Dispersion Of Active Components Research Articles

Carbon nanotubes-promoted Co–B catalysts for rapid hydrogen generation via NaBH4 hydrolysis

In this work, multiwalled carbon nanotubes (MWCNTs) promoted Co–B catalysts for NaBH4 hydrolysis have been designed and synthesized. The structural features of as-prepared catalysts have been investigated and discussed as a function of MWCNTs contents by X-ray diffraction, X-ray photoelectron spectra, N2 adsorption/desorption isotherms, scanning electron microscope. The results show that the catalysts still maintain an amorphous structure with the addition of carbon nanotubes promoter. However, the appropriate amount of MWCNTs promoter in Co–B catalysts leads to large specific surface area, fine dispersion of active components, increased active sites and high electron density at active sites. Moreover, hydrogen spillover on the catalyst is promoted, which contributes to regeneration of active sites and accelerating catalytic cycle. Among all the experimental samples, it is found that the Co–B catalyst promoted by 10 wt% carbon nanotubes exhibits optimal catalytic activity with remarkably high hydrogen generation rate of 12.00 L min−1·gcatalyst−1 and relatively good stability.

The State of Platinum and Structural Features of Pt/Al2O3 Catalysts in the Reaction of NH3 Oxidation

The work is related to the fundamental research of the process of ammonia neutralization using catalytic oxidation over Pt/Al2O3 catalysts in an excess of oxygen. The catalysts are synthesized using nitrate precursors on the supports prepared from Pural SCF-55 aluminum hydroxide by the calcination in air at 550°C or 750°C for 4 h. A number of physicochemical methods are used to study morphology, dispersion, structure, and electronic state of the catalyst active component before and after the reduction in hydrogen. It is shown that the synthesized Pt/Al2O3 catalysts are characterized by high dispersion of the active component: the size of deposited platinum particles is in the range from 0.5 nm to 2.0 nm, while the proportion of oxidized and reduced Pt forms varies. Based on the results of kinetic measurements, the catalyst activity and the selectivity to all major products (N2, N2O, NO, NO2) are determined depending on the reaction temperature. The results of the catalytic testing are discussed in relation to the data on dispersion and oxidation state of platinum.

Facile synthesis of magnesium ferrite nanoparticles supported on nitrogen and sulfur co-doped carbon black as an efficient electrocatalyst for oxygen reduction reaction

Novel nanohybrid MgFe2O4 (MFO) supported on carbon black co-doped by nitrogen and sulfur (CNS) was facilely synthesized as an efficient electrocatalyst (namely, MFO/CNS) for oxygen reduction reaction (ORR) in alkaline medium. Structural analysis by X-ray diffraction revealed the formation of MFO and confirmed its spinel structure in MFO/CNS nanocomposite. Transmission electron microscope images showed that the products synthesized by different annealing temperature displayed a diverse particle size and dispersion of active component. Electrochemical results indicated that the MFO/CNS hybrid with the controllable N, S-co-doping shows an enhanced ORR catalytic activity and desired direct four-electron reaction pathway, which is better than MFO and CNS synthesized under the same conditions. The excellent electrochemical performance of MFO/CNS should be attributed to the synergistic effect of MFO and CNS to form a conductive network structure, which offers the increased electrochemical active surface area, the facilitated electron transfer, and effective mass transport between oxygen molecules and active sites. The results demonstrated that the MFO/CNS nanohybrid in this study appears to be a promising cathodic electrocatalyst in alkaline fuel cells.

Catalytic performance of Zr-doped CuO[sbnd]CeO2 oxides for CO selective oxidation in H2-rich stream

Zr-doped CuOCeO2 catalysts for CO selective oxidation were designed and prepared by the hydrothermal method and coprecipitation. The experimental samples were characterized by means of N2 adsorption-desorption isotherms, powder X-ray diffraction, temperature-programmed reduction and X-ray photoelectron spectroscopy. It is observed that the catalyst prepared by hydrothermal method exhibits larger specific surface area, smaller crystalline size and higher dispersion of active components compared with those of the catalyst obtained by coprecipitation. Meanwhile, redox properties of copper oxide are improved significantly and highly dispersed copper species providing CO oxidation sites are present on the surface. Furthermore, adsorptive centers of CO and active oxygen species increase on the copper-ceria interfaces. The Zr-doped CuOCeO2 catalyst prepared by hydrothermal method possesses superior catalytic activity and selectivity for selective oxidation of CO at low temperature compared with those of the sample prepared by coprecipitation. The temperature corresponding to 50% CO conversion is only 73 °C and the temperature span of total CO conversion is expanded from 120 to 160 °C.

Efficient conversion of fructose to 5‐hydroxymethylfurfural by functionalized γ‐Al2O3 beads

Millimeter size γ‐Al2O3 beads were prepared by alginate assisted sol–gel method and grafting organic groups with propyl sulfonic acid and alkyl groups as functionalized γ‐Al2O3 bead catalysts for fructose dehydration to 5‐hydroxymethylfurfural (5‐HMF). Experiment results showed that the porous structure of γ‐Al2O3 beads was favorable to the loading and dispersion of active components, and had an obvious effect on the properties of the catalyst. The lower calcination temperature of γ‐Al2O3 beads increased the specific surface area, the hydrophobicity and the activity of catalysts. Competition between the reaction of alkyl groups and ‐SH groups with surface hydroxyl during the preparation process of the catalyst influenced greatly the acid site densities, hydrophobic properties and activity of the catalyst. With an increase in the alkyl group chain, the hydrophobicity of catalysts increased obviously and the activity of the catalyst was enhanced. The most hydrophobic catalyst C16‐SO3H‐γ‐Al2O3–650°C exhibited the highest yield of 5‐HMF (84%) under the following reaction conditions: reaction medium of dimethylsulfoxide/H2O (V/V, 4:1), catalyst amount of 30 mg, temperature of 110°C and reaction time of 4 hr.

Performance enhancement of NH3-SCR via employing hydrotalcite-like precursor to induce the decoration of NiO by TiO2 phase

In this work, NiO phase was decorated by titanium species to achieve NiTi mixed oxides acting as NH3-SCR catalysts, (NiTi-IMP, NiTi-SOL and NiTi-LDO) which were fabricated via solution-impregnation, one-pot sol-gel and urea homogeneous precipitation methods followed by a calcination process. The microstructure and morphology features as well as the inherent morphology-activity relationship of resultant samples were fully characterized by XRD, BET, SEM, TEM/HRTEM, XPS, ICP-AES, NH3-TPD and H2-TPR. The results pronouncedly affirmed that the NiTi-LDO behaved the optimum SCR performance, affording a desiring efficiency (over 90% NO conversion within the temperature region of 240–360 °C), preferable N2 selectivity (nearby 95% at the whole test temperature zone), superior catalytic stability and SO2/H2O resistance. The improvement of catalytic performance could be attributed to the assistance of hydrotalcite-like precursor possessing special morphology structure, and the subsequently generated favorable interfacial interaction as well as the atomic-level dispersion of active component during the calcination process.

Mn-CeOx/MeOx(Ti, Al)/cordierite preparation with ultrasound-assisted for non-methane hydrocarbon removal from cooking oil fumes

Cooking oil fumes (COFs) which contains a variety of volatile organic compounds (VOCs) is noxious not only to the environment but also to human health. Among COFs, the Non-methane Hydrocarbon (NMHC) removal rate is an index of the removal rate of COFs in the latest COFs purification standard (DB 11/1488-2018). Ultrasonic treatment can assist the synthesis of catalysts by creating “cavitation”, which can improve the surface microtopography of catalysts. The research results in this paper revealed that the NMHC conversion of catalysts with ultrasonic treatment increased significantly. Besides, the samples that coated TiO2 had a higher conversion of NMHC than that coated Al2O3 because TiO2 has better oxidation performance than Al2O3. According to the XPS, SEM, EDS and BET data, because of the enhancement of interaction of the active components of catalysts caused by ultrasonic intervention, T-UU-CTAB exhibited the best catalytic performance, which attributed to the high levels of Mn4+/Mn3+, Ce4+/Ce3+ and Oads/Olatt, more developed pore structure owing to the smaller particle size, higher dispersion of active components, larger specific surface area and larger total pore volume produced by the ultrasonic treatment. Moreover, the conversion of NMHC over T-UU-CTAB is 93.6% at 400 °C.

Control of Ni/Ce1-xMxOy Catalyst Properties Via the Selection of Dopant M = Gd, La, Mg. Part 1. Physicochemical Characteristics

To develop effective reforming catalyst a series of Ni catalysts (Ni content 2‒15 wt.%) supported on ceria-based oxides Ce1-xMxOy were synthesized by incipient wetness impregnation. To regulate dispersion and reducibility of the active component, the variation of chemical composition of support was performed. The prepared samples of supports and catalysts were characterized by X-ray spectral fluorescence analysis, N2 adsorption/desorption, X-ray diffraction, transmission electron microscopy, and thermal analysis. It was found that the support composition specified the forms of stabilization (NiO or Ni-M-O oxides, M = La, Mg) and capability to reduction of Ni-component through the realization of a different extent of interaction between Ni-containing species and support. The increase of M content in CexM1-xOy support induces the decrease of CexM1-xOy crystallite size, improvement of Ni active component dispersion and the increase of hard-to-reduce portion of nickel cations due to the growth in the degree of nickel- CexM1-xOy interaction. The identified variation of the textural, structural and redox characteristics of the Ni/CexM1-xOy catalysts should influence their performance in the catalytic process.

Copper oxide modified SBA-15 for the selective vapour phase dehydrogenation of cyclohexanol to cyclohexanone

Catalysts with efficient dispersion, high activity, and minimum leaching of active component are evergreen areas of interest in the field of catalysis. Incorporation of active component on high surface area materials helps to attain uniform dispersion, increased activity and stability for the catalyst system. Mesoporous materials like SBA-15 are widely used as catalyst support because of its high surface area, thermal and hydrothermal stability, uniform hexagonal mesopores, etc. Here we have synthesized copper oxide modified SBA-15 catalysts with various weight percentages of copper metal and its activity towards the dehydrogenation of cyclohexanol was studied. The reaction was monitored on a continuous flow fixed bed gas phase reactor. Various parameters for the reaction were optimized. SBA-15 with less than 10% Cu content was observed to be the most effective catalyst. The catalysts were found to be competent for the reaction with efficient dispersion of the active component and minimum deactivation.

Removal of elemental mercury by Ce and Co modified MCM‐41 catalyst from simulated flue gas

AbstractCo and Ce based catalysts have been proven to possess a high Hg0 removal efficiency. However, these catalysts have a low dispersion of active components and low mass transfer rate, which limits their catalytic activity. MCM‐41 has a large surface area and a highly ordered mesoporous structure, which can improve the dispersion of Co and Ce, resulting in a high mass transfer rate. In this paper, different amounts of Co and Ce were loaded on MCM‐41 to synthesize Cox‐Cex/MCM‐41. The characteristic results of the catalyst showed that catalysts with a lower Co and Ce loading amount had a high dispersion and a low crystallinity, leading to more activity sites on the catalyst surface. Hence, the Hg0 removal efficiency of the catalysts first increased with the increase of the Co and Ce loading amount. However, with the further increase of the Co and Ce loading amount, the crystallinity of the catalysts increased, which might cause the blockage of the pores and the decrease of BET surface areas, leading to a low Hg0 removal efficiency. Along with the factors mentioned above, Co0.15‐Ce0.15/MCM‐41 had the best catalytic activity, which showed above 85 % Hg0 removal efficiency in the temperature range of 200–300 °C at 180 000 h−1. Flue gas components had different effects on catalytic activity. O2 and NO could promote, but H2O and SO2 inhibit the Hg0 removal efficiency. The simulated flue gas of 300 ppm SO2, 400 ppm NO, 6 % H2O, and 5 % O2 have serious effects on catalytic activity leading to a lower Hg0 removal efficiency of 20 % for Co0.15‐Ce0.15/MCM‐4.

Esterification for biofuel synthesis over an eco-friendly and efficient kaolinite-supported SO42−/ZnAl2O4 macroporous solid acid catalyst

A series of raw kaolinite-supported SO42−/ZnAl2O4 (S/ZA-Kao) macroporous solid acid catalysts were synthesized and applied in esterification of both oleic acid with methanol and acetic acid with n-butanol for the biofuels synthesis. The structures and acidic properties of S/ZA-Kao catalysts were characterized by means of XRD, FE-SEM, EDS, BET, FT-IR (direct and NH3 adsorbed), NH3-TPD, TG and XPS. The results indicated the mass ratio of ZnAl2O4/kaolinite played a significant role in adjusting the active components dispersion, textural and acidic properties. The optimal S/ZA-Kao(6:4) catalysts performed the macroporous structure and the high dispersion of active components, which might be theessential reason for its improved acid sites and reduced limitation of mass transfer. As a result, the macroporous solid acid exhibited superior conversion of 98.2% in acetic acid esterification and 70.1% in oleic acid esterification. The kinetic study demonstrated that the relatively lower values of activation energy over the S/ZA-Kao(6:4) macroporous solid acid, further confirming that the macroporous solid acid was highly efficient for the biofuel synthesis via esterification. Moreover, the further investigation indicated the catalytic activities were closely related to the ratio of Brönsted acid sites on catalysts. Besides, S/ZA-Kao(6:4) macroporous solid acid particularly displayed excellent reusability, which was due to its structural stability and high dispersion of active components.

Novel drying of formulated naproxen sodium using microwave radiation: Characterization and energy comparison

The extent of moisture content (MC) present in pharmaceutical formulations has a vital role in controlling the textural properties of the pellet, dispersion of active component and its dissolution kinetics. In particular, hydrophilic drugs such as naproxen sodium (NapS) tend to absorb moisture readily which necessitates the selection of a drying technique to ensure the preservation of drug's textural properties without compromising its pharmaceutical effect and release kinetics. In this paper, a novel drying process for naproxen sodium drug granules has been used successfully by employing microwave radiation technique and compared with other drying techniques. The major objective of the present work is to evaluate the effect of microwave drying technique in the removal of moisture from naproxen sodium and its impact on the textural properties of the final product of tablets powder. The pharmaceutical formulation is synthesized by mixing appropriate amounts of NapS, Poly (vinyl pyrrolidine), and microcrystalline cellulose and moisturized using deionized water to 10, 20 and 30 wt%. Four different drying methods namely vacuum drying (VD), freeze drying (FD), convective drying (CD) and microwave drying (MWD) are used to dry NapS wet granules. The rate of moisture removal and the energy requirement are found to be different for each drying process. The product of drying is also found to have different particle size, morphology, and crystallinity for each process. Among the four techniques, MWD is found to be highly efficient because of its rapid moisture removal which can be ascribed to the interaction of microwave with NapS that has a permanent dipole moment. The results of this work suggest that moisture content of NapS tablets could be reduced rapidly by microwave radiation technique, which has the potential of improving the energy efficiency of the drying process while preserving the textural properties of the drug formulation.

Promotional removal of HCHO from simulated flue gas over Mn-Fe oxides modified activated coke

A series of MnxFey/AC catalysts synthesized by impregnation method were investigated on the efficient and stable removal of HCHO in the fix-bed reactor. Extensive characterizations, BET, SEM, XRD, H2-TPR, XPS and FT-IR, were conducted to study the physicochemical properties, HCHO oxidation and surface reaction of catalysts. The optimal Mn0.75Fe6.02/AC showed enhanced HCHO removal efficiency of 98.30%, as well as excellent performance for simultaneous removal of HCHO (89.96%) and Hg0 (77.51%). NO and SO2 balanced in N2 would inhibit the removal of HCHO, while the addition of 6% O2 weakened the negative effect of SO2 and NO + 6% O2 facilitated the removal of HCHO. Besides, the slight promotion effect of water vapor was contributed to the regeneration of consumed −OH via the activation of surface oxygen by adsorbed H2O. Characterization results indicated that Mn0.75Fe6.02/AC possessed larger BET surface area, well-developed porosity and better dispersion of active components. Mn0.75Fe6.02/AC exhibited higher reducibility due to the synergistic effect between MnOx and FeOx, and the interaction between Mn-Fe oxides and AC support. At the same time, the oxygen-containing functional groups (C-O-, COO), abundant active surface oxygen and –OH facilitated both adsorption and oxidation of HCHO. Besides, the formate and carbonate intermediates formed on the surface of Mn0.75Fe6.02/AC in HCHO removal process, which could be further oxidized into CO2 and H2O. On the basis of above investigations, the mechanism of enhanced HCHO catalytic removal over MnxFey/AC was proposed.

Sol-Gel Synthesis of Nanostructured Alumina Supports for CO Oxidation Catalysts

In present work, a new technique to prepare alumina nanoparticles and nanofibers using a sol-gel method was proposed. A solution combustion method was applied to form a nanostructured catalytically active layer of CuO–Co3O4–CeO2 on the surface of the alumina. The uniform distribution and fine dispersion of active components provide the appropriate activity of the catalysts obtained in a model reaction of CO oxidation. The morphology of nanostructured alumina was found to affect the catalytic behavior. Carbon monoxide conversion was observed at lower temperatures when alumina nanofibers were used as a catalyst support.

Pyridinic-N-dominated carbon frameworks with porous tungsten trioxide nano-lamellae as a promising bi-functional catalyst for Li-oxygen batteries.

The rational design and synthetic route to fabricate hybrid materials with desirable electrocatalytic functionalities remain critical but still challenging for sustainable energy devices. Here, we constructed a tungsten trioxide nano-lamellae chemically anchored with pyridinic-N-dominated doped CNT/graphene frameworks (W-NCG) via a general solution-based synthesis method. The detailed results indicated that this hybrid structure is composed of vacancy-defect abundant WO3 porous nanoflakes anchoring through or onto a 3D N-doped carbon matrix. After a facile post-annealing treatment, the W-NCG sample is utilized as a bi-functional catalyst for rechargeable lithium-oxygen batteries. The optimized sample with a large BET surface exhibits unprecedented ORR/OER activity in the cell, and satisfying specific capacity (∼7850 mA h g-1) and cycling stability. This excellent electrochemical performance can be ascribed to the pseudo 3D structure with sufficient microspace and good electrical conductivity, which facilitate the high dispersion of active components and effectivly relieve the formation of large/irreversible Li2O2. As such, this porous W-NCG framework is a prospective high-performance cathode material for Li-O2 batteries.

Promotional effect of iron modification on the catalytic properties of Mn-Fe/ZSM-5 catalysts in the Fast SCR reaction

A series of Mn-Fe/ZSM-5 catalysts with varying amounts of iron doping were prepared via the impregnation method and their catalytic activities in Fast SCR and NO oxidation evaluated. It was found that NOx (NO+NO2) conversion using the iron-modified catalysts was obviously improved, probably due to the interaction between manganese and iron. Mn-Fe/ZSM-5 with a molar ratio of Fe/Mn=0.49 exhibited the highest activity, achieving >96.15% NOx conversion at 100°C and stabilizing at about 100% conversion at between 150 and 250°C. The properties of the catalysts were characterized using ICP, BET, XRD, H2-TPR, NH3-TPD and XPS techniques. XRD analysis revealed that the coexistence of manganese and iron oxides promoted the dispersion of active components and lowered the crystallinity, while the XPS results showed that iron doping increased the ratio of Mn4+, increasing levels of oxygen vacancy and lattice oxygen, thereby facilitating the oxidation of NO to NO2 and ultimately accelerating the Fast SCR process. However, excessive iron loading can lead to the agglomeration of active components. Furthermore, Mn-Fe(0.490)/ZSM-5 also exhibited superior performance in terms of NO oxidation, with the maximum NO oxidation rate of 55.88% recorded at 300°C, indicating the former's potential as a pre-oxidation catalyst for the Fast SCR reaction.

Effect of coating modification of cordierite carrier on catalytic performance of supported NiMnO3 catalysts for VOCs combustion

NiMnO3 perovskite catalysts supported on cordierite modified by CexZr1-xO2 coatings were prepared using impregnation and sol–gel methods for catalytic combustion of single/double component VOCs at different concentrations and GHSV of 15,000 h−1, which were characterized by BET, XRD, SEM, FT-IR, H2-TPR and O2-TPD. After coating modification, the specific surface area of catalysts is improved obviously. Among the catalysts, the Ce0.75Zr0.25O2 coating modified NiMnO3 catalyst exhibits the best catalytic activity for VOCs combustion with 95.6% conversion at 275 °C and has stable activity when catalyst is embalmed at 800 °C. In addition, the catalyst also presents the excellent water-resistant and conversion stability over time-on-stream condition. The reason is that Ce0.75Zr0.25O2 coating can promote more lattice distortion and defects and smaller crystal size, which improve oxygen transfer capability and dispersion of active component.

Dehydrogenation of ethanol over carbon-supported Cu–Co catalysts modified by catalytic chemical vapor deposition

A bimetallic copper–cobalt catalyst supported on activated carbon fibrous (ACF) material was prepared by the incipient wetness impregnation of the support with an aqueous solution of corresponding nitrates. Reference monometallic Cu/ACF and Co/ACF samples were synthesized analogously. In order to enhance the metal-support interaction and stabilize the dispersion of active components, the Cu–Co/ACF catalyst was subjected to catalytic chemical vapor deposition of ethylene at 600 °C with the formation of carbon nanofibers (CNF). As a result, the catalytic system consisting of Cu–Co particles anchored on carbon–carbon composite was obtained. All samples were characterized by a set of physicochemical methods. The catalytic performance of pristine and CNF-modified samples was studied in the ethanol dehydrogenation reaction. The activity of Cu–Co/CNF/ACF catalyst was shown to be two times higher compared with the unmodified bimetallic sample.

The behavior of the manganese-cerium loaded metal-organic framework in elemental mercury and NO removal from flue gas

Mn-Ce loaded metal-organic framework (MnCe@MOF) catalyst was obtained by incipient wetness impregnation of MOF with manganese-cerium nitrate. The obtained materials were investigated as potential catalysts for elemental mercury (Hg0) and NO removal from simulate flue gas and the results indicated that MnCe@MOF exhibited superior activity in comparison with the conventional catalysts Mn-Ce loaded ZrO2, especially at low temperatures (<250°C). It was established that the crystalline structure of MOF support influenced the catalytic behavior in a complex way. The MOF support played an important role in promoting dispersion of active components, improving the Hg0 adsorption and enhancing oxygen utilization, which resulted in a desirable catalytic activity. To understand the mechanism of the Mn-Ce catalyst better, dynamic valence state evolution during the Hg0 oxidation for the active components was investigated. The ratio of Mn3+/Mn4+ remained constant during the reaction at various temperatures, indicating the stability of Mn in the catalytic process. However, the ratio of Ce3+/Ce4+ gradually decreased with extended periods of reaction time, which most likely lead to the decreased of chemical adsorbed oxygen on the catalyst.

Effect of the well-designed functional groups and defects of porous carbon spheres on the catalytic oxidation performance

The oxygen functional groups and defects of carbon material played an important role in dispersion of active components and additives, reduction of Ce4+, etc. The reduction of Ce4+ and structure defects would increase surface oxygen concentration and oxygen vacancies. The dispersion of active components and additives, surface oxygen concentration and structure defects were key factor on CO oxidation. The oxygen functional groups and structure defects of porous carbon spheres (PCSs) increased by O3 treatment method. The effects of O3 treatment concentration on structures, properties of PCSs support and Pd-Ce/PCSs were investigated in detail. The particle size of PCSs had not been changed basically after O3 treatment. However, the outer of PCSs became uneven, which was main reason of the external surface area increase. The content of surface Pd4+, surface adsorption oxygen concentration, oxygen vacancies, defects, increased with increasing O3 treatment concentration. Relationship between the functional groups, defects of porous carbon spheres and their catalytic performance was investigated in detail. CO oxidation test showed that the Pd-Ce based catalysts supported by the PCSs after O3 treatment concentration for 45 mgL−1 had the best activity. The effect of moisture on CO conversion was explored, and the catalysts showed excellent stability under moisture condition.