Physico-Chemical Properties of Cobalt–Ruthenium (10% Co–0.5% Ru) Catalysts Supported on Binary Oxides 8.5%ZrO<Subscript>2</Subscript>/Support (SiO<Subscript>2</Subscript>, Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, TiO<Subscript>2</Subscript>) for Fischer-Tropsch Synthesis

The promotion of Fischer-Tropsch catalysts 10%Co/Al₂O₃, 10%Co/SiO₂, 10%Co/TiO₂ by 0.5% Ru and the modification of supports by 8.5 wt% ZrO₂ have been studied. The following properties: catalyst specific surface area as well as reducibility and dispersion of metallic phase were studied by different techniques: BET, TPR, and H₂ chemisorption. The modification of supports by non-reducible ZrO₂, results in a decrease of cobalt oxide reduction on Al₂O₃ and TiO₂ but not on SiO₂ supports. Additionally the enhancement of cobalt dispersion was found for all catalysts with ZrO₂ modified supports. The impact of Ru promotion is likely due to the stabilization of applied supports, prevention or blockage of interaction between surface Co species and support and an increase in cobalt oxide reducibility to the catalytically active metallic cobalt phase.     

A Pd–Fe/α-Al2O3/cordierite monolithic catalyst for CO coupling to oxalate

A novel Pd–Fe/α-Al₂O₃/cordierite monolithic catalyst was prepared for the synthesis of diethyl oxalate from CO and ethyl nitrite. The palladium-based monolithic catalyst with an optimal thickness (15 μm) of Al₂O₃ washcoat showed excellent catalytic activity and selectivity in a continuous flow, fixed-bed microreactor. The physicochemical properties of catalyst were studied by a variety of characterization techniques. Catalytic performances of Pd–Fe/α-Al₂O₃/cordierite monolithic catalysts were dependent on particle size of alumina-sol, thickness of Al₂O₃ washcoat, pore structure, surface acidity of carrier, and distribution of active metal component on the Al₂O₃ washcoat. Under the mild reaction conditions, CO conversion was 32% and the space–time yield of diethyl oxalate was 429 g/(L h). Pd efficiency (DEO(g)/Pd(g)/h) of the monolithic catalyst (274 h⁻¹) was much higher than that of a reference pellet catalyst (46 h⁻¹), probably due to high dispersion of the Pd nanoparticles on the surface of the monolithic catalyst.     

Effect of method of preparation on activity of Pd/Al2O3 monolith catalysts

Pd/Al₂O₃ monolithic catalyst of different washcoat thicknesses were prepared by two methods and tested for the activity of hydrogenation of α‐methyl styrene. These catalysts were prepared by two methods; either the palladium was impregnated on γ‐alumina and this Pd/Al₂O₃ powder was used to prepare the slurry for washcoating (Cat 1) or γ‐alumina washcoating was followed by impregnation of palladium (Cat 2). The effect of slurry concentration, pH of the slurry, and addition of binders on the catalyst properties was investigated. The monolithic catalysts were characterised by determination of metal dispersion, surface area, scanning electron microscopy, and weight loss of washcoat during ultrasonication. Well‐adhered washcoats were obtained with slurry prepared using milled γ‐alumina, whereas the adhesion of the washcoat prepared using Pd/Al₂O₃ powders was very poor. Addition of binders significantly improved the adhesion of the washcoats prepared from Pd/Al₂O₃. Metal dispersion for Cat 2 decreased with washcoat loading but did not change with loading for Cat 1. The activity tests were conducted at different washcoat loadings and the productivity of the monolithic catalyst prepared in both methods has been compared.     

Promotional effect of Ca on the Pd/Ce–Zr/Al2O3 catalyst for low-temperature catalytic combustion of methane

Promotional effect of Ca on the catalytic property of Pd/Ce–Zr/Al₂O₃ catalyst towards methane combustion is examined. The surface properties and the oxidation/reduction behavior of these catalysts are investigated by BET, TEM, XPS, TPR, TPO and TPSR techniques. Activity tests in methane combustion show that addition of Ca to Pd/Ce–Zr/Al₂O₃ can promote remarkably its low-temperature activity. The thermal stability of the Pd/Ce–Zr/Al₂O₃ catalyst to the exposure at high temperature is also enhanced by Ca loading. XPS and TEM results show that the addition of Ca to Pd/Ce–Zr/Al₂O₃ catalyst generates well-dispersed PdO particles on support. H₂–TPR, O₂–TPO and CH₄/O₂–TPSR experiments show that the addition of Ca improves the reduction/reoxidation properties and thermal stability of the active PdO species, which increases the catalytic activity and thermal stability of the Pd/Ce–Zr/Al₂O₃ catalyst.     

Beneficial effect of adding γ-AlOOH to the γ-Al2O3 washcoat of a PdO catalyst for methane oxidation

The beneficial effect of adding γ-AlOOH to the γ-Al₂O₃ washcoat of a ceramic cordierite (2MgO · 2Al₂O₃ · 5SiO₂) monolith, used to support a PdO catalyst, is reported for methane oxidation in the presence of water at low temperature (<500°C). The mini-monolith (400 cells per square inch (CPI), 1 cm diameter × 2.54 cm length; ~52 cells) was washcoated using a suspension of γ-Al₂O₃ plus boehmite (γ-AlOOH), followed by calcination and then deposition of Pd by wet impregnation. An optimum solid content of 25 wt% in the washcoat suspension was used to obtain a ~25 wt% washcoat on the monolith. The presence of γ-AlOOH enhanced the thermal and mechanical stability of the washcoat, provided that the γ-AlOOH content was <8 wt%. Temperature-programmed methane oxidation (TPO) showed that the addition of γ-AlOOH to the γ-Al₂O₃ washcoat decreased the catalyst activity. However, when H₂O (2 vol% and 5 vol%) was present in the feed gas, the γ-AlOOH improved the catalyst activity and stability. A γ-AlOOH content of ~5 wt% in the washcoat was determined to provide the highest catalyst activity and stability for CH₄ oxidation in the presence of water.     

SSITKA studies of the catalytic flameless combustion of methane

This paper presents results which were obtained for the flameless combustion of methane over the Pd(PdO)/Al₂O₃ catalyst by using the steady state isotopic transient kinetic analysis method. During the reaction switches between ¹⁶O₂/Ar/CH₄/He and ¹⁸O₂/CH₄/He were carried out. The obtained results indicate the presence of large amounts of oxygen as well as of intermediates leading to the formation of carbon dioxide on the surface of the palladium catalyst. Additionally, information was obtained proving that the complete oxidation of methane over Pd/Al₂O₃ catalyst proceeds according to the Mars and van Krevelen redox mechanism. With the increase of the reaction temperature there is an increase in the number of active centres on the Pd(PdO)/Al₂O₃ catalyst surface—a larger amount of oxygen from the lattice of the catalyst is accessible for the reaction of methane oxidation.     

Influence of PdO content and pathway of its formation on methane combustion activity

The methane oxidation reaction is known to induce changes in the surface structure and composition of Pd catalysts; making it extremely arduous to relate the methane oxidation activity to specific catalyst properties by conventional methods (continuous flow reactor studies). To circumvent this, methodical pulse reactor studies have been undertaken to obtain correlations between the initial methane combustion activity and the catalyst properties (Pd⁰/PdO content and path of PdO formation). While the initial methane combustion activity (at 160–280 °C) continuously increased with increasing PdO concentration (0–100%) in the catalyst, it continuously decreased with increasing Pd⁰ content (0–100%). Controlled studies were undertaken to obtain catalysts with identical PdO content by two pathways: (i) by controlled partial oxidization of Pd⁰/Al₂O₃ and (ii) by controlled partial reduction of PdO/Al₂O₃. Interestingly, for a given PdO content, the catalysts obtained by partial oxidation of Pd⁰/Al₂O₃ showed a significantly superior performance to the catalyst obtained by partial reduction of PdO/Al₂O₃ for all the temperatures investigated. These studies unambiguously show that along with the relative concentration of PdO, the PdO formation pathway is also critical in deciding the methane combustion activity of the catalyst.     

Catalytic activity of Pd/Al2O3 toward the combustion of methane

This work focuses on the improving of the activities and stabilities of Pd/Al₂O₃ catalysts for lean methane catalytic combustion. The influence of preparation conditions on performance of Pd/Al₂O₃ catalyst has been studied. Results showed that excellent performance of the catalyst was attributed to high hydrothermal stability at the support calcination temperature of 1100 °C. In addition, the catalytic activity was enhanced due to high dispersion of active species at lower catalyst calcination temperature. The catalysts were studied by XPS analysis. Results showed that the active phase of Pd/Al₂O₃ was Pd or Pd/PdO mixture. And the state transformation of Pd species resulted in the deactivation of Pd/Al₂O₃.     

Designing a structured catalyst for selective reduction of O<Subscript>2</Subscript> by hydrogen in the presence of NO

The influence of the promoter (Pd) modifying additives of oxides of rare-earth (La₂O₃, CeO₂) and transition (NiO, CuO) metal oxides on the catalytic activity of Co₃O₄/cordierite in reactions of O₂ and NO reduction by hydrogen was studied. Introducing Pd and rare-earth metal oxides into the composition of cobalt oxide catalyst results in an increase in its activity in H₂ + 1/2O₂ → H₂O, H₂ + NO → 1/2N₂ + H₂O reactions and an increase in selectivity upon oxygen reduction by hydrogen in the presence of nitric oxide, due possibly to a decrease in the strength of oxygen bounds with the surface and the formation of low-temperature forms of oxygen, which is not typical of unpromoted cobalt oxide catalyst. A structured Pd-Co₃O₄-La₂O₃/cordierite catalyst was developed that surpasses the commercial granulated silver-manganese catalyst used in industry to purify the technological gases used in the production of hydroxylamine sulfate of oxygen impurities with reference to activity and selectivity (in the process of oxygen reduction in the presence of nitric oxide), and to thermal stability.     

Nanostructured macro-mesoporous zirconia impregnated by noble metal for catalytic total oxidation of toluene

Hierarchical bimodal macro-mesoporous zirconia oxide has been synthesized by a simple method in the presence of CTMABr surfactant. The synthesized zirconia having uniform macropores of 300–600 nm in diameter with wormhole-like mesoporous walls and high surface area was calcined at 400 and 600 °C and impregnated with 0.5 wt.% of palladium and compared with classical 0.5 wt.% Pd/ZrO₂ catalyst for toluene oxidation. The highest activity of 0.5 wt.%/macro-mesoporous zirconia calcined at 600 °C was mainly explained by a rather high Pd dispersion and by H₂-TPR measurements showing a higher quantity of PdO species easily reducible at 0 °C.     

The effect of ceria content on the properties of Pd/CeO2/Al2O3 catalysts for steam reforming of methane

The effect of CeO₂ loading on the surface properties and catalytic behaviors of CeO₂–Al₂O₃-supported Pd catalysts was studied in the process of steam reforming of methane. The catalysts were characterized by S_BET, X-ray diffraction (XRD), temperature-programmed reduction (TPR), UV–vis diffuse reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FTIR). The XRD measurements indicated that palladium particles on the surface of fresh and reduced catalysts are well dispersed. TPR experiments revealed a heterogeneous distribution of PdO species over CeO₂–Al₂O₃ supports; one fraction of large particles, reducible at room temperature, another fraction interacting with CeO₂ and Al₂O₃, reducible at higher temperatures of 347 and 423 K, respectively. The PdO species reducible at room temperature showed lower CO adsorption relative to the PdO species reducible at high temperature. In contrast to Pd/Al₂O₃, the FTIR results revealed that CeO₂-containing catalyst with CeO₂ loading ≥12 wt.% show lower ratio (LF/HF) between the intensity of the CO bands in the bridging mode at low frequency (LF) and the linear mode at high frequency (HF). This ratio was constant with increasing the temperature of reduction. The FTIR spectra and the measurement of Pd dispersion suggested that Pd surface becomes partially covered with ceria at all temperature of reduction and with increasing ceria loading in Pd/CeO₂–Al₂O₃ catalysts. Although the PdO/Al₂O₃ showed higher Pd dispersion compared to that of CeO₂-containing catalysts, the addition of ceria resulted in an increase of the turnover rate and specific rate to steam reforming of methane. The CH₄ turnover rate of Pd/CeO₂–Al₂O₃ catalysts with ceria loading ≥12 wt.% was around four orders of magnitude higher compared to that of Pd/Al₂O₃ catalyst. The increase of the activity of the catalysts was attributed to various effects of CeO₂ such as: (i) change of superficial Pd structure with blocking of Pd sites; (ii) the jumping of oxygen (O^*) from ceria to Pd surface, which can decrease the carbon formation on Pd surface. Considering that these effects of CeO₂ are opposite to changes of the reaction rate, the increase of specific reaction rate with enhancing the ceria loading suggests that net effect results in the increase of the accessibility of CH₄ to metal active sites.     

Characterisation and microstructure of Pd and bimetallic Pd–Pt catalysts during methane oxidation

The catalytic oxidation of methane was studied over Pd/Al₂O₃ and Pd–Pt/Al₂O₃. It was found that the activity of Pd/Al₂O₃ gradually decreases with time at temperatures well below that of PdO decomposition. The opposite was observed for Pd–Pt/Al₂O₃, of which the activity decreases slightly with time. Morphological studies of the two catalysts showed major changes during operation. The palladium particles in Pd/Al₂O₃ are initially composed of smaller, randomly oriented crystals of both PdO and Pd. In oxidising atmospheres, the crystals become more oxidised and form larger crystals. The activity increase of Pd–Pt/Al₂O₃ is probably related to more PdO being formed during operation. The particles in Pd–Pt/Al₂O₃ are split into two different domains: one with PdO and the other likely consisting of an alloy between Pd and Pt. The alloy is initially rich in palladium, but the composition changes to a more equalmolar Pd–Pt structure during operation. The ejected Pd is oxidised into PdO, which is more active than its metallic phase. The amount of PdO formed depends on the oxidation time and temperature.     

Ruthenium promotion of Co/SBA-15 catalysts with high cobalt loading for Fischer–Tropsch synthesis

30 wt.%Co/SBA-15 catalysts with different ruthenium contents (0.05–0.5 wt.%) were prepared by incipient wetness impregnation and characterized by diffuse reflectance infrared fourier transform spectroscopy, N₂ adsorption-desorption, X-ray diffractometry, temperature-programmed reduction and H₂ desorption, oxygen titration as well as X-ray photoelectron spectroscopy. The addition of a small amount of Ru promoter to Co/SBA-15 shifted the reduction temperature of both steps (Co₃O₄ → CoO and CoO → Co⁰) to lower temperatures and suppressed the formation of Co²⁺ species. After reduction, ruthenium atoms were encapsulated partially with cobalt cluster. There was no strong electronic interaction between metal cobalt and ruthenium, however, hydrogen spillover from ruthenium to cobalt oxide clusters occurred. With increasing ruthenium content, catalyst reducibility increased and the surface was enriched in cobalt atoms. Moreover, the peak intensities of both the linear and bridge types CO adsorption increased with the increase of ruthenium content, enhancing the catalytic activity on Fischer–Tropsch synthesis.     

A Pd/Al2O3/cordierite monolithic catalyst for hydrogenation of 2-ethylanthraquinone

A novel Pd/Al₂O₃/cordierite monolithic catalyst was prepared and investigated in hydrogenation of 2-ethylanthraquinone (eAQ) for H₂O₂ production. It was found that there was an optimal penetrating depth on the monolithic catalyst. By adjusting the loading on the Al₂O₃, the penetrating depth of Pd could be efficiently confined in the Al₂O₃ washcoat. When Pd distribution matched well with Pd content, the higher yields of H₂O₂ could be obtained. As a result, the average yield on monolithic catalyst was 1.3 times of that on pellet catalyst, and the products distribution confirmed the monolithic catalyst was the optimal for H₂O₂ production.     

Selection of modifying additives for improving the steam tolerance of methane afterburning palladium catalysts

In this work, we discuss the problem of the afterburning of methane from the exhaust gases of automobile engines fueled by natural gas. In exhaust neutralizers, the PdO/Al₂O₃ catalyst, the main drawback of which is the reduction of its activity under the action of steam that always present in exhaust gases, is commonly used. To improve the tolerance to steam, a series of PdO-Me _x O _y /Al₂O₃ binary catalysts (Me is Co, Cu, Fe, Ni, Mn, or Sn) was prepared and studied. Comparative tests under conditions modeling the methane afterburning process in automobile neutralizers show that Pd catalysts promoted with nickel, cobalt, and tin oxides are more resistant to the inhibiting action of steam. The high crystallinity of supported PdO and its uniform distribution over the surface of modified Al₂O₃ are indicated as criteria for the stability of catalysts in the presence of steam. Optimization of the concentration of promotors and the preparation method used for their introduction allows the deactivation of Pd catalysts under the action of steam to be almost completely eliminated.     

Decomposition and oxidation of CH3 13CH2OH on A12O3, Pd/Al2O3, and PdO/Al2O3 catalysts

Temperature-programmed desorption (TPD) and oxidation (TPO) were used to investigate the decomposition and oxidation of ethanol on Al₂O₃, Pd/Al₂O₃, and PdO/Al₂O₃. Ethyl--¹³C alcohol (CH₃ ¹³CH₂OH) was adsorbed on the catalysts so that reaction pathways of the two carbons could be distinguished. Alumina was mainly a dehydration catalyst, but dehydrogenation was also observed and some carbon remained on the surface. In the presence of O₂, A1₂O₃ oxidized the decomposition products and the-carbon was oxidized faster. Ethanol, which was adsorbed on A1₂O₃, decomposed much faster on Pd/A1₂O₃ by diffusing to Pd and undergoing CO elimination to form CH₄,¹³CO, H₂, and surface carbon. On PdO/A1₂O₃, the decomposition was slower than on Pd/A1₂O₃ until lattice oxygen was extracted above 450 K; the decomposition products were oxidized by lattice oxygen. In the presence of gas phase O₂, Pd/Al₂O₃ was an active oxidation catalyst at low temperature, but lattice oxygen had to be extracted from PdO/A1₂O₃ before it had significant oxidation activity.     

Improvement of thermal stability of NO oxidation Pt/Al2O3 catalyst by addition of Pd

The present work has been undertaken to tailor Pt/Al₂O₃ catalysts active for NO oxidation even after severe heat treatments in air. For this purpose, the addition of Pd has been attempted, which is less active for this reaction but can effectively suppress thermal sintering of the active metal Pt. Various Pd-modified Pt/Al₂O₃ catalysts were prepared, subjected to heat treatments in air at 800 and 830 °C, and then applied for NO oxidation at 300 °C. The total NO oxidation activity was shown to be significantly enhanced by the addition of Pd, depending on the amount of Pd added. The Pd-modified catalysts are active even after the severe heat treatment at 830 °C for a long time of 60 h. The optimized Pd-modified Pt/Al₂O₃ catalyst can show a maximum activity limited by chemical equilibrium under the conditions used. The bulk structures of supported noble metal particles were examined by XRD and their surface properties by CO chemisorption and EDX-TEM. From these characterization results as well as the reaction ones, the size of individual metal particles, the chemical composition of their surfaces, and the overall TOF value were determined for discussing possible reasons for the improvement of the thermal stability and the enhanced catalytic activity of Pt/Al₂O₃ catalysts by the Pd addition. The Pd-modified Pt/Al₂O₃ catalysts should be a promising one for NO oxidation of practical interest.     

Co–Pd/γ‐Al2O3 catalyst for heavy oil upgrading: Desorption kinetics,reducibility and catalytic activity

The influence of Pd on a Co–Pd/γ‐Al₂O₃ heavy oil upgrading catalyst is investigated using different physicochemical and reactive Characterization techniques. Nitrogen adsorption isotherm analysis shows that the specific surface area and porosity of the support alumina is significantly decreased due to the blockage of the pores by the loaded cobalt species. The estimated activation energy of NH₃ desorption is found to be less for Co–Pd/γ‐Al₂O₃ sample, which confirms improved acidity due to Pd. TPR experiments show that the reducibility of the catalyst is significantly improved with the presence of Pd. Higher metal dispersion and hydrogen spillover effects are the main reasons for the enhanced reducibility of the Pd promoted catalyst as revealed by the H₂‐pulse chemisorptions study. When evaluated using VGO as feed stock, the Co–Pd/γ‐Al₂O₃ displayed superiority both in hydrodesulphurisation (HDS) and hydrocracking (HC) activities as compared to the unpromoted Co/γ‐Al₂O₃ catalyst. The coke deposition on the spent catalyst is also found to be low due to the Pd promotional effects. This is an encouraging result, given that higher hydrogenation activity of the catalyst can be achieved without compromising the cracking activity and sustained activity of the catalyst.     

The Effect of Sulphur on the Activity of Pd/Al2O3, Pd/CeO2 and Pd/ZrO2 Diesel Exhaust Gas Catalysts

Pd/Al₂O₃, Pd/CeO₂ and Pd/ZrO₂ diesel oxidation catalysts and their washcoat materials were studied after sulphur treatment. The catalytic activities were analysed in simplified diesel exhaust gas composition by FT-IR technique. ICP-OES or XRF, physisorption and CO chemisorption was used to catalyst characterisation. The result shows that the sulphur treatment clearly deactivates the studied catalysts.     

Characterization of some perovskite oxides based on YBa2Cu3O7 − x in relation to their use in methanol production

The oxidized and weakly reducible perovskite oxide YBa₂Cu₃O_{7 − x} (YBCO) has been prepared as a catalyst, supported on γ‐Al₂O₃. It was further modified by (i) impregnation with Ru and Pd and (ii) cobalt incorporation via co‐precipitation. All the catalysts were either 20% (w/w) YBCO/γ‐Al₂O₃ or 2% (w/w) Ru, Pd or Co/20% (w/w) YBCO/γ‐Al₂O₃. The catalysts were characterized using temperature programmed reduction (TPR), surface area measurements and X‐ray diffraction (XRD) studies before and after various treatments. They were studied as catalysts in the pressure range 20–50 atmospheres and in the temperature range 523–573 K in an autoclave equipped with a spinning basket catalyst container. The Pd‐, Ru‐ and Co‐modified catalysts gave predominantly methanation products, along with some C₂–C₄ hydrocarbons. However the YBCO/γ‐Al₂O₃ catalyst exhibited significant methanol selectivity at 50 atmospheres and at 523 K X‐ray diffraction studies revealed the presence of Cu(0), Cu(I) and Cu(II) after reduction and the species Cu(0) and Cu(I) are probably essential to CH₃OH production. © 2000 Society of Chemical Industry