Modified Impregnation Method Research Articles

Supported Bimetallic AuPd Nanoparticles as a Catalyst for the Selective Hydrogenation of Nitroarenes.

The solvent-free selective hydrogenation of nitrobenzene was carried out using a supported AuPd nanoparticles catalyst, prepared by the modified impregnation method (MIm), as efficient catalyst >99% yield of aniline (AN) was obtained after 15 h at 90 °C, 3 bar H2 that can be used without any further purification or separation, therefore reducing cost and energy input. Supported AuPd nanoparticles catalyst, prepared by MIm, was found to be active and stable even after four recycle experiments, whereas the same catalyst prepared by SIm was deactivated during the recycle experiments. The most effective catalyst was tested for the chemoselective hydrogenation of 4-chloronitrobenzene (CNB) to 4-chloroaniline (CAN). The activation energy of CNB to CAN was found to be 25 kJ mol−1, while that of CNB to AN was found to be 31 kJ mol−1. Based on this, the yield of CAN was maximized (92%) by the lowering the reaction temperature to 25 °C.

Effective conversion of cellobiose and glucose to sorbitol using non-noble bimetallic NiCo/HZSM-5 catalyst

The tandem hydrolysis and hydrogenation of saccharides into sorbitol is an especially attractive reaction in the conversion of biomass. Here, an economical and efficient bimetallic catalyst for the transformation of glucose and cellobiose into sorbitol is reported. Non-precious metal based catalysts such as NiCo, Ni, and Co, were prepared via modified impregnation method, and NiCo/HZSM-5 showed superior performance for the synthesis of sorbitol (86.9% from cellobiose, 98.6% from D -glucose). Various characterizations, such as Brunner-Emmet-Teler (BET), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), confirmed that NiCo alloy formed and highly dispersed in NiCo/HZSM-5 catalyst. The high performance of fabricated catalyst would be attributed to the formation of nickel-cobalt alloy over HZSM-5 zeolite surface. High temperature and H2 pressure were favorable for the tandem hydrolysis and hydrogenation reaction. Besides, the reaction pathway was also proposed based on the kinetics study. Cellobitol was detected as the intermediate in the reaction mixture. Furthermore, in the catalytic stability study, it was found that active metal species of NiCo/HZSM-5 were stable. The deactivation of catalyst would be due to the covering of acidic sites over NiCo/HZSM-5.

Effect of ammonia‐derived species on visible‐light photocatalytic activity of Au supported on amorphous TiO2 activated by plasma

Amorphous TiO2 supported Au photocatalyst (Au/AmT) is prepared via modified impregnation method with ammonia washing, followed by cold plasma treatment to activate the photocatalysts. Residual ammonia ([NH3]s) is formed due to the hydrogen bond between surface OH groups on AmT and ammonia. The [NH3]s suppressed the reduction of Auδ+ and occupied active sites, leading to a poor activity of as‐prepared Au/AmT. The performance of cold plasmas in activation strongly depends on discharge gases. N2 and O2 plasmas not only cannot reduce Auδ+ into Au0 but also convert [NH3]s into poisoning species [NOy]s during activation. H2 plasma with a strong reducibility can simultaneously reduce Auδ+ and remove [NH3]s, thus enabling Au/AmT to achieve the highest visible‐light photocatalytic activity in CO oxidation.

Sacrificial Carbon Strategy toward Enhancement of Slurry Methanation Activity and Stability over Ni-Zr/SiO2 Catalyst

Mesoporous silica-supported Ni-Zr catalysts prepared via the modified impregnation method by applying different solvents and calcination atmospheres were employed for CO methanation in a slurry-bed reactor. The results show that the glycerol-impregnated Ni-Zr/SiO2 catalyst exhibited higher specific surface area and Ni species dispersion and more intensive nickel–support interaction than the water-impregnated one and thus enhanced the catalytic activity and stability. Furthermore, the carbon could be constructed on the surface of the Ni-Zr/SiO2 catalyst from the carbonization of glycerol via calcination under an inert atmosphere and be removed through successive calcination in air. Owing to the improved nickel–support interaction, the carbon-sacrificed Ni-Zr/SiO2 catalyst exhibited higher Ni dispersion and smaller and more uniform Ni particle sizes, leading to catalytic activity for CO methanation that is higher than that of the catalysts without carbonization.

Modified impregnation synthesis of Ru-loaded WO3 nanoparticles for acetone sensing

In this paper, WO3 nanoparticles in a lamellar-structured were fabricated via an acidification method and the surface of nanoparticles were catalytically modified by Ru through a modified impregnation method based on an electronic adsorption mechanism. Gas sensors based on neat and Ru-loaded WO3 nanoparticles were fabricated based on screen printing and sensor responses of acetone were evaluated under a dry and humid ambient, respectively. Experimental results clearly indicated that most of Ru was removed from the WO3 during the washing process, however, a strong sensitization effect of Ru was achieved with a very few loading amount. Accordingly, the basic sensitization mechanism of Ru was investigated based on TPR results and oxygen adsorption behaviors. It is revealed that Ru is loaded on the surface with an oxidized state contributing to an electronic sensitization effect. In addition, Ru on the surface of WO3 as a catalyst significantly enhanced the activity of surface lattice oxygens. As a consequence, surface lattice oxygens could also react with acetone and reduce sensor resistance leading to a sensitization effect. However, we do not expect that reactions of lattice oxygens dominate the sensing process.

Synthesis of CuO nanostructures on zeolite-Y and investigation of their CO2 adsorption properties

Abstract

Superparamagnetic graphene oxide-based dispersive-solid phase extraction for preconcentration and determination of tamsulosin hydrochloride in human plasma by high performance liquid chromatography-ultraviolet detection

In the present study, superparamagnetic graphene oxide-Fe3O4 nanocomposites were successfully prepared by a modified impregnation method (MGOmi) and their application as a sorbent in the magnetic-dispersive solid phase extraction (M-dSPE) mode to the preconcentration and determination of tamsulosin hydrochloride (TMS) in human plasma was investigated by coupling with high performance liquid chromatography-ultraviolet detection (HPLC-UV). The structure, morphology and magnetic properties of the prepared nanocomposites were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and vibrating sample magnetometry (VSM). Some factors affecting the extraction efficiency, including the pH value, amount of sorbent, extraction time, elution solvent and its volume, and desorption time were studied and optimized. Magnetic nanocomposites plasma extraction of TMS following HPLC analyses showed a linear calibration curve in the range of 0.5–50.0ngmL−1 with an acceptable correlation coefficient (R2=0.9988). The method was sensitive, with a low limit of detection (0.17ngmL−1) and quantification (0.48ngmL−1). Inter- and intra-day precision expressed as relative standard deviation (n=3) and the preconcentration factor, were found to be 5.6–7.2%, 2.9–4.2% and 10, respectively. Good recoveries (98.1–101.4%) with low relative standard deviations (4.2–5.0%) indicated that the matrices under consideration do not significantly affect the extraction process. Due to its high precision and accuracy, the developed method may be a HPLC-UV alternative with M-dSPE for bioequivalence analysis of TMS in human plasma.

Development of Mo/γ-Al<sub>2</sub>O<sub>3</sub>-CeO<sub>2</sub> Catalyst with High Thermal Stability by Modified Impregnation Method

In the present studies, different characterization techniques have been utilized to evaluate the stability of catalysts prepared by modified impregnation method. The results indicated that strong metal-support (Mo-support) interaction existed in the γ-Al2O3-CeO2 supported catalyst with higher CeO2 loading as compared to the Mo/γ-Al2O3 catalyst. This suggested that the addition of CeO2 into the γ-Al2O3 enhanced the metal-support interaction, thus decreases the reducibility, depending on the CeO2 loading. Similarly, the catalyst with higher CeO2 loading exhibited lower Ce 3d and higher Mo 3d binding energies respectively, supporting the TPR results.

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.

Employing a Nickel‐Containing Supramolecular Framework as Ni Precursor for Synthesizing Robust Supported Ni Catalysts for Dry Reforming of Methane

AbstractThis work presents a facile and efficient approach for preparing well dispersed supported Ni catalyst (HMA@Ni/SBA‐15) for dry reforming of methane (DRM) through the modified impregnation method by using a hexamethylenetetramine (HMA) Ni(II) complex, a three‐dimensional hydrogen‐bonded supramolecular framework, as Ni precursor. By employing this method, the NiII cation was discretely impregnated into the mesoporous channels of SBA‐15 support by the “obstacle effect” of the HMA coordination shell of the Ni complex; and then the Ni nanoparticles were stabilized inside the mesoporous channels of SBA‐15 by the confinement effect. The developed HMA@Ni/SBA‐15 catalyst demonstrated much higher catalytic activity and much better catalytic stability than the traditional Ni/SBA‐15 towards this reaction. The superior catalytic activity was suggested to be associated with the enhanced Ni dispersion and the improved reduction degree of NiO. In addition, the confinement effect of mesopore channels and strengthened interaction between Ni and support by improved Ni dispersion contributed to stabilizing Ni particles during the reduction and reaction process at high temperature. The strengthened Ni–support interaction of HMA@Ni/SBA‐15 favored the formation of whisker‐like carbon, which did not depress the accessibility of Ni active sites. However, owing to the weaker Ni–support interaction, the clearly observed shell‐like carbon closely encapsulated on Ni nanoparticles of spent Ni/SBA‐15 would significantly depress the accessibility of Ni active sites to reactants. The combination of stabilized Ni nanoparticles and well‐kept Ni accessibility of HMA@Ni/SBA‐15 catalyst allows it to show outstanding catalytic stability for DRM reaction. The much superior catalytic activity and stability of the developed HMA@Ni/SBA‐15 catalyst to the traditional Ni/SBA‐15 make it a promising candidate for producing synthesis gas through DRM reaction.

Performance of carbon-supported palladium and palladium[sbnd]ruthenium catalysts for alkaline membrane direct ethanol fuel cells

The activity of carbon supported palladium-based catalysts towards ethanol oxidation reaction in alkaline medium is investigated. To this end, Pd and PdxRu (x = 1, 6, 12) materials are synthesized supported on Vulcan XC72R by a modified impregnation method. These materials are characterized physicochemically and their composition varies between 40 and 50 wt. % of metal content. The mean size of nanoparticles is below 4 nm, and the size of the majority of particles ranges from 2 to 6 nm. The catalytic activity of these samples is also tested in half-cell and alkaline membrane direct ethanol fuel cell (AMDEFC). Lower onset potential and higher oxidation current densities is observed in palladium-rich bimetallic catalysts. By using the prepared samples as anode of AMDEFC and a commercial membrane of polybenzimidazole as solid electrolyte, the maximum power density is observed for Pd12Ru/C, 97 mW cm−2, almost doubling the value achieved by the catalyst Pd/C (50 mW cm−2), and above the obtained by commercial PtRu/C catalyst (89 mW cm−2).

Synergetic effect of Ni and Co in Ni–Co/SBA-15-CD catalysts and their catalytic performance in carbon dioxide reforming of methane to syngas

xNiyCo/SBA-15-CD (x + y = 5%, x/y = 0/5–5/0, mass ratio) catalysts, prepared by a β-cyclodextrin (CD) modified impregnation method, were characterized and employed in the carbon dioxide reforming of methane. Ni and Co interacted strongly with each other, and the Co species dissolved into the NiO lattice during the preparation process. The new H2 consumption peaks in the H2-temperature programmed reduction (TPR) should be attributed to the reduction of NixCoyO, which was the precursor of the Ni–Co alloy. The lattice parameters of the metal particles on reduced and spent catalysts followed Vegard's law, which confirmed the formation of the alloy. The TOFs of the bimetallic catalysts were greater than the monometallic catalysts and the stabilities of the bimetallic catalysts with Ni/Co = 2.5/2.5–4.5/0.5 were better than the monometallic catalysts. The synergistic effect of Ni and Co, the addition of β-CD, the sequence of impregnation and the confinement effect of the ordered mesoporous structure contributed to the better catalytic performance. Among the bimetallic catalysts, 4.5Ni0.5Co and 3Ni2Co showed the best stability. The better stability of 4.5Ni0.5Co can be attributed to a Co-enriched surface segregation structure, whereas the highest proportion of the Ni–Co alloy (precursor) in 3Ni2Co should be the primary reason to its better performance.

Anti-sintering ZrO2-modified Ni/α-Al2O3 catalyst for CO methanation

The ZrO2-modified Ni/α-Al2O3 catalysts prepared by a modified impregnation method show obvious enhancement of Ni anti-sintering because of the special distribution of ZrO2 nanoparticles on the surface of the catalyst.

Development of Platinum-Niobium as a CO Tolerant Catalyst for PEFC Operating with CO Contaminated Hydrogen

Traditional Polymer Electrolyte Fuel Cells (PEFC) are fed with hydrogen in the anode and oxygen in the cathode. This type of fuel cell is especially attractive because of the high efficiency at low temperature. However, the use of reformate hydrogen compromise cell performance due to the presence of traces of carbon monoxide (CO). This contaminant is adsorbed on the surface of Pt, blocking the sites necessary for the hydrogen oxidation reaction. In this context, to improve the CO tolerance of fuel cell anodes, several bimetallic Pt-based catalysts have been proposed. [1] Some studies reported in the literature have suggested the use of niobium (Nb) as the second element in bimetallic catalysts. [2] Thus, this study aims at analyzing the effect of the addition of Nb to Pt in order to develop a CO tolerant catalyst. Pt3Nb/C catalyst was prepared using a modified impregnation method, [1] physically and morphologically characterized and tested electrochemically in a single fuel cell operating on the traditional Nafion® membranes at 85 oC. Figure 1 shows the ionic currents signal m/z = 44 obtained by on-line differential electrochemical mass spectrometry (DEMS) experiments, corresponding to CO2 formation. Lower CO oxidation overpotential is observed for the material with Nb, which is a consequence of the facilitated CO oxidation on Pt3Nb/C catalyst. Figures 2 and 3 show the results corresponding to performance of a single fuel cell operating on H2 or H2 + 100 ppm CO. As it can be seen, the Pt3Nb/C catalyst outperforms Pt/C 20%. The high CO tolerance of this material is usually explained by two distinct mechanisms: the bifunctional and electronic mechanisms. In the first, the Nb act as a source of oxygenated species, required for the electro-oxidation of CO to CO2 at overpotentials lower than that for pure Pt. The electronic effect can be discussed in terms of the changes of the position of the Pt 5d-band center induced by the presence of the second metal that modifies the CO adsorption energy, reducing the CO coverage on Pt, and leaving more free Pt sites available for H2 electro-oxidation. These effects will be discussed using on-line DEMS measurements and in situ X-ray absorption spectroscopy (XAS) analyses. ACKNOWLEDGEMENTS Authors thank FAPESP, CNPq and CAPES, Brazil, for the financial support. REFERENCES [1] Pereira, L. G. S., Paganin, V. A., Ticianelli, E. A. Electrochimica Acta, 54, 192 (2009). [2] Rocha, T. A., Ibanhi, F., Colmati, F., Linares, J. J., Paganin, V. A., Gonzalez, E. R. Journal of Applied Electrochemistry, 43, 817 (2013). Figure 1

Stabilization Strategies for PtCo/C Catalysts for Htpem Fuel Cells

Because conventional platinum based electrocatalysts in HTPEM fuel cells do not catalyse the oxygen reduction reaction (ORR) sufficiently fast, large amounts of the scarce and expansive noble metal is used. Due to the impact of platinum on the overall system costs, the loading has to be reduced on the roadway towards commercialization of fuel cell systems. Corrosive operating conditions of HTPEM fuel cells require high stability of all compounds that are used within the electrodes. Because not many materials fulfil the stability requirements, increasing the activity of platinum by alloying with transition metals is probably the best approach [1,2]. Due to an easy up-scalability we are using a modified impregnation method to synthesize PtM/C catalysts (M = first row transition metal). Stability and activity increasing post-preparation treatments are conducted. The as-prepared electrodes are leached in acidic solutions in order to remove inactive material from the surface resulting in platinum skeleton type nanoparticles. Additionally, heat treatments are conducted to decompose any undesired organic residues and to rearrange platinum and the alloy metal at the surface [1–4]. Fig.1: Comparison of a standard Pt/C catalyst (a) to in-house prepared and stabilized PtCo/C catalysts (b) [1]. All catalysts are testes preliminary ex-situ by means of cyclic voltammetry employing a rotating disk electrode (RDE) and accelerated stress test (AST) protocols. Promising formulations were tested in-situ in HTPEM single cell tests at 160 °C. In Fig. 1 typical cyclic voltammograms are shown of a commercial Pt/C catalyst and of a PtCo/C catalyst before and after AST procedures. After evaluating the most promising composition and post-preparation treatment, in-situ tests were performed. The polarization curves of MEAs with commercial and in-house prepared cathode catalysts combined with a standard anode are shown in Fig. 2. Both electrodes show similar performance although the commercial Pt/C based electrode has a 20% higher platinum loading than the PtCo/C based electrode. While the Pt/C MEA performance decreases slightly the PtCo/C MEA shows slight increase within the first 600 hours of operation. Fig.2: a) Polarization curves of the PtCo/C based MEA and the commercial Pt/C based MEA in HTPEM fuel cell operation; b) cell voltages during 600 h long-term operation. The insert shows the voltage gain during the first hours of operation [1]. Acknowledgements Support by NAWI Graz and financial support by the Austrian Federal Ministry of Transport, Innovation and Technology (BMVIT) and The Austrian Research Promotion Agency (FFG) through the program a3plus and the IEA research cooperation is gratefully acknowledged.

Research on methanol-tolerant catalysts for the oxygen reduction reaction

Direct methanol fuel cells (DMFCs) generate electricity in a clean and efficient way, so they are a valuable alternative to traditional environmentally harmful technologies. Portable power sources are one of the applications of passive DMFCs. One of the requirements in these devices is the use of high alcohol concentration. Methanol permeation across the polymer electrolyte membrane (methanol crossover) causes a loss of fuel cell efficiency as the oxygen reduction reaction (ORR) and the methanol oxidation reaction (MOR) occur simultaneously at the cathode. To develop methanol-tolerant catalysts with suitable activity, different PtM/C and PtMRu/C combinations with M = Co or Fe were prepared by a modified impregnation method. The synthesized catalysts were studied to determine the role of the components in enhancing the ORR and simultaneously discouraging the MOR. The materials were characterized by TEM, XPS and EDS. Well-distributed particles for all the catalysts were shown by TEM. XPS spectra revealed that the method produces a great amount of metallic Pt. The electrochemical characterization was carried out by linear sweep voltammetry and cyclic voltammetry, in a three-electrode electrochemical cell with a glassy carbon rotating disk electrode covered with a thin catalytic layer and a Nafion® film as the working electrode. Binary and ternary catalysts have a good activity for the ORR. However, the enhanced activity of binary catalysts is lost when the ORR is studied in the presence of methanol. Ternary catalysts containing Ru showed higher methanol-tolerance, regardless of the composition.

Promoting effect of glucose and β-cyclodextrin on Ni dispersion of Ni/MCM-41 catalysts for carbon dioxide reforming of methane to syngas

Mesoporous silica MCM-41 supported Ni-based catalysts were prepared by glucose (Glu) and β-cyclodextrin (βCD) modified impregnation method, respectively. The physicochemical properties of the catalysts (Ni/MCM-41-βCD and Ni/MCM-41-Glu) were characterized with BET, XRD, H2-TPR and TEM techniques, and their catalytic performance in CO2 reforming of methane to syngas was evaluated. The results revealed that the prepared catalysts remained the ordered mesoporous structures of MCM-41, and no obvious NiO particles could be viewed on catalysts prepared with β-cyclodextrin or glucose modified method. In contrast, on the catalyst prepared with the conventional impregnation method (Ni/MCM-41), large NiO particles could be observed. In the reaction of CO2 reforming of methane to syngas, compared with Ni/MCM-41, Ni/MCM-41-βCD and Ni/MCM-41-Glu exhibited higher catalytic activities and better catalytic stabilities.

Solvent-free aerobic oxidation of alcohols using supported gold palladium nanoalloys prepared by a modified impregnation method

The synthesis of stable, supported, bimetallic nanoalloys with controlled size, morphology and composition for selective alcohol oxidation.

Effects of Polyvinylpyrrolidone on the Preparation of Supported La2O3Catalysts by a Modified Impregnation Method for the Oxidative Coupling of Methane

Ministry of Science and Technology of China [2010CB732303]; National Natural Science Foundation of China [21033006, 21373169]; NFFTBS [J1310024]; Program for Changjiang Scholars and Innovative Research Team in the University [IRT1036]

Magnesia doped Ag/Al2O3 – Sulfur tolerant catalyst for low temperature HC-SCR of NOx

A series of magnesia doped Ag/Al2O3 catalysts were prepared by modified impregnation method using boehmite as alumina precursor. The prepared catalysts were characterized and tested for the SCR of NOx using propene as reductant under lean condition. Doping of magnesia improved the low temperature catalytic activity for HC-SCR of NOx as well as sulfur tolerance. Maximum 98% NO conversion with 100% selectivity for N2 was obtained at 350°C with 7% Mg doping to Ag/Al2O3. The improvement in low temperature activity and the sulfur tolerance has been correlated to decreased acidity after addition of magnesia to alumina support. In situ FTIR study showed that the deactivation in the presence of SO2 was due to the sulfation of silver and aluminum sites in Ag/Al2O3 catalyst, however its formation was suppressed in case of magnesia doped Ag/Al2O3 improving its sulfur tolerance.