Traditional Impregnation Method Research Articles

Polyethyleneimine NH2-UiO-66 nanofiller-based mixed matrix membranes for natural gas purification

Effective separation of CO2 from CH4 is crucial for the purification of natural gas, which requires membrane materials with high permeability, selectivity, and stability of under high pressures. In this work, a high CO2-affinity MOF-based nanofiller (Pin@NH2-UiO-66) was prepared and integrated in polyetherimide (PEI) to prepare mixed matrix membranes (MMMs) for enhanced CO2/CH4 separation capabilities. The Pin@NH2-UiO-66 nanofiller comprised an in situ-formed polyethyleneimine-NH2-UiO-66 composite prepared via a one-pot synthesis. The polyethyleneimine was covalently attached to the H2BDC-NH2 ligand allowing for a stronger integration within the PEI matrix. The polyethyleneimine affects the nucleation of MOF, leading to miniaturization of the MOF particles. The smaller-sized filler is beneficial for improved interaction at the filler-matrix interface. The numerous amino functionalities grafted onto the NH2-UiO-66 increased the CO2 adsorption sites, thereby enhancing the affinity for CO2. Owing to the improved interaction, the elevated CO2 attraction, and the inherent properties of the porous NH2-UiO-66, the fabricated MMMs preformed superior in separating CO2/CH4. The 30-Pin@NH2-UiO-66-PEI membrane (containing 30 wt% nanofiller) exhibited a CO2/CH4 selectivity of 27.7 and a CO2 permeability of 2498.9 Barrer. The CO2 permeability was 21 times greater than that of the pristine PEI membrane, and 4 times higher compared to P@NH2-UiO-66 MMM with polyethyleneimine modified MOF filler prepared by a traditional wet impregnation method. Additionally, the novel MMM demonstrates excellent separation stability under conditions that mimic industrial settings, demonstrating its potential application for natural gas purification.

Enhancement of Ni-NiO-CeO2 Interaction on Ni-CeO2/Al2O3-MgO Catalyst by Ammonia Vapor Diffusion Impregnation for CO2 Reforming of CH4.

Ni-based catalysts have been widely used for the CO2 reforming of methane (CRM) process, but deactivation is their main problem. This study created an alternative electronic Ni-NiO-CeO2 interaction on the surface of 5 wt% Ni-5 wt% CeO2/Al2O3-MgO (5Ni5Ce(xh)/MA) catalysts to enhance catalytic potential simultaneously with coke resistance for the CRM process. The Ni-NiO-CeO2 network was developed on Al2O3-MgO through layered double hydroxide synthesis via our ammonia vapor diffusion impregnation method. The physical properties of the fresh catalysts were analyzed employing FESEM, N2 physisorption, and XRD. The chemical properties on the catalyst surface were analyzed employing H2-TPR, XPS, H2-TPD, CO2-TPD, and O2-TPD. The CRM performances of reduced catalysts were evaluated at 600 °C under ambient pressure. Carbon deposits on spent catalysts were determined quantitatively and qualitatively by TPO, FESEM, and XRD. Compared to 5 wt% Ni-5 wt% CeO2/Al2O3-MgO prepared by the traditional impregnation method, the electronic interaction of the Ni-NiO-CeO2 network with the Al2O3-MgO support was constructed along the time of ammonia diffusion treatment. The electronic interaction in the Ni-NiO-CeO2 nanostructure of the treated catalyst develops surface hydroxyl sites with an efficient pathway of OH* and O* transfer that improves catalytic activities and coke oxidation.

Novel strategy to regulate the geometric and electronic structure of Pt catalyst for efficient propane combustion

The geometric and electronic structure of Pt active sites plays a crucial role in determining the catalysts performance, but precise regulation remains challenging. Herein, we propose a novel approach to modulate the nature of Pt active sites by combining photo-deposition of Pt nanoparticles with ultra-low Mo loading (0.1 wt%) modification on Pt/SiO2 catalysts. The addition of ultra-low loading Mo promoter not only effectively reduces the size of Pt particles but also donates electrons to the Pt particles. Furthermore, the photo-deposited Pt particles exhibit a higher proportion of metallic Pt species, which is more stable than that metallic Pt species obtained by H2 reduction, compared to those prepared using traditional wetness impregnation methods. Propane oxidation activity evaluations confirm that the photo-deposited and Mo-modified Pt/0.1Mo/SiO2-P catalyst exhibits the highest activity among all the prepared catalysts. Combined with experiments of C3H8-TPSR and in-situ DRIFT spectra of propane oxidation, it is found that the Pt/0.1Mo/SiO2-P catalyst remarkably promotes propane activation and C-H bond cleavage due to the nature change of Pt active sites, and the presence of gaseous oxygen benefits propane cleavage on active sites. Our primary results provide a promising strategy for designing superior platinum catalysts by regulating Pt active sites nature for efficient propane complete oxidation.

Atomic Pt Sites Anchored in the Interface between Grains on Vacancy-Enriched CeO2 Nanosheets: One-Step Precursor Combustion Synthesis.

Atomic metal catalysts have unique electronic, structural, and catalytic properties, which are widely used in the field of catalysis. However, designing new simple synthesis methods to fabricate atomic metal catalysts is a challenge in catalytic applications. Herein, a one-step precursor combustion strategy is presented that starts directly from precursors of metal salts, using a spontaneous combustion process convert platinum nitrate to atomic Pt sites. The atomic Pt sites with low valence are anchored in the formed interface between grains on vacancy-enriched CeO2 nanosheets. The obtained Pt/CeO2-2 catalyst exhibits much higher three-way catalytic activities at low temperatures than Pt/CeO2-C catalysts prepared using the traditional impregnation method. Density functional theory calculations show that the generated lower valent Pt atoms in the CeO2 interface promote catalytic activity through reducing the energy barrier, and lead to an overall improvement of three-way catalytic activities. This facile strategy provides new insights into the study of the properties and applications of atomic noble metal catalysts.

In-situ reconstruction of LaCoO3-Co3O4 hetero-interface over lanthanum modified Co3O4 nanocatalyst for improved catalytic activity and sintering resistance in methane combustion

Nanoparticles-based catalysts still suffer from deactivation due to sintering and structural collapse through long-time running at high reaction temperature. Developing simple strategy for improving the sintering resistance of nanoparticles is of great importance for fabrication of durable heterogeneous catalysts. In this work, lanthanum was used to prevent Co3O4 nanoparticles from sintering with restricting growth of nanocrystals by in-situ generation of LaCoO3 perovskite phase during thermal ageing process, further building LaCoO3-Co3O4 hetero-interface with strong interfacial effect. Specifically, the Co3O4 nanocatalyst was loaded with different amount of La by traditional impregnation method and a series of characterizations were carried out to explore the physical and chemical properties of the as-prepared catalysts, including XRD, Raman, BET, SEM, HRTEM, XPS, H2-TPR and O2-TPD. It was found that 5 wt% La-Co3O4 has the highest catalytic activity in CH4 combustion and the value of T90 (temperature of 90% methane conversion) between fresh and aged was only 9 ºC, while this value was 108 ºC over pure Co3O4 sample. The Raman, XPS, H2-TPR and O2-TPD results exhibited that the synergistic effect between Co3O4 and LaCoO3 could not only induce lattice distortion in Co3O4 with more defects and adsorbed oxygen species, enhanced oxygen mobility and reducibility, but also significantly suppress the growth of Co3O4 nanocrystals during thermal ageing treatment.

Plasma‐catalytic CO2 methanation over NiO/bentonite catalysts prepared by solution combustion synthesis

AbstractA solution combustion synthesis (SCS) process to prepare nickel catalyst over bentonite (NiO/Ben) is reported. Compared to the traditional impregnation method, NiO/ben produced by SCS has smaller nickel particle size and higher dispersion. With a metal loading of 20 wt%, the afforded NiO/Ben demonstrates excellent catalytic activity for CO2 methanation in a dielectric barrier discharge reactor. In certain discharge conditions (H2:CO2 ratio of 5 in feed gas, discharge input power of 45 W, and gas hourly space velocity of 11 320 h−1), CO2 conversion and CH4 selectivity are as high as 55.8% and 84.6%, respectively. Under the conditions of plasma configuration, the strong interaction between the nickel species and the support plays an important role in the CO2 methanation process.

Mechanochemistry: A Green and Fast Method to Prepare a New Generation of Metal Supported Catalysts

In this review, we report on recent advances in the use of mechanochemistry to synthesise new catalytic materials. We report recent results obtained by our groups where a rational design of the milling parameters led to the synthesis of advanced materials with novel properties such as unconventional arrangements of metals on the surface of oxide support materials, highly dispersed metals or the stabilisation of species in particular oxidation states. These properties resulted in superior catalytic performances of the mechanochemically-synthesised catalysts compared to their counterparts prepared by traditional impregnation methods. To illustrate these advances, we review the progress made in two important fields of catalysis where noble metals are used: (i) emission control catalysis using palladium-based materials; (ii) the development of photocatalysts to produce hydrogen based on gold and palladium materials.

Air-stable and reusable porous silica-supported ultrafine Nix-NiO nanoparticles for semi-hydrogenation of alkynes

The practical application of non-noble metal-based hydrogenation catalysts is limited because of their low activity and easy oxidation in air. Here, porous silica-supported ultrafine nickel oxide (NiO) was prepared by calcining an organic–inorganic hybrid 3D nanomaterial that was formed via the Michael addition/Schiff’s base reaction, and hydrolyzation of triethoxysilane. NiO nanoparticles with ca. 2.6 nm diameter was uniformly dispersed and confined in the cogenerated mesoporous SiO2 skeleton, thanks to the coordination between pyrogallol/amino units and Ni2+ ions, and the isolation effect of Si-O-Si network. The as-prepared catalyst featured mesoporous structure and high specific surface area (715 m2/g), and exhibited excellent activity, selectivity and reusability in the semi-hydrogenation of alkynes. Small amount of metallic nickel (Nix-NiO) that formed on the surface of NiO nanoparticles during the semi-hydrogenation acted as the active species, and the moderate adsorption/desorption energies on Nix-NiO facilitated the activity enhancement. Most importantly, it showed constant catalytic activity and selectivity after a long-term storage in air. This work provides a green and feasible strategy, as an alternative to the traditional impregnation method, for the preparation of ultrafine metal-supported catalysts with air-stability and reusability.

Densification of SiCf/mullite composite via vacuum pressure impregnation process towards excellent mechanical and microwave absorbing performance

A simple and low-cost method for preparing SiCf/mullite composites with high density, mechanical, and absorbing performance using a vacuum pressure impregnation (VPI) system has been developed. The densification mechanism of the mullite matrix was investigated, and the effects of impregnation pressures on the flexural strength, interfacial bonding strength, and the electromagnetic wave (EMW) absorbing performance of SiCf/mullite composites were also studied. The dense composite was prepared under 3 MPa pressure with a porosity of 6.23 % and median pore diameters (MPDs) of 13.02 nm. The preparation efficiency was improved with the impregnation circles decreased from 20 times to 13 times. The flexural strength of SiCf/mullite composites prepared by VPI is 297 MPa, which is improved 230 % of the one prepared by the traditional vacuum impregnation method. Benefiting from the synergistic effects of appropriate impedance matching and multiple polarization loss, the effective absorption bandwidth (EAB, RL < −10 dB) of the SiCf/mullite composites increases from 2.17 GHz to 2.80 GHz in the X band.This work has a positive application value for the manufacture of high-strength EMW absorbing composites in terms of significantly reducing the preparation cost and cycle duration.

Architecting multi-active center on 3DOM La0.76Ce0.19Ag0.05Mn0.9Co0.1O3-δ perovskite for soot oxidation

Precise construction of multiple active centers on perovskite oxides is recognized as a feasible and promising strategy to cooperatively promote the catalytic performances. Herein, 3DOM La0.76Ce0.19Ag0.05Mn0.9Co0.1O3-δ perovskite was designed and further treated within H2/N2 flow. High-temperature reduction did not destroy the original structure of perovskite, while the lattice Ag and Co were exsolved on perovskite surfaces to form Ag/Ag2O and Co@Co3O4. Compared with the traditional impregnation method, this strategy provided the active nanoparticles with smaller size, higher dispersion, and stronger interaction with perovskite matrix. XPS and O2-TPD indicated that the exsolved Ag and Co components could not only act as the O2 activation sites to accelerate the generation of active oxygen species on surfaces, but also offered the electrons to the oxygen vacancy on the perovskite. In addition, the vacancy formed after A-site and B-site cations exsolution could also adsorb and activate O2, ultimately boosting the catalytic combustion of soot. As a result, the developed perovskite exhibited a competitive catalytic activity with the T50 of 364 ℃ under the condition of 500 ppm NO + 5 % O2/N2. This work offered a facile and effective pathway to assemble high-performance perovskite-type oxides for heterogeneous catalysis.

Novel BaO-decorated carbon-tolerant Ni-YSZ anode fabricated by an efficient phase inversion-impregnation approach

In this study, an efficient phase inversion-impregnation approach is developed for fabricating BaO-decorated Ni-8 mol% yttria-stabilized zirconia (YSZ) anode-supported tubular solid oxide fuel cells (SOFCs) toward anti-coking. This technique involves a simple phase-inversion process, along with the saturated barium nitrate solution as coagulation bath. Experimental results show that BaO nanoislands with particle size of less than 100 nm have been successfully and uniformly introduced inside the Ni-YSZ anode. The corresponding peak power densities are determined to be 0.30 W cm−2 and 0.22 W cm−2 at 800 °C in wet hydrogen and methane fuel, respectively. The long-term stability in methane fuel with the BaO-decorated anode is significantly improved with respect to the pristine one. Density functional theory (DFT) calculations suggest that the loading of BaO nanoislands can efficiently capture and dissociate the H2O molecules to generate OH, which subsequently serves as effective carbon elimination medium. The OH diffusion from BaO to BaO/Ni interface coupling with the formation of COH is the key step involved in the carbon elimination mechanism. The as-proposed phase inversion-impregnation approach exhibits advantage in time and cost savings compared to traditional impregnation methods, providing a new route for fabricating anti-coking SOFC anodes.

Supported Ni Catalysts: Simple Vapor Deposition Preparation Method and Improved Catalytic Performance for Oxidative Dehydrogenation of Ethane.

Developing new methods of catalyst preparation is one of the most important tasks in the field of catalysis. A simple one-tube vapor deposition (VD) is provided in this paper for preparing the supported Ni catalyst. Ni(acac)2 was used as the Ni precursor. This preparation method was successfully applied to three types of catalytic supports, that is, Al2O3 and zeolites 5A and Hβ. Varying Ni contents of less than 8 wt % can be obtained by employing different conditions. The Ni content, depending on different deposition conditions, was preliminarily explored. The catalytic performance for oxidative dehydrogenation of ethane (ODHE) was tested for the prepared Ni catalysts by the VD method. Several cases of catalytic tests showed that for the same Ni content, the VD-prepared Ni catalyst presented better performance for ODHE than the one prepared by a traditional impregnation method. Besides the improvement in catalytic performance, several advantages of our VD preparation method for catalysis are discussed.

Sintering resistance of Pt-based oxidation catalyst via constructing Pt/MnOx interface

It is a challenge to improve the catalytic activity and hydrothermal stability of platinum-based catalyst in concurrently oxidizing CO/C3H6/NO. The construction of Pt/MnOx interface over Pt-based diesel oxidation catalyst via overlayer deposition to form partial-embedded structure, inhibiting the aggregation of platinum nanoparticles in Ostwald Ripening process. Even after hydrothermal aging, the average platinum particle size is equal to that of the fresh catalyst via traditional impregnation method. The electronic-transferring from platinum to manganese results in a weaker CO adsorption ability on Pt species and an improved oxygen activation ability with the help of the redox cycle of Pt and MnOx, as well as the formation of more active nitrate species via in situ DRIFTs. Measurement on the activity shows the lower apparent activation energy, so that the light-off temperature of CO/C3H6/NO on the partial-embedded catalyst via overlayer deposition method decreases by around 20 °C and 40% NO maximum conversion still keeps after severely aging comparing with the traditional catalyst. The work enlightens us the importance of interface sites in stabilizing platinum atoms and creating oxidize active sites.

Modulating Pt nanoparticles confined in UiO-66 by linker functional groups for controllable hydrogenation

Encapsulation of clean metal nanoparticles (NPs) into interior of metal–organic framework (MOF) is of great importance to remarkably improve the stability and tune the catalytic performance of metal NPs. Herein, highly dispersed Pt NPs are encapsulated in UiO-66 with different functional groups on linker (UiO-66-X, X = F, H, NH2, OH) through enhanced electron attraction of metal precursor by MOF node and proper reduction by H2/Ar gas. Compared with traditional impregnation method, the encapsulation method gives well-defined Pt NPs and controllable microenvironment. Detailed characterizations reveal that functional group of the linker can effectively tune the microenvironment and electronic properties of guest Pt NPs. In situ FTIR was utilized to investigate the adsorption capability and strength of reactants on the catalysts. The electron-deficient Pt species and appropriate surface hydrophobicity match well with the reactants, which is responsible for enhanced catalytic hydrogenation activity of CC and nitro groups. The surface hydrophobicity plays a major role in promoting alkyne hydrogenation. This work is devoted to rationalize the relationship between hydrogenation performance and catalyst property of UiO-66 encapsulated Pt NPs, in terms of energy adaptability in electronic state and structure adaptability in surface chemistry. Rational design strategy of Pt-confined-in-MOF composites through molecular level regulation is provided for hydrogenation.

Confining Co-Based Nanocatalysts by Ultrathin Nanotubes for Efficient Transfer Hydrogenation of Biomass Derivatives.

Catalytic transfer hydrogenation (CTH) based on non-noble-metal catalysts has emerged as an environmentally friendly way for the utilization of biomass resources. However, the development of efficient and stable non-noble-metal catalysts is crucially challenging due to their inherent inactivity. Herein, a metal-organic framework (MOF)-transformed CoAl nanotube catalyst (CoAl NT160-H) with unique confinement effect was developed via a "MOF transformation and reduction" strategy, which exhibited excellent catalytic activity for the CTH reaction of levulinic acid (LA) to γ-valerolactone (GVL) with isopropanol (2-PrOH) as the H donor. Comprehensive characterizations and experimental investigations uncovered that the confined effect of the ultrathin amorphous Al2O3 nanotubes could modulate the electronic structure and enhance the Lewis acidity of Co nanoparticles (NPs), thus contributing to the adsorption and activation of LA and 2-PrOH. The synergy between the electropositive Co NPs and Lewis acid-base sites of the CoAl NT160-H catalyst facilitated the transfer of α-H in 2-PrOH to the C atom of carbonyl in LA during the CTH process via a Meerwein-Ponndorf-Verley mechanism. Moreover, the confined Co NPs embedded on am-Al2O3 nanotubes endowed the CoAl NT160-H catalyst with superior stability and the catalytic activity was nearly unchanged for at least ten cycles, far surpassing that of the Co/am-Al2O3 catalyst prepared by the traditional impregnation method.

Selective Amination of Benzaldehyde over the Fine Ru Nanoparticles Anchored in NiO Catalysts

The selective amination of benzaldehyde (BZH) is one of the important industrial reactions for the production of fine chemicals. Herein, we synthesized a Ru/NiO nanocatalyst with an extremely low loading of noble metals (0.22%) via a facile ball-milling method efficient for the conversion of BZH to N-benzylidenebenzylamine (N-BDB). Compared with the benchmark im-Ru/NiO catalyst prepared via the traditional impregnation (im) method, the Ru/NiO catalyst exhibited the higher yield of N-BDB, with a full conversion of BZH and a 91.5% selectivity to N-BDB in 0.1 MPa NH3 and 2 MPa H2 pressure. After that, various parameters that influenced the catalytic performance and potential reaction pathway were investigated. In addition, the catalyst maintained high stability, which could be recycled even for five runs without obvious deactivation. Extensive characterizations verified that the H2 activation ability of Ru and the overall acidity of the Ru/NiO catalyst were improved, which should account for the superior catalytic performance. This work provides a facile strategy of catalyst synthesis for the selective production of fine chemicals.

Mercaptopropane-assisted synthesis of graphitic carbon-supported Pt nanoparticles for enhancing fuel cell start-stop performance

Although graphitic carbons, as a support for the cathode catalyst in proton exchange membrane fuel cells, have significant advantages in enhancing the corrosion resistance of the catalyst, the preparation of small-sized Pt particles on the graphitic carbon support often faces challenges due to its low porosity and lack of defect structures. Here, we report a mercaptopropane-assisted impregnation method to achieve size control of Pt nanoparticles on graphitic carbon. We show that mercaptopropane can coordinate with Pt during the impregnation process and transform into sulfur-doped carbon coatings through the subsequent thermal reduction process, which ensures the formation of small-sized Pt nanoparticles on graphitic carbon. Due to effective size control, the prepared cathode catalyst exhibited enhanced fuel cell performance compared to the catalyst prepared by the traditional impregnation method. We performed the accelerated stress test on the synthesized catalyst using the durability protocol recommended by the U.S. Department of Energy (DOE). After 5000 voltage cycles in the range of 1.0–1.5 V, the catalyst showed a negligible voltage loss of only 10 mV at a current density of 1.5 A·cm&lt;sup&gt;−2&lt;/sup&gt;, meeting the DOE support durability target (30 mV).

Mesoporous sol-gel silica supported vanadium oxide as effective catalysts in oxidative dehydrogenation of propane to propylene.

Vanadium oxide incorporated mesoporous silica (V-m-SiO2) were designed and synthesized using a surfactant-modified sol-gel method. Detailed characterization shows that monomeric [VO4] sites containing one terminal V[double bond, length as m-dash]O bond and three V-O-support bonds are dominated until atomic ratio of vanadium to silicon approaches to 5%. It is also confirmed that such V-m-SiO2 catalyst contains high proportion of vanadium oxide species interacting strongly with silica. Compared to vanadium oxide supported mesoporous silica (V/m-SiO2) prepared using a traditional impregnation method, present V-m-SiO2 catalyst exhibits more superior ability to catalyze oxidative dehydrogenation of propane to propylene. By correlation with structural data, superior catalytic performance of present V-m-SiO2 catalyst can be reasonably attributed, in part, to its favorable geometric and electronic properties rendered by the unique preparation method.

Designing high efficiency graphite felt electrode via HNO3 vapor activation towards stable vanadium redox flow battery

A new method of preparing nitric acid vapor treated graphite felt for vanadium redox flow battery (VRFB) is developed. This method outperforms traditional impregnation methods in convenience, efficacy and controllability of fabrication process. A sequence reaction mechanism is proposed for nitric acid vapor treated graphite felt reactions occurring at 200 °C. The modified-graphite felt (m-GF) with excellent electrocatalytic redox reversibility toward VO2+/VO2+ and V2+/V3+ redox couples is prepared in the conditions of VHNO3/mpGF=0.45 mL g−1 at 200 °C in 300 min (m-GF-0.45). The nitric acid vapor reaction with graphite felts occurs preferentially on the surface of amorphous carbon and at defect sites in the graphitic structure, yields N2 and carbon-oxygen surface complexes, resulting in a higher double layer capacity (DLC) from 146 μF mg−1 (p-GF) to 1514 μF mg−1 (m-GF-0.45). Thus, the energy efficiency and discharge capacity of m-GF-0.45 electrode increases significantly by 8.7% and 100% at 150 mA cm−2, respectively.

Exploratory Pressure Impregnation Process Using Supercritical CO2, Co-Solvents, and Multi-Cycle Implementation

Supercritical carbon dioxide (scCO2) is extensively used for extracting chemicals from materials, but the impregnation of materials with chemicals using scCO2 has received little attention in comparison. To the best of our knowledge, most technologies described in the literature operate by the principle of diffusion, where impregnation yield is limited by solubility. The objective of this exploratory study is to prove the feasibility of an scCO2 impregnation process that can extract solutes from one material and release them into another material through a single extraction/impregnation stage that can be applied in cycles to increase the yield. The feasibility of the concept was proven in the laboratory using radiata pine bark wax as the solute and radiata pine wood as the impregnated material. Extraction/impregnation tests were performed at temperatures between 40 and 60 °C, pressures between 12 and 16 MPa, and with the addition of ethanol and acetone as co-solvents. The study demonstrated the feasibility of multi-cycle scCO2 impregnation of wax into wood, where the novelty of the concept is the implementation as traditional pressure impregnation methods.