Cordierite Honeycomb Ceramics Research Articles

Cordierite ceramic membrane preparation using gas solid reaction growth for nanoparticles filtration

Mullite whiskers have been successfully grown on the surface of cordierite honeycomb ceramics by the gas-phase growth method. The cilia-like structure can significantly improve the filtration precision. The acicular mullite whiskers grew on the cordierite present nanometer-sized (200–300 nm) diameters and micrometer-sized (1–2 μm) lengths. Owing to mullite whiskers growth on surface of pores, the morphology of pores is changed and the microstructure change will lead to filtration precision increasing. The composites with the largest ratio of length/diameter mullite whiskers possess the highest filtration precision, which can reach 122.42 nm, 255.00 nm and 458.67 nm in intercepting different particle size of nano-SiO2, respectively. Moreover, the bending strength of the cordierites were enhanced due to the generation of mullite whiskers, these generated whiskers intersected with each other forming many unfixed lap-jointing points. The porous ceramics membrane with the unique microstructure has great potential application in gas-solid separation field and liquid-solid separation field.

Low-Temperature Catalytic Oxidation of Volatile Organic Compounds (VOCs) using Transition Metal Mixed Oxide Catalysts

This paper discusses the modification of MnOx by doping various metals, such as Cu, supported on cordierite honeycomb ceramics, which were easily synthesized by using the impregnation method. The physicochemical properties were comprehensively featured via the BET, XRD, SEM-EDX and H2-TPR techniques. Activity results suggested that the introduction of doping metals significantly enhanced the catalytic performance of Cu1Mn2Ox compared to single metal oxides. Furthermore, in the catalytic oxidation of benzene and toluene, the monolithic Cu1Mn2Ox catalyst demonstrates the best catalytic performance. It was able to completely oxidize the two compounds at 275oC with a reaction velocity (WHSV) of about 18,000 mL/(g•hr) and pollutant concentrations of 7000 ppm and 12000 ppm, respectively. The formation of a Cu-Mn solid solution with spinel Cooper-Manganese structure was thought to be the cause of the excellent catalytic performance of monolithic Cu1Mn2Ox. This resulted in an increase in the amount of adsorbed oxygen species on the surface and a high lattice oxygen mobility. This can improve catalyst reducibility and oxygen species activity, as demonstrated by significantly higher dehydrogenation temperatures of Cu-Mn composite oxides through H2-TPR. Meanwhile, the monolithic Cu1Mn2Ox catalyst showed good stability in 16 hours of testing and cycle ability test and showed great potential in practical application.

Quench-induced Cu-ZnO catalyst for hydrogen production from methanol steam reforming

Methanol steam reforming (MSR) is considered as a promising approach to provide hydrogen for proton-exchange membrane fuel cells. However, it is challenging to develop effective and durable Cu-based catalysts. Herein, Cu-ZnO catalysts are prepared by facile quenching of ZnO in copper nitrate solution followed by reduction to obtain the desired metal loading and induce the doping of surface metal heteroatoms for producing more vacancies. Catalysts enriched with oxygen vacancies can efficiently activate H2O and rapidly transform C-containing intermediates, resulting in higher methanol conversion and lower CO selectivity. As a result, the quenched optimal catalyst achieves 100 % methanol conversion and 0.05 % CO selectivity at 280 ℃, exhibiting the excellent catalytic performance in MSR reaction. In practical applications, structured catalysts are more attractive for large-scale catalytic reactions owing to the low pressure drop and high utilization efficiency. Therefore, ZnO-Cu3 catalyst is coated on cordierite honeycomb ceramics with 100 % methanol conversion and 0.04 % CO selectivity at 280 ℃. After 100 h of the reaction, the structured catalyst remains ∼ 92.3 % with CO selectivity varying from 0.02 to 0.06 %, demonstrating the good catalytic stability in the long-term experiment. In addition, the evolution of reactants and intermediates on the catalyst surface are briefly described by FTIR spectra. This study offers a novel and efficient approach to obtain highly active and durable catalysts with great potential for industrial-scale preparation and application.

Preparation and characterization of Na4Mn9O18 whiskers on channel surface of cordierite honeycomb ceramics for soot catalytic combustion

Na4Mn9O18 whiskers were prepared on the wall of cordierite honeycomb ceramics using the molten salt synthesis, and Na4Mn9O18 whiskers were grew on channel surface of cordierite honeycomb ceramics to form hierarchical microstructure for catalytic combustion of soot. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were used to characterize the structural morphology and phase compositions. Na4Mn9O18 whiskers with aspect ratio of 24.4 measured by statistics. It was found that the loading rate of the monolithic catalyst reaches 3.588% while the binding rate after sonication almost no change. Whiskers are tightly combined with the cordierite ceramic substrate by the binding strength experiments and EDS analysis. The oxygen temperature-programmed desorption (O2-TPD) measurements were performed to investigate the O2 adsorption property. The catalytic performance of the samples were examined by semi-quantitative thermal gravimetric analysis (TG-DTG) and temperature-programmed oxidation (TPO). The catalyst performance study demonstrates that Na4Mn9O18 whiskers decrease the soot combustion temperature apparently. Experiments show the characteristic temperature could be reduced by increasing the catalyst loading. The Na4Mn9O18 decreased the ignition temperature of soot particles oxidation, and the cycle stability experiment confirmed that the sample (0h-m-k) has good structural stability and stable catalytic performance. The coarseness of the interface increased because Na4Mn9O18 whiskers grew on the cordierite substrate, and the trapping ability improved. Na4Mn9O18 is an important type of catalyst which is rarely studied in catalytic oxidation of soot. This catalyst displays good activity and stability in the soot catalytic oxidation. This unique microstructure has potential application in the DPF field.

Study on the Adsorption Properties of Oxalic Acid-Modified Cordierite Honeycomb Ceramics for Neutral Red Dyes.

Removal of organic dyes from water by monolithic adsorbents is considered as an efficient and no-secondary pollution method. Herein, for the first time cordierite honeycomb ceramics (COR) treated with oxalic acid (CORA) were synthesized. This CORA exhibits outstanding removal efficiency toward the azo neutral red dyes (NR) from water. After optimizing the reaction conditions, the highest adsorption capacity of 7.35 mg·g-1 and a removal rate of 98.89% could be achieved within 300 min. Furthermore, investigation of the adsorption kinetics indicated this adsorption process could be described as a pseudo-second-order kinetic model with k 2 and q e of 0.0114 g·mg-1·min-1 and 6.94 mg·g-1, respectively. According to the fitting calculation, the adsorption isotherm could also be described as the Freundlich isotherm model. The removal efficiency could be maintained above 50% after 4 cycles, negating the need for toxic organic solvent extraction, offering a method for bringing the technology one step closer to industrial application and giving CORA promising potential in practical water treatment.

Hydrogen production employing Cu/Zn-BTC metal-organic framework on cordierite honeycomb ceramic support in methanol steam reforming process within a microreactor

Three metal-organic frameworks Cu-BTC, Zn-BTC, and Cu/Zn-BTC were prepared and impregnated in nitrate solutions to obtain the precursors. After calcination, three metal-BTC-derived CuO/ZnO/CeO2/ZrO2 catalysts were obtained. The samples were characterized and the catalyst-coated cordierite honeycomb ceramics were used in a microreactor for methanol steam reforming at different reaction conditions. Results showed that the Cu/Zn-BTC-derived catalyst exhibited the most fine and uniform particles, the best reducibility, the largest specific surface area, and the optimal surface elemental state due to the difference in the formation mechanisms, resulting in its remarkable catalytic performance. The ceramic support coated with Cu/Zn-BTC-derived catalyst could achieve 100% methanol conversion rate and 0.336 mol/h H2 output at 260 °C in the microreactor. Stability tests demonstrated that the Cu/Zn-BTC-derived catalyst could maintain its excellent performance without deactivation within 30 h continuous reaction, which was connected with the Ce–Zr–O solid solution with high concentration of oxygen vacancies and surface oxygen.

Preparation and characterization of diesel particle filter (DPF) with hierarchical microstructure for catalytic combustion of soot

Mullite whiskers were prepared on the wall of cordierite honeycomb ceramics using the gas-phase growth method. Subsequently, Co/Ce0.75Zr0.25O2 catalyst was loaded on the mullite whiskers to form hierarchical microstructure by the sol-gel technology for catalytic combustion of soot. Scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform-infrared spectroscopy, X-ray diffraction and Transmission electron microscopy were used to characterize the structural morphology and phase compositions. The filtration capability can be improved by mullite whiskers growth on the wall of cordierite honeycomb ceramics, and the microstructural feature is similar to the pseudostratified ciliated epithelium on the tracheal cavity surface (one section of human respiratory system). The Co/Ce0.75Zr0.25O2 catalyst decreased the ignition temperature of soot particles oxidation, and the cycle stability experiment confirmed that Co/CZ@M/C sample has good structural stability and stable catalytic performance. The high-efficiency filtration and the low-temperature catalytic oxidation of soot particles are combined with the hierarchical microstructure of Co/CZ@M/C, which has potential application in the diesel particulate filter (DPF) field.

Potassium titanate whiskers on the walls of cordierite honeycomb ceramics for soot catalytic combustion

In this paper, potassium titanate whiskers was prepared via the Molten salt synthesis on the surface of cordierite ceramics for the regeneration of diesel particulate filters (DPFs). SEM, EDS, XRD, FT-IR, TG-DSC and TPO were carried out to characterize the morphology, microstructure, growth mechanism and catalytic performance of the samples. Potassium titanate whiskers with diameter (100–500 nm) and length (about 3 μm) is tightly combined with the cordierite ceramic substrate. The catalyst performance investigation demonstrates that potassium titanate whiskers decrease the soot combustion temperature apparently. The soot combustion process was studied by thermal analysis tests, and the activation energy of the combustion reaction can be calculated using Freeman-Carroll method. The carbon oxidation activation energy is 14.009 kcal/mol, and the activation energy for the catalytic reaction with potassium titanate whiskers is 6.287 kcal/mol, it can be illustrated that potassium titanate whiskers/cordierite catalyst possess excellence performance for carbon catalytic combustion. The coarseness of the interface increased because potassium titanate whiskers grew on the cordierite substrate, and the trapping ability could improve. This unique microstructure has potential application in the DPF field.

Effect of sintering atmosphere on the crystallizations, porosity, and thermal expansion coefficient of cordierite honeycomb ceramics

High-porosity cordierite ceramics were sintered in two different atmospheres, that is, in air (oxidizing) or in double-enclosed crucibles (mildly reducing). Paste slurries of cordierite compositions mixed with organic binders and pore formers were extruded into honeycomb-type substrates to produce diesel particulate filters (DPFs). The present study was conducted to explore the effects of sintering atmosphere on pore size, crystallization, amorphous phase, and thermal expansion coefficient (CTE) of sintered DPF honeycombs. Crystal phases were quantitatively analyzed using the Rietveld refinement method using powder X-ray diffraction (XRD) data. Amorphous phases were quantified using the Rietveld-internal standard method, and their presence was qualitatively confirmed by high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) analysis. The most notable features observed were a dramatic decrease in the pore-size distribution and an enhanced rate of cordierite/indialite phase crystallization when sintering was performed in a double-enclosed crucible. A relatively high concentration of carbon monoxide (CO) in the double-enclosed crucible reduced the liquid-phase viscosity. This low-viscosity liquid phase spread relatively easily on the surfaces of crystal phases and enhanced the crystallization rate owing to a relatively large liquid–solid contact area in the mildly reducing atmosphere. The higher CTEs of DPFs produced in air compared with those produced in enclosed crucibles are discussed in relation to the amounts of amorphous and crystal impurity phases and crystal texture.

MnOx-CuOx cordierite catalyst for selective catalytic oxidation of the NO at low temperature.

Low-value solid waste cordierite honeycomb ceramics were used as carrier of SCO denitration catalyst, and the active component was supported by the impregnation method to improve the performance of the catalyst. Firstly, the effect of calcination conditions on the denitration performance of the Mn-loaded cordierite catalyst was studied for the cordierite-loaded active component MnOX. Secondly, the preferred catalyst was reloaded with another active component to further improve its denitration performance; the bimetal ratios were affected by the denitration performance, which was, finally, characterized by XRD, XPS, and SEM. The result shows the following: (1) Mn-loaded cordierite prepared at 450°C for 3h has a good denitration effect; (2) the MnOX-CuOX/CR catalyst is superior to MnOX-FeOX/CR, MnOX-CoOX/CR, and MnOX-CeOX/CR; (3) the MnO2 crystal form in the single metal-supported catalyst plays a major role, and Cu2Mn3O8 in the bimetallic catalyst affects the performance and activity of the catalyst. Graphical abstract.

Synthesis and performance of high efficient diesel oxidation catalyst based on active metal species-modified porous zeolite BEA

With the appearance of the low temperature combustion (LTC) diesel engines, diesel oxidation catalyst (DOC) becomes more and more important in removing the CO and hydrocarbons (HC) emitted from LTC diesel engines, especially in cold start-up process. Herein, metal species-modified hierarchically porous zeolites BEA (H-BEA) containing 0.8 wt% Pt have been synthesized by an ion-exchange and subsequent deposition-reduction method. It is found the obtained catalyst PtFeMg/H-BEA shows super catalytic activity, high water and sulfur resistance, i.e., the temperatures T90 are as low as 95 °C and 225 °C in the CO and C3H8 oxidation, respectively. It is believed that the strong interaction between Pt species and metal Fe, Mg-modified zeolite H-BEA is conductive to the CO and C3H8 catalytic oxidation. Further integrated into commercial cordierite honeycomb ceramics substrates, the obtained monolithic DOC still exhibits an excellent catalytic activity and anti-aging performance even under high velocity and multiple reaction atmosphere, indicating its promising prospects in the practical application. Besides, FTIR results indicate that there are two forms of Pt species: Pt atom in the zeolite BEA framework and metal Pt nanoparticles/clusters dispersed on the surface of BEA, which jointly promotes the adsorption and oxidation of CO and C3H8.

Monolithic LaBO3 (B=Mn, Co or Ni)/Co3O4/cordierite Catalysts for o‐Xylene Combustion

AbstractPerovskite/perovskite‐like (LaBO3, B=Mn, Co or Ni)/Co3O4 with different morphologies were successfully integrated onto the surface of three‐dimensional (3‐D) cordierite honeycomb ceramics by two‐step combination method of hydrothermal synthesis and impregnation for the catalytic combustion of o‐xylene. The La2NiO4/Co3O4 composite exhibits a 3D hierarchical hollow microsphere construction assembled by numerous nanowires, which is different from the nanowire structure of LaMnO3.15/Co3O4 and LaCoO3/Co3O4. Compared to LaMnO3.15/cordierite, Co3O4/cordierite, LaMnO3.15/Co3O4/cordierite and LaCoO3/Co3O4/cordierite, the La2NiO4/Co3O4/cordierite catalyst possesses lower light‐off temperature and better catalytic performance. The higher catalytic activity of La2NiO4/Co3O4/cordierite catalyst may be correlated with higher specific surface area, larger oxygen storage and the synergistic effect of the La2NiO4 and Co3O4. In addition, when the perovskite‐like loading was 11.39 wt% and calcined at 600 °C for 4 hours, it exhibited the best catalytic performance for o‐xylene oxidation with 90% conversion at 299 °C. In addition, the catalyst also has good conversion stability.

Structural origin of negative thermal expansion of cordierite honeycomb ceramics and crystal phase evolution with sintering temperature

The structural origin of the negative coefficient of thermal expansion (CTE) along the c-axis in cordierite is investigated using high temperature X-ray diffraction. The evolution of the lattice parameters, bond length, covalent character, and electron density distributions are analyzed with increasing temperature. The increase of covalent character of the tetrahedral bonds in the six-membered hexagonal ring is considered as the possible origin for the negative expansion. In addition, the bridging oxygen can act as a buffer absorbing thermal energy and prevents the increase in M1-O-M2 bond. The electron density distribution indicates that the linking oxygen strongly vibrates transversely across two coordinate M1-O-M2 linkages. The CTE and pore size and distribution change drastically at near 1300 °C due to the substantial increase in cordierite phase proportion and the formation of a liquid phase. Raw materials are consumed completely at 1450 °C and the CTE decreases to 1.3 ppm K−1.

Crystal Structure and Thermal Expansion Coefficient of Cordierite Honeycomb Ceramics

Cordierite honeycomb ceramics are sintered under a range of sintering atmosphere and temperature conditions. The linear thermal expansion coefficient (CTE) is measured along the extrusion direction. The samples sintered in an enclosed crucible have a much lower CTE than those sintered in open air. The CTE decreases with increasing sintering temperature up to 1450 °C. The polymorphic phases, texture, amorphous phase, impurity crystals, and porosity are analyzed using scanning electron microscopy, HR‐TEM, porosimeter, and Rietveld refinement method. The sintered samples consist of two polymorphic phases: indialite (hexagonal symmetry) and cordierite (orthorhombic symmetry). Both the volume % of the cordierite phase and the crystal texture increase with increasing sintering temperature. The orthorhombic distortion of cordierite from the hexagonal lattice (indialite) increases with increasing sintering temperature. The characteristic six‐membered ring of the (Si,Al)‐O4 tetrahedra in the cordierite structure shows substantial changes in the bond length due to Al‐Si ordering. Amorphous phase and impurity crystal phases such as silimanite and spinel remain at temperatures as high as 1450 °C. The effect of the polymorphic phases, the degree of texture, amorphous phase, impurity crystal phases, and the orthorhombic distortion is discussed in relation to the CTE characteristics of honeycomb.

Shielding of Enzyme by a Stable and Protective Organosilica Layer on Monolithic Scaffolds for Continuous Bioconversion

In this study, a kind of robust monolithic biocatalyst was constructed through shielding enzymes on the surface of cordierite honeycomb (cordierite-H) ceramics with an organosilica layer. In brief, penicillin G acylase, as a typical enzyme, was immobilized on the cordierite-H surface modified with polydopamine. Then, an organosilica layer was formed through the sol–gel process with (3-aminopropyl)tetraethoxysilane and tetraethyl orthosilicate. The buffering effect of the organosilica and polydopamine layer as well as the cage effect of the organosilica layer could effectively protect the enzyme from denaturation and detachment, thus significantly improving its structural and operational stability. A fixed-bed reactor containing the above monolithic biocatalysts was then constructed. The enzyme could retain up to 89.7% of its initial activity after a 195 min reaction at 313 K and 73.1% of its initial activity after 15 reaction cycles. Furthermore, continuous bioconversion of penicillin G potassium was also achieved, with a final product yield of 41.8% after five cycles of reaction.

Experimental Study on Preparation and Operating Conditions over a Promising Monolithic Catalysts for NO<sub>x</sub> Removal: MnO<sub>x</sub>/TiO<sub>2</sub>/Cordierite

The samples of MnOx/TiO2 catalysts supported on cordierite honeycomb ceramics were prepared by a sol-gel-impregnation method, and evaluated for low-temperature (353-473 K) selective catalytic reduction (SCR) of NOx with NH3. The influences of pretreatment on cordierite and catalyst dosage were investigated at first and optimized as follows: pickling for cordierite honeycomb ceramics with 1 mol/L HNO3 for 3 h prior to loading procedure as well as the catalyst dosage of 3-5 wt.%. The activity results indicated that there was an optimum working condition for MnOx/TiO2/cordierite catalysts: NH3/NO molar ratio=1.1, [O2]=3 vol.%, GHSV=5514 h-1, the highest activity of nearly 100% NO conversion could be obtained. As a comparison, the performances of commercialized vanadium-based honeycomb catalyst were also employed, which revealed the narrower scope of application of GHSV and the higher active temperature window. In conclusion, it turns out that the prepared MnOx/TiO2/cordierite catalysts are more applicable as a low-temperature SCR catalyst for NOx removal in a more complicated application environment.

Preparation and performance of V-Wreparation and performance of V-W/x(Mn-Ce-Ti)/y(Cu-Ce-Ti)/cordierite catalyst by impregnation method in sequence for SCR reaction with urea

Mn-Ce/TiO2 (M) and Cu-Ce/TiO2 (C) were prepared by sol-gel method, and the cordierite honeycomb ceramics (CC) was coated with M and/or C and V2O5-WO3 in sequence by impregnation method. A series of monolith catalysts were evaluated for the selective catalytic reduction (SCR) of NOx by urea. The physical and chemical properties of the catalysts were well examined using nitrogen adsorption, CO2-TPD, NH3-TPD, XRD, XPS and H2-TPR experiments. The results showed that when the M phase was coated onto catalyst prior to C phase, the complex catalyst V/3C/3M/CC was more active than the catalysts with only M or C phase in the presence of 0.01% SO2 and 10% H2O, and a small quantity of SO2 may favor the urea-SCR activity. XRD analysis indicated that Cu, Ce modified TiO2 sol favors the formation of anatase phase, and Mn, Ce modified TiO2 sol facilitates the formation of rutile phase. The BET surface area of catalyst only has relationship with the amount of M or C phase, and loading sequence does not influence it so much. The introduction of M phase and C phase increases the surface acid sites of different intensity. TPR results showed the interaction between vanadium and copper and/or manganese species enhances the reduction of vanadium, which can increase the amount of H2 consumption. XPS results indicated that both high V4+/V5+ ratio and large amount of surface chemisorbed oxygen may beneficial to the activity of the catalysts.

Modification of Cordierite Honeycomb Ceramics Matrix for DeNOx Catalyst

ABSTRACTTo obtain highly dispersed and highly active catalysts by impregnating of active species onto the monolith directly, cordierite honeycomb ceramics were modified by nitric acid solution of 68wt%. Effects of acid treatment temperature and time on the performance of cordierite were investigated. Specific surface area, pore size distribution, morphology and structure of cordierite were characterized by N2-physical adsorption, SEM, XRD, respectively. Concentrations of ions in the acid solution were measured by AAS. It is shown that the corrosion content of cordierite increases and more micropores are generated with increasing time of acid treatment, leading to an upward trend of specific surface area. The coefficient of thermal expansion and compression strength decrease obviously at a higher temperature, which is mainly attributed to the removal of Al and Mg ions from the silicate structure and delayed formation of free amorphous silica on the surface of the cordierite. The optimal modification process of cordierite matrix acid erosion is at 110°C for 6 h.

Effect of Electroless Plating Conditions on Toluene Catalytic Combustion Performance of Palladium-Based Catalyst

Catalytic combustion of volatile organic compounds (VOCs) is a high efficient and low-polluted technique. In this paper, the palladium-based combustion catalysts on cordierite honeycomb ceramics (CHC) substrate without interlayer film — Pd/CHC, were prepared by electroless plating method, and the effect of preparing conditions for the catalysts on the catalytic performance of toluene combustion was mainly studied. The optimal conditions were confirmed as follows: plating bath temperature is 60°C, plating time is 30min, palladium salt concentrationis 0.2g/L, and calcination temperature after plating is 500°C. Finally, the stability test further indicated that the Pd/CHC catalyst prepared by the optimal electroless plating conditions has good catalytic stability.

Palladium-Based Catalyst without Interlayer Film Prepared by Electroless Plating for Catalytic Combustion of Toluene

The palladium-based combustion catalysts on cordierite honeycomb ceramics (CHC) substrate without interlayer film (Pd/CHC) were prepared by electroless plating method. By means of scanning electron microscopy (SEM) and BET specific surface area, it was found that the palladium phases on the prepared catalyst after calcination treatment at 500°C were well dispersed on substrate with small and uniform particles. The X-ray diffraction, energy dispersion X-rays (EDX) analysis, adherence test and temperature programmed reduction (H2-TPR) analysis further indicated that the palladium phase had good adherence strength on the surface of CHC substrate and the moderate ratio of metallic Pd and PdO phase was only obtained on the catalyst calcined at 500°C . Moreover, the results of activity tests for toluene combustion showed that the 0.24%Pd/CHC catalyst had good low temperature catalytic activity and temperature-resistance property. The total combustion temperature (T90) for toluene over catalyst calcined at 300, 500 and 900°C was at 239, 225 and 233°C respectively. And the toluene conversion could keep up above 97% during the stability test of Pd/CHC catalyst at 230°C for 105 h, indicating the good catalytic stability of the prepared catalyst.