Alumina Support Research Articles

Influence of the Catalyst Supporting Material on the Growth of Carbon Nanotubes

Catalytic chemical vapor deposition (CCVD) is considered as the most suitable technique for the large scale and low-cost production of carbon nanotubes (CNTs). Catalytic activity of Fe-Co, Fe-Ni and Co-Ni mixture supported on Al2O3 has been investigated in the production of carbon nanotubes (CNTs). Absolute ethanol was used as a source of carbon and nitrogen as the carrier gas. The Carbon nanotubes prepared by the catalytic decomposition of ethanol at 1173°K over iron supported alumina or silica catalysts with 5Wt% iron loading in a horizontal tube furnace under flow of nitrogen. The morphological structure of deposits CNTs were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that the alumina supported catalysts more active towards CNTs formation than silica supported catalysts even with changing the percentage of metal loading (2.5% - 10%). Further investigation for alumina support with other metals and their binary metals heve been done to see for how far the alumina is suitable as a support. The yield of the carbon deposit obtained varied from 11.2 to 34.9% of the initial weight of the catalyst. The results revealed that CNTs prepared by Fe-Ni/Al2O3 catalyst has high length/diameter ratio and small tube diameter ≈ 17 nm.

Highly Active and Stable Palladium Catalysts on Novel Ceria-Alumina Supports for Efficient Oxidation of Carbon Monoxide and Hydrocarbons.

Precious metal catalysts with superior low-temperature activity and excellent thermal stability are highly needed in environmental catalysis field. In this work, a novel two-step incipient wetness impregnation (T-IWI) method was developed for the fabrication of a unique and highly stable CeO2/Al2O3 support (CA-T). Pd anchored on CA-T exhibited a much higher low-temperature catalytic activity and superior thermal stability in carbon monoxide (CO) and hydrocarbon (HC) oxidations, compared to Pd anchored on conventional CeO2/Al2O3 (CA), which was prepared by a one-step IWI method. After aging treatment at 800 °C, the CO oxidation rate on Pd/CA-T (1.69 mmol/(gPd s)) at 120 °C was 4.1 and 84.5 times of those on Pd/CA (0.41 mmol/(gPd s)) and Pd/Al2O3 (0.02 mmol/(gPd s)), respectively. It was revealed that the CA-T support with well-controlled small CeO2 particles (ca. 12 nm) possessed abundant defects for Pd anchoring, which created rich Pd-CeO2 interfaces with strengthened interaction between Pd and CeO2 where oxygen could be efficiently activated. This resulted in the significantly improved oxidation activity and thermal stability of Pd/CA-T catalysts. The T-IWI method developed herein can be applied as a universal approach to prepare highly stable metal oxide-alumina-based supports, which have broad application in environmental catalyst design, especially for automobile exhaust aftertreatment.

Regenerability of complex (PdO)xPd0.05-xCe0.95O2-y catalyst stabilized on functionalized alumina surface

The catalyst comprising Pd0.05-xCe0.95O2-y nanoparticles (2−5 nm) and larger PdO particles stabilized on the functionalized alumina support, active in the propane oxidation reaction, was prepared and characterized in detail. The catalyst showed high structural stability in the reducing and oxidizing environment and high reducibility of ceria in the low-temperature range (≤ 400°C the content of Ce3+ in reference to the total content of Ce obtained by H2-TPR method was ∼50 %). As a result, the catalytic activity in the propane oxidation reaction was very high (T50 % = 295°C for oxidized and 264°C for the reduced catalyst). The reaction parameters obtained for the activated catalyst were: turnover frequency TOF300℃ = 2.2∙103 s−1 and specific reaction rate r300℃ = 0.64 μmol∙g−1∙s−1). What is very important, the catalyst can be easily regenerated after the catalytic reaction by the reduction in hydrogen, because the shape and sizes of the active nanoparticles were very stable in the reaction environment.

Continuous 2-Methyl-3-butyn-2-ol Selective Hydrogenation on Pd/γ-Al2O3 as a Green Pathway of Vitamin A Precursor Synthesis

In this work, the effect of pretreatment conditions (10% H2/Ar flow rate 25 mL/min and 400 °C, 3 h or 600 °C, 17 h) on the catalytic performance of 1 wt.% Pd/γ-Al2O3 has been evaluated for hydrogenation of 2-methyl-3-butyn-2-ol in continuous-flow mode. Two palladium catalysts have been tested under different conditions of pressure and temperature and characterized using various physicochemical techniques. The catalytic performance of red(400 °C)-Pd/γ-Al2O3 and red(600 °C)-Pd/γ-Al2O3 are affected by the coexistence of several related factors like the competition between PdH and PdCx formation during the reaction, structure sensitivity, hydrogen spillover to the alumina support and presence or absence of Pd–Al species. High-temperature reduction leads to formation of Pd–Al species in addition to pure Pd. The Pd–Al species which reveal unique electronic properties by decreasing the Pdδ− surface concentration via electron transfer from Pd to Al, leading to a weaker Pd–Alkyl bonding, additionally assisted by the hydrogen spillover, are the sites of improved semi-hydrogenation of 2-methyl-3-butyn-2-ol towards 2-methyl-3-buten-2-ol (97%)—an important intermediate for vitamin A synthesis.

Deshidratación y deshidrogenación de 2-propanol en catalizadores de Pt/Al2O3 y Pt/Al2O3-CeO2

A series of Pt-based catalysts were tested in 2-propanol parallel reactions to produce mainly propylene and water plus acetone and hydrogen. Alumina and alumina-ceria catalytic supports (AC) were prepared by the sol-gel method. Pt catalysts were obtained by IWI and characterized by AAS, TPR, and FTIR. It was found the calcined catalysts (PtOx/AC) increased the dehydration capacity when compared to their respective catalytic supports, both series with no appreciable dehydrogenation products. The reduced catalysts (Pt0/AC) showed high dehydrogenation activity in 2-propanol reactions, with high selectivity towards acetone and hydrogen at low temperatures. These catalytic systems present a change in selectivity towards propylene above 230°C and the loss of activity of Pt-reduced species. This deactivation was related with the bands of asymmetric vibrations of C-H and C-O bonds in the post-reaction material characterized by FT-IR, which have been attributed to either carbon deposition or oxygenated intermediates chemisorbed on Pt surface. Moreover, the temperature range, where Pt0 is deactivated, is progressively shifted to higher values as the amount of ceria increases. This is attributed to the fact that ceria modifies the surface interactions of Pt sites with the molecules that cause deactivation. Catalysts were completely regenerated with a mild treatment in a N2 flow at 500ºC.

Methane oxidation over supported Pd catalysts prepared by magnetron sputtering

Abstract While magnetron sputtering has been used to deposit metals onto a range of solid substrates, its application to produce porous heterogeneous catalysts in powder form is relatively unstudied. Here, magnetron sputtered Pd heterogeneous catalyst powders were prepared using a shaker operated at optimal experimental settings to give uniform coverage of the powders, and tested in the abatement of exhaust emissions in natural gas fuelled engines via the oxidation of methane. Pd nanoparticles were deposited onto alumina, titania and zeolite supports, in powder form. X-ray diffraction confirmed that the characteristic structure of each support was maintained following sputtering. The quantity of Pd increased (a) with deposition time and (b) as a function of support in the order alumina

Synthesis of FAU-Zeolite Membrane by a Secondary Growth Method: Influence of Seeding on Membrane Growth and Its Performance in the Dehydration of Isopropyl Alcohol-Water Mixture.

Y-type zeolite membranes were prepared on a porous tubular α-alumina support by a secondary growth process. Various experimental conditions such as seed size, pH of seed solution, and degassing of support were examined for understanding their influence on the membrane deposition process. The experimental results showed that the potential of alumina support surface and the USY seed slurry plays a significant role in controlling the electrostatic interaction between seed particles and support surface and also the aggregation of USY seed particles in the slurry. In addition, we also noted the significance of the capillary forces working at the three-phase interface on the support surface and is a key factor that governs the seeding behavior onto the tubular support surface. Optimization of these parameters resulted in crack-free compact membranes that were able to effectively separate a mixture of isopropyl alcohol and water in a vapor-phase separation process.

Vapor-phase hydrogenation of levulinic acid to γ-valerolactone over Cu-Ni alloy catalysts

Vapor-phase hydrogenation of levulinic acid (LA) to ɤ-valerolactone (GVL) was investigated over supported-type Cu-Ni/Al2O3 catalysts in H2 flow at 250 °C. Ni-rich Cu-Ni/Al2O3 catalysts, typically 6 wt.% Cu and 14 wt.% Ni, achieved high LA conversion with high stability and high GVL selectivity. XRD analyses of the catalysts clarified that Cu-Ni alloy nanoparticles were produced on the alumina support by forming a solid solution of CuO-NiO. The Cu-Ni/Al2O3 catalyst showed the highest GVL productivity of 11.0 kg kgcat−1 h−1 with a selectivity of 98.6 %, although the catalyst was gradually deactivated with time on stream under high space velocity conditions. In the characterization of the used catalysts, the catalyst deactivation would be caused by the sintering of active Cu-Ni alloy nanoparticles, which could be induced by the cycle of the oxidation with H2O and the reduction with H2.

Effect of the Addition of Alkaline Earth and Lanthanide Metals for the Modification of the Alumina Support in Ni and Ru Catalysts in CO2 Methanation

In order to reduce greenhouse gas emissions, which are reaching alarming levels in the atmosphere, capture, recovery, and transformation of carbon dioxide emitted to methane is considered a potentially profitable process. This transformation, known as methanation, is a catalytic reaction that mainly uses catalysts based on noble metals such as Ru and, although with less efficiency, on transition metals such as Ni. In order to improve the efficiency of these conventional catalysts, the effect of adding alkaline earth metals (Ba, Ca, or Mg at 10 wt%) and lanthanides (La or Ce at 14 wt%) to nickel (13 wt%), ruthenium (1 wt%), or both-based catalysts has been studied at temperatures between 498 and 773 K and 10 bar pressure. The deactivation resistance in presence of H2S was also monitored. The incorporation of La into the catalyst produces interactions between active metal Ni, Ru, or Ru-Ni and the alumina support, as determined by the characterization. This fact results in an improvement in the catalytic activity of the 13Ni/Al2O3 catalyst, which achieves a methane yield of 82% at 680 K for 13Ni/14La-Al2O3, in addition to an increase in H2S deactivation resistance. Furthermore, 89% was achieved for 1Ru-13Ni/14La-Al2O3 at 651 K, but it showed to be more vulnerable to H2S presence.

The Effect of Addition Method of Impregnation Solution on Properties and Performance of Pd-Ag/Al2O3 Catalyst in Tail-End Acetylene Selective Hydrogenation

The impregnation of alumina support with PdCl2 solution was investigated in batch and semi-batch operation modes using a recycle packed-bed reactor. UV-visible analysis was used to evaluate the kinetics of Pd adsorption on alumina support. Transient palladium adsorption data showed that Pd adsorption was very rapid completing within few minutes. Bi-metallic Pd-Ag/Al2O3 catalysts were synthesized by sequential impregnation method. CO-chemisorption, CO-TPD and FE-SEM tests were used to characterize the synthesized bi-metallic samples. Catalytic performance of the samples was evaluated for tail-end acetylene selective hydrogenation process in a fixed-bed reactor. Moreover, the deactivation of the catalysts was evaluated mathematically by integral method of analysis, considering reaction kinetics as power laws in terms of nth orders in H2 and C2H2 partial pressures. It was observed that by batch-wise addition of Pd precursor solution, a sample was obtained with lowest amount of Pd dimmers that had highest ethylene selectivity and lowest hydrogenation reaction rate.

Effects of alumina phases on the structure and performance of VOx/Al2O3 catalysts in non-oxidative propane dehydrogenation

Abstract Supported vanadium oxides are promising in propane non-oxidative dehydrogenation and the activity of which shows clear support effects. The present study reports the effects of alumina polymorphs on the structure and performances of VOx-based catalysts. VOx/Al2O3 catalysts with the same V surface density were prepared over four different alumina supports (γ-Al2O3, δ-Al2O3, θ-Al2O3, θ,α-Al2O3) obtained by varying the calcination temperature of boehmite. The alumina calcination temperature was shown to affect the surface acid properties and VOx-support interactions and make it possible to tune the activity and coking behavior of catalysts. Weakening the VOx-support interactions due to the change in alumina surface properties was found critical to improve the intrinsic activity of catalysts. The coking behavior of catalysts was shown to depend on both total acid sites and VOx polymerization degree. This study may provide basic principles to tune the performance of VOx-based catalysts for non-oxidative dehydrogenation.

Modification of the properties of γ-alumina as a support for nickel and molybdate catalysts by addition of silica

Commercial pure γ-Al2O3 and SiO2 (1−30 wt.%) doped γ-Al2O3 were characterized as acid catalysts in ethanol conversion and used as supports for NiO and MoO3. Supported catalysts were prepared by incipient wetness impregnation. All catalytic materials were characterized by BET, XRD, FE-SEM microscopy, UV–vis and IR spectroscopies. Pure and silica-doped NiO/Al2O3 materials were used as precursors of metal catalysts for CO2 hydrogenation. Pure and silica-doped MoO3/Al2O3 materials were used as catalysts for ethanol oxidative dehydrogenation to acetaldehyde.These data show that the addition of silica in moderate amounts selectively influences a part of the alumina surface and strongly modifies the dispersing properties of alumina support. In particular, silica preferentially bonds over the strongest Lewis acid-base sites of γ-Al2O3, where also Ni2+ and molybdate species tend to interact. Being the SiO2-Al2O3 interaction stronger than the NiO-Al2O3 interaction and the MoO3-Al2O3 interaction, silica displaces nickel and molybdate species to less preferential sites where their interaction with exposed alumina is weaker. This results in more easily reducible Ni2+ species and larger Ni metal particles for silica doped Ni/Al2O3, and more monomeric and less polymeric molybdate species for silica doped MoO3/Al2O3.

Optimizing acido-basic profile of support in Ni supported La2O3+Al2O3 catalyst for dry reforming of methane

The increasing alarm of global warming always draws interest in reactions like dry reforming of methane (DRM) where both global warming gases (CO2 and CH4) are converted into value-added chemical building blocks, such as syngas. Nickel catalyst active sites along with support acid-base profiles play a key role in DRM. Herein, xLa2O3+(100-x) Al2O3 (x = 0, 10, 15, 20%) supports are prepared and followed by NiO dispersion over the produced support by impregnation method. It was tested for DRM reaction and characterized with TGA, XRD, TEM, IR, Surface area and porosity measurement, H2-TPR, CO2-TPD and NH3-TPD techniques. Upon increasing the basic lanthana proportion in the acidic alumina support, the crystallinity of alumina and acidity of total support decline. Up to 15% Lanthana addition in support claims a low acid and rich basic surface including super basic sites (related to unidentate carbonates) which governed optimum catalytic performance 64% CH4 conversion, 79% CO2 conversion and H2/CO ~ 1 up to 460-min in time on stream test. 20% lanthanum oxide loading led to inferior performance due to rapid loss of surface area, pore-volume, pore diameter, acidity and medium basic strength sites. Fine-tuning of acid-base lanthana-alumina support with dispersed Ni species are a means for understanding DRM.

Influence of Alumina Precursor Properties on Cu-Fe Alumina Supported Catalysts for Total Toluene Oxidation as a Model Volatile Organic Air Pollutant

The structure–property relationship of catalytic supports for the deposition of redox-active transition metals is of great importance for improving the catalytic efficiency and reusability of the catalysts. In this work, the role of alumina support precursors of Cu-Fe/Al2O3 catalysts used for the total oxidation of toluene as a model volatile organic air pollutant is elucidated. Surface characterization of the catalysts revealed that the surface area, pore volume and acid site concentration of the alumina supports are important but not the determining factors for the catalytic activity of the studied catalysts for this type of reaction. The determining factors are the structural order of the support precursor, the homogeneous distribution of the catalytic sites and reducibility, which were elucidated by XRD, NMR, TEM and temperature programed reduction (TPR). Cu–Fe/Al2O3 prepared from bayerite and pseudoboehmite as highly ordered precursors showed better catalytic performance compared to Cu-Fe/Al2O3 derived from the amorphous alumina precursor and dawsonite. Homogeneous distribution of FexOy and CuOx with defined Cu/Fe molar ratio on the Al2O3 support is required for the efficient catalytic performance of the material. The study showed a beneficial effect of low iron concentration introduced into the alumina precursor during the alumina support synthesis procedure, which resulted in a homogeneous metal oxide distribution on the support.

Supported Silver Nanoparticles as Catalysts for Liquid-Phase Betulin Oxidation.

Herein, it has been shown that betulin can be transformed into its biologically active oxo-derivatives (betulone, betulinic and betulonic aldehydes) by liquid-phase oxidation over supported silver catalysts under mild conditions. In order to identify the main factors determining the catalytic behavior of nanosilver catalysts in betulin oxidation, silver was deposited on various alumina supports (γ-alumina and boehmite) using deposition–precipitation with NaOH and incipient wetness impregnation methods, followed by treatment in H2 or O2. Silver catalysts and the corresponding supports were characterized by X-ray diffraction, nitrogen physisorption, inductively coupled plasma optical emission spectroscopy, photoelectron spectroscopy and transmission electron microscopy. It was found that the support nature, preparation and treatment methods predetermine not only the average Ag nanoparticles size and their distribution, but also the selectivity of betulin oxidation, and thereby, the catalytic behavior of Ag catalysts. In fact, the support nature had the most considerable effect. Betulin conversion, depending on the support, increased in the following order: Ag/boehmite < Ag/boehmite (calcined) < Ag/γ-alumina. However, in the same order, the share of side reactions catalyzed by strong Lewis acid centers of the support also increased. Poisoning of the latter by NaOH during catalysts preparation can reduce side reactions. Additionally, it was revealed that the betulin oxidation catalyzed by nanosilver catalysts is a structure-sensitive reaction.

Alumina Support for Cobalt Catalyst in a Methane Dry Reforming Reaction: The Role of Water Content in a Solvent Medium

This study aimed to synthesize alumina from an inorganic aluminum nitrate precursor in various binary solvent systems of ethanol and water using the sol-gel self-assembly (SSA) method, employing a triblock copolymer, pluronic P123, as the pore-directing agent. The resulting materials were implemented as a support for the cobalt (Co) catalyst in a methane dry reforming (MDR) reaction at 1073 K under 1 atm. Regardless of the water percentage used in the support synthesis, the methane dry reforming reaction over Co catalysts on alumina supports showed the negligible change in conversion during the 12 h reaction. Moreover, there was evidence of large quantities of amorphous carbon and graphitic carbon on the spent catalyst surface. However, the low oxidation temperature of these deposited carbons could help maintain the balance between the carbon formation and the carbon elimination processes on the catalyst surface during the reforming reaction, hence prolonging the lifetime of the catalyst. The high conversion of methane (CH4) from 64.6% to 82.8% and carbon dioxide (CO2) from 70.7% to 86.6% for the MDR reaction over the as-prepared alumina-supported Co catalyst demonstrated a significant improvement in catalyst production for the MDR reaction from the viewpoint of large-scale applications.

The role of Pd–Pt Interactions in the Oxidation and Sulfur Resistance of Bimetallic Pd–Pt/γ-Al2O3Diesel Oxidation Catalysts

Diesel oxidation catalysts (DOC) were investigated for oxidation activity, NO conversion stability, and sulfur poisoning/regeneration on Pd/Al2O3, Pt/Al2O3, and Pd-Pt/Al2O3 catalysts. The Pd/Al2O3 catalyst was more active for CO and hydrocarbon (C3H6 and C3H8) oxidation, while the Pt/Al2O3 catalyst efficiently oxidized NO. The formation of a Pd-Pt alloy in the Pd-Pt/Al2O3 catalyst maintained Pd in a more reduced phase, resulting in the superior activity of this catalyst for the oxidation of CO, C3H6, and NO in comparison with its monometallic counterparts. The Pd-Pt alloy not only provided more low-temperature activity but also retained the stability of NO oxidation. The Pd-Pt alloy also favored the spillover of SO2 to the alumina support, resulting in significantly higher adsorption capacity of the Pd-Pt/Al2O3 catalyst, extensively prolonging its lifetime. However, the stable sulfates on Pd-Pt/Al2O3 made it difficult to completely regenerate the catalyst. The bimetallic sample showed higher activity for CO, C3H8, and C3H6 after sulfur poisoning and regeneration.

A Robust Mesoporous Al2 O3 -Based Nanocomposite Catalyst for Abundant NOx Storage with Rational Design of Pt and Ba Species.

The nanostructural design of heterogeneous catalysts has often been demanded for assessing synergetic effects, which should be developed further by using high-surface-area porous metal oxide supports. However, such opportunities have been undermined by the poor stability of ordered mesoporous structures. Herein, rational design is demonstrated to obtain nanocomposite catalysts showing improved NOx storage properties owing to the presence of Ba species over a well-designed mesoporous alumina (Al2 O3 ) support. It is found that Ba species are impregnated successfully only after the stabilization of the mesoporous structure by full crystallization of Al2 O3 frameworks to the γ-phase, with the formation of Pt nanoparticles coinciding with complete removal of organic components. All the insights during this synthetic procedure are essential for designing high-performance catalysts to purify and recover NOx molecules, and are applied for designing a variety of cutting-edge mesoporous nanocomposite catalysts.

An investigation on the relationship between physicochemical characteristics of alumina-supported cobalt catalyst and its performance in dry reforming of methane.

This study deals with the development of alumina-supported cobalt (Co/Al2O3) catalysts with remarkable performance in dry reforming of methane (DRM) and least carbon deposition. The influence of Co content, calcination, and reduction temperatures on the physicochemical attributes and catalyst activity of the developed catalysts was extensively studied. For this purpose, several characterization techniques including ICP-MS, H2 pulse chemisorption, HRTEM, H2-TPR, N2 adsorption desorption, and TGA were implemented, and the properties of the developed catalysts were carefully analyzed. The impact of reaction temperature, feed gas ratio, and gas hourly space velocity (GHSV) on the reactants conversion and products yield was investigated. Use of 10%Co/Al2O3 catalyst, calcined at 500°C and reduced under H2 at 900°C in DRM reaction at 850°C, CH4/CO2 ratio of 1:1, and GHSV of 6 L.g-1.h-1 resulted in a remarkable catalytic activity and sustainable performance in long-term operation where great CO2 (96%) and CH4 (98%) conversions and high H2 (83%) and CO (91%) yields with a negligible carbon deposition (3 wt%) were attained in 100-h on-stream reaction. The good performance of the developed catalyst in DRM reaction was attributed to the small Co particle size with well-dispersion on the alumina support which increased the catalytic activity and also the strong metal-support interaction which inhibited any serious metal sintering and enhanced the catalyst stability.

Example on the Use of Operando Spectroscopy for Developing Mechanistic Insights into Industrial Catalysts and Catalytic Processes

In this contribution, we present an industrial example on how tailored operando spectroscopic methodologies provide the insights needed for the development of new catalytic technologies and support their global utilization. We describe the use of operando spectroscopic methods to investigate how the CO oxidation performance of catalysts is impacted by NOx, H2, temperature, and moisture, as well as the catalyst support. This operando spectroscopic analysis provides mechanistic insights into the current diesel oxidation catalyst (DOC) system and shines light on the material and process development efforts on future DOC catalysts for low-temperature emission control to meet the new regulations. This investigation has shown that at cold-start temperatures, the nitrate growth can occupy the precious metal–alumina support interfacial sites that are critical for O2 dissociation and/or oxygen transfer and hinder CO conversion. Introduction of hydrogen on the catalyst surface can inhibit the nitrate growth, which in turn keeps these critical interfacial sites open.