Honeycomb Catalyst Research Articles

Natural Gas Steam Reforming over Rhodium/Alumina Catalysts: Experimental and Numerical Study of the Carbon Deposition from Ethylene and Carbon Monoxide

Natural gas steam reforming (SR) over technically used rhodium/alumina (Rh/Al2O3) honeycomb catalysts is studied experimentally at temperatures between 923 and 1073 K and steam-to-carbon ratios (S/C) of unity, with regard to coke deposition caused by the decomposition of the product species ethylene (C2H4) and carbon monoxide (CO). Furthermore, the process is modeled using detailed reaction mechanisms, and numerical simulations are carried out to describe the coke formation on Rh/Al2O3 catalysts quantitatively. The amount of deposited carbon was detected and analyzed for varying feed mixtures of the products CO and C2H4 diluted in N2. During the decomposition of CO, the saturation of the amount of coke is monitored by feeding CO in high concentrations. No saturation occurs for the same amounts of coke resulting from the decomposition of C2H4. The coking rate caused by the decomposition of C2H4 is found to be ∼25 times higher than the coking rate caused by the decomposition of CO. The differences in coking behavior caused by C2H4 and CO, respectively, are described by coking models.

4-3-1 ハニカム触媒を用いた高含水エタノール改質による水素製造(Session 4-3 水素製造・貯蔵 1)

4-3-1 ハニカム触媒を用いた高含水エタノール改質による水素製造(Session 4-3 水素製造・貯蔵 1)

Catalytic ozonation of reactive red X-3B in aqueous solution under low pressure: decolorization and OH· generation

Catalytic ozonation of Reactive Red X-3B in aqueous solution had been carried out in an ozone oxidation reactor where Mn-Fe-ceramic honeycomb was used as the catalysts. The presence of Mn-Fe-ceramic honeycomb catalyst could obviously improve the decoloration efficiency of Reactive Red X-3B and the utilization efficiency of ozone compared to the results from non-catalytic ozonation. Adsorption of Reactive Red X-3B had no obviously influence on the degradation efficiency. Addition of tert-butanol significantly decreased the degradation efficiency, indicating that the degradation of Reactive Red X-3B followed the mechanism of hydroxyl radical (OH·) oxidation. The operating variables such as reaction pressure and ozone supply had a positive influence on the degradation efficiency, mainly attributing to facilitate the ozone decomposition and OH · formation.

Selective catalytic reaction of NOx with NH3 over Ce–Fe/TiO2-loaded wire-mesh honeycomb: Resistance to SO2 poisoning

Ce–Fe/TiO2/Al2O3/wire-mesh honeycomb catalyst (Ce–Fe/WMH) exhibited a high activity for the selective catalytic reduction (SCR) of NOx in SO2-containing gases. Analysis of fresh and spent catalysts by XRD, BET, XPS, TG and FTIR indicated that Ce sites were sulfated preferentially over Ce–Fe/WMH during the SCR reaction in the presence of SO2, which could increase the amount of surface active oxygen species. On the other hand, the formation of surface hydroxyls due to the hydration of SO42− could supply more Brønsted acid sites to adsorb NH3 in the form of NH4+. These two factors played significant roles in the good SO2 durability of Ce–Fe/WMH. In addition, the sulfation of CeO2 on catalyst surface might approach a stable state upon certain amount of SO2 in reactant gas. The reaction mechanism study showed that only Eley–Rideal reaction pathway between ionic NH4+, coordinated NH3 and gaseous NO dominated in the reaction; the Langmuir–Hinshelwood reaction pathway was cut off by the sulfation, resulting in the rapid decrease of NOx conversion in the early period of SCR reaction in the presence of SO2.

Catalysts Based on Nanopowders Supported on Foam Materials for Deep Oxidation of Organic Substances

Foam catalysts have physicochemical, gas-dynamic and catalytic characteristics exceeding the indices of the traditional granular and honeycomb catalysts. Nanopowders have high catalytic activity due to high surface area and special electronic state. Catalysts of new structural type nanopowders supported on foam metals and foam ceramics - have been tested in the process of deep oxidation of organic substances.

Effect of pressure in the autothermal catalytic partial oxidation of CH4 and C3H8: Spatially resolved temperature and composition profiles

Operation under pressure is a major requirement for the intensification of the catalytic partial oxidation (CPO) of light hydrocarbons. Related issues are the increase of the thermal loads experienced by the catalyst and the promotion of gas phase chemistry, which can lead to the formation of coke precursors. In this work, we analyze the autothermal CPO of C3H8 and CH4, carried out between 1 and 4bar at constant mass flow rate over a Rh-coated honeycomb catalyst. Spatially resolved temperature and concentration profiles are presented and analyzed with a mathematical model of the reactor, which includes appropriate mass and heat transfer correlations and detailed kinetic schemes for the homogeneous and the heterogeneous chemistry. The results show that pressure affects the heterogeneous process thermodynamically but not kinetically. In fact, in the final part of the catalyst, where the reaction approaches the equilibrium, higher pressures cause an increase of the outlet temperatures and a decrease of the selectivity to syngas. In the first part of the catalyst, where the progress of the reaction is controlled by kinetics, pressure has no effect on both temperature and concentration profiles due to the dominant role of mass transfer on the consumption of O2 and fuel. In the case of CH4 CPO, there is no evidence of homogenous reactions, whereas, in C3H8 CPO pressure promotes gas phase cracking, which leads to the formation of methane and intermediate C2+ species. Experiments performed on a thin catalyst slice confirm that heterogeneous steam reforming reactions have a key role in cleaning the gas phase from these C2+ species, preventing the catalyst from coking.

Honeycomb Shaped Monolithic Fe-β Zeolite Catalyst for N<sub>2</sub>O Decomposition

Honeycomb shaped monolithic Fe-β zeolite catalyst for N2O decomposition prepared by direct extrusion method was investigated. In this paper, we optimized the parameters of the molding process and studied the decomposition properties of the honeycomb catalysts. Monolithic materials could be extruded successfully only with the plasticity ranging from 0.177 to 0.473. The content of SB powder, nitrate and water was shown to have a significant influence on the mechanical strength of the extruded materials. The monolithic samples were characterized by using XRD. Catalytic performances of various monolithic zeolites with diverse density (49 cells/in.2, 81cells/in.2, 169 cells/in.2) were thereafter studied. As shown from the result, catalyst activity increased significantly with the increase of monolithic catalyst density.

Combination of Plasma with a Honeycomb-Structured Catalyst for Automobile Exhaust Treatment

To activate a catalyst efficiently at low temperature by plasma for environmental control, we developed a hybrid reactor that combines plasma with a honeycomb-structured catalyst in a practical manner. The reactor developed generated stable cold plasma at atmospheric pressure because of the dielectric and conductive nature of the honeycomb catalyst by consuming low amounts of power. In this reactor, the applied voltage and temperature determined the balance between the oxidation and adsorption by the plasma and catalyst. The synergistic reaction of the plasma and catalyst was more effective at low temperatures, resulting in a reduction in a lowered light-off temperature.

Preparation and characterization of a novel washcoat material and supported Pd catalysts

A nanosized Ce0.5Mn0.5O1.5 powder was successfully synthesized by macromolecule surfactant modified method and then it was used as the cordierite honeycomb washcoat of VOCs combustion catalysts. The effect of Ce-Mn-O powder with different Ce/Mn molar ratio on the catalytic activity and the cohesive ability of washcoat on the cordierite honeycomb substrate was also investigated. The structure and catalytic properties of Ce0.5Mn0.5O1.5 washcoat were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), differential thermal analysis and thermo-gravimetric analysis (TG/DTA), and N2 adsorption and desorption techniques. The results indicated that the Ce0.5Mn0.5O1.5 powder belongs to a novel washcoat with the advantages of strong cohesiveness, high surface area and without agglomeration even after 1000°C calcination. The total oxidation temperature for toluene, acetone and ethyl acetate over the 0.1 wt % Pd/Ce0.5Mn0.5O1.5/cordierite honeycomb catalysts was at 200, 220 and 220°C, respectively. Compaired with the catalysts without Ce0.5Mn0.5O1.5 washcoat, the catalyst with Ce0.5Mn0.5O1.5 as washcoat on the cordierite honeycomb could improve the dispersion of PdO and shows a good catalytic activity for toluene, acetone and ethyl acetate.

A novel nickel-based catalyst for methane dry reforming: A metal honeycomb-type catalyst prepared by sol–gel method and electroless plating

A honeycomb-type nickel-based catalyst was prepared by a combination technique consisting of a sol–gel method and an electroless plating method on a stainless steel substrate. The catalyst layer formed onto the fin substrate consisted of an alumina layer and a nickel component. The alumina layer was porous and was about 7μm in thickness, and the nickel component was deposited not only on the alumina surface but also inside the pores. The nickel particles formed on the surface were 70–150nm in diameter. The prepared nickel-based honeycomb catalyst demonstrated a high performance for methane dry reforming, indicating that the catalyst degradation was quite small even under severe CO2/CH4 conditions. The amount of the deposited carbon onto the nickel-based catalyst was much smaller than that on the commercial catalyst, which was thought to be one of the factors in the reduced deterioration of this honeycomb catalyst. Furthermore, the H2/CO ratio as a synthesis gas over this nickel-based catalyst was a smaller value than that of the commercial catalyst, which is a convenient reforming property for alkane manufacturing. The deposited carbon on the nickel-based honeycomb catalyst was a whisker carbon with non-condensed state.

Selective catalytic oxidation of ammonia to N2 over wire–mesh honeycomb catalyst in simulated synthetic ammonia stream

The novel wire–mesh honeycomb (WMH) was reported to be an excellent substrate of active component for selective catalytic oxidation of ammonia under laboratory-simulated synthetic ammonia stream, and was also evaluated in comparison with traditional ceramic honeycomb (CH). WMH possessed higher open frontal area (OAF), larger geometric surface area (GAS), and lower pressure drop compared with CH, which induced the excellent mass- and heat-transfer rate and conversion efficiency. Different active components displayed the different catalytic performance. The active Ag species exhibited better NH3 conversion, and the Cu species could evidently improve N2 selectivity. The addition of Ce species into Cu catalyst promoted the NH3 conversion but decreased in the N2 selectivity. Comparatively, the Ag–Cu/WMH catalyst exhibited higher resistance to high gas hourly space velocity (GHSV) and the superior NH3-SCO activity and N2 selectivity, which was appropriately used to eliminate higher concentration NH3. Moreover, the Ag–Cu/WMH catalyst displayed the excellent NH3 conversion in the long-term stability and accelerated deactivation experiment, which indicated that the Ag–Cu/WMH catalyst would have an extremely potential application in NH3 abatement for synthetic ammonia industry.

The modification of industrial grade metatitanic and application in SCR DeNOX catalyst preparation

In this paper, industrial grade metatitanic (H2TiO3) from sulphate process was used as the raw material to prepare TiO2 through a series of modification. Granular and honeycomb SCR DeNOX catalysts were made by granulation and molding processes respectively with those TiO2 as the carrier material. The characterisation, mechanical strength and denitration performance of the carrier/catalyst samples were tested and compared with those of commercial anatase nano‐TiO2 products. The results showed that the TiO2 sample after the modified operation was remarkably improved in particle diameter, dispersion characteristic (average particle size from 15.79 to 1.746 µm) and the degree of crystallinity (from 93.7% to 98.1%), also the impurity content of K, Na, Ca, Mg, Al, S, etc. was significantly reduced; however, the grain size was increased (from 7.0 to 9.9 nm), and the specific surface area was decreased slightly (from 148.1 to 112.6 m2/g). As a whole, the characterisation was extremely close to commercial anatase nano‐TiO2. Catalyst samples prepared with TiO2 after the modified operation had an upgrade on catalytic activity (the maximum denitration rate of granular catalyst from 95.0% to 97.1%; honeycomb catalyst from 92.2% to 93.3%), and the mechanical properties of honeycomb catalysts have been enhanced significantly (compressive strength of axial direction changed from 0.1063 to 0.5965 Mpa). The work indicated that TiO2 prepared with the industrial grade metatitanic from sulphate process was suitable as a carrier material for SCR DeNOX catalyst production. Also the modification was necessary.

Oxidation of ammonia to NOx in a two bed reactor (Pt gauzes + oxide monolytic layer): Experimental studies and mathematical modelling

The behavior of one- and two-bed systems consisting of Pt–Rh gauze pack (the first bed) and monolith honeycomb catalyst (the second bed) in the conditions corresponding to those in the industrial medium pressure plant for NH3 oxidation to NOx was experimentally studied. At complete NH3 conversion in the gauze pack installation of the monolith results in the increase of the temperature in the gauzes and NOx yield. One dimensional mathematical model with heat and mass exchange between gas and solid phases and considering the effect of monolith as a heat shield was developed. The effect of monolith was supposed to consist preferentially in increasing the coefficients of heat and mass exchange between gas and solid phases in the gauze pack and determined by “hydrodynamic factor” γ depending on monolith geometry. It results in the shift of temperature front towards the frontal gauze and the reasonable increase of NOx yield.

A novel CoOx/La-modified-CeO2 formulation for powdered and washcoated onto cordierite honeycomb catalysts with application in VOCs oxidation

A novel Co (15wt.%)/La-modified-CeO2 catalyst was prepared for the oxidation of toluene and ethyl acetate, showing lower light-off temperature (around 20–40°C) than that of a Pt (3wt.%)/La-CeO2 catalyst under the same experimental conditions. Upon washcoating onto cordierite it was still more active than the noble metal reference. The activity remained stable even after 80h of reaction. Adherence tests indicated a 98% stability of the washcoat, while SEM–EDS study evidenced its homogeneous distribution on the cordierite. ICP analysis and X-ray diffraction demonstrated that the composition and cobalt phase (Co3O4) of the powdered catalyst were the same in the washcoat. Moreover textural properties improved according to N2 physisorption studies due to inclusion of colloidal alumina in the slurry.

SCR catalyst coated on low-cost monolith support for flue gas denitration of industrial furnaces

NH3–SCR honeycomb catalyst was prepared by coating powdery active metal components on the surface of blank monolith supports and tested at the temperatures of 250–350°C, and superficial gas velocities of 5.3–6.3m/s. The tests were performed with a simulated gas mixture containing NO, SO2, O2, H2O and N2 or a real flue gas produced on line. The results showed that the coated honeycomb catalyst has an extraordinary high activity for low-temperature deNOx in the presence of 5vol.% steam and 1000ppm SO2. Its activity increased with increasing the coating thickness and reached at 110μm thickness as comparable as that of the 100% active components-molded catalyst, suggesting the deNOx reaction proceeded mainly in the surface layers of the honeycomb cell wall and hence coated honeycomb catalyst should be more cost-efficient than 100% active components-molded one. In a real coal-burned flue gas stream the catalyst maintained essentially its low temperature activity and stability, further verifying its high industrial applicability. Then, the effects of NO concentration and NH3/NO ratio on NO conversion were investigated to seek a suitable kinetic model for prediction of the catalyst’s deNOx rate and reactor design for pilot plant research. The data obtained showed that a simple power-law kinetic equation with first order in NO and zero order in ammonia can be applied to the coated honeycomb catalyst, and was used for determination of the kinetic parameters. Finally, simulation calculation was performed under arbitrary conditions to provide valuable information for design of pilot-plant scale reactors.

Critical evaluation of in situ probe techniques for catalytic honeycomb monoliths

Collecting spatially resolved gas-phase concentration profiles in catalytic monoliths by applying suction probe techniques has become an important tool for understanding the reaction sequence and for optimizing the design of structured catalysts. Here, the significance of the probing technique’s impact on the measured data is investigated by means of CFD simulations and experimental investigation of catalytic partial oxidation of CH4 on a Rh-coated honeycomb catalyst. Different positions of a suction probe (diameter=170μm) inside a rectangular channel (height=795μm) of a monolith are compared with respect to the influence on flow field, residence time, and reaction progress. The influence of the probe on the measured data is shown to strongly depend on its position. The maximum error can be over 50% with respect to the residence time. For an isothermal process, the error in the concentration profiles can be corrected by using a function which is only dependent on the geometrical structure of the monolith. However, for a process with a temperature gradient along the catalytic channel, such as CPOX of methane, the correction function is not applicable. An appropriate comparison of experiments and simulations requires a three-dimensional CFD simulation taking the probe into account.

Generation of non-thermal plasma combined with catalysts and their application in environmental technology

Non-thermal plasma (NTP) promotes formation and reaction of radicals at low temperature condition. In order to use NTP, selectivity and energy efficiency should be improved. For this purpose combination of NTP and catalysts has been proposed for several industrial applications. Several systems are at first introduced in this review, and then generation of NTP suitable for combination with catalysts will be introduced. The first generation of NTP combined with catalysts was a pulsed streamer corona with a TiO2 solid catalyst. This combination has been commercialized successfully as an indoor air cleaner attached to an air conditioner. However, this system cannot use honeycomb catalysts. A packed bed has therefore been used for testing the combination of NTP and pellet type catalysts. Packed bed uses a layer of ferroelectric pellets of a few mm in diameter. The pellet layer is sandwiched by the electrode energized with AC or pulsed voltages. Each contacting point of the pellets is ionized. The packed bed can be an important candidate for plasma-assisted combustion. An existing application for the packed bed is the volatile organic compounds (VOCs) decomposition. Recently, discharges in honeycomb catalysts have been developed. One end of a honeycomb catalyst is attached with a packed bed or a surface dielectric barrier discharge to generate NTP. This electrode serves as a plasma electrode. When a DC electric field is applied, ionization proceeds along the surface of fine channels of ceramic honeycomb. This honeycomb discharge could be used for various processes to combine NTP and catalysts. It could also be used for surface treatment of honeycomb catalysts by NTP.

Study of Pt–Rh/CeO2–ZrO2–MxOy (M = Y, La)/Al2O3 three-way catalysts

CeO2–ZrO2–MxOy (M=Y; La) mixed oxides, prepared by co-precipitation method and characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Raman spectra (RM) and oxygen pulse reaction, were comparatively investigated to elucidate the combinational effects of Y and/or La oxide promoters on the catalytic activity and anti-aging performance of monolithic cordierite honeycomb catalysts with low Pt and Rh content. The catalytic activities, water-gas shift (WGS) and steam reforming reaction (SR) were studied under a simulated gas mixture. The catalysts were also characterized by H2-temperature-programmed reduction (H2-TPR) and O2-temperature-programmed desorption (O2-TPD). The results showed that the prepared CeO2–ZrO2–MxOy oxides have a face-centered cubic fluorite structure and are nanosize. La3+ ions can significantly improve thermal stability and efficiently retard CeO2–ZrO2 crystal sintering and growth. Doped CeO2–ZrO2 with Y3+ and La3+ has 105 and 60m2/g surface area and 460 and 390μmol/g OSC before and after aging. The T50 of fresh Pt–Rh/CZYL/LA is 170°C for CO, 222°C for C3H8 and 189°C for NO, and shift to 205, 262 and 228°C after hydrothermal aging, which are better than those of Pt–Rh/CZY/LA or Pt–Rh/CZL/LA. WGS and SR are relate to the OSC of oxygen storage materials and absorbed oxygen species on the catalyst surface and affect the three-way catalytic activities of catalysts. The reductive property of noble metals and the dissociatively adsorbed O2 on the surface of catalysts are closely related to the catalytic activities.

Experimental and Modelling Study of a Dual-Layer NH3 Slip Monolith Catalyst for Automotive SCR Aftertreatment Systems

The approach to the development of a chemically and physically consistent mathematical model of ASC dual-layer (SCR + PGM) washcoated monolith converters is herein presented. Steady-state and transient kinetic runs were performed over each one of the two ASC components (SCR and PGM) in the form of powders and also over the two mixed powdered catalysts, thus acquiring information on the interactions between the SCR and the PGM catalytic chemistries. Global kinetic models were fitted to the SCR and to the PGM catalyst data, and validated against experiments performed over both washcoated single-layered SCR and PGM monoliths and over a full dual-layer ASC honeycomb catalyst (SCR layer on top). It was found that the dual-layer (SCR + PGM) ASC architecture grants increased N2 selectivities compared to a PGM-only washcoat.

Catalytic combustion of brown coal particulates over ceramometal honeycomb catalyst

Catalytic combustion of brown coal particulates over CuO/Al 2 O 3 /FeAlO/ FeAl honeycomb ceramometal catalyst in the fluidized bed regime with the sand as a heat transfer material has been studied during 100 hours at 973-1023 K. The catalyst before and after tests has been analyzed. The coal conversion in the presence of cermet catalyst was found to be in the range of 97.8-98.5% while without catalyst it was lower (91.2-94.6%). A substantial decrease of CO, NOx and SO 2 emissions in catalytic combustion was also demonstrated.