Conventional Impregnation Method Research Articles

Synthesis effects on activity and stability of Pt-CeO2 catalysts for partial oxidation of methane

The objective of this study is to explore the effect of catalyst synthesis procedure on the activity of catalysts for partial oxidation of methane. In this aspect, Pt-nanoparticles supported CeO2 catalysts were prepared by Hydrothermal, co-precipitation, impregnation and by controlled deposition of platinum nanoparticles on hydrothermally prepared cerium oxide. Prepared catalysts were characterized by BET-surface area, X-ray diffraction, H2-Chemisorption, Transmission electron microscopy, Temperature programmed reduction, Inductively coupled plasma atomic emission spectroscopy and X-ray photoelectron spectroscopy. The study revealed that the catalyst preparation procedure plays a very crucial role on morphology, catalyst particle size, metal support interaction and activity of the catalysts. Catalytic activities were tested for partial oxidation of methane in the temperature range 350–800°C. The study revealed that the catalyst prepared by controlled deposition of Pt-nanoparticles on hydrothermally prepared cerium oxide showed better activity for partial oxidation of methane compared to the catalysts prepared by other conventional methods. Controlled deposition of Pt-nanoparticles generated better metal-support interaction compared to the catalysts prepared by conventional hydrothermal, co-precipitation and impregnation methods. All the catalysts showed excellent coke resisting ability but the deactivation of most of the catalyst was found to be caused by catalyst particles sintering and re-oxidation of the Pt particles during catalysis.

Preparation, characterization, and catalytic performances of cobalt catalysts supported on KIT-6 silicas in oxidative desulfurization of dibenzothiophene

Sulfur-containing compounds in oils are harmful to the ecosystem whose cost-effective removal is still a challenge. In this study, novel heterogeneous catalysts of cobalt supported on KIT-6 mesoporous silicas were prepared and evaluated for oxidative desulfurization (ODS) under ambient conditions using cyclohexanone peroxide (CYHPO) as the oxidant. The model oil was obtained via dissolving DBT in the n-octane. The conventional wet impregnation method was applied for the preparation of the catalysts, and cobalt nitrate was used as the precursor. The catalysts were characterized by XRD, N2-physisorption, FT-IR, TGA, SEM/TEM and XPS. Then their catalytic activities in total oxidation of dibenzothiophene (DBT) were evaluated at various conditions. DBT conversion by this heterogeneous ODS system reached 98.68%. Co/KIT-6 catalysts showed high ODS activity due to Ia3d mesoporous structure resulting in better cobalt dispersion, higher activity of Co, and faster diffusion of reactant and products. The Box-Behnken design showed that the optimum values for the conversion of DBT were 93°C (oxidation temperature), 1.6×10−1g (catalyst amount) and 5.7 (O/S molar ratio), respectively. The inhibitory effect of quinoline on ODS was higher than carbazole and indole, adding quinoline into model oil under same conditions led to a decrease of the conversion of DBT from 98.68% to 65.67% when the concentration of quinoline increased from 160ppm to 4845ppm. Kinetics data correlated well with the pseudo-first-order equation. These data showed that this novel Co/KIT-6 catalysis system has the potential to be applied in ODS from oils.

An Efficient and Reusable Embedded Ru Catalyst for the Hydrogenolysis of Levulinic Acid to γ-Valerolactone.

To achieve a higher activity and reusability of a Ru-based catalyst, Ru nanoparticles were embedded in N-doped mesoporous carbon through a hard-template method. The catalyst showed excellent catalytic performance (314 h-1 turnover frequency) and recyclability (reusable five times with 3 % activity loss) for the hydrogenolysis of levulinic acid to γ-valerolactone. Compared with the mesoporous carbon without N-doping and conventional activated carbon, the introduction of N-dopant effectively improved the dispersion of Ru nanoparticles, decreased the average size of Ru nanoparticles to as small as 1.32 nm, and improved the adsorption of levulinic acid, which contributed to the increase in the activity of the catalyst. Additionally, the embedding method increased the interaction between Ru nanoparticles and carbon support in contrast with the conventional impregnation method, thus preventing the Ru nanoparticles from migration, aggregation, and leaching from the carbon surface and therefore increasing the reusability of the catalyst.

The impact of the hydrodechlorination process on the physicochemical properties of bimetallic Ag-CuBeta zeolite catalysts

Beta zeolites with two Si/Al ratios of 17 and 1300 were used for synthesis of Ag2.0Cu2.0HAlBeta and Ag2.0Cu2.0SiBeta zeolites by conventional wet impregnation and two-step postsynthesis methods, respectively. The calcination of Ag2.0Cu2.0HAlBeta and Ag2.0Cu2.0SiBeta at 773 K for 3 h in air led to formation of C-Ag2.0Cu2.0HAlBeta and C-Ag2.0Cu2.0SiBeta. After reduction at 873 K for 3 h in flowing 10% H2/Ar, red-C- Ag2.0Cu2.0HAlBeta and red-C-Ag2.0Cu2.0SiBeta were obtained and investigated as the catalysts in gas phase hydrodechlorination of 1,2-dichloroethane at atmospheric pressure, at relatively low reaction temperature (523 K). The state of silver and copper in catalysts at different stages of their biography was characterized by low-temperature N2 sorption, temperature – programmed reduction (TPR), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and temperature-programmed hydrogenation (TPH). We have shown that the state of silver and copper species change under HDC conditions. After catalytic run both agglomeration of metal particles and their re-dispersion took place. According to TPH, XRD and XPS measurements we postulate that the cause of this phenomenon is the formation of chlorine containing species in spent zeolite catalysts.

Creation of Pd/Al2O3 Catalyst by a Spray Process for Fixed Bed Reactors and Its Effective Removal of Aqueous Bromate

Palladium nanoparticles were grown on sub-millimeter activated Al2O3 particle support by spraying H2PdCl4 solution evenly onto the support, followed with a thermal reduction under H2 atmosphere. Compared with its counterpart created by the conventional impregnation method, the Pd/Al2O3 catalyst created by the spray process could enrich the existence of active Pd nanoparticles on the surface of the catalyst support and increase their degree of dispersion, resulting in a much higher activity in the catalytic reduction of bromate in water. The effect of Al2O3 support particle size on the bromate removal rate was also investigated, which demonstrated that smaller support particle size could have higher activity in the catalytic reduction of bromate in water because of its larger exposed surface. This Pd/Al2O3 catalyst could be easily used in the fixed bed reactor due to its large support size and demonstrated excellent stability in the catalytic reduction of bromate in mineral water. This Pd/Al2O3 catalyst also exhibited a good catalytic reduction performance on azo dyes as demonstrated by its effective catalytic hydrogenation of methyl orange. Thus, catalysts prepared by the spray method developed in this work could have the potential to be used in fixed bed reactors for various water treatment practices.

Improvement of Cobalt Dispersion on Co/SBA-15 and Co/SBA-16 Catalysts by Ultrasound and Vacuum Treatments during Post-Impregnation Step

The Co/SBA-15 and the Co/SBA-16 catalysts having 20 wt% of cobalt were prepared by the conventional impregnation method. Then, the post-impregnation treatments including vacuum and ultrasound treatments were applied. The synthesized catalysts were characterized by means of N 2 physisorption, small angle X-ray diffraction (SAXRD), wide angle X-ray diffraction (XRD), scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDX), transmission electron microscopy (TEM), and temperature-programmed reduction (TPR). The results show that the synthesized SBA-15 had hexagonal structure and the synthesized SBA-16 had the cubic structure. The vacuum and the ultrasound treatments after incipient wetness impregnation can apparently enhance the dispersion of cobalt on the SBA-15 catalysts due to the decrease of the metal crystallite size. However, only the vacuum treatment was suitable for the Co/SBA-16. After reduction, no cobalt-silicate compound was detected based on XRD measurement. Both post-impregnation treatments can also decrease the metal-support interaction resulting in increased activity for CO 2 hydrogenation under methanation.

Effect of mesoporosity of bimetallic Ni-Ru-Al2O3 catalysts for hydrogen production during supercritical water gasification of glucose

A well-known problem with metal supported alumina catalysts during gasification processes for H2 formation is catalyst deactivation by coke formation and pore plugging. Poorly controlled catalyst structure with low surface area and microporous structure also accounts for low catalyst activity. This work investigated bimetallic Ni-Ru/Al2O3 catalysts that are both effective and durable for glucose gasification in supercritical water with minimal coke formation. Both non-ionic (Pluronic P-123) and cationic (CTAB) templates were examined for mesoporous alumina synthesis with Ni and Ru loadings and compared with a conventional incipient impregnation method. Gas formation during SCWG catalysis was monitored for hydrogen formation while the catalysts were examined both before and after reaction by a variety of physico-chemical techniques including BET surface area, BJH pore size analysis, XRD, TG-DTA, TPR, TPO, Raman spectroscopy & TEM microscopy. The results showed that templating helped disperse both Ni and Ru particles homogeneously inside the pores of mesoporous Al2O3 catalysts; whereas the impregnated catalyst gave poorer dispersion. Comparing with the impregnation method, a six-fold increase of BET surface area was observed using the one-pot synthesis method. Hydrogen production during glucose gasification increased by 25mol% for both templated catalysts, with the CTAB catalyst showing slightly higher activity. This method provided insignificant coke deposition indicating that the new Ru-Ni/Al2O3 templated catalyst is promising for the development of hydrogen production for an emerging biorefinery.

Oxidative desulfurization of thiophene derivatives with H2O2 in the presence of catalysts based on MoO3/Al2O3 under mild conditions

The catalysts based on MoO3/Al2O3 were synthesized and tested using aqueous hydrogen peroxide as the oxidant in the oxidative desulfurization of thiophene, benzothiophene (BT) and dibenzothiophene (DBT) into the corresponding sulfones. Among catalysts tested, 15%(MoO3–WO3)/Al2O3 prepared by a conventional impregnation method was considerably active for the oxidation of thiophene, BT and DBT, which could achieve higher than 99.2% conversions at lower reaction temperature (≤338 K). The use of hexadecyltrimethyl ammonium bromide as the phase-transfer reagent in small amounts could promote the reaction efficiently.

Bimetallic Pd-Cu/ZnO-Al2O3 and Pd-Cu/ZrO2-Al2O3 Catalysts for Methanol Synthesis

Monometallic copper and bimetallic palladium-copper catalysts supported on ZnO-Al 2 O 3 and ZrO 2 -Al 2 O 3 were prepared by conventional impregnation method and tested in methanol synthesis reaction under elevated pressure (3.5 MPa) in gradientless reactor at 220 °C. The physicochemical properties of prepared catalytic systems were studied using BET, X-Ray, TPR-H 2 , TPD-NH 3 techniques. The promotion effect of palladium on catalytic activity and selectivity of copper supported catalyst in methanol synthesis reaction was proven. The highest activity of this system is explained by the Pd-Cu alloy formation.

Pd catalyst supported on ZrO2‐Al2O3 by double‐solvent method for methane oxidation under lean conditions

AbstractThe Pd catalyst supported on the Zr0.5Al0.5O1.75 composite material was prepared by the conventional impregnation and double solvent impregnation method. The effects of preparation method on the catalytic properties of the Pd/Zr0.5Al0.5O1.75 catalyst for methane combustion have been investigated systematically. The measurement was evaluated in a multiple fixed‐bed continuous flow micro‐reactor by passing a gas mixture simulating the exhaust emissions from lean‐burn natural gas vehicles. The as‐prepared catalysts were characterized by CO chemical adsorption, transmission electron microscopy (TEM), hydrogen‐temperature programmed reduction (H2‐TPR),and X‐ray photoelectron spectroscopy (XPS) measurements. The results of TEM and CO chemisorption showed that the introduction of double solvent during the preparation of Pd/Zr0.5Al0.5O1.75 was beneficial for the dispersion of Pd nanoparticles and obtained superior resistance to the sintering of Pd on the surface of Zr0.5Al0.5O1.75. The H2‐TPR measurements demonstrated that the double solvent method increased the reducibility of the Pd catalyst. The XPS results further indicated that more active surface oxygen species also can be formed on the catalyst prepared via double solvent process. Thus, this catalyst exhibited better catalytic performance and hydrothermal aging resistance in the methane oxidation compared to its analogues with the same Pd content prepared by the conventional impregnation method.

Syngas production through methane oxy‐steam reforming over a Ni/SiO 2 nanocatalyst prepared by a modified impregnation method

Synthesis gas can be converted into a number of important energy carriers and fuels and it is playing a growing role in the energy sector. In this work oxy-steam reforming of methane was performed over a modified 5%Ni/SiO2 catalyst in a fixed bed reactor at atmospheric pressure with the aim of producing syngas with high yield. The modified catalyst was synthesised by oleylamine-assisted impregnation method and characterised by X-ray diffraction, Fourier-transformed infrared spectroscopy, N2 physisorption measurement, temperature-programmed H2 reduction and transmission electron microscopy. For the comparative study, an unmodified 5%Ni/SiO2 catalyst was also prepared by conventional impregnation method. The reaction test results demonstrated that the value of methane conversion and the yield of syngas over the modified catalyst were almost 2 and 2.5 times more than ones over the unmodified catalyst. During the 10 h stability test, catalytic activity of the modified catalyst remained at high and constant values (92.5%) while the unmodified catalyst was rapidly deactivated during the stability test. The effective catalytic performance of the modified catalyst was related to the nanosize nickel species that interacted with the silica support strongly.

In situ formation of Ru nanoparticles on La1−x Sr x TiO3-based mixed conducting electrodes and their application in electrochemical synthesis of ammonia using a proton-conducting solid electrolyte

In situ formation of highly dispersed 2–5 nm Ru nanoparticles was successfully achieved in highly Ru-doped (40% Ru) perovskite cathode material, Ru-doped La0.3Sr0.6TiO3 (LSTR), used for electrochemical ammonia synthesis in a proton-conducting fuel cell (PCFC). Highly dispersed Ru nanoparticles were observed by exsolution of doped Ru from the B-site in the LSTR perovskite lattice under PCFCs operating conditions, that is, a reducing atmosphere, without agglomeration, which is difficult to achieve with a conventional impregnation method. The particle size and dispersion were successfully controlled by reduction temperature and Ru doping amount. The optimized microstructure was finally adopted for the electrochemical synthesis of ammonia with BaCe0.9Y0.1O3 solid electrolyte at 500 °C. Ammonia formation using a 40% Ru-doped LSTR (LSTR40) cathode was observed by applying cathodic overpotentials. The maximum ammonia formation rate using the LSTR40 cathode was 3.8 × 10−12 mol s−1 cm−2 at −0.1 V. The results suggest that Ru nanoparticles exsoluted from the LSTR perovskite act as a active site effectively for the electrochemical reaction.

Activated Carbons Prepared through H3 PO4 -Assisted Hydrothermal Carbonisation from Biomass Wastes: Porous Texture and Electrochemical Performance.

Hydrothermal treatment of biomass in the presence of phosphoric acid is proposed for the production of activated carbons (ACs). Interestingly, H3 PO4 promotes the fixation of carbon atoms in the solid during hydrothermal treatment, which renders higher preparation yields than those of the conventional impregnation method. Upon carbonisation of the resulting hydrochars at 450 °C, a notable development of porosity is achieved by using a low amount and concentration of phosphoric acid; these conditions are not adequate for conventional activation. The viability of this process for the sustainable production of ACs has been successfully checked in four biomasses of different composition and structures, and ACs of surface areas above 2000 m2 g-1 and tuneable pore size distribution have been obtained. Electrochemical characterisation of ACs prepared at 750 °C in 1 m H2 SO4 demonstrates that capacitances of approximately 150 F g-1 with acceptable rate performance can be obtained through this simple method.

Functional rice husk as reductant and support to prepare as-burnt Cu-ZnO based catalysts applied in low-temperature methanol synthesis

A novel method, that the precursor is burnt in argon without further reduction to directly prepare metallic catalyst, is developed using low-valued by-product. Rice husk not only contributed as catalyst support, but also as reductant and fuel. The XRD, TPR and TG-DTA analysis prove that Cu phase in the as-burnt catalyst is almost reduced to metallic Cu0. The as-prepared catalysts exhibit higher activity and methanol selectivity than those prepared by a conventional impregnation method. This method may open a new way to prepare metallic catalysts without further reduction, especially for some catalytic reactions promoted by K, Ca, Mg and Mn.

High iso-alkanes production from palmitic acid over bi-functional Ni/H-ZSM-22 catalysts

Bi-functional Ni/H-ZSM-22 catalysts with melt infiltration, incipient wetness impregnation and wet impregnation methods, were used to catalyze palmitic acid. Compared to parent zeolite, there were decrease of relative crystallinity, some blockage effects of micro pores and less strong acid sites after Ni loading. The complete conversion of palmitic acid and 100% alkanes selectivity were achieved at lower temperature (200°C). No deactivation was observed in five recycle reaction, indicating the excellent catalytic performance and stability of Ni/H-ZSM-22 catalysts. Higher reaction temperature (240–260°C), more iso-alkanes/n-alkanes formed, while less C16/C15 produced. Additionally, the catalysts prepared by melt infiltration were more inclined to HDO routes and produced more iso-alkanes (0.8mol ratio of iso-alkanes/n-alkanes) than their counterparts prepared by conventional impregnation methods.

Effect of crystalline structure and pore geometry of silica based supported materials on the catalytic behavior of metallic nickel particles during methane decomposition to COx-free hydrogen and carbon nanomaterials

This paper aims to study the effect of crystalline structure and pore geometry of some silica supported materials on the catalytic performance of the active Ni component. Therefore, 40 wt.% Ni loaded ZSM-5(25), ZSM-5(400) and amorphous silica (AS) catalysts were prepared by conventional impregnation method and evaluated as catalysts for methane decomposition to COx-free hydrogen production. Several techniques such as XRD, BET, HRTEM, TPR, TGA and Raman spectroscopy were performed for characterizing the fresh and reacted catalysts. The results revealed that the crystalline structure and pore geometry of the supports play an essential role on the catalytic efficiency in terms of H2 yield and stability as well as on the morphology of as-deposited carbon material. The characterization results showed that the particle size and dispersion of NiO were strongly influenced by the crystalline structure of the support. The channels and cages of both zeolite samples could inhibit the agglomeration of NiO particles during the calcination and catalytic runs. On the other hand, the amorphous structure of SiO2 induced serious aggregation of NiO particles, leading to a remarkable inhibition in the activity. TEM images showed that different types of carbon nanomaterials were obtained on the catalysts depending on the crystalline nature of the support. Filamentous carbon was formed on both Ni/ZSM-5(25) and Ni/ZSM-5(400) catalysts, whereas graphene nanosheets were obtained over Ni/SiO2 catalyst.

One-pot synthesis of Pd nanoparticles on ordered mesoporous Al2O3 for catalytic hydrogenation of 2-ethyl-anthraquinone

Pd/Al2O3 catalysts were synthesized via one-pot evaporation-induced self-assembly and hydrothermal methodology, and the conventional impregnation method. XRD, N2 adsorption-desorption and TEM showed that the one-pot synthesized catalyst, especially evaporation-induced self-assembly one (EISA-Pd/Al2O3) possesses the large specific surface area, ordered mesopores with the narrow pore size distribution and well-dispersed Pd particles encapsulated inside the mesopores of Al2O3. Catalytic hydrogenation of 2-ethyl-anthraquinone (EAQ) to form anthrahydroquinone at 0.3MPa and 70°C showed that EISA-Pd/Al2O3 exhibits superior performance, with the improvement of 50% in the selectivity and 82% in the activity compared with the impregnated catalyst. The high selectivity is due to the increased electron density of Pd particles and lower amount of acid sites measured by NH3-TPD, which had an inhibitory effect on the formation of the by-product and degradation products. The high activity could be ascribed to the higher proportion of linear carbonyls which has a positive correlation with low-coordinated Pd atoms, characterized by in situ FTIR. DFT calculations revealed that the high activity of the defective Pd surface with low-coordinated Pd atoms is due to the larger adsorption energy and longer length of carbonyl bond of EAQ adsorbed on it than on the perfect Pd surface.

Preparation of PdCu Alloy Nanocatalysts for Nitrate Hydrogenation and Carbon Monoxide Oxidation

Alloying Pd with Cu is important for catalytic reactions such as denitrification reaction and CO oxidation reaction, but understanding of the catalyst preparation and its correlation with the catalyst’s activity and selectivity remains elusive. Herein, we report the results of investigations of the preparation of PdCu alloy nanocatalysts using different methods and the catalytic properties of the catalysts in catalytic denitrification reaction and CO oxidation reaction. PdCu alloy nanocatalysts were prepared by conventional dry impregnation method and ligand-capping based wet chemical synthesis method, and subsequent thermochemical activation as well. The alloying characteristics depend on the bimetallic composition. PdCu/Al2O3 with a Pd/Cu ratio of 50:50 was shown to exhibit an optimized hydrogenation activity for the catalytic denitrification reaction. The catalytic activity of the PdCu catalysts was shown to be highly dependent on the support, as evidenced by the observation of an enhanced catalytic activity for CO oxidation reaction using TiO2 and CeO2 supports with high oxygen storage capacity. Implications of the results to the refinement of the preparation of the alloy nanocatalysts are also discussed.

Enhancing tungsten oxide/SBA-15 catalysts for hydrolysis of cellobiose through doping ZrO2

The number of strong acid sites on a hydrolysis catalyst accessible by the bulky cellulose limits its efficiency in the conversion and utilization of biomass-based resources. In this work, high surface area WZr/SBA-15 catalysts (>400m2/g) were prepared by hydrothermal method and characterized using XRD, N2 adsorption, TEM, Raman, UV–vis, XPS and FTIR of pyridine adsorption. The results showed that doping a moderate amount of ZrO2 into the WO3/SBA-15 catalyst stabilized the tungstate species in the form of a polytungstate species as a result of the strong ZrOx-WOx interaction as well as increased the surface area of the catalyst. The resulting polytungstate species provided strong Brønsted acid sites for hydrolysis. Consequently, the cellobiose conversion was maximized at 5% ZrO2 loading, corresponding to a maximized surface area and density of Brønsted acid sites. This catalytic activity is significantly higher than that of a WO3/ZrO2 catalyst prepared using the conventional impregnation method, indicating the importance of mesoporous structure to the dispersion of active species and to the accessibility of the active sites by the bulky reactant. This result indicates that the density of the strong Brønsted acid sites with improved accessibility by the bulky reactant is essential to achieve a high hydrolysis activity.

Formation of Ru Shell on Co/Al2O3 by Galvanic Deposition Method and Its High Catalytic Performance for Three-Way Conversion

Abstract A supported Ru catalyst was prepared by a galvanic deposition (GD) of Ru on Co particles supported on Al2O3 (Ru/Co-GD). The structure and chemical state of Ru/Co-GD was characterized by using a pulsed CO chemisorption technique, STEM-EDS, XAFS, XPS, CO adsorption FT-IR spectroscopy, and temperature-programed reduction (TPR) method. It is indicated that Ru/Co-GD forms Ru shell on Co nanoparticles. Such a unique structure was not formed on Ru/Co/Al2O3 prepared by a conventional sequential impregnation method (Ru/Co-seq). The Ru shell of Ru/Co-GD showed higher reducibility than Ru species of Ru/Co-seq as well as higher than Ru/Al2O3. Owing to the Ru shell having high reducibility, Ru/Co-GD showed enhanced catalytic activity for NO–C3H6 reaction. In addition, Co oxide on Ru/Co-GD exhibited high catalytic activity for CO and C3H6 oxidation. As a result, Ru/Co-GD showed superior performance for NO–C3H6–CO–O2 reaction compared to the conventional catalysts. The Ru shell structure also contributed to the suppression of Ru vaporization.