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1.
Supported Pd catalysts were prepared by solid-phase crystallization (spc) starting from MgAl hydrotalcite anionic clay minerals as the precursors, and were tested for the methanol decomposition to synthesis gas. The precursors based on [Mg6Al2(OH)16CO3
2-] · 4H2O were prepared by coprecipitation from raw materials containing Pd2+, Mg2+ and Al3+ ions as the components of hydrotalcite. The precursors were thermally decomposed and reduced to afford supported Pd catalysts on MgAl mixed oxide. Pd-supported catalysts as a reference were also prepared by the impregnation (imp) method. The spc-Pd catalysts thus prepared afforded highly dispersed Pd metal particles and showed higher activity as well as lower activation energy than the imp-Pd catalysts. When the precursor was prepared under mild conditions, finer particles of Pd metal were formed over the catalyst, resulting in a high activity. In the case of spc-Pd catalysts, carbon monoxide adsorbed on Pd easily desorbed, compared with imp-Pd catalysts. It is likely that the high activity is due to the highly dispersed and stable Pd metal particles and the easy desorption of carbon monoxide. 相似文献
2.
Methanol decomposition to synthesis gas over supported Pd catalysts prepared from synthetic anionic clays 总被引:2,自引:0,他引:2
Ryuji Shiozaki Takashi Hayakawa Yan-yong Liu Tomoko Ishii Mikio Kumagai Satoshi Hamakawa Kunio Suzuki Tatehiko Itoh Tetsuya Shishido Katsuomi Takehira 《Catalysis Letters》1999,58(2-3):131-140
Supported Pd or Rh catalysts were prepared by the solid-phase crystallization method starting from hydrotalcite anionic clay
minerals based on [Mg6Al2(OH)16CO
2
2−
]·4H2O as the precursors. The precursors were prepared by a coprecipitation method from the raw materials containing Pd2+ and various trivalent metal ions which can replace each site of Mg2+ and Al3+ in the hydrotalcite. Rh3+ was also used for preparing the catalyst as comparison. The precursors were then thermally decomposed and reduced to form
supported Pd or Rh catalysts and used for the methanol decomposition to synthesis gas. Among the precursors tested, use of
Mg–Cr hydrotalcite containing Pd2+ resulted in the formation of efficient Pd supported catalysts for the production of synthesis gas by selective decomposition
of methanol at low temperature. Although Pd2+ cannot well replace the Mg2+ site in the hydrotalcite, the Pd supported catalyst (Pd/Mg–Cr) prepared by the solid-phase crystallization method formed
highly dispersed Pd metal particles and showed much higher activity than that prepared by the conventional impregnation method.
When the precursor was prepared under mild conditions, more fine particles of Pd metal were formed over the catalyst, resulting
in high activity. It is likely that the high activity may be due to the highly dispersed and stable Pd metal particles assisted
by the role of Cr as the co-catalyst.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
3.
Menno Kappers Carlo Dossi Rinaldo Psaro Sandro Recchia Achille Fusi 《Catalysis Letters》1996,39(3-4):183-189
Magnesia-supported palladium catalysts were prepared from chemical vapour deposition (CVD) of [Pd(C3H5)(C5H5)] and incipient wetness impregnation of [Pd(C3H5)Cl]2 and [Pd(acac)2]. DRIFT spectroscopy of adsorbed CO on prereduced catalysts indicates that the electronic state of metal particles depends on the preparation methodology and markedly on the organometallic precursor. Inn-heptane reforming at 500°C, the highest activity and selectivity were shown by the CVD-based system. Chloride ions deriving from the impregnation solvent exchange with surface hydroxyls. Acidic Mg-Cl sites are thus formed, which induce a beneficial effect on the catalytic properties. The reforming activity collapsed when a chlorine-containing precursor was used, due to a partial coverage of the palladium surface with chemisorbed chlorine atoms. 相似文献
4.
E. Tzimpilis N. Moschoudis M. Stoukides P. Bekiaroglou 《Applied catalysis. B, Environmental》2008,84(3-4):607-615
Perovskite-type oxides, containing Pd, were prepared via a combined sol–gel and combustion synthesis method and were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and BET specific surface area (SSA). Their activity as three-way catalysts for the abatement of carbon monoxide, methane and nitrogen oxides, emitted from stoichiometrically operating natural-gas-fuelled vehicles, was investigated under simulated exhaust conditions. The preparation conditions concerning the complexing agent, the use of additives and the thermal treatment of the precursor solutions, were investigated. The La0.91Mn0.85Ce0.24Pd0.05Oz and La1.034Mn0.966Pd0.05Oz phases were the most active. Their activation by high-temperature hydrothermal treatment was ascribed to the migration of Pd out of the perovskite lattice and the formation of segregated PdO. The role of Pd was crucial for the catalytic activity of the active phase. A low Pd content favored the dispersion of oxidized Pdx+, 2 ≤ x ≤ 4, and thus, enhanced catalytic activity. Oxidized Pdx+ with x > 2 appeared to be less active than Pd2+. The catalytic activity of La1.034Mn0.966Pd0.05Oz increased significantly when 8 ppm SO2 were introduced in the reaction mixture. 相似文献
5.
A series of Pd/Ce0.2Y0.8O2-δ catalysts were prepared and tested for CO and CH4 oxidation. It is found that the Pd/Ce0.2Y0.8O2-δ catalysts are thermal stable, and the catalytic activity enhances with increasing calcination temperature. The enhancement of the activity is due to the decomposition of surface carbonate species and the increase in average oxidation state of Pd. 相似文献
6.
Sirima Somboonthanakij Okorn Mekasuwandumrong Joongjai Panpranot Tarit Nimmanwudtipong Reto Strobel Sotiris E. Pratsinis Piyasan Praserthdam 《Catalysis Letters》2007,119(3-4):346-352
In this study, Pd/SiO2 catalysts with 0.5–10 wt.% Pd loadings were prepared by one-step flame spray pyrolysis (FSP) and characterized by N2 physisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), CO chemisorption, and X-ray photoelectron
spectroscopy (XPS). The average cluster/particles size of Pd as revealed by TEM were ca. 0.5–3 nm. The turnover frequencies (TOFs) of the flame-made catalysts decreased from 66.2 to 4.3 per s as Pd loading increased
from 0.5 to 10 wt.%, suggesting that the catalytic activity was dependent on Pd particle/cluster size. However, there were
no appreciable influences on 1-heptene selectivity. The flame-made Pd/SiO2 showed better properties than the conventional prepared catalysts. Their advantages are not only the presence of large pores
that facilitates diffusion of the reactants and products, but also the high-catalytic activity of as-synthesized catalysts
so that further pretreatment is not necessary. 相似文献
7.
Rajesh Gopinath N. Seshu Babu J. Vinod Kumar N. Lingaiah P. S. Sai Prasad 《Catalysis Letters》2008,120(3-4):312-319
A series of alumina supported Pd catalysts were prepared by the novel deposition-precipitation method adopting the chloride
precursor (DP-Cl) of Pd and varying the metal content from 0.25 to 1.0 wt%. The catalytic properties of prepared catalysts
were studied by various characterization techniques such as N2 adsorption, CO chemisorption, TPR, XRD, XPS, and TEM techniques. The activity and stability of the catalysts were evaluated
for the gas phase hydrodechlorination (HDC) of chlorobenzene operating at atmospheric pressure. At 1 wt% of Pd the catalyst
showed higher chlorobenzene conversion with good stability when tested for a period of 25 h, whereas the other catalysts exhibited
a loss in activity with time. In order to elucidate the exceptional activity and stability of this catalyst, a few more catalysts
with 1 wt% Pd were prepared by impregnation technique and also using a non-chloride precursor, palladium nitrate. The 1 wt%
DP-Cl catalyst again was found to be the best among the others. The activity and stability of the DP-Cl catalyst was also
found to be superior to two low-dispersed catalysts, each with 10 wt% Pd, prepared by conventional impregnation method using
the chloride and nitrate as the precursors. The characterization results reveal that the high activity and stability of the
DP-Cl catalyst is related to the formation of electron deficient Pd species and its stabilization in the octahedral vacancies
of alumina. 相似文献
8.
Pd catalysts supported on TiO2, ZrO2, ZSM-5, MCM-41 and activated carbon were used in catalytic wet oxidation of hydrocarbons such as phenol, m-cresol and m-xylene.
It was found that the Pd/TiO2 catalyst was highly effective in the wet oxidation of hydrocarbon. The activities of catalysts with various hydrocarbon species,
catalyst support, oxidation state of catalyst performed in a 3-phase slurry reactor show that reaction on Pd surface is more
favorable than that in aqueous phase and that the active site is oxidized Pd in catalytic wet air oxidation of hydrocarbons.
Based on the experimental results, a plausible reaction mechanism of wet oxidation of hydrocarbons catalyzed over Pd/TiO2 catalyst was proposed. This catalyst is superior to other oxide catalysts because it suppressed the formation of hardly-degradable
organic intermediates and polymer. 相似文献
9.
Pd catalyst supported on Vulcan XC‐72 carbon black was prepared by a modified polyol process. Its performance was compared with that of Pd/C catalyst prepared by impregnation reduction method by using NaBH4 as a reducing agent for formic acid electrooxidation. Their physical characterisations were tested by means of energy dispersive analysis of X‐ray, X‐ray diffraction and transmission electron micrographs. Their activities were presented by cyclic voltammetry and chronoamperometry. The results show that the particle sizes of Pd/C catalysts prepared by modified polyol process and impregnation reduction method are 3.9 and 7.9 nm, respectively. The size dispersion of the former is narrower and more homogeneous than that of the latter. However, both of Pd/C catalysts display the characteristic diffraction peaks of a Pd face‐centred cubic (f.c.c.) crystal structure. The results of electrochemical measurements present that the Pd/C catalyst prepared by modified polyol process has the higher electrocatalytic activity and stability for formic acid electrooxidation in comparison to the Pd/C one by impregnation reduction method due to the particle size effect, and its peak current density of CV and the current of chronoamperometric curve at 1,000 s reach 33.2 and 11.2 mA cm–2, respectively. 相似文献
10.
The temperature programmed (palladium) hydride decomposition appeared very effective method for diagnosing the extent of alloying in Pd-Pt/SiO2 catalysts. Introduction of Pt to Pd catalysts moves the TPHD peak gradually towards lower temperatures and the shift in hydride decomposition peak is accompanied by a decrease in the amount of released hydrogen. The catalysts prepared the direct redox method showed much better alloy homogeneity than the samples prepared by coimpregnation. The results of probing with other techniques, i.e. catalytic probing with hydrodechlorination of CCl2F2 and XRD, were in line with TPHD data. The catalytic probing showed the presence of synergistic effect, a clear indication of Pd-Pt mixing. XRD data of post-reaction samples showed carbon incorporation into Pd-rich phase, whereas separate Pt-rich phase did not experience any bulk carbiding. 相似文献
11.
Nazli Asgari Mohammad Haghighi Sirous Shafiei 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2013,88(4):690-703
BACKGROUND: The effect of Pd loading, xylene concentration and GHSV on xylene oxidation was tested over Pd/CeO2(30%)‐clinoptilolite nanocatalysts at low temperatures. The catalysts were prepared by acid treatment of clinoptilolite, followed by the incipient wetness method of synthesized ceria and modified clinoptilolite in PdCl2 solution. The synthesized nanocatalysts were characterized by XRD, FESEM, EDAX, TEM, BET, FTIR and TG‐DTG analysis. RESULTS: The XRD patterns confirmed the formation of crystalline ceria with an average crystallite size of 11.8 nm. FESEM images showed nanostructures in cavities of natural zeolite, brought about by ceria incorporation and acid activation. TEM analysis showed high dispersion of Pd with a size distribution between 6.6 and 36.7 nm. The quantitative analysis showed that the specific surface area of Pd(1%)/CeO2(30%)‐clinoptilolite was 77 m2 g?1. The results showed that Pd(1%)/CeO2(30%)‐clinoptilolite is the most appropriate catalyst, with the conversion more than 90% at 275 °C. CONCLUSIONS: Experimental results established effective performance and durability for the catalysts. As a result, clinoptilolite modification and ceria incorporation significantly altered the samples' morphology at nanoscale, improving the structure of composites and distribution of noble metals. A reaction path was suggested based on the adsorption‐migration of species to reveal the mechanism of p‐xylene oxidation over nanocatalysts. © 2012 Society of Chemical Industry 相似文献
12.
《Catalysis communications》2007,8(8):1287-1292
The catalytic methane combustion was investigated over alumina-supported monometallic and bimetallic palladium and manganese oxide catalysts. The catalytic activity of these systems showed that palladium incorporation on MnOx/Al2O3 catalyst leads to an enhancement in methane combustion. The higher catalytic activity of the PdMn/Al2O3 catalysts is related to a greater mobility of lattice oxygen in manganese oxide in the presence of palladium. These bimetallic catalysts also showed a significant improvement in catalysts stability with respect the monometallic ones. Surface analysis of the used catalysts revealed less amount of coke and Mn/Al and Pd/Al atomic ratios almost unchanged, which is indication of absence of active phase sintering. 相似文献
13.
Activation of Supported Pd Metal Catalysts for Selective Oxidation of Hydrogen to Hydrogen Peroxide 总被引:1,自引:0,他引:1
Catalytic activity of supported Pd metal catalysts (Pd metal deposited on carbon, alumina, gallia, ceria or thoria) showing almost no activity in the liquid-phase direct oxidation of H2 to H2O2 (at 295 K) in acidic medium (0.02 M H2SO4) can be increased drastically by oxidizing them using different oxidizing agents, such as perchloric acid, H2O2, N2O and air. In the case of the Pd/carbon (or alumina) catalyst, perchloric acid was found to be the most effective oxidizing agent. The order of the H2-to-H2O2 conversion activity for the perchloric-acid-oxidized Pd/carbon (or alumina) and air-oxidized other metal oxide supported Pd catalysts is as follows: Pd/alumina < Pd/carbon < Pd/CeO2 < Pd/ThO2 < Pd/Ga2O3. The H2 oxidation involves lattice oxygen from the oxidized catalysts. The catalyst activation results mostly from the oxidation of Pd metal from the catalyst producing bulk or sub-surface PdO. It also caused a drastic reduction in the H2O2 decomposition activity of the catalysts. There exists a close relationship between the H2-to-H2O2 conversion activity and/or H2O2 selectivity in the oxidation process and the H2O2 decomposition activity of the catalysts; the higher the H2O2 decomposition activity, the lower the H2-to-H2O2 conversion activity and/or H2O2 selectivity. 相似文献
14.
Stefania Albonetti Giovanni Baldi Andrea Barzanti Enrique Rodriguez Castellon Antonio Jimenz Lopez Dolores Eliche Quesada Angelo Vaccari 《Catalysis Letters》2006,108(3-4):197-207
Pd/Rh and Pd/Pt catalysts supported on two different mesoporous materials – a Zr-doped MCM-41-type silica [Si/Zr = 5 w/w (SiZr)]
and a commercial silica-alumina [Si/Al = 40:60 w/w (SiAl)] – were prepared by incipient wetness impregnation using nanosized
suspensions of alloy particles prepared by polyol-mediated synthesis in diethylene glycol (DEG). The catalytic behaviour of
these catalysts was investigated in the hydrogenation and hydrogenolysis/ring-opening of naphthalene at 6.0 MPa, by checking
the role of both the main reaction conditions (temperature, contact time and H2/naphthalene molar ratio) and increasing amounts of dibenzothiophene (DBT). The catalysts supported on SiAl showed higher
activity than catalysts supported on SiZr, thus suggesting that activity is favoured by higher acidity of the support and/or
higher interaction of the nanosized metal particles with the support. While using the SiZr support, weaker metal-support interactions
took place by forming catalysts with bigger metal and/or metal oxide particles. Besides, the catalyst with lowest noble-metal
content (0.3 wt.%) (SiAl-0.3Pd/Pt-5) had the greatest acidity and metal surface and, consequently, the highest activity. Furthermore,
it exhibited a good thiotolerance in presence of increasing amounts of DBT in the feed, thus maintaining a high catalytic
activity in the hydrogenation of naphthalene, although with decreased yield in trans- and cis-decalin (decahydronaphthalene or DeHN) and high-molecular-weight compounds (H.M.W.), with a corresponding increased yield
in the partially hydrogenated tetralin (tetrahydronaphthalene or TeHN). 相似文献
15.
Characterization study of CeO2 supported Pd catalyst for low-temperature carbon monoxide oxidation 总被引:1,自引:0,他引:1
Catalysts consisting of palladium supported on cerium dioxide (Pd/CeO2) were prepared and used for carbon monoxide oxidation in a stoichiometric mixture of carbon monoxide and oxygen. Pd/CeO2 exhibits high catalytic activity for the oxidation of CO, showing markedly enhanced catalytic activities due to the combined
effect of palladium and cerium dioxide. The Pd/CeO2 catalyst is superior to Pd/ZrO2, Pd/Al2O3, Pd/TiO2, Pd/ZSM-5 and Pd/SiO2 catalysts with regard to the activity under the conditions examined. The catalysts were characterized by means of XRD and
TPR. The position of the H2-TPR peak shifts to lower temperature with increasing Pd loading from 0.25 to 2.0%. CeO2 inhibits the hydrogen reduction of PdO. CO-TPR measurements have shown the existence of three peaks. The low-temperature
peak (α) is due to the Pd hydroxide species. The β peak has been attributed to finely dispersed PdO. The high-temperature
peak (γ) has been attributed to crystal phase PdO. Crystal phase PdO is more difficult to reduce by CO than finely dispersed
PdO. On the basis of the catalytic activity and CO-TPR results, we conclude α species (Pd hydroxide) mainly contribute to
the catalytic activity for low-temperature CO oxidation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
CO species adsorbed on the surface of oxidized bimetallic Rh–Pd catalysts, prepared by coimpregnation and sequential impregnation
methods, were analyzed in situ by IR spectroscopy, during the reaction of CO with O2 in an oxidizing atmosphere. The results show that the two methods of impregnation lead to the existence of oxidized Rh on
the surface of the bimetallic catalyst, however, in the case of the sequential impregnation method, the Pd surface is more
reduced than in the case of catalysts prepared by coimpregnation. The simultaneous presence of reduced Pd and oxidized Rh
that occurs in the catalysts prepared by sequential impregnation allows the existence of a synergistic effect similar to that
proposed in the literature for the Pt–Rh system. The lower degree of oxidation of the Pd in the catalysts prepared by sequential
impregnation, is mainly due to the fact that the Pd in these catalysts comes from the organic precursor palladium acetylacetonate,
while in the catalysts prepared by coimpregnation, the Pd comes from the precursor PdCl2.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
Big variations in overall activity and product selectivity in the cyclopentane/deuterium exchange reaction were found in effect
of various pretreatments of two chlorine‐free Pd/γ‐Al2O3 catalysts. The most important changes are observed when severely prereduced (at 600 °C) Pd/Al2O3 catalysts have been reoxidised and mildly rereduced: the multiple type of exchange, typical of mildly pretreated Pd catalysts,
is replaced by a stepwise mode, and a big increase in catalytic activity occurs. At this state, the Pd/γ‐Al2O3 catalysts retain some water (as surface hydroxyls) generated by reoxidation and mild reduction. Deuterium spillover from
Pd onto alumina and changes in acidity of alumina are invoked to rationalize the kinetic results. Changes in the state of
Pd after various pretreatments, as probed by temperature‐programmed hydride decomposition, can hardly be correlated with changes
in the catalytic behaviour in the exchange reaction.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
18.
Properties and performance of Pd based catalysts for catalytic oxidation of volatile organic compounds 总被引:1,自引:0,他引:1
Catalytic oxidations of volatile organic compounds (VOCs) (benzene, toluene and o-xylene) over 1 wt% Pd/γ-Al2O3 catalyst were carried out to assess the properties and performance of the Pd based catalyst. The properties of the prepared catalysts were characterized by the Brunauer Emmett Teller (BET) surface area, H2 chemisorption, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) analyses. The experimental results revealed a significant increase in VOCs conversion with the lapse of the reaction time at certain reaction temperatures. On the other hand, the hydrogen pretreated 1 wt% Pd/γ-Al2O3 catalyst, whose shape of conversion curve is similar to the non pretreated catalyst, led the conversion curves for the total oxidation of VOCs to be shifted to lower temperature. It was also found that such increases in VOCs conversion were highly dependent on the oxidation state of Pd and the growth of Pd particles in the catalyst. In addition, in the case of the catalyst consisting of the same oxidation state (PdO/Pd2+ or Pd0), the particle sizes possibly play a more important role in the catalytic activity. The activity order of 1 wt% Pd/γ-Al2O3 catalyst with respect to the VOC molecule was o-xylene > toluene > benzene. 相似文献
19.
The incorporation of Bi or Pb as promoting elements in Pd-based carbon-supported catalysts drastically increases the catalytic activity in the selective oxidation of glyoxal into glyoxylic acid. Because partial dissolution of the promoter was clearly demonstrated by atomic absorption analysis of the reaction medium, experiments are performed to examine the stability of these catalysts. Dissolution tests in the presence of the individual constituents of the reaction medium (glyoxal, glyoxylate, glycolate, oxalate) were carried out in air or nitrogen to identify the factors responsible for Pb or Bi leaching. Pb- or Bi-promoted Pd/C catalysts were prepared by thermal degradation of acetate-type precursors and characterized by X-ray diffraction and X-ray photoelectron spectroscopy before and after their use in glyoxal oxidation. Promoter leaching increases with the reaction time. Monometallic Bi/C and Pb/C catalysts were found to lose smaller amounts of promoting agent than the bimetallic M–Pd/C (M=Bi, Pb) catalysts. Losses are more pronounced from Pb–Pd/C catalysts than from their Bi-based partners. Both glyoxal and glyoxylate seem to be among the main factors responsible for the promoter losses in relation to their complexing properties. 相似文献
20.
Xiao-Ming Wang 《Electrochimica acta》2010,55(3):851-842
The influence of the crystal structure of TiO2 support material on Pd catalyst-mediated formic acid electrooxidation was investigated. Pd/TiO2 catalysts were synthesized by loading Pd on TiO2 with different crystal structures obtained by calcinations at different temperatures. Electrochemical tests showed that TiO2 with the rutile structure improved the catalytic activity of Pd nanoparticles toward formic acid electrooxidation. Physicochemical and electrochemical characterizations revealed that the enhancement of Pd/TiO2 (rutile) catalytic activity arose from uniform dispersion of Pd nanoparticles, an increase in surface-active sites, and good tolerance to the adsorption of poisonous intermediates (such as COad, COOHad and so on). 相似文献