Honeycomb Catalyst Research Articles

The Influence of Pt Additives on The Activity and Stability of Rh-containing Catalyst Performance in Diesel Fuel Conversion into Syngas

The influence of platinum additives on the properties of rhodium catalysts in steam and autothermal reforming processes of diesel fuel was investigated. It was found that the Rh/CZF catalyst exhibited higher activity, with a higher degree of fuel conversion and lower production of side reaction products compared to the bimetallic Rh–Pt/CZF catalyst. The proposed two-zone catalytic Pt/CZF+Rh/CZF structured honeycomb catalyst demonstrated stable performance and high activity in autothermal reforming of commercial diesel fuel. However, the presence of platinum in the frontal zone of the catalyst reduced its resistance to coking compared to the rhodium-containing sample. The obtained results are of practical significance in the development of efficient systems for the conversion of heavy hydrocarbons into synthesis gas.

Performance of Transition Metal Supported Al2O3 Coated on Honeycomb Catalysts and Its Segmentation on Exhaust Gasses Oxidation

The oxidation of carbon monoxide (CO) and unburnt hydrocarbons (HC) under segmented honeycomb catalysts was investigated using actual exhaust gas mixtures from a gasoline-fueled internal combustion engine of a motorcycle. The honeycomb catalysts were prepared through a wet process, resulting in four types coated with transition metals (Cu, Cr, Fe, and Ni) supported on Al2O3. The oxidation of CO and HC was monitored using an exhaust gas analyzer across a range of air-to-fuel ratios (AFR), from lean to rich, under stationary conditions. The results demonstrate that the honeycomb catalysts effectively decreased CO and HC concentrations in the exhaust gas. Among the transition metal oxide honeycomb catalysts, Cr and Ni exhibited high CO and HC conversion rates, surpassing those observed with Cu. The average CO and HC conversion calculations, spanning from lean to rich air-to-fuel ratios, were consistent with the actual conversion rates achieved. Furthermore, the study investigated the effect of honeycomb segmentation on CO and HC conversion. Surprisingly, the catalytic performance of Cr and Ni remained high even with longer gaps in the honeycomb. Interestingly, the conversion of CO and HC over the iron oxide honeycomb catalyst increased as the gap in the honeycomb became longer. This is likely due to an increase in the gap size and enhanced re-mixing of reactants (CO, HC, and O2) caused by recirculation. Thus, this study provides valuable elucidation on the potential application of segmented honeycomb catalysts for reducing CO and HC emissions in exhaust gases.

Investigations on the Influence of Catalyst Geometry on Emission Reduction in Small‐Scale Combustion System

Legal regulations for exhaust gas treatment in small‐scale combustion systems demand both emission and dust reduction. Simultaneously removing both pollutants using catalysts presents a significant challenge due to constraints on the very low allowed pressure drop over the catalyst. It can be demonstrated that the total oxidation of CO, as one of the main pollutants in the combustion of biogenic materials, in small‐scale combustion systems can be quantitatively achieved using precious metal‐based catalysts based on Pt/CeO2/TiO2. The highest CO conversion rate can be observed with a 233 cpsi honeycomb catalyst, whereas the foam ceramic catalysts with 30, 20, and 10 ppi show progressively decreasing activity. However, concerning dust reduction, it can be demonstrated that the ceramic foam with 10 ppi is superior, as evidenced in real‐world experiments conducted on an Leda Novia W small‐scale combustion device with 8 kW combustion capacity. Particle deposition on the catalysts is observed with all catalysts, whereby catalysts with small pores show rapid pore blockage. It is observed that only with the 10 ppi foam catalyst, dust deposition does not lead to pore blockage, allowing a reduction in dust of more than 50% over the measurement cycle.

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.

Numerical investigation of honeycomb channel design: Effect of rounded corners on selective catalytic reduction of NO

In this work, single-channel models are established to investigate the effect of rounded corners on overall performance of honeycomb catalyst with various channel geometries and cell densities (Ncell). As channel shape factor (γ) increases, pressure drops all rise slowly at low γ (0 ∼ 0.5) and increases dramatically when γ > 0.5, aligning with monolith voidage and hydraulic diameter variations. Hexagon-channel catalysts with open corners exhibit the smallest pressure drop increase (17.3 %), while triangle-channel catalysts with acute corners show the highest rise (100.1 %). The increase in Ncell leads to a similar rise (43 %) in pressure drop. NO conversions decrease with γ due to reduced external surface area, with maximum conversions observed for triangle-channels (low γ) and hexagon-channels (high γ). Increasing Ncell enhances NO removal and mitigate rounded-corner effect on conversion (4.5 % to 1.2 % reduction). Based on that, a design strategy suggesting γ = 0.5 is proposed to eliminate ash accumulation and maintain acceptable catalyst performance.

Metallic Honeycomb Catalysts for Methane Steam Reforming: Effect of the Bimetallic Surface Coating on Catalytic Properties

Metallic honeycomb catalysts are promising candidates for fuel cell and small-scale onsite hydrogen production applications. In this study, high-cell-density Ni honeycomb catalysts coated with a series of bimetallic surface layers were synthesized. Their catalytic performance for CH4 steam reforming was investigated under a low steam-to-carbon ratio of 1.36 and a gas hourly space velocity of 6400 h-1 in the temperature range of 400–700°C. The catalysts coated with Ni-Mg and Ni-Zr showed excellent catalytic performance, reaching a high CH4 conversion and CO selectivity close to the equilibrium values within the test temperature range. The enhanced catalytic performance of the Ni-Mg and Ni-Zr coatings was attributed to the formation of oxide-supported fine Ni particles. In contrast, the catalysts coated with Ni-Fe and Ni-Sn exhibited an extremely low activity, which was lower than that of the catalyst coated with only Ni. The low activity of the Ni-Fe and Ni-Sn coatings is supposed to be due to the formation of aggregated Ni3Fe, Ni3Sn, and Ni3Sn2 phases.

Single atomic Fe-based honeycomb catalysts with hierarchically ordered meso- and macropore for the oxygen reduction reaction

Single atomic Fe-based honeycomb catalysts with hierarchically ordered meso- and macropore for the oxygen reduction reaction

Potential of V2O5-WO3/TiO2 catalyst usage as the secondary measure for household heating combustion unit

The active substance used in oxidation honeycomb catalysts determined for real flue gas purification usually consists of precious metals such as platinum or palladium, while the most common is the mixture of the two mentioned elements, however high prices and limited availability of these elements encourages producers for the search for new, equally or better effective alternatives. In this study V2O5-WO3/TiO2 honeycomb catalyst was tested during the combustion test with commonly sold manually loaded stove. The catalyst was installed in the flue gas duct at the stove outlet. The experimental comparison of the flue gas composition at the catalyst inlet and at the catalyst outlet was performed. Flue gas sampling took place for whole combustion periods. Relatively high conversion rates by catalyst of CO (up to 87.1%), C3H8 (up to 61.3%) and TSP (up to 17.7%) were reached, which meant that the limit values of Commission regulation for mentioned kind of equipment were met during four, not only one period (in case of non-use of the catalyst). The V2O5-WO3/TiO2 catalyst has a great potential as the secondary emission control device for achieving low mass concentration of the certain pollutants in the flue gas.

Kinetics-Based Prediction for Sintering of Pd/CeO2–ZrO2–Al2O3 Three-Way Catalysts during Engine-Bench Aging

The thermal deactivation of Pd/CeO2–ZrO2–Al2O3 (Pd/CZA) three-way catalysts (TWCs) was studied using a full-sized washcoated monolithic honeycomb after engine-bench aging at 600–1000 °C under a stoichiometric-lean-rich cycling gas condition. This was followed by chassis dynamometer driving tests. The nanoscale structure of these aged catalysts was characterized by gas adsorption, X-ray diffraction, and electron microscopy imaging to elucidate the thermal deactivation mechanism. Aging at high temperatures and for long periods facilitated the Pd particle growth via surface migration and coalescence, which caused a drop in the number of active sites and thus the catalytic activity. The detailed particle growth kinetics was analyzed using simulated laboratory-scale aging of Pd/CZA powder samples at different temperatures (700–1000 °C) and periods of time (0–40 h). The as-obtained Pd particle size vs time data were successfully fitted by applying the Finke–Watzky model with two-step agglomeration, which provided the rate constants for the initial slow growth and the subsequent faster growth. The temperature dependence of the as-obtained rate constants showed simple Arrhenius-type behavior, which was expressed using the optimized frequency factor and activation energy for the Pd particle growth. Furthermore, these results were roughly consistent with the data obtained by the engine-bench aging test for the monolithic honeycomb catalysts. The sintering kinetic model developed in the present study will be useful for the prediction of TWC deactivation and lifetime.

Formation and properties of block vanadium SiO<sub>2</sub> nanomaterial catalyst for SO<sub>2</sub> oxidation

A method for producing a block vanadium catalyst for the oxidation of sulfur dioxide has been studied, which includes the stage of preparing a honeycomb structure framework based on silica raw materials in the form of white soot, followed by applying a substrate in the form of amorphous silicon dioxide and an active component to the surface of the channels. Data on the structural and mechanical properties of the honeycomb catalyst paste have been obtained. A mode of heat treatment of molded products with the production of mechanically strong blocks as carriers of the vanadium catalyst is proposed. Information about the performance of a block vanadium catalyst in comparison with an industrial catalyst of a granular form is given. Ill. 4. Ref. 14. Tab. 1.

Critical role of reactive species in the degradation of VOC in a plasma honeycomb catalyst reactor

This paper reports the nature of the reactive species formed and their role in the degradation of methyl ethyl ketone (MEK) using plasma catalysis in a honeycomb monolith reactor. A series of experiments were performed using plasma with different discharge gases (i.e., N2, O2, or air) in the presence of the honeycomb catalyst. A novel method is introduced to identify the reactive species that form during the plasma process and their contribution. We found the role of O atoms to be dominant compared with that of other reactive species in the plasma catalytic removal of MEK. In addition, the effect of introducing O3 over the catalyst surface was investigated, with oxygen activation resulting from surface chemisorption mainly contributing to MEK oxidation. Analysis of the byproducts enabled us to propose possible reaction mechanisms for the oxidation of MEK in the air plasma catalytic reactor.

Thermomechanical Responses of Microcracks in a Honeycomb Particulate Filter

Manufacturing honeycomb‐structured catalysts require a careful understanding of the microstructure of the solid substrate and its dependence on thermal‐processing conditions. Herein, it is the thermal responses of microcracks in an uncoated microcracked aluminum titanate honeycomb catalyst is investigated by analyzing the material's resonance frequency using the high‐temperature impulse excitation technique. The resonance frequencies are presented as Young's modulus values to avoid sample size effects. Dynamic Young's modulus measurements show closed‐loop hysteresis due to microcracks healing and reopening, causing a reversible response. The hysteresis is further used to understand microcracks’ dependence on critical thermal‐processing conditions used in a catalyst manufacturing plant, including peak operating temperature (800–1000 °C), dwell period (1–3 h), and heating rates (1–5 °C min−1). Microcracks are observed to have two healing responses: instantaneous and delayed healing. Both responses significantly influence the design of catalyst manufacturing. Complete reopening of microcracks from their healing temperature (1150 °C) is a very time‐consuming process (50–60 h). However, it is shown in the analysis that microcrack relaxation is a critical phenomenon that must be considered in quality‐controlled environments.

The co-combustion of pellets with pistachio shells in residential units additionally equipped by Pt-based catalyst

There are several published studies evaluating the possibilities of thermal and non-thermal utilization of pistachio hard shells in many technical sectors; however, there are no relevant data about the possibilities of usage of this homogenous biomass-based by-product as a fuel for automatic household heating appliances for partial or full substitution of standard ENplus A1 pellets, which is the aim of the presented study. The composition and basic properties of both fuels were compared as well as the flue gas composition formed during the 6 different fuel mixture combustion in two real-scale pellet burners. The mass concentration of observed pollutants (CO, total suspended particles, and C3H8) in the flue gas was strongly affected by increasing of pistachio shell mass fraction in the fuel mixture (from 10 to 100%). In comparison to the combustion of ENplus A1 pellets, CO was increased up to 25.9 times, total suspended particles up to 15.3 times, and C3H8 up to 13.7 times. Based on the results of real combustion tests, the equations were listed, describing the increase of the mass concentration of pollutants for the whole spectrum of pellets/pistachio shell ratios applied on the chosen designs of the pellet burners. The Pt-based oxidation honeycomb catalyst, additionally installed at the combustion unit outlets for flue gas purification, showed conversion rates up to 82.2% in the case of CO and up to 33.1% in the case of C3H8. This enables the reaching of the same or lower mass concentrations of mentioned pollutants in the flue gas, formed during the co-combustion of appropriately selected fuel ratios in comparison to ENplus A1 pellet combustion without the catalyst.

The synergy between substrate architecture of 3D-printed catalytic converters and hydrogen for low-temperature aftertreatment systems

This study proposes 3D-printed diamond-based lattice substrates as catalytic converters in the automotive aftertreatment system to improve vehicle cold-start emissions. The study aimed to compare the influence of 3D-printed diamond-based catalyst structures on the light-off behaviour compared to the conventional 400 Cell Per Square Inch (CPSI) honeycomb catalyst design in a real exhaust gas environment. Moreover, the benefits of H2 addition on the performance of advanced lattice structures are examined for the first time to further increase the low-temperature catalytic efficiency. Digital Light Processing (DLP) technology was effectively utilised to manufacture lattice structures with high cell density to allow a comparison between conventional and advanced geometry designs. Further, the 3D-printed substrates were catalyst coated, and their light-off behaviour was studied in a diesel exhaust environment. The results of the light-off showed a significant improvement in the light-off temperatures for CO, THC and NO in the 3D-printed lattice structures. Furthermore, H2 presence additionally enhanced the low-temperature activity of the AM lattice structures.

Approaches to the design of efficient and stable catalysts for biofuel reforming into syngas: doping the mesoporous MgAl2O4 support with transition metal cations.

The mesoporous MgAl2O4 support is promising for the design of efficient and stable to coking catalysts for natural gas and biofuel reforming into syngas. This work aims at doping this support with transition metal cations (Fe, Cr, Ti) to prevent the incorporation of Ni and rare-earth cations (Pr, Ce, Zr), loaded by impregnation, into its lattice along with providing additional sites for CO2 activation required to prevent coking. Doped MgAl1.9Me0.1O4 (Me = Fe, Ti, Cr) mesoporous supports prepared by the one-pot evaporation-induced self-assembly method with Pluronic P123 triblock copolymers were single-phase spinels. Their specific surface area varies in the range of 115-200 m2 g-1, decreasing to 90-110 m2 g-1 after successive addition of the supporting nanocomposite active component 10 wt% Pr0.3Ce0.35Zr0.35O2 + (5 wt% Ni + 1% Ru) by impregnation. Mössbauer spectroscopy for iron-doped spinels confirmed the spatially uniform distribution of Fe3+ cations in the lattice without clustering being mainly located at the octahedral positions. Fourier-transform infrared spectroscopy of the adsorbed CO molecules was performed to estimate the surface density of metal sites. In methane dry reforming, the positive effect of MgAl2O4 support doping was observed from both a higher turn-over frequency as compared with the catalyst on the undoped support as well as the highest efficient first-order rate constant for the Cr-doped catalyst as compared with published data for a variety of Ni-containing catalysts based on the alumina support. In the reaction of ethanol steam reforming, the efficiency of catalysts on the doped supports is comparable, while exceeding that of Ni-containing supported catalysts reported in the literature. Coking stability was provided by a high oxygen mobility in the surface layers estimated by the oxygen isotope heteroexchange with C18O2. A high efficiency and coking stability were demonstrated in the reactions of methane dry reforming and ethanol dry and steam reforming in concentrated feeds for the honeycomb catalyst with a nanocomposite active component on the Fe-doped MgAl2O4 support loaded on the FeCrAl-alloy foil substrate.

A Model for Predicting the Erosion Rate Induced by the Use of a Selective Catalytic Reduction Denitrification Technology in Cement Kilns Flue Gas

Selective catalytic reduction (SCR) is a technology by which nitrogen oxides are converted with the aid of a catalyst into diatomic nitrogen and water. It is known that the catalyst can be easily eroded if a cement kiln with a high-dust content is considered. To understand this process, numerical simulations have been carried out considering a single catalyst channel in order to study the collision and erosion of fly ash and catalysts at meso scale. Based on a response surface methodology, the effects of five factors on the erosion rate have been studied, namely, the catalyst particle velocity, the particle size, the particle concentration, the incidence angle and the catalyst porosity. The results show that the influence of particle velocity, particle size and particle concentration is statistically significant and the particle size and incidence angle have a significant effect on the erosion rate. A quadratic polynomial prediction model for the erosion rate of honeycomb catalysts in cement kiln SCR reactors is finally proposed to support the future optimization of these systems.

CO2 methanation: on the modeling of reacting laminar flows in structured Ni/MgAl2O4 catalysts

This work presents an overview of issues for the modeling of laminar flows in monolith catalysts. Both 0-D and 3-D models are evaluated for a parallel channel structured honeycomb catalyst (PC-HC), and a gyroid 3-D printed structured catalyst (G-3D). At the 0-D homogeneous reactor modeling level, the analysis is focused on the effect of the bulk porosity, as well as the model choice to represent Nusselt number effects. Results show the better suitability of a long tube Nusselt number model for the representation of the maximum temperature achievable in the 0-D homogeneous reactor, as well as a modest effect of the porosity on the catalyst CO2 conversion. A more detailed insight on heat transfer and the core reaction zone inside the monolith can be obtained at the 3-D homogeneous reactor modeling level.

Effect of metal on corona discharge plasma in a honeycomb catalyst and optimization of the critical parameters for ethylene removal

This work focused on the factors affecting the effective generation of corona discharge plasma in a honeycomb catalyst reactor. Pd, Co, and Ag were used as the active metal catalysts to investigate the plasma formation and decomposition of ethylene. Unlike the Ag-coated honeycomb catalyst, which resulted in excessive arcing, the Co-coated honeycomb monolith was able to generate stable plasma, but the discharge power was insufficient to decompose ethylene at an acceptable level. The incorporation of a small amount of Pd with Co significantly enhanced the discharge power and the ethylene removal performance. The catalytic activity of the prepared catalyst for the removal of ethylene was evaluated using plasma catalytic oxidation and thermal catalytic oxidation. ANOVA was used to assess the effect of single process factors and their relationships in the plasma process. All the process factors such as specific energy input (SEI), ethylene concentration, and flow rate were found to affect the ethylene conversion, CO2 selectivity, and energy efficiency (EE). Under the optimal conditions, i.e., an SEI of 80 J/L, an ethylene concentration of 20 ppm, and a flow rate of 20 L/min, the ethylene conversion was 85 %, CO2 selectivity was 70 %, and EE was 0.86 g/kW h.

Plasma-Catalytic Reforming of Naphthalene and Toluene as Biomass Tar over Honeycomb Catalysts in a Gliding Arc Reactor.

Biomass gasification is a promising and sustainable process to produce renewable and CO2-neutral syngas (H2 and CO). However, the contamination of syngas with tar is one of the major challenges to limit the deployment of biomass gasification on a commercial scale. Here, we propose a hybrid plasma-catalytic system for steam reforming of tar compounds over honeycomb-based catalysts in a gliding arc discharge (GAD) reactor. The reaction performances were evaluated using the blank substrate and coated catalytic materials (γ-Al2O3 and Ni/γ-Al2O3). Compared with the plasma alone process, introducing the honeycomb materials in GAD prolonged the residence time of reactant molecules for collision with plasma reactive species to promote their conversions. The presence of Ni/γ-Al2O3 gave the best performance with the high conversion of toluene (86.3%) and naphthalene (75.5%) and yield of H2 (35.0%) and CO (49.1%), while greatly inhibiting the formation of byproducts. The corresponding highest overall energy efficiency of 50.9 g/kWh was achieved, which was 35.4% higher than that in the plasma alone process. Characterization of the used catalyst and long-term running indicated that the honeycomb material coated with Ni/γ-Al2O3 had strong carbon resistance and excellent stability. The superior catalytic performance of Ni/γ-Al2O3 can be mainly ascribed to the large specific surface area and the in situ reduction of nickel oxide species in the reaction process, which promoted the interaction between plasma reactive species and catalysts and generated the plasma-catalysis synergy.

High-throughput volatile organic compounds removal in a sandwich-type honeycomb catalyst system combined with plasma

This paper reports on the ethyl acetate (EA) removal over a honeycomb catalyst using an experimental design methodology. A mathematical model based on the response surface methodology is developed to evaluate the effect of parameters such as specific input energy (SIE), humidity, and EA concentration on the response variables (i.e., removal and energy efficiency). A set of experiments based on a statistical three-level full-factorial design of the experimental method were performed to collect the removal data. The model (R12 = 0.9858 and R22 = 0.9305 for removal and energy efficiency, respectively) indicates a satisfactory correlation between the experimental and predicted values. The analysis results using the model show that SIE is the principal parameter affecting the EA removal. Besides, verification of the experimental results indicates that the EA removal of 90.93% and the energy efficiency of 2.91g.kWh−1 at 235 J L-1, 1.5%, and 30.3 ppm were achieved under optimal conditions.