Characterization Of Catalysts Research Articles

Structure characterization of aged automobile exhaust catalysts using electron probe microanalysis

BackgroundDriven by emission regulations, the technology of emission control catalysts has been under increasing need for development. Understanding the deactivation mechanism of aged or spent automobile exhaust catalysts is the key to extending their service lifetime. However, the lack of comprehensive microstructural characterization results in an incomplete understanding of their physicochemical properties. Deactivation mechanism of automobile exhaust catalysts is a considerably complex phenomenon, it can be classified into three groups based on its origin: thermal sintering, chemical poisoning and mechanical deactivation. ResultsIn this study, an aged high-mileage automobile exhaust catalyst with Pd and Rh active phases supported on a cerium zirconium oxide doped alumina coating on cordierite was analysed; six consecutive monolithic blocks along the inlet to the outlet of the aged catalyst were extracted, and the corresponding metallographic samples were fabricated using the vacuum impregnation resin method. The purpose of this study was to accurately characterize the different regions of the monolith via electron probe microanalysis and to infer potential causes of catalyst deactivation. Two major causes of deactivation were found: (1) aggregation and alloying of precious-metal particles caused by thermal sintering and (2) chemical poisoning caused by sulphur and phosphorus. Other mechanisms, such as mechanical degradation, which mainly manifests as the loss or wear of the washed coating, were also found to be involved in deactivation. Additionally, the catalytic activity tests showed a considerable decrease in the aged catalyst. The poison concentration trends in the washcoat indicated that P is detrimental to CO oxidation, while S accumulation affects propane oxidation. SignificanceThis analysis method can be of substantial practical significance in developing advanced washcoat materials. Meanwhile, it has great potential in the washcoat analysis of honeycomb-shaped monolithic catalyst, such as natural gas catalyst, diesel vehicle oxidation catalyst and other honeycomb catalysts applied in chemical industry.

Dual-function macroalgae biochar: Catalyst for hydrogen production and electrocatalyst

In the current study, Enteromorpha intestinalis, a green macroalgae, has been utilized as a substrate to synthesise a new environmentally friendly and cheap dual-functional (catalyst and electrocatalyst) material. The catalyst was used for efficient hydrogen production from alcoholises sodium borohydride and as an anode catalyst for direct methanol fuel cell applications. At the catalyst synthesis stage, orthogonal arrays of Taguchi is used to find the optimum levels of independent variables for the superior catalyst performance that bears the modest kinetics. The experiments performed in accordance with the L16(45) type orthogonal array. The samples treated at relatively moderate acid, impregnation temperature, impregnation time, burning temperature and burning time showed higher catalytic activities with Exp(5) presenting the optimal catalytic activity followed by Exp(1), Exp(15), Exp(8) and Exp(12), respectively. The experimental levels of coded variables (acid molarity, impregnation temperature and time, burning temperature and time) for Exp(5) were 3 M, 50 °C, 24 h, 500 °C and 2 h., respectively. These finding suggest that providing maximum levels of each of independent variable will not provide high catalytic activity. Taking into account the binary and ternary interactions is an efficient way to determine optimal level of each parameter with regards to maximum hydrogen production rate. The morphological and structural characterization of the optimal catalyst was finally carried out with SEM- EDS, XRD and FT-IR. CV and EIS measurements were taken to determine the electrocatalytic activity of final biochar. Experimental studies revealed that the utilization of E. intestinalis-based electrocatalyst as an anode catalyst for direct fuel cell applications is promising. By employing advanced Taguchi-based experimentation, this research establishes the optimum levels of independent variables, enhancing the catalyst's performance, and highlighting a novel approach to modest kinetics improvement.

Hierarchical ZSM-5 zeolite supported RuOx catalysts via organic mesoporous porogens for catalytic oxidation of vinyl chloride

Hierarchical ZSM-5 zeolites supported RuOx catalysts were prepared via the addition of various organic mesoporous porogens (namely starch, cellulose and sucrose) for catalytic oxidation of vinyl chloride (VC). The usage of mesoporous porogens during catalysts preparation was favorable for boosting the catalytic activity of the resultant catalysts, and 1%RuOx/HZ5-10%sucrose exhibited the optimum catalytic activity, impressive catalytic stability and long-term durability. The structure-activity dependence from catalysts characterizations revealed that the higher specific surface area, more abundant strong acid sites and surface adsorbed oxygen species were regarded as the critical parameters for the noticeable improvement of catalytic activity. Based on in situ infrared spectroscopy analysis, 1%RuOx/HZ5-10%sucrose exhibited higher adsorption capacity and more efficient conversion of VC molecules with fewer formation of organic intermediates because of its superior catalytic activity in comparison with the single 1%RuOx/HZ5. Additionally, enol and carboxylate species were demonstrated to be the key organic intermediates in catalytic VC oxidation.

Dehydrative decarbonylation of fatty acids into long-chain olefins over CoNx/NC catalysts

The development of highly efficient, low-cost supported catalysts is crucial for directly deoxygenating biomass fatty acids to long-chain olefins. However, additive-free olefin production, by dehydrative decarbonylation from fatty acids, is scarcely conducted owing to competing decarboxylation reactions. Herein, a green and cost-effective strategy is presented to improve the Co-catalyzed dehydrative decarbonylation of stearic acid, which produces a mixture of heptadecenes with yields of up to 41.3 % and a paraffin yield of 14.7 %. Experimental data, along with a detailed catalyst characterization, revealed that the surface CoNx species acted as the dominant active sites. Furthermore, the specific catalytic performance can be attributed to the dense defect sites, abundant vacancies, and mesoporous structures of the N-doped Carbon (NC) support. The as-prepared CoNx/NC catalysts were recovered and reused up to three times without significant deactivation. Additionally, we propose a possible reaction mechanism for fatty acid deoxygenation. This research makes a significant contribution toward advancing the performance of noble-metal-free deoxygenation catalysts for the production of unsaturated compounds in biomass conversions.

Preparation and NH3-SCR catalytic performance of CeTiOx catalysts with different pore structures

To investigate the influence of pore structure on the catalytic activity of catalysts, four catalysts including three-dimensionally ordered macroporous-mesoporous (3DOM-m) CeTiOx, three-dimensionally ordered macroporous (3DOM) CeTiOx, three-dimensionally ordered mesoporous (3DOm) CeTiOx and disordered mesoporous (DM) CeTiOx were synthesized by the sol-gel method. The NH3-SCR denitration testing results show that the performance of the catalysts with different pore structures follows the sequence of 3DOM-m CeTiOx>3DOm CeTiOx>3DOM CeTiOx>DM CeTiOx, and the 3DOM-m CeTiOx shows an excellent catalytic activity, with more than 90% NO conversion in the range of 250–400 °C at a GHSV of 60000 h−1. The characterization of catalysts by XRD, SEM, BET, NH3-TPD and in-situ DRIFTS indicates that the surface area is not the dominant factor determining the catalytic activity of CeTiOx. 3DOM-m CeTiOx has a highly ordered macroporous-mesoporous structure and abundant Bronsted acidic sites, thereby improving the denitrification activity. The NH3-SCR reaction over the 3DOM-m CeTiOx mainly follows the L-H and E-R mechanisms.

Coprecipitation and hydrothermal synthesis of CaO from dolomite in the presence of Sapindus rarak extract for biodiesel production: catalysts characterization and optimization.

High-purity CaO cubic crystallites extracted from limestone exhibited excellent activity as base catalysts for waste cooking oil (WCO) conversion into biodiesel. Saponin from Sapindus rarak extract acted as a surfactant in CaO extraction and transformation into well-defined cubic microcrystallites. The application of saponin from Sapindus rarak extract as a surfactant for CaO production results in a high level of CaO purity and particle size reduction compared to directly calcined limestone (CaO-MgO). The catalytic activity was evaluated on CaO from hydrothermal and co-precipitation synthesis, MgO and CaO-MgO derived from limestone, giving hydrothermal CaO catalysts enhanced biodiesel yield. Optimization of transesterification conditions using Box Behnken Design response surface methodology achieved 92.40% biodiesel yield at 65 °C, 3 h reaction time and when using 5% of CaO catalysts.

Study of promoted Cu/ZnO and Cu/ZrO2 catalysts for dimethyl adipate hydrogenolysis

Two supports (ZnO, ZrO2) and four promoters (Al2O3, ZnO, CoOx, NiO) were investigated to design environmentally-friendly Cu-based hydrogenolysis catalysts. Both catalyst characterization and activity in dimethyl adipate hydrogenolysis were described....

Revisiting ion-pair interactions in phase transfer catalysis: from ionic compounds to real catalyst systems.

Ion-pairing is a fundamental phenomenon that significantly influences phase-transfer catalysis. In this study, we conduct a comprehensive investigation of ion-pair interactions, aiming to establish a comprehensive understanding of their nature and implications. The study begins with the examination of polar ionic compounds to define the concept of an ion-pair in the context of phase-transfer catalysis. Subsequently, a diverse range of ion-pair catalyst models were explored to gain insight into the factors governing their interactions. Finally, the focus shifts towards the characterisation of real phase-transfer catalysts, bridging the gap between theoretical models and practical applications. Through a combination of computational approaches and theoretical analysis, this work provides valuable insight into the nature of ion-pair interactions within phase-transfer catalysis fields.

Characterization, Application and Optimization of Low Cost Heterogeneous Catalyst in the Production of Biodiesel Using Waste Vegetable Frying Oil

Characterization, Application and Optimization of Low Cost Heterogeneous Catalyst in the Production of Biodiesel Using Waste Vegetable Frying Oil

A Comprehensive Experiment Based on Electrocatalytic Nitrate Reduction into Ammonia: Synthesis, Characterization, Performance Exploration, and Applicable Design of Copper-based Catalysts

A Comprehensive Experiment Based on Electrocatalytic Nitrate Reduction into Ammonia: Synthesis, Characterization, Performance Exploration, and Applicable Design of Copper-based Catalysts

Recent advances in the synthesis, characterization, and catalytic consequence of metal species confined within zeolite for hydrogen-related reactions

We summarize and discuss the progress in the synthesis and characterization of zeolite-encapsulated metal catalysts, and the consequences of encapsulation in terms of activity, selectivity, and stability for the hydrogen-related catalytic reactions.

Preparation of Co-based nanoboxes as Oxygen Electroreduction Nanoreactor

Investigating the constituents of active catalysts is crucial for the advancement of ORR electrocatalysts that are both high in performance and stability, aiming to supplant the expensive platinum-based alternatives, yet this task continues to be a persistent challenge. Firstly, HA nanoplates of hydroxyapatite nanocontainers were decorated with zeolite imidazole salt framework (named as HA-ZIF) by hydrothermal synthesis method, and then Co-based imidazole zeolite framework decorated with Zn group was synthesized by simple self-assembly method, and it was calcined at different temperatures. Finally, the ORR performance obtained samples (named as Co2(PO4)2@NC-800, Co2(PO4)2@NC-900 and Co2(PO4)2@NC-1000) was tested by cyclic voltammetry (CV) and linear scanning voltammetry (LSV), and the morphological and structural characterization of composite catalysts at different temperatures were analyzed by PXRD and SEM. It was found that the Co2(PO4)2@NC-900 had the best catalytic performance. The study presents a flexible approach for creating versatile non-precious catalysts applicable to various energy-related electrocatalytic processes.

Alkaline earth modified activated carbon supported Cu catalysts with enhanced selectivity in the hydrogenation of dimethyl oxalate to methyl glycolate.

In this work, the effect of alkaline earth metal modification on the catalytic performance of activated carbon supported Cu was investigated. The experimental results showed that the introduction of Ca and Sr improved the selectivity of methyl glycolate (MG) during hydrogenation of dimethyl oxalate (DMO) in gas phase. The optimal loading amount of Ca was 0.1 wt%, and under the optimal conditions (temperature 240 °C, pressure 2 MPa, hydrogen-ester ratio of 80, feedstock 15% DMO methanol solution, and WLHSVDMO = 0.9 h-1) the selectivity of MG was as high as 94%, and the conversion of DMO was 97%. The optimal loading of Sr was 0.2 wt% with MG selectivity up to 89% and DMO conversion of 98%. The results of catalyst characterization showed that both Ca and Sr modifications were beneficial to further reduce the particle size of Cu, improve the dispersion of Cu, increase the basicity of the catalyst, and improve the stable presence of Cu+ during the reaction process. Cu+ was beneficial to the stabilization of the MG species, in which Cu+ accounted for more in the Ca-modified catalysts Cu+/(Cu+ + Cu0) = 0.65, and in the Sr-modified ones Cu+/(Cu+ + Cu0) = 0.51. Therefore, both Ca and Sr modified catalysts showed improvement in the selectivity of MG.

Improved phenol degradation by catalytic wet air oxidation on the Co3O4 spinel catalysts supported on SBA-15 modified with TiO2

The removal of phenol from aqueous industrial effluents by catalytic wet-air oxidation (CWAO) is a challenging process that requires novel catalysts resistant to leaching of the active phases during residence time in a batch reactor. In this sense, this work demonstrated that this can be archived with the catalyst having the spinel phase Co3O4 supported on mesoporous silica SBA-15 doped with an optimized amount of TiO2 (3 wt%). In the phenol CWAO reaction carried out at 160 °C and 10 bar O2, this best Co3O4/TiO2/SBA-15 catalyst showed an increase of phenol conversion from 49.0 % to 68.3 % and of CO2 selectivity from 87 % to 98 %. The extensive catalyst characterization and overall activity results indicated that this was related to the strength and nature of the acid sites and the oxidation states of the cobalt oxide phases. Combined factors influenced the final behaviour of the catalyst, such as its intrinsic activity, dispersion of the active phase, inhibition of CoSiO4 phase formation, high Lewis acidity and the large amount of active Co3O4 spinel phase. The presence of TiO2 nanoparticles (NPs) decorating the support surface improved the stability of the catalyst by inhibiting the leaching of cobalt species during the reaction. After three reaction cycles, the most efficient Co/3Ti/S15 catalyst showed high CO2 selectivity (∼92.7 %) and low selectivity towards carboxylic acid (∼5.3 %) and polyphenolic compounds (∼2%). It is proposed that surface oxidation is the rate-determining step in the CWAO reaction over TiO2/SBA-15-supported Co3O4 spinel catalysts.

Utilization of Sulfonated Natural Zeolite as Catalyst for Glycerolysis Monooleate: Thermodynamic and Kinetic Study

The development and production of alternative fuels such as biodiesel that continues to be carried out further increases glycerol as a by-product of the biodiesel process. The accumulation that continues to occur will cause a decrease in the price of glycerol. To solve this problem, glycerol is reprocessed into its derivative products, one of which is Glycerol Mono Oleate (GMO). In this study, natural zeolite was modified using a sulfonation process. The results of catalyst characterization based on FTIR indicate that the modification in natural zeolite was successful when the catalyst had the expected functional groups. The thermodynamic parameters (ΔH, ΔS, ΔG) are determined for this reaction using the Eyring equation. The reaction fits with the pseudo-2nd order kinetic model. The activation energy of the esterification reaction using sulfonated zeolite is reported as 37.855 kJ/mol. The result shows that the best variable to produce GMO is the reaction at a temperature of 220oC with the conversion value was 95.00%.

Bimetallic platinum rhenium catalyst for efficient low temperature dehydrogenation of perhydro benzyltoluene

H2 release from the liquid organic hydrogen carrier perhydro benzyltoluene (H12-BT) was accelerated using bimetallic Pt–Re/Al2O3 catalysts. An optimum Pt : Re ratio was identified and catalysts characterisation provided insight on Pt–Re interaction.

Fe–Mo/Kaolin Catalyst Optimization and Characterization for the Production of Carbon Nanotube Using the Wet Impregnated Method

Abstract: The synthesis of the bimetallic Fe–Mo/kaolin catalyst for carbon nanotube (CNT) production involves the pre-calcination and calcination processes, employing the wet impregnated method. In the pre-calcination stage, we explored the effects of synthesis parameters such as oven drying temperature, mass of kaolin, and heating time using a 23 factorial experimental design, ultimately obtaining the highest yield sample. In the calcination phase, the effect of temperature and heating time using a 22 factorial experimental design was examined. The as-prepared nanoparticles were characterized by scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDS), thermogravimetric analysis (TGA), differential thermal analysis (DTA), x-ray diffraction (XRD), and Brunauer-Emmet-Teller (BET). SEM/TGA revealed a well-dispersed metallic particle on the kaolin support and its ability to maintain high thermal stability. XRD analysis of the catalyst confirmed its crystal nature and the presence of mixed oxides of different intensities, conducive to CNT growth. The optimum yield obtained after oven drying was 75.25%. At the optimum calcination temperature of 300° C and calcination time of 16 hours, BET analysis determined the surface area and pore volume. For kaolin, the surface area and pore volume were 1.932x102 m2/g and 1.762x10-1 cc/g, respectively. The optimal calcine sample showed increment for both the surface area (3.103 x102 m2/g) and the pore volume (2.459 x10-1cc/g) making it more suitable for CNT production. Lastly, statistical analysis showed that heating time, calcination time, temperature, and mass of kaolin have a significant influence on the catalyst yield in CNT. Keywords: catalyst, wet impregnation, optimization, carbon nanotubes.

Regulating local electron density of Cu active site by the lamellar structure of hydrotalcite for selective-hydrogenation of furfural

Rational modulation of the local electron density of Cu active site is the key to improve the efficient transfer hydrogenation (CTH) of furfural (FF) on the surface of catalysts with low Cu-loadings. In this paper, a CuMgAl/LSC catalyst with lower Cu content (<3.5 %wt) was prepared by using porous biochar as a carrier and exploiting the local dispersion and electron-modulation effects of structural elements of hydrotalcite laminates. CTH experiments showed that the conversion of FF and the selectivity of FA could reach more than 99.0 % in isopropanol solution at 170 °C and within 1 h. Catalyst characterization and density functional theory (DFT) calculations demonstrated that the Cu(I) species was the main active site during the CTH process of FF. Doping laminate metals (i.e., Mg, Al) can not only form electron-rich centers by local electron modulation of the active site through the coordination structure of Cu-O-M, lowering its D-band center and achieving higher catalytic activity; Due to the Jahn-Teller effect, the local spatial misalignment of Cu sites formed, which can reduce the risk of over-hydrogenation and improve the FA selectivity. In addition, it can be also found that the Coulomb tractive force of reactive intermediates can lead to the crystal surface reconstruction and structure deterioration of Cu species. The new discovery of the deactivation mechanism can provide a reference for the future design of copper-based catalysts in CTH process of FF.

(Invited) 25 Years of the Thin-Film Rotating Disk Electrode Technique

Twenty-five years ago, in summer 1998, the first paper introducing the thin-film rotating disk electrode (TFRDE) method was published in the Journal of the Electrochemical Society [1]. At this time, we demonstrated that by preparing a thin layer of a supported Pt/Vulcan catalyst mixed with a small amount of Nafion could reliably be coated on top of a glassy carbon disk, electrochemical reactions like the hydrogen oxidation reaction could be measured on an RDE taking advantage of the well-known mass-transport conditions of an RDE. By keeping the layer thickness in the range of 1 micrometer, additional mass-transport resistances induced by the catalyst layer/Nafion film became negligible. That is, all equations valid on an RDE could be applied without modification. Further work on the oxygen reduction reaction by using the TF Rotating Ring-Disk electrode allowed detecting peroxide formation on a supported catalyst [2]. Both publications grounded the path for catalyst development in fuel cell. The method has been used since then as a standard method for catalyst screening and characterization in both academia and industries. In addition, many researchers improved the TFRDE method within their research. The application span of the TFRDE developed from fuel cell research, oxidation of small organic molecules, to work on Li-O2 batteries, water electrolysis, and CO2 reduction.This presentation will offer a journey over the last 25 years and the application of the TFRDE technique in catalyst development and characterization.[1] T.J. Schmidt, H.A. Gasteiger, G.D. Stäb, P. Urban, D.M. Kolb, R.J. Behm Characterization of High-Surface-Area Electrocatalysts Using a Rotating Disk Electrode Configuration J. Electrochem. Soc. 145 (1998) 2354-2358 [2] U.A. Paulus, T.J. Schmidt, H.A. Gasteiger, R.J. Behm Oxygen Reduction on a High-Surface Area Pt/Vulcan Carbon Catalyst: A Thin-Film Rotating Ring-Disk Study J. Electroanal. Chem. 495 (2001) 134-145 [3] T.J. Schmidt, H.A. Gasteiger Rotating Thin-Film Method for Supported Catalysts, in Handbook of Fuel Cells: Fundamentals, Technology and Applications, Vol. 2 Part 3, W. Vielstich, H.A. Gasteiger, A. Lamm (Eds.), John Wiley & Sons, New York, 316-333 (2003)

Enhanced lignin hydrogenolysis through synergy-induced bimetallic NiCu catalyst for chemocatalytic production of aromatic monomers

Bimetallic catalysts are widely favored for catalytic reactions due to their superior performance and cost-effectiveness. This study delves into the utilization of a non-noble bimetallic catalyst, NiCu/C, in the hydrogenolysis of lignin to yield valuable aromatic monomers. Under optimized temperature, this catalyst achieves an impressive 92.4% conversion of lignin into liquid products, yielding 17.7 wt% of monomers. These results outperform the performance of the monometallic catalysts (Ni/C and Cu/C). To gain insight into the detailed catalytic reaction mechanism, the catalysts underwent advanced characterization techniques such as N2 physisorption, XRD, XPS, H2-TPR, and TEM, which provided information on their textural properties, structure, oxidation states, and more. The findings clearly highlight the significant role played by the synergistic interaction between Ni and Cu metallic species in bolstering the H2 adsorption capacity, thereby resulting in elevated catalytic hydrogenolysis activity. Characterization of the lignin hydrogenolysis products was also conducted to understand the effects of bimetallic and monometallic catalysts. These findings align with the catalyst characterizations and lend further support to the significant enhancement in catalytic hydrogenolysis attributed to the synergistic impact of the NiCu/C catalyst.