Characterization of CeO2 Promoter of a Nanocrystalline Ni/MgO Catalyst in Dry Reforming of Methane

Ceria‐promoted nickel catalysts supported on nanocrystalline MgO were prepared and employed in methane reforming with CO₂. Their characterization was accomplished by X‐ray diffraction, BET, temperature‐programmed oxidation, and temperature‐programmed reduction (TPR) techniques. Cerium oxide (CeO₂) proved to have a positive effect on catalytic activity, stability, and carbon suppression in methane reforming with CO₂. A higher CeO₂ content increased the catalyst activity and decreased the amount of deposited carbon over the spent catalysts. The suppression of carbon was related to the high oxygen storage capacity of CeO₂. In addition, TPR analysis revealed that the CeO₂ promoter reduced the chemical interaction between nickel and support, resulting in an increase in reducibility and higher dispersion of nickel.     

Cr‐Doped La‐Ni‐O Catalysts Derived from Perovskite Precursors for CH4‐CO2 Reforming under Microwave Irradiation

The nickel catalysts derived from Cr‐doped LaNiO₃ perovskite‐like precursors were characterized by X‐ray diffraction, high‐resolution transmission electron microscopy, temperature‐programmed oxidation, temperature‐programmed reduction, and X‐ray photoelectron spectroscopy. Their catalytic performance in CO₂ reforming of methane under microwave irradiation was investigated. It was found that the structure and morphology of the oxide composites in this research were influenced by the ratio of Ni and Cr, and the mismatch of La³⁺, Ni³⁺, and Cr³⁺ may cause phase segregation. The catalytic performance of the Ni catalysts is dependent on the oxygen mobility of the perovskite oxide matrix, the content of the reduced Ni⁰, and the content of the remaining perovskite structure. The mobile oxygen in the perovskite matrix in the catalyst may enhance the conversion of CO₂ during the reaction.     

NO x Reduction by Ethanol on Pd/Sulphated Zirconia

The NO reduction by ethanol was studied on palladium catalyst supported on sulphated zirconia. Temperature programmed desorption of NO and ethanol (TPD) and temperature programmed surface reaction (TPSR) analyses as well as catalytic tests in reducing and oxidizing conditions (O₂ presence), besides diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed the formation of intermediate species during the reaction, such as ethoxy species that reacted forming ethylene. Besides dehydrogenate formed adsorbed acetate species, which than decompose and/or react with hydroxyls of the support. The sulphated zirconia support increased the acid sites with the formation of strong Brönsted sites, favoring the formation of ethoxy species. Acetate species also react with NO adsorbed on Pd forming N₂, N₂O, CO and CO₂. The excess of O₂ favored ethanol oxidation to CO₂, consequently less ethanol was available to react with NO _x .     

Effect of the Mg/Al Atomic Ratio of Ni‐Mg‐Al Catalysts for the Hydrodealkylation of 1,2,4‐Trimethylbenzene

The hydrodealkylation of 1,2,4‐trimethylbenzene (1,2,4‐TMB) to benzene, toluene and xylenes (BTX) was investigated on Ni‐Mg‐Al catalysts prepared by the coprecipitation method. The catalytic performances of these catalysts were considerably influenced by the Mg content of the catalyst. The catalysts were characterized via X‐ray diffraction, H₂‐temperature‐programmed reduction, NH₃‐temperature‐programmed desorption (TPD), CO₂‐TPD, and Fourier transform infrared spectroscopy. The results demonstrated that the appropriate amount of Mg species significantly affected the structural properties and caused the Ni nanoparticles to become highly dispersed. The higher activity of the catalysts might be ascribed to the homogenous distribution of the Ni nanoparticles, and the synergetic effects between Ni⁰, NiAl₂O₄ and MgAl₂O₄ were the key factor for obtaining the BTX.     

Synergy between tungsten and palladium supported on titania for the catalytic total oxidation of propane

Titania-supported palladium catalysts modified by tungsten have been tested for the total oxidation of propane. The addition of tungsten significantly enhanced the catalytic activity. Highly active catalysts were prepared containing a low loading of 0.5 wt.% palladium, and activity increased as the tungsten loading was increased up to 6 wt.%. Catalysts were characterised using a variety of techniques, including powder X-ray diffraction, laser Raman spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction and aberration-corrected scanning transmission electron microscopy. Highly dispersed palladium nanoparticles were present on the catalyst with and without the addition of WO_x. However, the addition of WO_x slightly increases the average palladium particle size, and there was some evidence for the Pd forming epitaxial islands on the support in the tungsten-doped samples. Surface analysis identified a combination of Pd⁰ and Pd²⁺ on a Pd/TiO₂ catalyst, whereas all of the Pd loading was found in the form of Pd²⁺ with the addition of tungsten into the catalysts. At low tungsten loadings, isolated monotungstate and some polytungstate species were highly dispersed over the titania support. The concentration of polytungstate species increased as the loading was increased, and it was also promoted by the presence of palladium. The coverage of the highly dispersed tungstate species over the titania also increased as the tungsten loading increased. Some tungstate species were also found to be associated with the palladium oxide particles, and there was an enrichment of oxidised tungsten species at the peripheral interface of the palladium oxide nanoparticles and the titania. Sub-ambient temperature–programmed reduction experiments identified an increased concentration of highly reactive species on catalysts with palladium and tungsten present together, and we propose that the new WO_x-decorated interface between PdO_x and TiO₂ particles may be responsible for the enhanced catalytic activity in the co-impregnated catalysts.     

Characterization and oxidation states of Cu and Pd in Pd–CuO/ZnO/ZrO2 catalysts for hydrogen production by methanol partial oxidation

Copper and zinc oxide based catalysts prepared by coprecipitation were promoted with palladium and ZrO₂, and their activity and selectivity for methanol oxidative reforming was measured and characterized by N₂O decomposition, X-ray absorption spectroscopy, BET, X-ray photoelectron spectroscopy, X-ray diffraction, and temperature programmed reduction. Addition of ZrO₂ increased copper dispersion and surface area, with little effect on activity, while palladium promotion significantly enhanced activity with little change of the catalytic structure. A catalyst promoted with both ZrO₂ and palladium yielded hydrogen below 150 °C. EXAFS results under reaction conditions showed that the oxidation state of copper was influenced by palladium in the catalyst bulk. A palladium promoted catalyst contained 90% Cu⁰, while the copper in an unpromoted catalyst was 100% Cu¹⁺ at the same temperature. Palladium preferentially forms an unstable alloy with copper instead of zinc during reduction, which persists during reaction regardless of copper oxidation state. A 100-h time on stream activity measurement showed growth in copper crystallites and change in copper oxidation state resulting in decreasing activity and selectivity. A kinetic model of the reaction pathway showed that palladium and ZrO₂ promoters lower the activation energy of methanol combustion and steam reforming reactions.     

Complete oxidation of 2-propanol over gold-based catalysts supported on metal oxides

This paper concerns the preparation of metal oxide-supported gold catalysts and their application to 2-propanol abatement in order to lower the light off temperature. Catalytic oxidation of 2-propanol was investigated on Au/CeO₂, Au/Fe₂O₃, Au/TiO₂ and Au/Al₂O₃ catalysts prepared from the deposition–precipitation (DP) method. The catalysts are characterized by XRD (X-ray diffraction), BET (Brunner–Emmett–Teller), TEM (transmission electron microscopy), NH₃-TPD (NH₃-temperature programmed desorption), H₂-TPR (H₂-temperature programmed reduction), ICP-AES (inductively coupled plasma-atomic emission spectroscopy) and XPS (X-ray photoelectron spectroscopy) techniques. The catalytic activity of Au/metal oxide samples towards the deep oxidation of 2-propanol to CO₂ and water has been found to be strongly dependent on the kind of supports, the amount of gold loading, the calcination temperature and the moisture content in the feed.     

The effect of the addition of Y2O3 to Ni/α-Al2O3 catalysts on the autothermal reforming of methane

The addition of Y₂O₃ to Ni/α-Al₂O₃ catalysts was investigated by BET surface area measurements, hydrogen chemisorption, X-ray diffraction, UV–vis diffuse reflectance spectroscopy, X-ray fluorescence, temperature programmed reduction, temperature programmed oxidation and cyclohexane dehydrogenation. Autothermal reforming experiments were performed in order to evaluate the methane conversion and proceeded through an indirect mechanism consisting of total combustion of methane followed by CO₂ and steam reforming generating the synthesis gas. The Y₂O₃·Al₂O₃ supported catalysts presented better activity and stability in autothermal reforming reaction. Temperature programmed oxidation analysis demonstrated that the addition of Y₂O₃ resulted in a change of the type or the location of coke formed during reaction. None of the prepared catalyst presented deactivation by sintering under the tested conditions. The improved stability of supported catalysts Y₂O₃·Al₂O₃ was the result of minimizing the formation of coke on the surface of nickel particles.     

Structure and Catalytic Performance of Mg‐SBA‐15‐Supported Nickel Catalysts for CO2 Reforming of Methane to Syngas

A series of Mg‐modified SBA‐15 mesoporous silicas with different MgO contents were successfully synthesized by a simple one‐pot synthesis method and further impregnated with Ni. The Mg‐modified SBA‐15 materials and supported Ni catalysts were characterized by N₂ physisorption (BET), X‐ray diffraction (XRD), temperature‐programmed desorption of CO₂ (CO₂‐TPD), temperature‐programmed H₂ reduction (H₂‐TPR), and temperature‐programmed hydrogenation (TPH) techniques and used for methane dry reforming with CO₂. CO₂‐TPD results proved that the addition of Mg increased the total amount of basic sites which was responsible for the enhanced catalytic activity over the Mg‐modified Ni catalyst. The excellent catalytic stability of Ni/8Mg‐SBA‐15 was ascribed to less coking and higher stability of the Ni particle size due to the introduction of Mg.     

Palladium Supported on Cross‐Linked Imidazolium Network on Silica as Highly Sustainable Catalysts for the Suzuki Reaction under Flow Conditions

Highly cross‐linked imidazolium‐based materials, obtained by radical oligomerization of bis‐vinylimidazolium salts in the presence of 3‐mercaptopropyl‐modified silica gel, were used as supports for palladium catalysts. Thanks to the high imidazolium loading these materials were able to support a high amount of the metal (10 wt%). Such materials were characterized by several techniques (¹³C magic angle spinning nuclear magnetic resonance, the Brunauer–Emmett–Teller technique, X‐ray photoelectron spectroscopy, and transmission electron microscopy). The palladium catalysts displayed good activity allowing the synthesis of several biphenyl compounds in high yields working with only 0.1 mol% of palladium loading at 50 °C in ethanol/water under batch condition. Moreover, a flow apparatus, to optimize the efficiency of the isolation of the pure products and minimize waste (E‐factor), was investigated. For the first time the palladium catalyst and base (K₂CO₃) were placed in two separate columns allowing an easy recovery of the products with very low E‐factor values (<4). Waste production was reduced by over 99% compared to classic batch conditions. Because of the high Pd loading only 42 mg of catalysts were employed in the Suzuki reaction between 160 mmol of 4‐bromotoluene and 180 mmol of phenylboronic acid. No loss in activity was observed.     

SO42−/ZrO2 supported on γ‐Al2O3 as a catalyst for CO2 desorption from CO2‐loaded monoethanolamine solutions

In this work, the composite catalysts, SO₄²/ZrO₂/γ‐Al₂O₃ (SZA), with different ZrO₂ and γ‐Al₂O₃ mass ratios were prepared and used for the first time for the carbon dioxide (CO₂)‐loaded monoethanolamine (MEA) solvent regeneration process to reduce the heat duty. The regeneration characteristics with five catalysts (three SZA catalysts and two parent catalysts) of a 5 M MEA solution with an initial CO₂ loading of 0.5 mol CO₂/mol amine at 98°C were investigated in terms of CO₂ desorption performance and compared with those of a blank test. All the catalysts were characterized using X‐ray diffraction, Fourier transform infrared spectroscopy, N₂ adsorption–desorption experiment, ammonia temperature programmed desorption, and pyridine‐adsorption infrared spectroscopy. The results indicate that the SZA catalysts exhibited superior catalytic activity to the parent catalysts. A possible catalytic mechanism for the CO₂ desorption process over SZA catalyst was proposed. The results reveal that SZA1/1, which possesses the highest joint value of Brφnsted acid sites (BASs) and mesopore surface area (MSA), presented the highest catalytic performance, decreasing the heat duty by 36.9% as compared to the catalyst‐free run. The SZA1/1 catalyst shows the best catalytic performance as compared with the reported catalyst for this purpose. Moreover, the SZA catalyst has advantages of low cost, good cyclic stability, easy regeneration and has no effect on the CO₂ absorption performance of MEA. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3988–4001, 2018     

Effect of the preparation method on Au/Ce-Ti-O catalysts activity for VOCs oxidation

Studies concerning the preparation of gold phases dispersed on binary Ce-Ti oxide (Ce_0.3Ti_0.7O₂) were performed in order to elaborate catalysts for total oxidation of VOCs. Solids containing gold, cerium and titanium were synthesized by impregnation and deposition precipitation (DP) method using NaOH, Na₂CO₃ or urea as precipitant agent. These catalysts have been characterized by means of total surface area (BET), X-ray diffraction (XRD), diffuse reflectance ultra-violet–visible spectroscopy (DR/UV–vis) and temperature programmed reduction (TPR) and their reactivity towards the oxidation of propene was studied. Thus, it was revealed that the gold-based material prepared by DP method using urea as precipitant agent was the most efficient catalyst towards the total oxidation of propene. Based on the characterisation data, it has been shown that the preparation method has an effect on the catalytic activity.     

Plasma-driven CO2 hydrogenation to CH3OH over Fe2O3/γ-Al2O3 catalyst

We report a plasma-assisted CO₂ hydrogenation to CH₃OH over Fe₂O₃/γ-Al₂O₃ catalysts, achieving 12% CO₂ conversion and 58% CH₃OH selectivity at a temperature of nearly 80°C atm pressure. We investigated the effect of various supports and loadings of the Fe-based catalysts, as well as optimized reaction conditions. We characterized catalysts by X-ray powder diffraction (XRD), hydrogen temperature programmed reduction (H₂-TPR), CO₂ and CO temperature programmed desorption (CO₂/CO-TPD), high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), x-ray photoelectron spectroscopy (XPS), Mössbauer, and Fourier transform infrared ( FTIR). The XPS results show that the enhanced CO₂ conversion and CH₃OH selectivity are attributed to the chemisorbed oxygen species on Fe₂O₃/γ-Al₂O₃. Furthermore, the diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) and TPD results illustrate that the catalysts with stronger CO₂ adsorption capacity exhibit a higher reaction performance. In situ DRIFTS gain insight into the specific reaction pathways in the CO₂/H₂ plasma. This study reveals the role of chemisorbed oxygen species as a key intermediate, and inspires to design highly efficient catalysts and expand the catalytic systems for CO₂ hydrogenation to CH₃OH.     

Vapor‐phase selective hydrogenation of citral over Pd/bentonite: effect of reduction method

BACKGROUND: Well‐dispersed nanoparticles of palladium were synthesized by wet impregnation technique over bentonite followed by three different reduction methods (H₂ or NaBH₄ or ethanol) and characterized by transmission electron microscopy, X‐ray diffraction, temperature‐programmed reduction and atomic absorption spectroscopy. Hydrogenation of citral over Pd‐supported bentonite catalysts was studied in vapor phase using a micro‐reactor. The effect of reduction method and metal loading on the conversion of citral and selectivity towards nerol and geraniol were examined. RESULTS: Among the catalysts evaluated in the vapor phase, Pd/bentonite reduced by ethanol was found to give the highest conversion and Pd/bentonite reduced by NaBH₄ was found to give the highest selectivity towards nerol and geraniol. This may be attributed to the smallest particle size of Pd in the former catalyst and presence of boron species on the latter catalyst, respectively. CONCLUSION: The presence of boron in proximity to palladium particles polarized C?O bond and helped C?O adsorption, thereby yielding nerol and geraniol (the unsaturated alcohols). Copyright © 2008 Society of Chemical Industry     

The Oxidative Destruction of Hydrocarbon Volatile Organic Compounds Using Palladium–Vanadia–Titania Catalysts

A range of titania supported palladium catalysts modified by the addition of vanadium have been prepared and tested for the total oxidation of short chain hydrocarbons. The addition of vanadium promoted the rates of oxidation at lower temperatures. Vanadium loadings between 0.5 and 3.0 wt.% were investigated and the most active catalyst was 0.5% Pd1.5% V/ TiO₂. The addition of vanadium decreased the palladium dispersion, but temperature programmed reduction studies showed that the combination of palladium with vanadium dramatically increased the ease of catalyst reduction. It is proposed that the increased catalyst activity is related to the modified redox properties of the catalysts.     

Selective Oxidation of Methanol to Dimethoxymethane over Mesoporous Al‐P‐V‐O Catalysts

The synthesis and application of bifunctional mesoporous Al‐P‐V—O catalysts with both acidic and redox sites for selective oxidation of methanol to dimethoxymethane (DMM) is described. The catalysts were characterized by N₂ adsorption/desorption, X‐ray diffraction, temperature‐programmed desorption, X‐ray photoelectron spectroscopy, and infrared spectroscopy. It is shown that porosity; redox property and surface acidity of the catalysts were greatly influenced by the Al/V/P ratio. The synergistic effect of phosphorus and vanadium was investigated. Al‐P‐V—O catalysts exhibited good catalytic activity because of the controlled reducibility and the acidic sites. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2587–2593, 2013     

Methane oxidation on alumina supported palladium catalysts: Effect of Pd precursor and solvent

Palladium precursors and solvents were studied for their effects on the activities of alumina-based palladium catalysts in methane combustion and the resistance of the catalysts to thermal aging. The properties of the catalysts were compared with those of a commercial reference. The palladium precursors were Pd(propionate)₂, Pd(acetate)₂ and Pd(acetyl acetonate)₂ and the solvents were acetone, acetic acid, propionic acid and toluene. Catalysts were prepared by the wet impregnation method.Catalysts were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). The surface areas were measured by Brunauer–Emmett–Teller method (BET). Acidity of the alumina support was measured by NH₃ desorption. Activities of the catalysts in methane oxidation were screened under lean burn conditions.In methane oxidation with fresh catalyst, the best performance was obtained with a combination of Pd(acetate)₂ and acetic or propionic acid. The light-off temperatures of the fresh catalysts (562 K and 557 K, respectively) were slightly lower than the light-off temperature (567 K) of the commercial reference. Differences between the light-off temperatures of the aged and fresh catalysts were least when the catalysts were prepared with Pd(acetyl acetonate)₂ as Pd precursor and in acetic or propionic acid as solvent: +12 K and +18 K, respectively. The corresponding value for the reference was +64 K. For several of the fresh catalysts, conversion in methane oxidation at 623 K was over 90%. A comparison of methane combustion and NH₃ desorption results indicated that acidity of the support material affects catalysts activity.     

Biogas Catalytic Reforming Studies on Nickel‐Based Solid Oxide Fuel Cell Anodes

Heterogeneous catalysis studies were conducted on two crushed solid oxide fuel cell (SOFC) anodes in fixed‐bed reactors. The baseline anode was Ni/ScYSZ (Ni/scandia and yttria stabilized zirconia), the other was Ni/ScYSZ modified with Pd/doped ceria (Ni/ScYSZ/Pd‐CGO). Three main types of experiments were performed to study catalytic activity and effect of sulfur poisoning: (i) CH₄ and CO₂ dissociation; (ii) biogas (60% CH₄ and 40% CO₂) temperature‐programmed reactions (TPRxn); and (iii) steady‐state biogas reforming reactions followed by postmortem catalyst characterization by temperature‐programmed oxidation and time‐of‐flight secondary ion mass spectrometry. Results showed that Ni/ScYSZ/Pd‐CGO was more active for catalytic dissociation of CH₄ at 750 °C and subsequent reactivity of deposited carbonaceous species. Sulfur deactivated most catalytic reactions except CO₂ dissociation at 750 °C. The presence of Pd‐CGO helped to mitigate sulfur deactivation effect; e.g. lowering the onset temperature (up to 190 °C) for CH₄ conversion during temperature‐programmed reactions. Both Ni/ScYSZ and Ni/ScYSZ/Pd‐CGO anode catalysts were more active for dry reforming of biogas than they were for steam reforming. Deactivation of reforming activity by sulfur was much more severe under steam reforming conditions than dry reforming; a result of greater sulfur retention on the catalyst surface during steam reforming.     

Oxidation of CO on hydrogen-loaded palladium

The oxidation of CO adsorbed on the surface of palladium electrodes loaded with different amounts of hydrogen was studied by single potential alteration infrared reflectance spectroscopy (SPAIRS). In the absence of hydrogen, only CO₂ was detected during anodic oxidation of CO. Adsorption of CO in the presence of hydrogen in palladium led to a more negative onset of its electrooxidation, and the formation of other products, such as ethanol and formaldehyde, as well as CO_{_2}. The results indicate that hydrogen occluded in palladium contributes to the displacement of carbon monoxide from the interface; this may assist in the continual electrooxidation of organic compounds at palladium electrodes.     

Silver catalysts supported over activated carbons for the selective oxidation of CO in excess hydrogen: effects of different treatments on the supports

Commercial activated carbon (AC) was used as a support either in its original form or after various modifications, giving diverse textural and surface chemical characteristics. The changes of these properties were monitored by N₂ adsorption–desorption isotherms, temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Ag catalysts were prepared over the AC supports by a conventional wet impregnation method. The catalytic performances of supported Ag/AC catalysts in the selective oxidation of CO in excess H₂ were tested. The results indicate the textural and surface chemical characteristics are responsible for the different catalytic performances.