Monolithic Catalysts Research Articles

Nickel foam based monolithic catalyst supporting transition metal oxides for toluene combustion: Experimental and theoretical study of interfacial synergistic oxidation and water resistance

Composite oxides obtained by calcining layered double hydroxides (LDHs) were used to construct a functional hydrolysis interface. Using nickel foam (NF) as a carrier, LDH was produced on the surface of this monolithic catalyst. The original morphology was retained after calcination. NF provided better thermal conductivity for catalytic combustion than conventional cordierite carriers. The clear phase interface between the different mixed metal oxides (CuxCo3-xFe-MMO/NF) promoted oxidation and hydrolysis during toluene combustion. Physicochemical investigations were performed using XRD, SEM, TEM, H2-TPR, ESR, and XPS. GC–MS, in situ DRIFT, H2O-TPD, and DFT were also used to explore the deep hydrolysis mechanism. The dissociation of water to form the surface *OH was the main hydrolysis process owing to the existence of the Cu-Co functional interface, with the largest energy emission (0.56 eV from DFT calculations). This hydrolysis process also altered the toluene degradation pathway, as confirmed by the in situ DRIFTS and GC/MS results, which guaranteed significant stability of the Cu1Co2Fe-MMO/NF catalyst in a highly humid environment and the removal efficiency and mineralization of toluene were both >90 % below 270 °C. This monolithic catalyst exhibits excellent water resistance and the toluene conversion rate remained stable at 90 % without any attenuationhas >40 h, which provides potential utility in the combustion of volatile organic compounds in high-humidity industrial streams.

Rapid Plasma Electrolytic Oxidation Synthesis of Intermetallic PtBi/MgO/Mg Monolithic Catalyst for Efficient Removal of Organic Pollutants.

The intermetallic PtBi/MgO/Mg monolithic catalyst was first prepared using non-equilibrium plasma electrolytic oxidation (PEO) technology. Spherical aberration-corrected transmission electron microscope (ACTEM) observation confirms the successful synthesis of the PtBi intermetallic structure. The efficiency of PtBi/Mg/MgO catalysts in catalyzing the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of NaBH4 was demonstrated. The activity factor for the catalyst is 31.8 s-1 g-1, which is much higher than reported values. In addition, the resultant catalyst also exhibits excellent catalytic activity in the organic pollutant reaction of p-nitrobenzoic acid (p-NBA) and methyl orange (MO). Moreover, benefiting from ordered atomic structures and the half-embedded PtBi nanoparticles (NPs), the catalyst demonstrates excellent stability and reproducibility in the degradation of 4-NP. This study provides an example of a simple method for the preparation of intermetallic structures as catalysts for organic pollutant degradation.

Structure characterization of aged automobile exhaust catalysts using electron probe microanalysis

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

Synergistic roles of Ru, CeO2, and HZSM-5 in a ternary-active center catalyst for catalytic destruction of dichloromethane

Developing well-qualified industrial catalysts with excellent oxidation ability, selectivity, and resistance is still a challenge for chloroalkane destruction. Herein, we optimized the composition of multi-component catalysts with diverse active sites to adjust their acidic and redox properties for reasonable catalytic performance. The synergy of redox center Ru, activation center CeO2, and acid center HZSM-5 endowed the ternary catalyst Ru/CeO2/HZSM-5 with superior low-temperature activity (30 ∼ 60 °C lower for 50 % conversion), promoted stability and chlorine tolerance (100 % conversion for at least 30 h), and less toxic by-products for dichloromethane (DCM) destruction compared with the binary ones, promising for industrial application under tough conditions (e.g., thermal shock, HCl, H2O). The strong interaction of Ru and CeO2 enhanced the redox property of Ru/CeO2/HZSM-5 and thus promoted the deep oxidation of DCM and intermediates, thereby generating more CO2 and less dechlorinated by-products (e.g., CH3Cl). The synergistic effects of Ru, CeO2, and HZSM-5 facilitated chlorine removal and suppressed the generation of polychlorinated by-products (e.g., CHCl3) over the Ru/CeO2/HZSM-5 catalyst by improving redox capacity and inhibiting reactivity of chlorine. Notably, the introduction of CeO2 weakened the hydrophilicity of Ru and HZSM-5, improving the water resistance of the catalyst. The corresponding monolithic catalyst could achieve complete oxidation of DCM at 400 °C with the total concentration of dioxins measured at 0.026 ng I-TEQ kg−1 after continuous operation at 250 °C for 30 h.

Detailed kinetic modeling of catalytic oxidative coupling of methane

The oxidative coupling of methane (OCM) at high temperature over monolithic Pt-based catalysts operated at short contact times is investigated as an attractive method for methane upgrading to higher value products like ethylene and acetylene. An experimental measurement campaign aiming at elucidating the effect of operation parameters on the catalyst performance revealed that lower N2 dilution, lower CH4/O2 ratio, and higher space velocities promote high C2 yields. A maximum C2 yield of 10 % with 94 % CH4 conversion was obtained at a CH4/O2 ratio of 1.1, 50 % N2 dilution, and a space velocity of 4.5 × 105 h−1. Since both heterogenous and homogenous gas-phase chemistry together are required for determining C2 formation pathways, a detailed OCM surface reaction mechanism over Pt is presented consisting of 26 species and 86 reactions that are consistent from the view of thermodynamics and micro-kinetic reversibility. The combination of this OCM surface mechanism with a detailed gas-phase mechanism allows a numerical micro-kinetic description of the experimental measurements. The simulations presented in this study suggest that C2 formation takes place in the gas-phase at temperature above 1200 K with both oxidative and pyrolytic pathways for methane dehydrogenation to form CH3 radicals, whose coupling results in C2H6, C2H4 and C2H2 formation. Furthermore, the simultaneous presence of sufficient oxygen content and heat are vital for high C2 species yields.

Logical formulation and in-situ assembly of MnCo2O4@MnO2 nanoflower arrays on nickel foam as monolithic catalyst for formaldehyde degradation at indoor temperature

The development and design of efficient and cost-effective catalysts for oxidizing low concentrations of formaldehyde at low temperatures, has been a significant challenge in HCHO oxidation. In this study, MnCo2O4@MnO2-NF (Ni foam) was synthesized as a monolithic catalyst for the degradation of HCHO in indoor environments. Using carrier immobilization, morphology modulation, and doping modification. The results revealed that the Co3O4 nanoarrays could be grown in a directional and orderly manner on the surface of the substrate through morphological modulation, showing a pompom-like, flower-like shape of the nanoneedles, thus providing sufficient growth sites for MnO2. Doping the Co3O4 nanoarrays with Mn via in-situ growth resulted in MnCo2O4 nanoarrays, following which the MnO2 expanded the pore sizes of the sample and provide more surface adsorption sites upon using MnCo2O4 as the carrier. In addition, numerous oxygen vacancies formed on the catalyst surface because of the synergistic interaction between Co and Mn, which formed more Mn3+ species and Oads, resulting in superior low-temperature redox ability and catalytic cycle stability. The catalyst achieved a HCHO removal efficiency of over 85 % within 60 min for five test cycles when the KMnO4 concentration was 0.05 M and Mn/Co ratio was 1:2.

Catalytic combustion of toluene over cerium modified CuMn/Al2O3/cordierite monolithic catalyst

Catalytic combustion is an effective approach to remove volatile organic compounds, in which the development of highly active and durable catalyst is extremely crucial. Herein, a series of CuMnCex/Al2O3/cordierite monolithic catalysts were synthesized by using the ultrasonic-assisted impregnation method. The physicochemical properties were comprehensively characterized via the BET, XRD, SEM, EDX, H2-TPR, O2-TPD, XPS and EPR techniques. The results showed that the catalytic activity of CuMnCex/Al2O3/Cor for toluene combustion was strongly affected by the Ce content. The CuMnCe2/Al2O3/Cor monolithic catalyst showed the best catalytic activity with toluene conversion of 90% at 263 °C under toluene concentration of 1 g/L and space velocity of 78000 mL/(g·h). Meanwhile, the well-dispersed CeO2 in the CuMn matrix not only improved the content of oxygen vacancies and the mobility of oxygen species, but also enhanced the low-temperature reducibility of the catalyst. Moreover, the CuMnCe2/Al2O3/Cor monolithic catalyst exhibited an excellent stability in the long-term test and cycle ability test.

Ionic liquids assisted construction of efficient ceramic-based catalyst by direct ink writing 3D printing for ultra-deep oxidative desulfurization of diesel

3D-printed monolithic catalysts have attracted extensive attention in the petrochemical industry due to significant advantages of excellent circulation, mass and heat transfer efficiency and convenience. However, according to the characteristics of each chemical reaction, there are diversity and difficulty in the design of monolithic catalysts, especially the regulation of catalyst ink, the introduction of active centers and the construction of reaction pores. In this work, we report a preparation of ceramic-based catalysts with direct ink writing (DIW) 3D printing technology for ultra-deep oxidative desulfurization (ODS) of diesel. Through a series of rheological analyses of catalyst inks, the effects of ink composition and content on fluidity and viscoelasticity are explored for the forming mechanism of high-quality 3D printed inks. Besides, ionic liquids (ILs) [C12Vim]3PMo12O40 and mordenite are cleverly introduced into the 3D printed ink for assisted construction of active center and reaction channel in functionalization of the ODS catalyst. The DBT removal of 3D-MoO3/BT-MOR can reach 100 % and this monolithic catalyst is easy to be separated from oil. This work is deeply focused on the preparation and molding of catalyst inks to achieve efficient monolithic catalysts that provide an excellent path for many industrial oxidation reactions.

3D printed cross-scale structured TS-1 catalysts for continuous scale-up reactions

Structured catalysts and reactors have great application prospects in gas-liquid conversion engineering due to excellent process intensification. However, the conventional fabrication process limits the designability of the hierarchical structure of monolithic catalysts, the establishment of structure-activity relationships, and slows down the speed of catalyst development. Here, we establish a structure-activity mechanism for cross-scale structures of a 3D-printed functionally gradient modular monolithic TS-1 catalyst (FGMMC) and catalytic performance by adjusting hierarchical structure distribution based on catalytic reaction simulations. The effects of uniform and gradient structures with different TS-1 contents and unit cell sizes on the catalytic properties of modular monolithic TS-1 catalyst (MMC) were investigated. In one-step scale-up reactions of ethylene to high-value-added ethylene glycol (EG), FGMMC exhibits superior catalytic efficiency than traditional powder, extrusion-dripping beads, and uniform catalysts. After a 27-h continuous scale-up catalytic test, FGMMCs exhibit excellent wear resistance (only 1.39% mass loss) and an outstanding EG yield of 82.5%. 3D-printed FGMMCs act as self-activators with a 37% reaction rate increase after rapid post-activation treatments. This work provides a low-cost and recyclable manufacturing method for achieving the functional and structural integration of catalysts and reactors by 3D printing while predicting and rapidly validating scale-up reactions.

Highly stable 3D-printed monolithic Al2O3-supported Ni-based structured catalysts for dry reforming of methane

Nickel (Ni)-based powder catalysts with poor stability used in dry reforming of methane (DRM) suffer from severe coking and high bed pressure drop. We successfully prepared a monolithic NiAl2O4/Al2O3 structured catalyst using 3D printed α-Al2O3 topological carrier followed by Ni impregnation and calcination at 1400 oC to improve the stability and decrease the pressure drop. The monolithic Ni/NiAl2O4/Al2O3 structured catalyst reduced from NiAl2O4/Al2O3 could inhibit coke accumulation effectively and exhibit excellent catalytic performance. During the 750-h stability test, monolithic Ni/NiAl2O4/Al2O3 catalyst exhibited 3% CH4 conversion degradation and 0.37 mgC h-1 gcat-1 coke accumulation rate. The formation mechanisms of two different types of cokes were proposed to explain the performance. Monolithic Ni/NiAl2O4/Al2O3 structured catalyst also exhibited a lower pressure drop and superior stability than the powder catalyst. This work serves as a guide for preparing the monolithic Ni-based structured catalyst with outstanding stability and low pressure drop for practical application in DRM.

Spatiotemporal insights into forced dynamic reactor operation for fast light-off of Pd-based methane oxidation catalysts

Spatial profiling uncovers axial gradients in a monolithic methane oxidation catalyst during dynamic operation, which enables a substantial activity enhancement.

A 3D-printed CuNi alloy catalyst with a triply periodic minimal surface for the reverse water-gas shift reaction

A monolithic CuNi alloy catalyst with a typical triply periodic minimal surface, which is fabricated using 3D printing technology, exhibits significantly enhanced mass and heat transfer as well as exceptional stability towards the RWGS reaction.

Monolithic catalysts loaded with ZIF-derived Co3O4 on copper foam for the catalytic oxidation of toluene: the impact of synthetic methods

Monolithic catalysts loaded with ZIF-derived dodecahedral Co3O4 on copper foam for the efficient catalytic oxidation of toluene.

Te-doped-WSe2/W as a stable monolith catalyst for ampere-level current density hydrogen evolution reaction.

The development of efficient electrocatalysts for the hydrogen evolution reaction (HER) holds immense importance in the context of large-scale hydrogen production from water. Nevertheless, the practical application of such catalysts still relies on precious platinum-based materials. There is a pressing need to design high-performing, non-precious metal electrocatalysts capable of generating hydrogen at substantial current levels. We report here a stable monolith catalyst of Te-doped-WSe2 directly supported by a highly conductive W mesh. This catalyst demonstrates outstanding electrocatalytic performance and stability in acidic electrolytes, especially under high current conditions, surpassing the capabilities of commercial 5% Pt/C catalysts. Specifically, at current densities of 10 and 1200 mA cm-2, it exhibits a minimal overpotential of 79 and 232 mV, along with a small Tafel slope of 55 mV dec-1, respectively. The remarkable catalytic activity of Te-WSe2 can be attributed to the exceptional electron transfer facilitated by the stable monolithic structure, as well as the abundant and efficient active sites in the material. In addition, density functional theory calculations further indicate that Te doping adjusts H atom adsorption on various positions of WSe2, making it closer to thermal neutrality compared to the original material. This study presents an innovative approach to develop cost-effective HER electrocatalysts that perform optimally under high current density conditions.

Novel TPMS carbon-based monolithic catalysts by three-dimensional printing for enhancement of nitrobenzene hydrogenation reaction

Preparation of periodic curved surface, structured, carbon-based catalysts using a 3D printing method achieved good results in the hydrogenation of nitrobenzene to aniline in a packed-bed micro-reactor.

Atomic layer deposition of Pd nanoparticles and single atoms on self-supported carbon monolithic catalysts synergistically boosts the hydrogen evolution reaction

Pd nanoparticles and Pd single atoms were anchored on carbonized wood. Pd NPs facilitated the decomposition of water while the Pd SAs promoted the adsorption of H.

CeO2-modified monolithic ceramic foams for efficient catalytic ozonation of refractory organic pollutants in a continuous-flow reactor

The monolithic catalyst of CeO2-loaded ceramic foam for the catalytic ozonation of organic pollutants operated in a continuous-flow mode was developed, achieving effective TOC removal of organic pollutants and high utilization efficiency of ozone.

Monolithic Catalyst of Ni Foam-Supported MnOx for Boosting Magnetocaloric Oxidation of Toluene.

Catalytic oxidation has been considered an effective technique for volatile organic compound degradation. Development of metal foam-based monolithic catalysts coupling electromagnetic induction heating (EMIH) with efficiency and low energy is critical yet challenging in industrial applications. Herein, a Mn18.2-NF monolithic catalyst prepared by electrodeposition exhibited superior toluene catalytic activity under EMIH conditions, and the temperature of 90% toluene conversion decreased by 89 °C compared to that in resistance furnace heating. Relevant characterizations proved that the skin effect induced by EMIH encouraged activation of gaseous oxygen, leading to superior low-temperature redox properties of Mn18.2-NF under the EMIH condition. In situ Fourier transform infrared spectroscopy results showed that skin effect-induced activation of oxidizing species further accelerated the conversion of intermediates. As a result, the Mn18.2-NF monolithic catalyst under EMIH demonstrated remarkable performance for the toluene oxidation, surpassing the conventional nonprecious metal catalyst and other reported monolithic catalysts.

Fabrication of bimetallic Co/Ni composite oxides on Ni-foam as a highly active monolithic membrane catalyst for the reduction of 4-nitrophenol

The development of highly active non-noble metal catalysts is the prerequisite for the practical application of the reduction of 4-nitrophenol (4-NP) into 4-aminophenol (4-AP) by NaBH4. In this work, inexpensive Co/Ni bimetallic composite oxide integral membrane catalysts with different metal-ion molar ratios towards 4-NP reduction were grown on the nickel foam (NF) substrate by a facile oxalate-pyrolysis method. Benefiting from the synergistic effect between Co and Ni elements, special crystalline phase of NiCo2O4 with high electron transfer capacity and uniform nanoflake array structure, the NF-based monolithic membrane catalyst with a Co/Ni molar ratio of 2:1 (Co2Ni1) exhibited the optimal activity for the catalytic reduction of 4-NP. A reduction ratio of 96.71% for 250 mL of 4-NP with an initial concentration of 15 mg/L could be reached within 25 min under the reaction conditions as follows: two pieces of Co2Ni1 catalytic membranes (20 × 40 mm2), 0.015 mol/L NaBH4 and a temperature of 25 °C. The corresponding kinetic reaction rate constant was 0.1410 min−1, which was 2.0 and 15.5 times higher than that of pure Co3O4 and NiO. Moreover, the activation energy, enthalpy and entropy for the reaction were calculated as 17.44 kJ/mol, 14.97 kJ/mol and −210.61 J•mol−1•K−1, respectively. Notably, the reduction rates of 4-NP remained at around 97% during thirteen consecutive catalytic runs, indicating the good reusability of the Co2Ni1 integral membrane catalyst. These results show that NF-based Co/Ni composite oxide membrane is a promising integral catalyst for converting of 4-NP into 4-AP owing to its excellent properties and easy recovery feature.

Selective catalytic oxidation of ammonia to nitrogen on mixed and dual-layer monolithic catalysts

In this paper, the effects of mixed and dual-layer monolithic catalysts on NH3 conversion efficiency and by-product formation performance were studied under different conditions, in order to find a coating structure with both high activity and high N2 selectivity. The results show that in the absence of NO, the dual-layer structure of Cu-SSZ-13 as the top layer and Ag/Al2O3 as the bottom layer reduces the NH3 conversion efficiency, and the NH3 conversion efficiency further decreases with the increase of the catalyst loading on the top layer, and this trend is further strengthened at higher space velocity. However, the dual-layer catalyst significantly reduces the formation of NOx byproducts. At 600 ℃, NO decreases from 305 ppm in single-layer to 51, 40 and 35 ppm respectively, NO2 and N2O are hardly produced on the dual-layer structure catalyst. In the presence of NO, the dual-layer catalyst is conducive to improving the conversion efficiency of NH3 and NO, and the conversion efficiency of NH3 and NO will be further improved with the increase of Cu-SSZ-13 catalyst loading. In addition, the results of catalytic oxidation performance of mixed structure and dual-layer catalyst under different air conditions show that the mixed structure catalyst has a higher NH3 conversion efficiency than the dual-layer catalyst in the absence of NO, but the by-product generation amount of the mixed structure catalyst is slightly higher than that of the dual-layer catalyst. In the presence of NO, the dual-layer catalyst showed a higher NO conversion efficiency than the mixed catalyst.