pd NPs within the supports thus restricting the migration of metals. The fabrication of core–shell architecture combined with the advantages of ionic liquid layer offers a promising guideline for efficient catalytic transfer of chemical resource.

Development of Facile and Simple Processes for the Heterogeneous Pd-Catalyzed Ligand-Free Continuous-Flow Suzuki–Miyaura Coupling

The Suzuki–Miyaura coupling reaction is one of the most widely utilized C–C bond forming methods to create (hetero)biaryl scaffolds. The continuous-flow reaction using heterogeneous catalyst-packed cartridges is a practical and efficient synthetic method to replace batch-type reactions. A continuous-flow ligand-free Suzuki–Miyaura coupling reaction of (hetero)aryl iodides, bromides, and chlorides with (hetero)aryl boronic acids was developed using cartridges packed with spherical resin (tertiary amine-based chelate resin: WA30)-supported palladium catalysts (7% Pd/WA30). The void space in the cartridge caused by the spherical catalyst structures enables the smooth flow of a homogeneously dissolved reaction solution that consists of a mixture of organic and aqueous solvents and is delivered by the use of a single syringe pump. Clogging or serious backpressure was not observed.

Selective Oxidation of 5‐Hydroxymethylfurfural to 2,5‐Furandicarboxylic Acid over MnOx‐CeO2 Supported Palladium Nanocatalyst under Aqueous Conditions

AbstractSelective aerobic oxidation of biomass‐derived 5‐hydroxymethylfurfural (HMF) into high value‐added 2,5‐furandicarboxylic acid (FDCA) is regarded as one of the most attractive biomass transformations due to a wide range of its application prospects, particularly as an important renewable alternative to petroleum‐derived terephthalic acid in the synthesis of useful polymers. Herein, a novel MnOx−CeO2 (MC) supported palladium catalyst was synthesized and applied for the aerobic oxidation of HMF into FDCA in KHCO3 aqueous solution. The physical and chemical properties of the obtained catalysts were systematically characterized by TEM, N2 adsorption and desorption, XRD, TG, XPS, and H2‐TPR characterization methods. And the highest yield of FDCA at 92.5 % was achieved under the optimal reaction conditions. Moreover, regeneration tests revealed the synthesized Pd/MC catalyst can be recovered and reused at least five times without significant loss of catalytic activity. The developed facile reaction system with Pd/MC catalysts offers a new route to large‐scale and economically viable processes for the oxidation of HMF into FDCA.

Hydrogenation of chlorate ions by commercial carbon supported palladium catalysts\u2014a comparative study

The chlorate elimination potential of three commercial activated carbon supported 10 wt% palladium catalysts (Cat-I, Cat-II and Cat-III) have been compared in heterogeneous catalytic hydrogenation. The physical–chemical properties of the catalysts were characterized by using high-resolution transmission electron microscopy, X-ray diffractometry, Fourier-transform infrared spectroscopy and ζ potential measurements. Chlorate reduction tests have been carried out by applying the same procedure and conditions in each case. The studied catalysts were active, but Cat-I and Cat-III showed higher activity, and eliminated 93% and 91% of chlorate, respectively. Reuse tests have also been carried out to compare the catalysts. Although Cat-I and Cat-III were shown almost equally high activity in the first cycle, the reuse tests showed that Cat-III could have a better applicability.

Palladium supported on N-Heterocyclic carbene functionalized hydroxyethyl cellulose as a novel and efficient catalyst for the Suzuki reaction in aqueous media

Bearing an intrinsic green nature, biopolymers are expected to serve as ideal alternatives in the sustainable conversion process. In this paper, a N-Heterocyclic carbene functionalized hydroxyethyl cellulose supported palladium catalyst (HEC-NHC-Pd) has been successfully prepared through a surface functionalization approach. The as-prepared catalyst was characterized through TEM, CP/MAS 13C NMR, and XPS analyses, etc. The new and eco-friendly catalyst was effectively employed in Suzuki reactions in ethanol aqueous solution. Dependent on dual coordination sites (OH and N-Methylimidazole) binding to the active component (Pd), the palladium complex exhibited high stability and low metal leaching (<1%). Additionally, the environmental friendliness catalyst could be retrieved through simple centrifugation within a few cycles. This study also offers a new pathway for the application of such biopolymer surface functionalization in organic transformations.

Unleash electron transfer in C-H functionalization by mesoporous carbon-supported palladium interstitial catalysts.

The functionalization of otherwise unreactive C–H bonds adds a new dimension to synthetic chemistry, yielding useful molecules for a range of applications. Arylation has emerged as an increasingly viable strategy for functionalization of heteroarenes which constitute an important class of structural moieties for organic materials. However, direct bisarylation of heteroarenes to enable aryl-heteroaryl-aryl bond formation remains a formidable challenge, due to the strong coordination between heteroatom of N or S and transitional metals. Here we report Pd interstitial nanocatalysts supported on ordered mesoporous carbon as catalysts for a direct and highly efficient bisarylation method for five-membered heteroarenes that allows for green and mild reaction conditions. Notably, in the absence of any base, ligands and phase transfer agents, high activity (turn-over frequency, TOF, up to 107 h−1) and selectivity (>99%) for the 2,5-bisarylation of five-membered heteroarenes are achieved in water. A combination of characterization reveals that the remarkable catalytic reactivity here is attributable to the parallel adsorption of heteroarene over Pd clusters, which breaks the barrier to electron transfer in traditional homogenous catalysis and creates dual electrophilic sites for aryl radicals and adsorbate at C2 and C5 positions. The d-band filling at Pd sites shows a linear relationship with activation entropy and catalytic activity. The ordered mesopores facilitate the absence of a mass transfer effect. These findings suggest alternative synthesis pathways for the design, synthesis and understanding of a large number of organic chemicals by ordered mesoporous carbon supported palladium catalysts.

Recyclable Heterogeneous Palladium-Catalyzed Cyclocarbonylation of 2-Iodoanilines with Acyl Chlorides in the Biomass-Derived Solvent 2-Methyltetrahydrofuran.

A highly efficient, green palladium-catalyzed cyclocarbonylation of 2-iodoanilines with acyl chlorides has been developed that proceeds smoothly in a biomass-derived solvent 2-methyltetrahydrofuran with N,N-diisopropylethylamine as base at 100 °C under 20 bar of carbon monoxide using an 2-aminoethylamino-modified MCM-41-anchored palladium acetate complex [2N-MCM-41-Pd(OAc)2] as a heterogeneous catalyst, yielding a wide variety of 2-substituted 4H-3,1-benzoxazin-4-one derivatives in good to excellent yields. This supported palladium catalyst could be facilely obtained by a two-step procedure from easily available starting materials and readily recovered via a simple filtration process and recycled at least 8 times without any apparent decrease in catalytic efficiency. The developed methodology not only avoids the use of toxic solvents such as tetrahydrofuran and dimethylformamide but also solves the basic problem of expensive palladium catalyst recovery and reuse and prevents effectively palladium contamination of the desired product.

Sequential growth reveals multi-spinel interface promotion for methane combustion over alumina supported palladium catalyst

Tailoring of active components/metal oxides interface is an effective strategy to improve the performance of supported noble metal catalysts. However, the trade-off between activity and stability accompanies with the modification process. Herein, we propose a facile multi-spinel interface promotion way for simultaneous improvement in activity and stability of Pd/Al2O3 for methane oxidation. Multi-spinel NiCo2O4/NiAl2O4 interface is introduced over γ-Al2O3 support through sequential growth, and then acts as a structural template for the growth and dispersion of PdO nanoparticles to obtain Pd/NiCo2O4/NiAl2O4/Al2O3. The reducible property of NiCo2O4, and structural matching between NiCo2O4/NiAl2O4 and PdO lead to the enhanced performance during catalytic methane oxidation with respect to a low CH4 activation energy, high turnover frequency value and Pd utilization efficiency as well as long-term stability. Such a multi-spinel interface promotion strategy provides a new way to design efficient supported noble metal catalysts.

Environmental remediation by chitosan-carbon nanotube supported palladium nanoparticles: Conversion of toxic nitroarenes into aromatic amines, degradation of dye pollutants and green synthesis of biaryls

Nitroarenes, organic dyes and solvents are recalcitrant pollutants commonly found in industrial effluents. These organic compounds are toxic to aquatic organisms, hence their removal from aquatic systems is of significance. Remediation systems based on metallic nanoparticles are superior to the conventional systems with respect to their efficiency. Biopolymers like chitosan are considered to be suitable support material because biopolymers are capable of forming gel and exhibit affinity for metal cations. Catalysis systems with palladium nanoparticles are efficient in reducing nitroarenes to aromatic amines through hydrogenation, degradation of dye molecules and forming C-C bonds in organic coupling reactions. This study reports the preparation of chitosan-carbon nanotube supported palladium catalyst and the results of characterization studies by FTIR, XRD, TGA and SEM-EDX. The catalyst system was effective in catalytic reduction of 4-nitrophenol, 2-nitroaniline, 4-nitro-o-phenylenediamine and 2,4-dinitrophenol, and in degradation of dyes i.e., Congo red, Methyl orange, Methylene blue and Methyl red. The heterogeneous catalyst system also showed an excellent activity in green and solvent-free synthesis of 18 different biaryl compounds simply by six-minute microwave irradiation. The study demonstrated that chitosan-carbon nanotube supported-Pd(0) nanoparticles can be used for environmental remediation and protection, and for green synthesis of biaryls through Suzuki-Miyaura coupling reactions.

Controllable synthesis of mesoporous alumina as support for palladium catalysts and reconstruction of active sites during methane combustion

Uniform mesoporous alumina (MA) nanospheres with excellent thermal stability and controllable pore size distribution were facilely obtained through ultrasonic assisted sol-gel method then taken as carriers for synthesizing a series of supported palladium catalysts. Results evidenced that the pore size distribution of MA significantly affected the catalytic performance of as-prepared catalysts. More importantly, the methane pretreatment tuned valence state of palladium species and distribution of surface oxygen species, along with promoting the adsorption of CH4 on catalysts and the generation of CH3∗ group to form methane-derived adsorbates. Moreover, the synergistic effect of PdO and surface adsorbed oxygen effectively activated CH4 and invoked the oxidation of methane-derived adsorbates, hence boosting the catalytic activity with the 90% CH4 conversion temperature (T90) decreased by 40 °C relative to the unpretreated catalyst. Noticeably, the T90 of Pd/MA(CH4) catalyst could be attained at 380 °C after subsequent long term and cyclic stability test.