Alumina-supported Catalysts Research Articles

Silica- and Alumina-Supported Sulfated Zirconia Catalysts for Hexane Isomerization: Effect of the Support Nature

Silica- and Alumina-Supported Sulfated Zirconia Catalysts for Hexane Isomerization: Effect of the Support Nature

Copper and iron-based monolithic catalysts for phenol Catalytic Wet Peroxide Oxidation (CWPO): Support and iron effects on the catalytic performance

Water is an invaluable resource of our planet, and our lives and those of the future generations rely on it. Phenolic compounds are part of many industries effluents and they are highly toxic and not biodegradable. Therefore, they could be eliminated from water through the Catalytic Wet Peroxide Oxidation (CWPO) reaction. In this work, alumina-supported and cordierite-supported copper and iron-based monolithic catalysts were synthesized and tested in the CWPO of phenol. These structured catalysts were characterized by stereoscopic microscopy, N2 adsorption, XRD, LRS, SEM/EDX and XPS, and their mechanical resistance was analyzed. The effect of both, the support and the presence of iron as a co-active phase on the metal species leaching, and therefore on the catalytic performance, were evaluated. Alumina-supported copper species were more accessible and reducible than cordierite-supported ones and, as a consequence, these rapidly converted the totality of phenol and achieved high mineralization and COD reduction. On the other hand, iron addition as a co-active phase decreased copper leaching in all cases due to Cu-Fe interactions. The bimetallic alumina-supported catalyst exhibited the best catalytic performance with low copper and iron leachings. Consequently, it was tested in a more complex reaction media (tap water). This catalyst resulted promising, converting all the phenol with high mineralization and COD reduction, although suffering some copper and iron leaching.

The rate determining steps and rate equation for the oxidative dry reforming of methane over supported Ni catalyst

Dry reforming of methane (DRM) and its modification with O2 co-feed, the ODRM reaction, have been gaining importance. However, a general rate equation applicable for the ODRM reaction with varying O2 co-feed has not been reported. This general rate equation should be applicable for the DRM and ODRM reactions depending on the amount of O2 co-feed. Microkinetic models simulate catalytic reactions without making any a priori assumptions for the RDS and are helpful in developing rate equations. Unfortunately, microkinetic modelling for ODRM over supported monometallic Ni has not been carried out. Here, we perform microkinetic modelling using an existing reforming reaction mechanism for ODRM over an alumina-supported Ni catalyst. Validation is achieved by comparing experimental and microkinetic outlet flow rates at different feed rates of O2 and applying R2 analysis and F-tests. Once the model is validated, we identify the RDS through a hierarchical strategy using microkinetic results and sensitivity analysis for varying amounts of O2 co-feed. The results reveal that CH4 activation is the RDS. CH4 activation can occur through direct dehydrogenation on an empty site or oxidative dehydrogenation aided by adsorbed O, depending on the amount of O2 co-feed. Once the RDSs are identified, we derive a general rate equation that effectively simulates the DRM reaction with different amounts of O2 co-feed. We further examine the effect of the amounts of O2 co-feed and ascertain the presence of maximum hydrogen production for certain amounts of O2 co-feed.

Fe-Promoted Alumina-Supported Ni Catalyst Stabilized by Zirconia for Methane Dry Reforming

The dry reforming of methane is a highly popular procedure since it can transform two of the most abundant greenhouse gases, methane and carbon dioxide, into useful syngases that can be further processed into valuable chemicals. To successfully achieve this conversion for the effective production of syngas, an optimal catalyst with advantageous physicochemical features must be developed. In this study, a variety of Ni-based catalysts supported by zirconia alumina (5Ni-10Zr + Al) were prepared by using the impregnation approach. Different loadings of Fe promoter were used, and the performances of the resulting catalysts in terms of activity and stability were investigated. The catalyst used in this study had an active metal component made of 5% Ni and x% Fe supported on 10ZrO2 + Al2O3, where x = (1, 2, 3, and 4). The physicochemical characteristics of both freshly calcined and used catalysts were studied using a range of characterization techniques, such as: N2 adsorption–desorption isotherms, XRD, H2-TPR, Raman spectroscopy, TGA, and TEM. An investigation of the effects of the Fe promoter on the catalytic activity of the catalyst (5Ni + xFe-10Zr + Al) was conducted. Amongst the studied catalysts, the 5Ni + 3Fe-10Zr + Al catalyst showed the best catalytic activity with CH4 and CO2 conversions of 87% and 90%, respectively, and had an H2/CO ratio of 0.98.

Process and catalyst improvements for the dry reforming of methane

Catalyst and process improvement strategies for dry reforming of methane (DRM) are shown by enhancing the performance of an existing Ni/Al2O3 catalyst and adding oxygen to the feed. Alumina-supported Ni-Co catalyst, Ni/Co molar ratio = 3, was synthesized and calcined at 500 and 850 °C to take advantage of the possible strong metal-support interactions. The freshly reduced catalysts contained Ni-Co alloys. Higher CH4 and CO2 conversions, H2 and CO yields and H2/CO ratio during DRM and oxidative dry reforming of methane (ODRM) were achieved at 600 and 750 °C and two space-velocities for Ni3Co-500 due to a higher effective dispersion of 4.9 %. Significant carbon formation and activity loss occurred during DRM. Increasing the reaction temperature and/or with O2 co-feed increased the CH4 conversion. The outlet concentrations were stable, and carbon formed was significantly less. Changes in the crystallite size and near-surface alloy composition in the spent catalyst were detected.

Preparation of an Anodic Alumina-Supported Ni Catalyst and Development of a Catalytic Plate Reformer for the Steam Reforming of Methane

A plate-type Al/Fe–Cr alloy/Al-clad substrate was used to prepare a sandwich-structured plate-type anodic alumina catalyst by anodization, post-modification treatment, and metal loading. The as-prepared plate-type catalyst was utilized in the design of a catalytic plate reactor for a methane steam reforming reaction, and a 3D model was developed to simulate the performance of tube-type and box-type reformers. The experimental results of the preparation of the clad materials showed that the hydrothermal treatment and subsequent high-temperature calcination transformed the amorphous skeletal alumina in the conventional anodic alumina layer into γ-alumina, and significantly increased its specific surface area. Simulation results showed that the temperature difference between the channel wall and the center of the gas phase of the thin-walled catalyst was only 30% of that of the particulate catalyst, indicating the potential advantages of the catalytic plate reactor in terms of heat transfer and energy saving. When the length-to-diameter ratio (or length-to-width ratio) of the reaction channel is small and the channel height is large, insufficient transverse mass transfer and backmixing are two major factors affecting reformer performance. For the tube-type channels, a length-to-diameter ratio of 10~35, and a diameter of 5~20 represent favorable choices. In contrast, for the box-type channel, the length-to-width ratio and the height should be set to 2~4 and 2~5 mm, respectively. Additionally, for box-type channels, the number of gas inlet ports has a significant effect on the reformer performance, and the distribution state provided by two inlet ports is close to the ideal distribution state.

Hydrotreatment of pyrolysis bio-oil with non-edible carinata oil and poultry fat for producing transportation fuels

The cost of producing biofuels has been more expensive than fuels from fossil energy due to the heterogeneous nature of biomass sources. Therefore, commercialization efforts for producing biofuels have focused on blending with oleochemical feedstocks. This study carried out co-hydroprocessing (50:50) of pyrolysis oil with carinata oil or poultry fat over two catalyst supports. Cobalt and molybdenum catalysts supported on Douglas fir-derived biochar and alumina were used. The major goal of this study was to understand the synergistic effect of mixing pyrolysis oil with triglycerides for hydrotreatment under various supports, the influence on the oil quality, hydrodeoxygenation (HDO) and coke formation. The catalyst aided by biochar displayed improved HDO. Higher hydrogen consumption and low coke formation were seen for biochar support, and oxygen was predominantly removed via dehydration. Large oxygen-containing functional groups, high surface area, and acid sites in biochar might have made it a better HDO catalyst. Blending pyrolysis oil with poultry fat yielded better pyrolysis bio-oil quality over carinata oil and produced a higher percentage of jet fuel fraction. In summary, pyrolysis bio-oil mixed with poultry fat and hydrotreated using biochar support catalysts was more effective in HDO activity and improving overall pyrolysis bio-oil quality than alumina-supported catalyst and carinata oil.

Alumina-Supported Silver Catalyst for O3-Assisted Catalytic Abatement of CO: Effect of Ag Loading

Alumina-Supported Silver Catalyst for O3-Assisted Catalytic Abatement of CO: Effect of Ag Loading

γ-Al2O3 supported silver nanoparticle applied in C3H8-SCR: Nanosphere and nanoflake

The γ-Al2O3 support (nanosphere and nanoflake) was used to support Ag nanoparticles and applied in C3H8-SCR to remove NOx. Ag/Al2O3-flake exhibited superior catalytic activity than Ag/Al2O3-sphere in C3H8-SCR. It is found that Al2O3-flake rich in Al octacoordinated ions promoted more Agnδ+ species to disperse on Ag/Al2O3-flake than Ag/Al2O3-sphere. Agnδ+ species could strengthen the low-temperature catalytic activity for HC-SCR while Ag metal particles were unbeneficial since they could promote complete oxidation of hydrocarbon. This was the first time to explore the remarkable effect of Al2O3 intrinsic properties on catalytic activity of alumina-supported catalyst for HC-SCR from the perspective of uniform morphology. Environmental implicationThe number of transport vehicles has increased dramatically during the past decades due to global economic growth. The accompanying concern is the huge consumption of fossil fuels, for example, gasoline and diesel, which speeds up global warming. Internal combustion engines produce toxic emissions, where NOx forms nitric acid in the atmosphere, reacts with HCs to form which causes acidification of land and lakes. Currently, it is urgent to develop a leading deNOx technique for the after-treatment of commercial engine-powered vehicles to meet stringent emission legislations.

Alumina-supported cobalt catalysts in the hydrogenation of CO2 at atmospheric pressure

20 wt.% cobalt catalysts supported on pure and 5 wt.% silica-containing alumina have been prepared and characterized by X-Ray Diffraction, IR and DR-UV-vis-NIR spectroscopies and Field-Emission Scanning Electron Microscopy (FE-SEM). The presence of a cobalt-containing surface spinel phase Co3-xAlxO4 and, for the silica-containing sample, of a segregated Co3O4 phase is evident. These catalysts have been tested in CO2 hydrogenation at atmospheric pressure in steady state conditions in the temperature range 523–773 K. Both catalysts are active in CO2 hydrogenation to methane (methanation) and to CO (reverse Water Gas Shift, rWGS). CO2 hydrogenation activity is higher on freshly pre-reduced silica-free Co/Al2O3, while selectivity to methane is slightly higher on the silica-containing sample. Spent catalysts contain clustered or amorphous cobalt metal centers as active sites for methanation. The silica-containing catalyst shows slow deactivation in CO2 hydrogenation upon 13 h experiments, with quite stable or even slightly increasing rWGS activity and decreasing CH4 selectivity. This confirms previous data suggesting that, over cobalt catalysts, sites for methanation are metal centers prone to deactivation by carbon deposition. However, in contrast with what happens with unsupported and silica-supported cobalt catalysts, where deactivation is very fast, over these alumina-based catalysts carbon deposition and deactivation occur much more slowly. Sites for rWGS are unreduced cobalt centers which do not undergo such a deactivation phenomenon.

Performance of Modified Alumina-Supported Ruthenium Catalysts in the Reforming of Methane with CO2

Ruthenium (1 wt%) catalysts supported on alumina doped with alkaline (Na and K) and alkaline earth metals (Ba, Ca, and Mg) of different concentrations (1, 5, and 10 wt%) were tested in the dry reforming of methane. All catalysts were prepared by the successive impregnation method. Supports were characterized by X-ray diffraction, BET surface area, temperature-programmed desorption of CO2, and 2-propanol dehydration. Additionally, catalysts were characterized by temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Stability tests to study coke deposition were performed using long-time dry reforming reactions. All the catalysts showed good catalytic activity, and activity falls were never detected. Ru metallic phase seemed to be resistant to coke formation even though its particles are sintered during a long-term reaction.

Small-angle X-ray scattering intensity of multiscale models of spheroids.

The microstructure of heterogeneous catalysts often consists of multiscale aggregates of nanoparticles, some of which are highly anisotropic. Therefore, small-angle X-ray scattering, in classical or anomalous mode, is a valuable tool to characterize this kind of material. Yet, the classical exploitation of the scattered intensities through form and structure factors or by means of Boolean models of spheres is questionable. Here, it is proposed to interpret the scattered intensities through the use of multiscale Boolean models of spheroids. The numerical procedure to compute scattered intensities of such models is given and then validated on asymptotic diluted Boolean models, and its applicability is demonstrated for the characterization of alumina catalyst supports.

Tuning the Cu/Ce Ratio for Improved Benzene Oxidation over Gold-Promoted Alumina-Supported CuO-CeO2

Increased levels and detrimental effects of volatile organic compounds (VOCs) stimulate research efforts to develop catalysts with high efficiency in complete hydrocarbon oxidation. This work is focused on the complete oxidation of benzene as a probe reaction for VOCs elimination over alumina-supported CuO-CeO2 mixed oxide promoted by gold. The benzene molecule is the most stable among the aromatic hydrocarbons with toxic and often carcinogenic effects known as BTEX (benzene, toluene, ethylbenzene, and xylenes) owing to the symmetry and stability of the benzene ring. Use of low-cost materials as support is an appropriate strategy aimed at improving catalyst economic profitability. The effect of the Cu-Ce ratio, namely 2:1 and 1:5, and the role of supported gold in the catalyst performance were evaluated. Analysis of the impact of support composition in benzene oxidation was based on sample characterization by textural measurements, PXRD, EPR spectroscopy, and the TPR technique. Special attention was paid to the disturbed symmetry of the ceria crystallographic structure by defects formation and its implication for the catalytic activity. Gold on alumina-supported binary oxide catalysts exhibited a significantly higher activity than promoted supported monometallic oxides. The best performance of the Au/Cu-Ce 1:5 sample was related to the highest concentration of paramagnetic Cu2+ ions and the best copper species dispersion evidenced by PXRD, EPR, and TPR results. The catalyst achieved stable total oxidation to CO2 and water by 94% benzene conversion at 250 °C, thus implying the potential of this composition in developing efficient catalytic materials for atmospheric pollutant abatement.

One-step upgrading of real flue gas streams into syngas over alumina-supported catalysts

Flue gas is a major source of CO2 and the development of technologies for its utilization is of utmost interest both by environmental and industrial perspectives. Recently investigated CO2 valorization processes still face techno-economic challenges for implementation for costs associated with different steps, including CO2 purification steps. Thus, for the first time in literature, the feasibility of the direct one-step upgrading of real untreated flue gas into syngas is investigated here. For that end, classical alumina-supported catalysts (Ni, Co and Fe) were used for concept validation. The influences of temperature (500–900 °C), metal load (10–15 %), residence time (GHSV = 315–1260 h−1) and the effects of flue gas impurities (NOX and SO2) are reported here. Best CO2 and H2O conversion performances (XCO2 = 53.9 %, XH2O = 67.0 %) were obtained with the nickel catalyst with 15 wt% Ni at 900 °C and the highest residence time (GHSV = 315 h−1). The highest H2/CO ratio of the produced syngas was 0.70 and it was obtained with the same 15 wt% Ni catalyst at T = 700 °C, GHSV = 630 h−1. The NOx present in the FG was completely removed as part of the one-step upgrading strategy, while SO2 did not interact with the tested catalysts. Finally, a long-term operation strategy was proposed by supplementing the flue gas with H2 (H2/CO2 = 1.0), which yielded 24 h stable operation with around 40 % CO2 conversion and a syngas with H2/CO = 1.2–1.3. The results presented here, for the first time in the literature, demonstrate the feasibility of a novel one-step process for direct valorization of flue gas. The direct upgrading of flue gas would potentially decrease the costs associated with CO2 purification and valorization.

Insights into Pt–CN species on an alumina-supported platinum catalyst as active intermediates or inhibitors for low-temperature hydrogen cyanide synthesis from methane and nitric oxide

In situ measurements revealed that the Pt–CN species function not only as intermediates but also as inhibitors for low-temperature HCN synthesis.

The adsorption of nitrobenzene over an alumina-supported palladium catalyst: an infrared spectroscopic study.

As part of an on-going programme of development of an aniline synthesis catalyst suitable for operation at elevated temperatures, the geometry of the adsorption complex for nitrobenzene on a 5 wt% Pd/Al2O3 catalyst is investigated by infrared (IR) spectroscopy. Via an appreciation of the reduced site symmetry resulting from adsorption, application of the metal surface selection rule, and observation of in-plane modes only, the adsorption complex (Pd-nitrobenzene) at 28 °C is assigned as occurring vertically or tilted with respect to the metal surface, adopting Csσv(yz) symmetry. Moreover, adsorption occurs via a single Pd-O bond. Single molecule DFT calculations and simulated IR spectra assist vibrational assignments but indicate a parallel adsorption geometry to be energetically favourable. The contradiction between calculated and observed structures is attributed to the DFT calculations corresponding to an isolated molecule adsorption complex, while IR spectra relate to multi molecule adsorption that is encountered during sustained catalytic turnover. Residual hydrogen from the catalyst reduction stage leads to aniline formation on the Pd surface at low nitrobenzene coverages but, on increasing nitrobenzene exposure, the aniline is forced on to the alumina support. A reaction scheme is proposed whereby the nitrobenzene adsorption geometry is inherently linked to the high aniline selectivity observed for Pd/Al2O3 catalysts.

Synthesis of highly-uniform titania overcoats on a mesoporous alumina catalyst support by atomic layer deposition and their application in hydroprocessing

The feasibility of gas phase deposition using a Ti alkoxide precursor for precise surface modification of catalysts was demonstrated by modifying a mesoporous alumina support with a Ti oxide overcoat.

Bimetallic PdFe catalysts in hydrodechlorination of diclofenac: Influence of support nature, metal deposition sequence and reduction condition

Monometallic palladium and bimetallic palladium-iron catalysts (1 wt% Pd, 10 wt% Fe) were prepared by sequential (denoted as “-s”) and co- (denoted as “-c“) impregnation of alumina and silica – zirconia (ZS) supports with metal nitrates. After reduction with H2 at 320 and 30 °C the catalysts were tested in hydrodechlorination of diclofenac in water at 30 °C in batch and flow-type reactors. The alumina-supported catalysts were more active than the ZS-supported ones, while the bimetallic catalysts were more efficient than the monometallic Pd ones. The co-impregnated bimetallic catalysts showed higher efficiencies than the catalysts prepared by the sequential deposition of metals. Pd/Al2O3 and PdFe/Al2O3-c provided the same rate of DCF conversion in the batch reactor after both types of preliminary reduction, opening the way for energy saving. The catalysts were studied by XRD, TEM, SEM-EDX, low-temperature N2 physisorption, Mössbauer spectroscopy, DRIFT-CO and by XPS after in situ reduction at 320 °C and ex-situ reduction at 30 °C. The improvements in catalyst efficiency resulted from wider pores, formation of PdFe alloys or Pd-Fe-Ox species on the surface, high Pd0/Pd2+ ratio, low extent of Pd encapsulation with the support and especially its coordinately unsaturated sites. The encapsulation degree was the lowest in the co-impregnated catalysts.

Effect of Basic Promoters on Porous Supported Alumina Catalysts for Acetins Production

A facile strategy for the design of porous supports was obtained by modifying the sol-gel method followed by the wet impregnation technique. In this respect, herein, the acidity of the γ-Al2O3 phase was modulated by adding basic MgO, La2O3 or ZnO promoters to form binary supported catalysts. The Ni and Co dispersion on the supports associated with their tunable acidity and morphologies resulted in highly porous supported alumina-based catalysts. The physicochemical properties of the solids were comprehensively investigated by XRD, textural properties, Raman and FTIR spectroscopy, SEM-EDS, TEM, EPR and XPS analyses. The catalytic performances in the esterification of glycerol in the presence of acetic acid (EG) for the acetins production were evaluated. The highly dispersed NiO and Co3O4 active species on binary porous supports produced synergistic effects appearing to be the reason for the activity of the solids in the EG reaction. Under the optimized reaction conditions, NiCo/MgO-Al2O3 was found to be a robust solid with superior catalytic performance and improved stability in four reaction cycles with 65.0% of glycerol conversion with an exclusive selectivity of 53% for triacetin. The presence of Co2+/Co3+ and Ni2+ strongly interacting with the spinel γ-Al2O3 and MgAl2O4 phases, the latter having a large number of lattice oxygen species, was considered another active component besides those of Ni and Co in the esterification of glycerol.

Analysis by temperature-programmed reduction of the catalytic system Ni-Mo-Pd/Al2O3

Alumina-supported nickel catalysts are used to facilitate many reactions at various scales. However, the deactivation of these catalysts is an important problem that has prompted the search for solutions such as the addition of other metals that act as promoters. In this research, the interactions that form between the support and the metals have been studied, a fundamental property that directly affects the performance of the catalyst. With this idea, several Ni-Pd and Ni-Mo bimetallic and various Ni-Mo-Pd trimetallic samples have been prepared, and the reduction capacity of the oxide phases by temperatura-programmed reduction has been analyzed and studied. It has been found that in bimetallic catalysts, Pd favors the appearance of NiO species that are more easily reducible than Mo. In the same way, the data obtained from the trimetallic simples suggest that the impregnation order of Mo and Pd is not a determining factor in these catalysts. In addition, it has been found that the co-impregnation of Ni with Pd gives better results than the sequential impregnation of these metals. The results obtained have also shown that the order of nickel impregnation is decisive. In the case of Ni-Mo catalysts, by impregnating the molybdenum first, catalysts with better reducing properties can be obtained.