Chlorobenzene total oxidation over palladium supported on ZrO2, TiO2 nanostructured supports

Two series of supported Pd catalysts were synthesized on new mesoporous–macroporous supports (ZrO₂, TiO₂) labelled M (Zr and Ti). The deposition of palladium was carried out by wet impregnation on the calcined TiO₂ and ZrO₂ supports at 400 °C (Pd/Zr₄, Pd/Ti₄) and 600 °C (Pd/Zr₆, Pd/Ti₆) and followed by a calcination at 400 °C for 4 h. The pre-reduced Pd/MX catalysts were investigated for the chlorobenzene total oxidation and their catalytic properties where compared to those of a reference catalyst Pd/Ti-Ref (TiO₂ from Huntsman Tioxide recalcined at 500 °C) and of a palladium supported on the fresh mesoporous–macroporous TiO₂ (Pd/Ti). Based on the activity determined by T₅₀, the Pd/Ti and Pd/Ti₄ catalysts have been found to be more active than the reference one. Moreover activity decreased owing to the sequence: Pd/TiX  Pd/ZrX and in each series when the temperature of calcination of the support was raised. The overall results clearly showed that the activity was dependant on the nature of the support. The better activity of Pd/TiX compared to Pd/ZrX was likely due to a better reducibility of the TiO₂ support (Ti⁴⁺ into Ti³⁺) leading to an enhancement of the oxygen mobility. Production of polychlorinated benzenes PhCl_x (x = 2–6) and of Cl₂ was also observed. Nevertheless at 500 °C the selectivity in HCl was higher than 90% for the best catalysts.     

Hydrogen Production by Methanol Steam Reforming Over Pd/ZrO2�CTiO2 Catalysts

Pd/ZrO₂?CTiO₂ catalysts were synthesized by sol?Cgel method and studied on the steam reforming of methanol reaction for hydrogen production. X-ray diffraction patterns of the Pd supported on single oxides showed crystalline structures associated with the zirconia or titania respectively. However, the XRD pattern of the mixed ZrO₂?CTiO₂ oxide showed broad diffraction pattern consistent with an amorphous material. The reducibility of the PdO supported on single and mixed oxides showed a negative peak associated with the desorption of H₂ due to the decomposition of Pd-hydride (PdH); as well as, positive peaks related with the hydrogen consumption on the reduction of the PdO supported. Catalytic activity on the palladium supported on the mixed ZrO₂?CTiO₂ oxide showed higher catalytic activity than the Pd supported on the single TiO₂ or ZrO₂ oxides. This finding was associated at the higher Pd species present in the Pd/ZrO₂?CTiO₂ than on the Pd/ZrO₂ or Pd/TiO₂ catalysts how was observed by TPR.     

ZrC–C and ZrO2–C as Novel Supports of Pd Catalysts for Formic Acid Electrooxidation

The Pd/ZrC–C and Pd/ZrO₂–C catalysts with zirconium compounds ZrC or ZrO₂ and carbon hybrids as novel supports for direct formic acid fuel cell (DFAFC) have been synthesized by microwave‐assisted polyol process. The Pd/ZrC–C and Pd/ZrO₂–C catalysts have been characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), energy dispersive analysis of X‐ray (EDAX), transmission electron microscopy (TEM), and electrochemical measurements. The physical characteristics present that the zirconium compounds ZrC and ZrO₂ may promote the dispersion of Pd nanoparticles. The results of electrochemical tests show that the activity and stability of Pd/ZrC–C and Pd/ZrO₂–C catalysts show higher than that of Pd/C catalyst for formic acid electrooxidation due to anti‐corrosion property of zirconium compounds ZrC, ZrO₂, and metal–support interaction between Pd nanoparticles and ZrC, ZrO₂. The Pd/ZrC–C catalyst displays the best performance among the three catalysts. The peak current density of formic acid electrooxidation on Pd/ZrC–C electrode is nearly 1.63 times of that on Pd/C. The optimal mass ratio of ZrC to XC‐72 carbon is 1:1 in Pd/ZrC–C catalyst with narrower particle size distribution and better dispersion on surface of the mixture support, which exhibits the best activity and stability for formic acid electrooxidation among all the samples.     

Dehydrogenation of ethylbenzene with CO2 over V2O5/Al2O3–ZrO2 catalyst

V-containing catalysts supported on Al₂O₃, modified with varying amounts of ZrO₂, were prepared by impregnation method. Dehydrogenation of ethylbenzene with CO₂ was run over these catalysts in a fixed-bed downflow stainless steel reactor. Compared with pure Al₂O₃ support, a small amount of ZrO₂ in the support led to a significant increase in catalytic activity. Partial reduction of vanadium oxides and carbon deposition were the main reasons for the decreased catalytic activity.     

Wet oxidation of wastewater containing hydrocarbons by novel supported Pd catalysts

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.     

Characterization of Supported NiSO4 and Effect of TiO2–ZrO2 Composition on Catalytic Activity for Acid Catalysis

A series of catalysts, NiSO₄/TiO₂–ZrO₂ having different TiO₂–ZrO₂ composition, for acid catalysis was prepared by the impregnation method using an aqueous solution of nickel sulfate. The addition of TiO₂ to ZrO₂ improved the surface area of the catalyst and enhanced its acidity remarkably because of the formation of new acid sites through the charge imbalance of Ti–O–Zr bonding. The binary oxide, TiO₂–ZrO₂ calcined above 600 °C resulted in the formation of crystalline orthorhombic phase of ZrTiO₄. Therefore, NiSO₄/TiO₂–ZrO₂ calcined at 500 °C exhibited a maximum catalytic activity for acid catalysis, and then the catalytic activity decreased with the calcination temperature. The correlation between catalytic activity and acidity held for both reaction, 2-propanol dehydration and cumene dealkylation. NiSO₄ supported on 50TiO₂–50ZrO₂ (TiO₂/ZrO₂ ratio = 1) among TiO₂–ZrO₂ binary oxides exhibited the highest catalytic activity for acid catalysis.     

Synergistic effect of Pt or Pd and perovskite oxide for water gas shift reaction

The water gas shift (WGS) reaction over Pt and Pd catalysts supported on various perovskite oxides has been investigated at 573 K without catalyst pretreatment. The Pt and Pd catalysts on LaCoO₃ support showed high catalytic activity. Interaction between Pt or Pd and the support is considered to promote the WGS reaction: Pt/LaCoO₃ had high initial activity but deactivated immediately; Pd/LaCoO₃ was less active than Pt/LaCoO₃, but had superior stability. Catalysts were characterized using XRD, STEM, XPS, and H₂-temperature programmed reduction (TPR). Results of this study showed that reduction of the support decreased the CO conversion on Pt/LaCoO₃. On the other hand, Pd/LaCoO₃ showed stable activity for the WGS reaction. Therefore, Pd was added to Pt/LaCoO₃ for stabilizing the catalyst activity, and 0.5 wt.% Pd/1 wt.% Pt/LaCoO₃ catalyst showed higher activity and stability.     

Effect of support on the apparent activity of palladium oxide in catalytic methane combustion

The support effect on the low temperature catalytic oxidation of methane over palladium catalysts was studied by comparing a series of metal oxides as the support. Samples of 0.010 g/g Pd catalysts supported on different grades and/or phases of TiO₂, Al₂O₃, and ZrO₂ were prepared via incipient impregnation and their catalytic activity was evaluated using a laboratory plug-flow reactor. The specific surface area of the supports determined by nitrogen adsorption varied from about 13-220 m²/g. Initial experiments conducted with titania (anatase) as a support showed a low apparent activity and a poor thermal stability. Focusing on anatase, we have successfully improved its thermal stability by additions of Al₂O₃ or by doping with CeO₂, or La₂O₃. However, contrary to expectations based on some information in the literature, we have found that the activity decreased in the sequence of Al₂O₃ > ZrO₂ > TiO₂, and was not a direct function of specific surface area. This was especially evident in the case of titania. The surface structure of the support and the nature of its interaction with the active component PdO seem to play a far more important role in activity than the apparent specific surface area. Moreover, anatase-supported catalysts present a very rapid deactivation, whereas rutile-supported catalysts are relatively stable. The observed phenomena could potentially be related to the interaction between support and the active phase of palladium. Several models have been proposed to describe the strong metal-support interaction, but either charge transfer or encapsulation seems to be the most probable.     

Influence of oxygen and promoting effect of barium on the reduction of NOx by ethanol on Pd/ZrO2 catalyst

The NO reduction by ethanol over barium promoted Pd/ZrO₂ catalyst and the effect of the oxygen on the selectivity were studied. The catalysts were prepared by incipient wetness impregnation with 14.3% of Ba over zirconia and 1% of palladium. The specific surface areas were 58 and 47 m²/g and the dispersions of Pd were 37% and 30% for the Pd/ZrO₂ and Pd–Ba/ZrO₂ catalysts, respectively. The X-ray diffraction patterns indicate the presence of monoclinic zirconia phase on the support and BaCO₃, which is decomposed at 715 and 815 °C. Temperature programmed desorption profiles of NO on Pd/ZrO₂ and Pd–Ba/ZrO₂ catalyst showed a huge amount N₂ formation for the promoted Ba catalyst. Catalytic results showed high NO conversion even at low temperature, in accordance with the TPD results and an increasing selectivity to N₂ when compared with Pd/ZrO₂. The effect of O₂ in the NO_x reduction with ethanol provoked less NO dissociation and lower selectivity to methane.     

Selective hydrogenation of cinnamaldehyde using Pd catalysts supported on Mg/Al mixed oxides: Influence of the Pd incorporation method

A series of hydrotalcite‐like compounds was synthesized by varying Mg/Al molar ratio with values of 2, 3, and 4. After thermal treatment at 823 K, the corresponding mixed oxides were obtained and used as catalytic supports. The incorporation of a Pd metallic phase (0.5 g/g loading), was carried out by two methods: 1) in situ vapour phase thermal decomposition, and 2) impregnation by organic method. Fresh and calcined samples were characterized by XRD and N₂ sorption experiments. The basic and metal functions were analyzed by CO₂‐TPD and H₂‐TPR. The Pd‐support interaction was studied by FTIR spectroscopy using CO as a probe molecule while the morphology of Pd nanoparticles on the catalysts was studied by SEM, HRTEM, and theoretical simulation using the Fast Fourier Transform (FFT) method. Finally, the catalytic activity results showed a higher conversion towards hydrocinnamaldehyde in the cinnamaldehyde hydrogenation reaction for the catalysts prepared by vapour phase thermal decomposition, compared with those prepared by organic method, showing the significant dependence on the catalytic activity and the Pd incorporation method.     

Water-gas shift reaction over supported Pt and Pt-CeOx catalysts

A comparison study was performed of the water-gas shift (WGS) reaction over Pt and ceria-promoted Pt catalysts supported on CeO₂, ZrO₂, and TiO₂ under rather severe reaction conditions: 6.7 mol% CO, 6.7 mol% CO₂, and 33.2 mol% H₂O in H₂. Several techniques—CO chemisorption, temperature-programmed reduction (TPR), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES)—were employed to characterize the catalysts. The WGS reaction rate increased with increasing amount of chemisorbed CO over Pt/ZrO₂, Pt/TiO₂, and Pt-CeO _x /ZrO₂, whereas no such correlation was found over Pt/CeO₂, Pt-CeO _x /CeO₂, and Pt-CeO _x /TiO₂. For these catalysts in the absence of any impurities such as Na⁺, the WGS activity increased with increasing surface area of the support, showed a maximum value, and then decreased as the surface area of the support was further increased. An adverse effect of Na⁺ on the amount of chemisorbed CO and the WGS activity was observed over Pt/CeO₂. Pt-CeO _x /TiO₂ (51) showed the highest WGS activity among the tested supported Pt and Pt-CeO_x catalysts. The close contact between Pt and the support or between Pt and CeO _x , as monitored by H₂-TPR, is closely related to the WGS activity. The catalytic stability at 583K improved with increasing surface area of the support over the CeO₂- and ZrO₂-supported Pt and Pt-CeO _x catalysts.     

Synthesis and Hydrodesulfurization Properties of Noble Metal Phosphides: Ruthenium and Palladium

Silica-supported ruthenium and palladium phosphide catalysts (Ru₂P, RuP, Pd₃P, Pd₅P₂) were investigated for the hydrodesulfurization (HDS) of dibenzothiophene (DBT). The Ru and Pd phosphide catalysts were prepared by temperature-programmed reduction of hypophosphite-based precursors consisting of uncalcined or calcined Ru/SiO₂ or Pd/SiO₂ impregnated with ammonium hyposphosphite (NH₄H₂PO₂). The Ru₂P/SiO₂ and RuP/SiO₂ catalysts prepared from uncalcined precursors had smaller average crystallite sizes, higher CO chemisorption capacities, and higher HDS activities than the catalysts prepared from the calcined precursors, while the effect of preparation method on catalytic properties was less clear for the Pd₃P/SiO₂ and Pd₅P₂/SiO₂ catalysts. Following HDS testing at 673?K, X-ray diffraction analysis revealed that the Pd₅P₂/SiO₂ catalysts decomposed to give Pd₃P on the silica support, while the other phosphides exhibited good stability during the testing period. At temperatures at which high DBT conversion was observed (>598?K), the Ru and Pd phosphide catalysts were less active than sulfided Ru/SiO₂ and Pd/SiO₂ catalysts prepared from the uncalcined metal precursors.     

Low temperature complete combustion of dilute toluene and methyl ethyl ketone over Mn‐doped ZrO2 (cubic) catalysts

Combustion of dilute toluene and methyl ethyl ketone over Mn‐doped ZrO₂ catalysts prepared using different precipitating agents, such as tetra‐alkyl ammonium hydroxides and NH₄OH, having Mn/Zr ratios from 0.05 to 0.67, and calcined at different temperatures has been thoroughly investigated. The Mn‐doped ZrO₂ catalyst shows high toluene or methyl ethyl ketone combustion activity, particularly when its ZrO₂ is in cubic form, when its Mn/Zr ratio is close to 0.2, and when it is prepared using tetra‐methyl ammonium hydroxide as a precipitating agent and calcined at 773 K. Copyright © 2005 Society of Chemical Industry     

Development of Ni-Pd bimetallic catalysts for the utilization of carbon dioxide and methane by dry reforming

The present research deals with catalyst development for the utilization of CO₂ in dry reforming of methane with the aim of reaching highest yield of the main product synthesis gas (CO, H₂) at lowest possible temperatures. Therefore, Ni-Pd bimetallic supported catalysts were prepared by simple impregnation method using various carriers. The catalytic performance of the catalysts was investigated at 500, 600 and 700 °C under atmospheric pressure and a CH₄ to CO₂ feed ratio of 1. Fresh, spent and regenerated catalysts were characterized by N₂ adsorption for BET surface area determination, XRD, ICP, XPS and TEM. The catalytic activity of the studied Ni-Pd catalysts depends strongly on the support used and decreases in the following ranking: ZrO₂-La₂O₃, La₂O₃ > ZrO₂ > SiO₂ > Al₂O₃ > TiO₂. The bimetallic catalysts were more active than catalysts containing Ni or Pd alone. A Ni to Pd ratio = 4 at a metal loading of 7.5 wt% revealed the best results. Higher loading lead to increased formation of coke; partly in shape of carbon nanotubes (CNT) as identified by TEM. Furthermore, the effect of different calcination temperatures was studied; 600 °C was found to be most favorable. No effect on the catalytic activity was observed if a fresh catalyst was pre-reduced in H₂ prior to use or spent samples were regenerated by air treatment. Ni and Pd metal species are the active components under reaction conditions. Best conversions of CO₂ of 78% and CH₄ of 73% were obtained using a 7.5 wt% NiPd (80:20) ZrO₂-La₂O₃ supported catalyst at a reaction temperature of 700 °C. CO and H₂ yields of 57% and 59%, respectively, were obtained.     

Palladium and platinum catalysts supported on carbon nanofiber coated monoliths for low-temperature combustion of BTX

In this work carbon nanofiber (CNF)-coated monoliths with a very thin, homogeneous, consistent and good adhered CNF layer were obtained by means of catalytic decomposition of ethylene on Ni particles.The catalytic behaviour of Pt and Pd supported on the CNF-coated monoliths was studied in the low-temperature catalytic combustion of benzene, toluene and m-xylene (BTX) and compared with the performance of Pt and Pd supported on γ-Al₂O₃ coated monoliths.The catalysts supported on CNF-coated monoliths were the most active, independent of the metal catalyst or the type of the tested aromatic compound. TPD experiments showed that the γ-Al₂O₃ phase retained important amounts of the water molecules produced during the reaction. When water vapour was supplied to the reactant flow, the activity of Pd catalysts decreased much stronger than the Pt ones, and the activity of the Pt catalysts supported on the γ-Al₂O₃ was more affected than that of the catalysts supported on CNF.BTX combustion reactions seem to be catalyzed by Pt and Pd through different kinetic mechanisms, explaining why Pt catalysts always were more active than the Pd ones deposited on the same type of support. Pd catalyzed combustion of benzene is strongly inhibited by oxygen and by water.Catalysts supported on CNF-coated monoliths showed a selectivity to burn benzene better than toluene or m-xylene, attributed to a better aromatic-CNF surface interaction.     

A comparative study of the water gas shift reaction over platinum catalysts supported on CeO2, TiO2 and Ce-modified TiO2

WGS reaction has been investigated on catalysts based on platinum supported over CeO₂, TiO₂ and Ce-modified TiO₂. XPS and XANES analyses performed on calcined catalysts revealed a close contact between Pt precursors and cerium species on CeO₂ and Ce-modified TiO₂ supports. TPR results corroborate the intimate contact between Pt and cerium entities in the Pt/Ce–TiO₂ catalyst that facilitates the reducibility of the support at low temperatures while the Ce–O–Ti surface interactions established in the Ce-modified TiO₂ support decreases the reduction of TiO₂ at high temperature. The changes in the support reducibility leads to significant differences in the WGS activity of the studied catalysts. Pt supported on Ce-modified TiO₂ support exhibits better activity than those corresponding to individual CeO₂ and TiO₂-supported catalysts. Additionally, the Ce–TiO₂-supported catalyst displays better stability at reaction temperatures higher than 573 K that observed on pure TiO₂-supported counterpart. Activity measurements, when coupled with the physicochemical characterization of catalysts suggest that the modifications in the surface reducibility of the support play an essential role in the enhancement of activity and stability observed when Pt is supported on the Ce-modified TiO₂ substrate.     

Cobalt-containing catalysts for the high-temperature combustion of methane

Cobalt was supported on ZrO₂, La-doped ZrO₂ and La₂O₃ through atomic layer epitaxy (ALE) and wet impregnation. The rate data obtained at 770 K is compared with literature information about cobalt inserted in other matrixes. The ALE technique using ZrO₂ and La-doped ZrO₂ yielded the best cobalt-containing catalysts. Bulk and surface characterization techniques provided key clues to understand the origin of the large difference in catalytic activity reported for cobalt-containing formulations.     

The Effect of Acidic and Redox Properties of V2O5/CeO2–ZrO2 Catalysts in Selective Catalytic Reduction of NO by NH3

V₂O₅ supported ZrO₂ and CeO₂–ZrO₂ catalysts were prepared and characterized by N₂ physisorption, XRPD, TPR, and NH₃-TPD methods. The influence of calcination temperature from 400 to 600 °C on crystallinity, acidic and redox properties were studied and compared with the catalytic activity in the selective catalytic reduction (SCR) of NO with ammonia. The surface area of the catalysts decreased gradually with increasing calcination temperature. The SCR activity of V₂O₅/ZrO₂ catalysts was found to be related with the support crystallinity, whereas V₂O₅/CeO₂–ZrO₂ catalysts were also dependent on acidic and redox properties of the catalyst. The V₂O₅/CeO₂–ZrO₂ catalysts showed high activity and selectivity for reduction of NO with NH₃.     

Effect of support on hydrogen production by auto-thermal reforming of ethanol over supported nickel catalysts

Nickel catalysts supported on various supports such as ZnO, MgO, ZrO₂, TiO₂, and Al₂O₃ were prepared by an impregnation method to investigate the effect of support on catalytic performance in hydrogen production by auto-thermal reforming of ethanol. Among the supported catalysts, the Ni/ZrO₂ and Ni/TiO₂ catalysts showed better catalytic performance than the other catalysts. The electronic structure of nickel species supported on ZrO₂ and TiO₂ was favorably modified for the reaction, and thus, the reducibility of nickel species supported on ZrO₂ and TiO₂ was increased due to the weak interaction between nickel and support. On the other hand, the Ni/MgO and Ni/ZnO catalysts exhibited poor catalytic performance in the auto-thermal reforming of ethanol due to the formation of a solid solution phase.     

Catalytic hydrolysis of chlorofluorocarbon (CFC-12) over WO3/ZrO2

The catalytic decomposition of CFC-12 (CCl₂F₂) in the presence of water vapor was investigated over a series of solid acids WO₃/ZrO₂. Compared with tungstic acid, ammonium metatungstate is a better source of tungsten oxide for the preparation of WO₃/ZrO₂ catalysts. CFC-12 decomposition activities of WO₃/ZrO₂ catalysts are in good agreement with their acidities. Enhancing the acidities of catalysts is favorable to increase their CFC-12 decomposition activities. WO₃/ZrO₂ catalysts calcined at higher temperature exhibit good catalytic activity and stability for the hydrolysis of CFC-12, and show better structural stability during the reaction.