Catalytic Activity Of Pd Catalysts Research Articles

Improving the activity in hydrodechlorination of Pd/C catalysts by nitrogen doping of activated carbon supports

Aqueous phase 4-chlorophenol hydrodechlorination reaction was used to study the effect of N-doping of activated carbon support on the catalytic activity of Pd catalysts. Activated carbon was doped using pyridine and 1,10-phenantroline, reaching nitrogen contents of 0.42–1.22 and 1.35–4.19 % (w), respectively. All catalysts (0.75 % Pd w, carbon basis) showed relatively large Pd nanoparticles (35−55 nm), but they exhibited fast and complete 4-chlorophenol disappearance in batch experiments. In runs at 30 °C 4-chlorophenol disappearance was mainly ascribed to hydrodechlorination, although N-doping of the support also increased adsorption. Catalysts with supports doped with pyridine yielded higher 4-chlorophenol disappearance rate in spite of lower bulk nitrogen content, however they showed higher concentration of nitrogen species at the external surface and lower loss of surface area during the doping. 4-chlorophenol disappearance rate was boosted at 60 °C, with minor differences between catalysts with undoped and N-doped supports, but generation of cyclohexanone was only observed for the ones with doped support. Phenol generation simultaneous to 4-chlorophenol disappearance was observed with all the catalysts. However, subsequent hydrogenation to cyclohexanone ocurred only with the catalysts supported on N-doped activated carbon.

Fiber-supported Pd Catalysts for Cross-coupling Reaction of Aromatic and Aliphatic Terminal Alkynes

Increasing the efficiency of cross-coupling reaction under mild condition and easy catalyst separation is a key issue in the realistically chemical industry application. Here, we report that the fiber-supported Pd catalyst shows a high activity and selectivity for the cross-coupling reaction of terminal alkynes. The yield of the asymmetric 1,3-diyne can reach 83% at 80 °C and 4 h reaction time in N,N-dimethylacetamide (DMAc), and about 87% selectivity. XPS, EDS and SEM results show that Pd metal ions are successfully loaded onto the fiber surface and are reduced to produce active component of Pd (0) by terminal alkyne in reaction. We consider that Pd (0) is the active center of the catalytic cycle, the coordination of the fibers can stabilize Pd particles on the supports and increases the catalytic activity of Pd catalysts. Cu (I) plays a synergistic catalytic role. This study provides an alternative pathway for the high efficient cross-coupling reaction.

Polymer Based Palladium Nanocatalyst for the Degradation of Nitrate and Congo Red

In this study, the Pd catalyst based on chitosan-tannin (CT) framework as support was prepared and characterized. The CT support and Pd catalyst were characterized by attenuated total reflection (ATR) spectroscopy and Raman spectroscopy, Scanning electron microscopy-energy dispersive X-ray analyzer (SEM–EDX) and transmission electron microscopy (TEM) and X-ray diffractometry (XRD). Attenuated total reflection (ATR) spectra revealed the coordination of Pd via hydroxyl and amino functional groups. Raman spectral analysis was carried out to give information about the structural defect of the catalyst compared to CT support. The SEM–EDX results revealed regular surface morphology and presence of Pd in the catalyst as compared to CT support. TEM analysis revealed that the deposition of Pd on organic support with a spherical shape possessing size in the range of 6.01 nm–20.7 nm (average particle size = 12.65 ± 3.14 nm). The XRD results revealed the amorphous nature of the catalyst compared to CT support. TGA analysis revealed that the catalyst is highly thermally-stable compared to CT support. The catalytic activity of Pd catalyst was investigated for the reduction of nitrate and Congo red in the presence and absence of H2. The catalytic activities exhibited 71.11% and 23% removal of nitrate and Congo red in 20 and 60 min, respectively. Thus, results suggested that Pd catalyst has a potential of catalytic activity toward reduction of nitrate and Congo red in presence H2.

Effect of the supports on catalytic activity of Pd catalysts for liquid-phase hydrodechlorination/hydrogenation reaction

ABSTRACTCarbon nanotubes (CNTs), activated carbon (AC), graphene, and aluminum oxide (Al2O3) supported 5% Pd catalysts were prepared by the conventional impregnation method, and catalytic activity was tested in the hydrogenation of 4-chlorophenol (4-CP) and nitrobenzene (NB) under ambient conditions (313 K and atmospheric pressure). It was found that catalytic activity was greatly affected by the supports. Moreover, Pd/CNTs catalyst exhibited much higher catalytic activity than the other three supported Pd catalysts. The mechanism of this phenomenon was studied through catalyst characterization (ICP-MS, Brunauer-Emmett-Teller [BET], TEM, and SEM). It was found that the mean particle size of Pd nanoparticles for Pd/CNTs (4.3 nm) was smaller than that for Pd/AC (6.9 nm), Pd/Al2O3 (5.0 nm), and Pd/graphene (5.2 nm). Moreover, the actual loading amounts of Pd and BET surface areas were not the main reasons for the different catalytic activity of the four supported Pd catalysts. Above all, the smaller Pd particles of Pd/CNTs enabled the Pd/CNTs catalyst to exhibit much higher catalytic activity for the hydrogenation reactions.

Novel palladium catalysts immobilized on functionalized chlorinated polyvinylchloride nanofiber mats

Well-defined chlorinated polyvinylchloride (CPVC) nanofiber mats were fabricated by electrospinning, and then chemically modified with 1,3-propanediamine (CPVC–NH) and glutaraldehyde (CPVC–NOH) to immobilize palladium active species. The chemical modification could significantly improve the tensile strengths of the CPVC nanofiber mats. Adsorption of Pd(II) ions showed that the treatment of fiber mats with glutaraldehyde decreases it schelating ability. Transmission electron microscopy and X-ray diffraction analysis indicated that palladium species were dispersed more homogeneously on the CPVC–NH fibers than on the CPVC–NOH fibers. Results of Mizoroki–Heck reaction showed that the catalytic activity of Pd catalyst supported on CPVC–NOH fibers was superior to that of the Pd catalyst supported on CPVC–NH fibers. Thus, chemical modification of supporting materials with suitable chelating groups is an efficient way to control the catalytic performance of supported Pd catalysts.

Effects of Pt on physicochemical properties over Pd based catalysts for methanol total oxidation

The physicochemical properties of Pd/CAT11CAT: CeO2-Al2O3-TiO2. and Pd-Pt/CAT catalysts synthesised by impregnation methods were investigated by techniques of XRD, Nitrogen adsorption-desorption, noble metal dispersion, XPS and H2-TPR. The catalytic activities for methanol total oxidation were tested to study the promoting effects of platinum on palladium based catalysts. The results of characterizations revealed that catalysts with Pd-Pt possessed more abundant Oβ (adsorbed oxygen), Ti4+ and TiOx/Ti than that of Pd catalysts. Additionally, the existence of PdPtTiOx might be conducive to the transmission of intermediate or Oβ, which further accelerated the rate of oxidation reaction. These factors resulted in the remarkable decrease of T50 and T90 which stated the enhanced catalytic activity of Pd catalysts by the addition of Pt. Based on the conclusions from characterizations and experimental results, a possible reaction pathway was also proposed about how Oβ took part in methanol oxidation through the transition between different oxides and the corresponding metals.

Methanol Oxidation on Ru- or Ni-Modified Pd-Electrocatalysts in Alkaline Media: A Comparative Differential Electrochemical Mass Spectrometry Study

The electrochemical oxidation of methanol on electrocatalysts is intensively investigated since direct methanol fuel cells (DMFCs) were proposed as a promising alternative as power source for mobile and back-up power applications. In DMFCs, methanol is oxidized at the anode and oxygen is reduced at the cathode to convert the chemical energy of the fuels to electric power. In recent years, the electrochemical oxidation of methanol in alkaline environment is rising in interest, because other electrocatalysts than the expensive platinum are feasible as anode and cathode catalysts in alkaline DMFCs. While multiple catalysts are feasible on the cathodic site, Palladium was proven to be a suitable substitute for Pt as anode catalyst for the electrochemical oxidation of alcohols in alkaline media [1], but needs further improvement to compete with Pt especially regarding methanol oxidation reaction. The catalytic activity of Pd catalysts was improved by alloying or mixing other metals (or metal oxides) to Pd [2,3] or by controlling the size and shape of Pd particles [4]. Besides high catalytic activity, the complete oxidation of methanol to CO2is of enormous interest, because the complete oxidation results in the highest possible faradaic efficiency with six electrons transferred per methanol molecule. In contrast, two or four electrons are transferred to the anode per methanol molecule, if methanol is not completely oxidized. Differential electrochemical mass spectrometry (DEMS) is used by different research groups to quantify a catalyst’s ability to completely oxidize methanol. While the methanol electrooxidation on Pt-based catalysts was investigated intensively via DEMS in acidic media, DEMS studies on Pd-based catalysts for methanol electrooxidation in alkaline media are rare. In former studies, we reported on PdXNi/C and PdXRu/C catalysts for methanol electrooxidation in alkaline media synthesized by wet-chemical reduction with sodium borohydride [2,3]. It was possible to show that these oxophilic metals have a positive effect on the catalytic activity towards methanol oxidation of Pd-based catalysts. Taking these studies into account, we herein investigated the influence of these metals on Pd-based electrocatalysts regarding methanol oxidation reaction via DEMS. Besides analyzing the product distribution from methanol bulk oxidation on PdXNi/C or PdXRu/C, the main interest of this work is to investigate how the addition of the metals to Pd influences the methanol oxidation mechanism and catalyst poisoning. Hence, standard electrochemical tests like cyclic voltammetry, chronoamperometry, COadsstripping or methanol adsorbate stripping were conducted in the DEMS flow cell. Figure 1 shows cyclic voltammograms and corresponding MS signals for produced CO2 (m/z = 44) and methyl formate (m/z = 60) for Pd/C, Pd5Ni/C and Pd3Ru/C during methanol electrooxidation. While both modified catalysts show higher current densities and lower onset potentials than Pd/C for the electrooxidation of methanol, the product distribution differs strongly depending on the added metal. For Ni-modified catalyst the formation of CO2 is significantly lower than for Pd/C. While the addition of Ni to Pd leads to a negative effect on the ability to completely oxidize methanol, Pd3Ru/C is able to oxidize methanol more efficiently to CO2 than Pd/C. For Pd3Ru/C, the CO2 formation is shifted to lower potentials while methyl formate is produced at higher potentials. This hints to a more selective production of CO2 at low potentials on Pd3Ru/C than on Pd/C or Pd5Ni/C. Besides DEMS experiments, measurements were carried out in dependence of methanol concentration or oxidation temperature using a 3-electrode setup with stationary electrolyte to determine the rate determining step and the activation energy of methanol electrooxidation on Pd/C and the modified catalysts. Fig. 1 – Methanol bulk oxidation on Pd/C, Pd5Ni/C and Pd3Ru/C investigated via cyclic voltammetry in a DEMS flow cell at 20 mV s-1 from 0.1 to 1.2 V (vs. RHE) with 0.1 M CH3OH + 0.5 M KOH solution as electrolyte. Corresponding mass spectrometry signals for CO2 (m/z 44) and HCOOCH3(m/z 60) are displayed to evaluate the product distribution during methanol oxidation reaction.

Reduction of NO by CO using Pd–CeTb and Pd–CeZr catalysts supported on SiO2 and La2O3–Al2O3

The catalytic activity of Pd catalysts supported on Ce0.73Tb0.27Ox/SiO2, Ce0.6Zr0.4Ox/SiO2, Ce0.73Tb0.27Ox/La2O3–Al2O3 and Ce0.6Zr0.4Ox/La2O3–Al2O3 was studied using the reduction of NO by CO. The catalysts were characterized by X-ray fluorescence, surface area, X-ray diffraction, temperature-programmed reduction, CO chemisorption and oxygen storage capacity. Temperature-programmed reduction results indicated that Tb or Zr incorporation improves the reducibility and oxygen storage capacity. CO chemisorption data suggested the presence of large PdO particles due to the low CO/Pd ratio. No significant differences were obtained in light off temperatures (TLight off) for all Pd catalysts and the most active was 1.5%Pd/Ce0.6Zr0.4Ox/SiO2.

Catalytic activity of Pd catalysts on different supports in hydrogenation of 1-phenylethenylphosphonic acid

Activity of palladium catalysts on different crystalline and amorphous supports was studied using hydrogenation of 1-phenylethenylphosphonic acid with molecular hydrogen as an example. Nanoscale Pd0 deposited on the surface of multi-wall carbon nanotubes (MWCNT) supported on microparticles of titanium oxide has proved the highest efficiency. The starting acid was quantitatively reduced for 1 h in the presence of this catalyst, 11 cycles of hydrogenation were carried out without loss of catalytic activity.

Pd–Ce0.33Zr0.67O2–Al2O3 catalyst for propane oxidation: Interactions between the precious metal and support under the hydrothermal ageing

To investigate the influencing of the Ce0.33Zr0.67O2 and Al2O3 supports on the catalytic activity of Pd catalysts for propane oxidation, and possible Pd migration/interaction on different supports during the hydrothermal ageing, four samples were prepared by mixing one supported catalyst and another support powders either before or after the ageing treatment in a steam-containing air at 1050°C for 5h. It is unlikely for the occurrence of migration of Pd from one support to another during the thermal treatment as evidenced by the SEM and EDS results. IR spectra after CO introduction and H2-TPR results indicate the enlargement of the interface between Pd and another support during the thermal ageing, which may result in different Pd-support interaction. TPHD and XPS results further attribute the nature of this interaction to an electron transfer effect. The propane light-off temperature of co-aged Pd/Ce0.33Zr0.67O2 and Al2O3 is 45°C lower than the mixture of aged Pd/Ce0.33Zr0.67O2 and Al2O3, indicating the Pd–alumina interface is found to be more effective for the catalytic oxidation of propane.

Enhancement of phenol hydrodeoxygenation over Pd catalysts supported on mixed HY zeolite and Al2O3. An approach to O-removal from bio-oils

This contribution describes the effect of the support (zeolite ultrastable HY, alumina (Al) and mixed HY–Al carriers) on the catalytic activity of Pd catalysts in the phenol hydrodeoxygenation (HDO) reaction carried out in a flow fixed-bed reactor at T=523–573–623K, P=15bar and WHSV=0.5h−1. Phenol dissolved in n-octane was used as model compound of bio-oil species derived from fast pyrolysis of lignocellulosic biomass. The catalysts were characterized by N2 physisorption, XRD, TPR, TPD-NH3, DRIFT spectroscopy of adsorbed CO, HRTEM, X-ray photoelectron spectroscopy (XPS) and TPO/TGA techniques. The largest phenol conversion (63%) achieved at 523K over the reduced Pd/20%HY–Al catalyst was similar to that obtained on a commercial NiMo/Al2O3–zeolite hydrocracking sample (HCK) activated by sulfidation. Regardless of the reaction temperature, the only products detected in the HDO of phenol over all catalysts studied were four O-free compounds: benzene, cyclohexene, cyclohexane, and methylcylopentene. Both reduced Pd/20%HY–Al and sulfided commercial HCK catalysts produced similar yields of O-free products. From the catalyst activity-structure correlation, it can be concluded that the HDO of phenol is favoured on the bifunctional Pd/20%HY–Al catalyst which possesses moderate acidity and improved Pd dispersion on the support surface. The contributions of the acid sites to the catalyst activity and deactivation by coke are discussed.

Effect of Aging Atmosphere on Catalytic Activity for NO–CO–C3H6–O2 Reaction of CeO2-Containing Oxide Supported Pd Catalysts

The catalytic activity for CO, hydrocarbon and NO removal on Al2O3 and CeO2 based oxides supported Pd catalysts were studied under switching of aging condition between air and N2 atmosphere. For CeO2-containing Pd catalysts, the deterioration of catalytic activities by aging in N2 was improved by oxidative treatment. Based on results of XPS and FT-IR measurements, it was presumed that the catalytic activity of Pd catalysts was strongly affected by the adsorbed form of CO on Pd, which occurs owing to a change of the chemical state of Pd.

Pulse electrodeposited Pd nanoclusters on graphene-based electrodes for proton exchange membrane fuel cells

This study describes a pulse electrodeposition approach for the synthesis of palladium (Pd) nanocatalysts supported on graphene oxide (GO) sheets and their electrocatalytic performance in a single stack of proton exchange membrane fuel cell (PEMFC). Star-like Pd clusters consisting of several nanotips are well deposited over the GO sheets, and the primary size of the cluster ranges from 100 to 150nm. Cyclic voltammetry (CV) has been adopted to examine the catalytic activity of Pd catalysts in 1M H2SO4, showing a reversible hydrogen adsorption/desorption. The presence of GO sheets is presumed to render multifunctional roles in facilitating the dispersion of metallic Pd clusters, ionic diffusion, and charge transfer. The PEMFC performance increases with an increase in cell temperature. The single cell delivers the maximal power density of ∼1.08kWg−1 at 70°C and exhibits the apparent activation energy of ∼27.5kJmol−1 within the temperature region of 40–70°C, according to an estimation of Arrhenius plots.

Synthesis and characterization of aluminum and Al/REE pillared clays and supported palladium catalysts for benzene oxidation

Volatile organic compounds (VOCs) are considered as a major pollutant in indoor and outdoor air. More stringent environmental regulations have been implemented in order to reduce the VOC emissions. One of the techniques available for destructive removal of VOCs is catalytic oxidation. In the present work, Al/Rare Earths (REE: Y, Ce, La, Pr and Nd) pillared clays (PILCs) were used to support 0.2 wt.% of palladium for the complete oxidation of low concentration of benzene. The supports and catalysts were characterized by XRD, N 2 adsorption/desorption, FTIR spectroscopy, HRTEM and H 2-TPR techniques. The results indicated that after Al and Al/REE pillaring, the basal spacing, S BET, A mic and V mic of Al and AlREE-PILC had a considerable increase compared with those of Na-mmt. Activity tests of deep oxidation of benzene showed that the catalytic activity of Pd catalysts supported on Al and AlREE-PILC were much higher than that on initial clays, which was due to the fact that optimized structure of PILCs, such as large basal spacing, high S BET and porosity, improved Pd dispersion and increased the active sites of Pd. Especially for Pd/AlCe-PILC, the temperature of complete oxidation was about 280 °C, exhibiting the highest catalytic activity.

Al/Ce pillared clays with high surface area and large pore: Synthesis, characterization and supported palladium catalysts for deep oxidation of benzene

Large pore Al/Ce pillared clays (AlCe-PILC) were synthesized and used as supports for Pd catalysts in deep oxidation of low concentration of benzene (130–160 ppm). The supports and catalysts are characterized by X-ray powder diffraction (XRD), N 2 adsorption/desorption, high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX) and temperature-programmed reduction techniques (TPR). The results showed that AlCe-PILC are characterized by basal spacings of 1.79–2.83 nm and have high surface areas of 343.6–377.4 m 2/g. Catalytic activity tests show that the catalytic activity of Pd catalysts in benzene deep oxidation is greatly dependent on the type of supports. Temperature for the complete benzene conversion using the following catalysts decreases in the order: Pd/Na-mmt (>400 °C) > Pd/Al-PILC (340 °C) > Pd/AlCe-PILC (≤300 °C). And the effects of hydrothermally treated time and different loading of Ce of Al/Ce pillaring solution on the activity of Pd/AlCe-PILC catalysts were also investigated, results of which show that high mesopore surface area and large pore structures of the supports are the key factors in improving the activity of the Pd/AlCe-PILC catalysts. The temperature for complete oxidation of benzene with Pd/AlCe-PILC (5;30) catalyst was 250 °C, exhibiting the highest catalytic activity.

Effects of ZrO 2/Al 2O 3 properties on the catalytic activity of Pd catalysts for methane combustion and CO oxidation

Zirconia supported on alumina was prepared and characterized by BET surface area, X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), temperature programmed desorption (TPD), and pulse reaction. 0.2% Pd/ZrO 2/Al 2O 3 catalyst were prepared by incipient wetness impregnation of supports with aqueous solution of Pd(NO 3) 2. The effects of support properties on catalytic activity for methane combustion and CO oxidation were investigated. The results show that ZrO 2 is highly dispersed on the surface of Al 2O 3 up to 10 wt.% ZrO 2, beyond this value tetragonal ZrO 2 is formed. The presence of a small amount of ZrO 2 can increase the surface area, pore volume and acidity of support. CO–TPD results show that the increase of CO adsorption capacity and the activation of C O bond after the presence of ZrO 2 lead to the increase of catalytic activity of Pd catalyst for CO oxidation. CO pulse reaction results indicate that the lattice oxygen of support can be activated at lower temperature following the presence of ZrO 2, but it does not accelerate the activity of 0.2% Pd/ZrO 2/Al 2O 3 for methane combustion. 0.2% Pd/ZrO 2/Al 2O 3 dried at 120 °C shows highest activity for CH 4 combustion, and the activity can be further enhanced following the repeat run. The increase of treatment temperature and pre-reduction can decrease the activity of catalyst for CH 4 combustion.

Complete oxidation of methane at low temperature over Pt and Pd catalysts for the abatement of lean-burn natural gas fuelled vehicles emissions: influence of water and sulphur containing compounds

The catalytic activity of fresh Pd and Pt catalysts supported on γ-alumina in the complete oxidation of CH 4 traces under lean-burn conditions was studied in the presence or the absence of water or H 2S. Steam-aged catalysts were also studied in order to simulate long-term ageing in real lean-burn natural gas fuelled vehicles (NGVs) exhaust conditions. Without water or H 2S added to the feed, Pd catalysts exhibit a superior catalytic activity in methane oxidation compared to Pt ones, whatever the catalysts were fresh or aged. The addition of 10 vol.% water vapour to the feed strongly affects the activity of the fresh Pd catalyst, thus being only slightly more efficient than the fresh Pt one. H 2S has a strong poisoning effect on the catalytic activity of Pd catalysts, while Pt catalysts are more resistant. The fresh H 2S-poisoned Pd/Al 2O 3 catalyst was studied by TPD in O 2/He. Poisoning species decompose above 873 K as SO 2 and O 2 in relative concentrations consistent with the decomposition of surface sulphate species. However, a treatment in O 2/He at temperatures as high as 923 K does not allow the complete regeneration of the catalytic activity of H 2S-poisoned Pd/Al 2O 3. A mechanism involving the poisoning of PdO by sulphate species is proposed. Different diffusion processes by which these sulphate species can migrate back and forth between PdO and the support, depending on the experimental conditions, are suggested.

Thermal stability, structural properties and catalytic activity of Pd catalysts supported on Al2O3–CeO2–BaO mixed oxides prepared by sol–gel method

Abstract Al2O3–CeO2–BaO oxides with constant Al/Ba mass ratio and increasing cerium content were prepared, using the sol–gel procedure, and calcined at 1000 °C for 5 h. The influence of barium oxide on the thermal stability and on the morphological and structural properties of the corresponding supports, in terms of increasing surface area of alumina and ceria dispersion, was studied. The corresponding Pd (1 wt.%) catalysts were prepared by a stepwise impregnation method with a solution of palladium acetylacetonate in benzene. Palladium was introduced in two sequential steps by impregnation 0.5 wt.% of Pd each time. The structural and textural properties of the materials were studied by X-ray diffraction (XRD) analysis, BET surface area and pore size distribution measurements. The effect of ceria on structural properties and methane combustion activity of the Pd-based catalysts was investigated. The light-off temperatures of low-ceria loaded catalysts are both shifted 60–90 °C, respectively, below the corresponding temperature observed on high-ceria loaded samples.