Honeycomb Catalyst Research Articles

Green Ce-based honeycomb catalyst with excellent water and sulfur dioxide resistances for low-temperature selective catalytic reduction of NOx with ammonia

Low-temperature selective catalytic reduction (SCR) is effective and promising for converting NOx in flue gas into N2, with wide application prospects. However, low-temperature denitration (DeNOx) catalysts are susceptible to SO2 and H2O poisoning. Here, we prepared a monolithic Mn-Fe-Ce/Al2O3 catalyst that exhibited excellent DeNOx performances at low temperatures. At 110 °C, the NO conversion rate of the catalyst was> 90%, exhibiting excellent resistances to H2O and SO2·H2O and SO2 are introduced at the same time, the efficiency is as high as 73%. Furthermore, The catalyst has a porous structure with abundant chemisorbed oxygen spices and exposed active, the reaction pathway on the catalyst proved to be the L-H mechanism based on in situ DRIFTS. This study also explored the mechanisms of low-temperature SCR catalyst poisoning by SO2 and H2O, providing insights into the effects of SO2 and H2O and theoretical support for the development of poisoning-resistant low-temperature SCR catalysts.

Tar induced deactivation and regeneration of a commercial V2O5-MoO3/TiO2 catalyst during selective catalytic reduction of NO with NH3

Tar species on catalyst’s surface promote the deposition of NH4HSO4/(NH4)2SO4 leading to the complete deactivation of V2O5-MoO3/TiO2 catalyst utilized in a glass kiln. The proposed pyrolysis method in this work effectively removes the poisoning substances. TG-IR and TG-MS results indicate that the pyrolysis products are mainly CO2 and SO2 representing the pyrolysis of tar species and NH4HSO4/(NH4)2SO4. The heating rate and pyrolysis temperature are the critical factors to keep a superior mechanical property. The axial and transverse compressive strength remained 1.77 MPa and 0.53 Mpa falling only by 4.8% and 13.1% respectively through the optimized treatment at 420 °C for 2 h with heating rate of 3 K min−1. The characterizations indicated that the surface area, pore volume and acid property were apparently restored after the heat treatment. As a result, the regenerated powder catalyst showed 100% NO conversion and more than 94% N2 selectivity at 250 – 300 °C and the regenerated honeycomb catalyst exhibited 91.6% NO conversion at 260 °C. The TPR and XPS results indicated changes of the redox behavior, which contracted the temperature range of excellent performance. Typically, the redox cycles shifting to high temperatures narrowed this temperature range, while the excessive oxidation ability decreased the N2 selectivity. The schematic of tar induced deactivation and regeneration was proposed. Overall, the tar induced deactivated catalyst was successfully regenerated by proper pyrolysis and can be reutilized in the original glass kiln at 260 °C.

Effect of Metal on Corona Discharge Plasma in a Honeycomb Catalyst and Optimization of the Critical Parameters for Ethylene Removal

Effect of Metal on Corona Discharge Plasma in a Honeycomb Catalyst and Optimization of the Critical Parameters for Ethylene Removal

Influence of flue gas parameters on conversion rates of honeycomb catalysts

• The most important parameter was the flue gas temperature at the catalyst inlet. • Average conversion rate of carbon monoxide was 69% in case of catalyst Cat A. • Average conversion rate of carbon monoxide was 96% in case of catalyst Cat B. • There was no dependence between C 3 H 8 conversion rate and observed parameters. • Tested manually operated stove is suitable for retrofit by catalysts installation. In this study, two honeycomb catalysts with palladium and platina-palladium as active elements were used for an oxidation of products of incomplete combustion such as carbon monoxide (CO) and propane (C 3 H 8 ) contained in flue gas produced by a small-scale stove. Catalysts were installed into the flue gas duct right behind the flue gas outlet of the wood log, and pellet stove. During the tests, the conversion rates of unburned pollutants were observed according to volume fraction of oxygen in the flue gas, space velocity of flue gas, temperature of flue gas at the catalysts inlet, and mass concentration of oxidized pollutants at the catalysts inlet. The CO conversion rates ranged between 37% and 95.4% (69% in average) in case of Cat A and 51.4% and 99.9% (96% in average) in case of Cat B. In terms of C 3 H 8 conversion rate, Cat B proved higher effectiveness (25% in average), than Cat A (4% in average). The most significant parameters were determined. The significant influence of combustion phase on C 3 H 8 conversion rate was observed in case of manually loaded stove.

Plasma-catalytic ethylene removal by a ZSM-5 washcoat honeycomb monolith impregnated with palladium

The effective removal of dilute ethylene in a novel honeycomb plasma reactor was investigated using a honeycomb catalyst (Pd/ZSM-5/monolith) sandwiched between two-perforated electrodes operating at ambient temperature. Herein, the dependence of catalyst performance on the binder fraction, catalyst preparation method, and catalyst loading was examined. Ethylene removal was carried out by a process comprising cycles of 30-min adsorption conjugated with 15-min plasma-catalytic oxidation. Interestingly, the performance of the cyclic process was superior to continuous plasma-catalytic oxidation and thermally activated catalyst in terms of energy conservation, i.e., ~36 compared to ~105 and ~300 J/L, respectively. Hence, the novel cyclic process can be considered advanced-oxidation technology that features room-temperature oxidation, offers low energy consumption, negligible hazardous by-products emissions such as NOx and O3. Moreover, the process operated under described conditions: low-pressure drop, ambient atmosphere, a mechanically stable system, and a simple reactor configuration, suggesting the practical applicability of this plasma process.

Plasma-catalytic oxidation of volatile organic compounds with honeycomb catalyst for industrial application

Efficiently processing volatile organic compounds (VOCs) with nonthermal plasma and honeycomb catalyst for practical industrial applications presents a sizable challenge. An attempt has been made to generate a large volume of uniform plasma at atmospheric pressure in a practical-scale honeycomb catalyst. H-ZSM-5, a type of zeolite, was washcoated on a commercial bare honeycomb monolith as the catalyst-supporting material, after which the monolith was impregnated with Pd. The plasma discharge power can be controlled by controlling the humidity in the feed gas, metal content, applied voltage, and total flow rate of the feed gas. The plasma was characterized by the voltage and current waveforms, and optical emission spectroscopy (OES). In this study, 85% of dilute toluene (15ppm) was successfully removed from an airstream at a large flow rate of 60L/min with an energy density of 84J/L. Under this condition, the selectivity of CO2 was 76%. This investigation demonstrated the practical applicability of the plasma-honeycomb catalytic reactor to process a fast-flowing feed gas without resulting in a significant large pressure drop, which can hardly be achieved with typical packed-bed plasma reactors.

Hierarchical sulphide - phosphide NiSP /NF catalyst prepared by gradient electrodeposition for oxygen evolution reaction

Rational design and fabrication of electrocatalysts with low-cost and high efficiency is highly desired. In this paper, a hierarchical honey-comb catalyst NiSP supported on nickel foam (NF) was synthesized by a facile gradient electrodeposition method. Attributed to the presence of Ni2P and NiS and the synergistic effect among phosphide and sulphide, NiSP /NF catalyst exhibited a low overpotential value of 281 mV to achieve 10 mA cm−2 and the Tafel value of 68.51 mV dec−1 in 1 M KOH. Benefited from the gradient electrodeposition process resulting in the nanoparticles decorate honey-comb structure, the electrochemical active surface area reaches to 3571.5 cm2, and the turnover frequency (TOF) value is 2.0781 s−1. Due to the good electric conductivity of phosphide and sulphide, NiSP /NF electrode kept to exhibit excellent stability for 60 h. Therefore, the electrode obtained by our gradient electrodeposition method was expected to be a promising candidate catalyst.

Highly Efficient Honeycomb Ir Coated LGDL with Low Loading for Green Hydrogen Generation in PEM Electrolyzer Cells

The catalyst-coated liquid/gas diffusion layers (CCLGDLs) have been demonstrated to promote the catalyst conductivity and utilization in proton exchange membrane electrolyzer cells (PEMECs) 1-3. In this study, honeycomb Ir catalysts are deposited on titanium thin and tunable liquid/gas diffusion layers (LGDLs) and developed as highly efficient anode electrodes in PEMECs. The uniform honeycomb catalyst structures provide abundant active sites and favorable bubble detachment and enhance the Ir catalyst kinetics and activity. As a result, the honeycomb catalyst-coated LGDL (CCLGDL) with low Ir catalyst loading and outstanding structural stability exhibits remarkable PEMEC performance. References J. Mo, Z. Kang, S.T. Retterer, D.A. Cullen, T.J. Toops, J.B. Green Jr, M.M. Mench, and F-Y. Zhang. “Discovery of true electrochemical reactions for ultrahigh catalyst mass activity in water splitting.” Science Advances, 2, 1600690 (2016).Z. Xie, S. Yu, G. Yang, K. Li, L. Ding, W. Wang, D.A. Cullen, H.M. Meyer III, S.T. Retterer, Z. Wu, P. Gao and F-Y. Zhang. "Ultrathin platinum nanowire based electrodes for high-efficiency hydrogen generation in practical electrolyzer cells." Chemical Engineering Journal. 410, 128333 (2021).Z. Kang, J. Mo, G. Yang, S.T. Retterer, D.A. Cullen, T.J. Toops, J.B. Green Jr, M.M. Mench, and F-Y. Zhang. “Investigation of thin/well-tunable liquid/gas diffusion layers exhibiting superior multifunctional performance in low-temperature electrolytic water splitting.” Energy & Environmental Science, 10, 166-175 (2017).

An Experimental Performance Study of a Catalytic Membrane Reactor for Ethanol Steam Reforming over a Metal Honeycomb Catalyst.

The present study deals with the combination of ethanol steam reforming over a monolithic catalyst and hydrogen separation by membrane in a lab-scale catalytic membrane reactor (CMR). The catalyst was comprised of honeycomb thin-walled Fechralloy substrate loaded with Ni + Ru/Pr0.35Ce0.35Zr0.35O2 active component. The asymmetric supported membrane consisted of a thin Ni-Cu alloy–Nd tungstate nanocomposite dense permselective layer deposited on a hierarchically structured asymmetric support. It has been shown that the monolithic catalyst-assisted CMR is capable of increasing the driving potential for hydrogen permeation through the same membrane as compared with that of the packed bed catalyst by increasing the retentate hydrogen concentration. Important operating parameters responsible for the low carbon deposition rate as well as the amount of hydrogen produced from 1 mol of ethanol, such as the temperature range of 700–900 °C, the water/ethanol molar ratio of 4 in the feed, have been determined. Regarding the choice of the reagent concentration (ethanol and steam in Ar), its magnitude may directly interfere with the effectiveness of the reaction-separation process in the CMR.

Practical-scale honeycomb catalytic reactor coupled with non-thermal plasma for high-throughput removal of isopropanol

A practical-scale sandwich-type honeycomb catalyst reactor incorporating non-thermal plasma was developed for the high-throughput removal of isopropanol (IPA) from air. The Pd/γ-Al2O3/honeycomb catalyst was fabricated by coating a cordierite monolith with γ-alumina powder on which to support the palladium (Pd). The supported catalyst showed good activity and the combination of the honeycomb structure with plasma produced a uniform plasma inside the catalyst chamber. The influence of different parameters, including the energy density (SIE), humidity, initial concentration, and flow rate, on the plasma characteristics and IPA removal efficiency was investigated. The results showed that the SIE has the strongest effect on the IPA removal efficiency. The efficiency of IPA removal was 94.5% and the CO2 selectivity was 85% for an SIE of 180 J/L. Using optical emission spectroscopy, we found that the increased formation of atomic oxygen and reactive species plays an essential role in the oxidation of IPA by plasma catalysis. The main byproducts were identified by GC-MS, which indicated that acetone is the major liquid product. A plausible reaction mechanism for the plasma-catalytic oxidation of IPA is proposed based on the intermediates and byproducts.

Catalytic Temperature Effects on Conversion Efficiency of PM2.5 and Gaseous Emissions from Rice Husk Combustion

Most studies on honeycomb catalysts have been conducted using simulation models and exhaust experiments from automobiles. Very few monolithic catalyst studies have been applied to the agricultural sector, especially the catalyst exhaust system for flue purification from the biomass industry. The importance of exhaust gas purification and particulate removal from biomass power plants has become critical for evaluating the performance and environmental sustainability of biomass combustion. This is one of the first studies to investigate the performance of honeycomb catalysts for the oxidation of flue (PM2.5), (CO), and (SO2) from a rice husk briquette combustion system. The experimental setup comprised a fixed-bed electric furnace, the catalyst, an aerosol sampler, and a flue gas analyzer. Rice husk (0.1 g/mL density) and rice husk briquettes (0.8 g/mL density), were burned at 600–1000 °C for 3 min. From the results, the catalyst CO conversion rate was 100% at the optimum heated temperatures of 427.4–490.3 °C. At these temperatures, the inhibition effect of the chemisorbed CO was significantly minimized, enhancing the adsorption of oxygen, which reacted with CO to form CO2. However, SO2 oxidation was lower than that of CO because platinum-based catalysts are generally more attracted to CO in the presence of oxygen. The emission of PM2.5 decreased from its uncatalyzed-value (1169.9 mg/m3 and 1572.2 mg/m3) to its catalyzed values (18.9 mg/m3 and 170.1 mg/m3). This is a significant result in ensuring cleaner production of energy from rice husk.

Decomposition of Tars on a Nickel Honeycomb Catalyst

Biomass can be considered a renewable energy source. It undergoes a gasification process to obtain gaseous fuel, which converts it into combustible gaseous products such as hydrogen, carbon monoxide, and methane. The process also generates undesirable tars that can condense in gas lines and cause corrosion, and after processing, can be an additional source of combustible gases. This study focused on the processing of tar substances with toluene as a model substance. The effect of discharge power and carrier gas composition on toluene conversion was tested. The process was conducted in a plasma-catalytic system with a new Ni3Al system in the form of a honeycomb. The toluene conversion reached 90%, and small amounts of ethane, ethylene, acetylene, benzene, and C3 and C4 hydrocarbons were detected in the post-reaction mixture. Changes in the surface composition of the Ni3Al catalyst were observed throughout the experiments. These changes did not affect the toluene conversion.

Roles of the basic metals La, Ba, and Sr as additives in Al2O3-supported Pd-based three-way catalysts

Three-way catalytic converters are widely used to regulate emissions from gasoline-powered vehicles. Although significant effort over the past 40 years has resulted in the discovery of several metal additives that improve the thermal stability of three-way catalysts (TWCs), their effects on the actual catalytic process have not been studied systematically. The present work examines the roles of the typical basic metal additives La, Ba, and Sr in Pd-based TWC systems, using various spectroscopic and kinetic studies. Metallic Pd0 species on Sr/Al2O3 and Ba/Al2O3 supports were found to be more electron-rich than those on pristine Al2O3, whereas those on La/Al2O3 were more electron-deficient. Consequently, Pd/La/Al2O3 showed a lessened CO poisoning effect during NO reduction reactions. Evaluations were performed using powdered catalysts as well as monolithic honeycomb catalysts under conditions simulating actual use. Pd/La/Al2O3 was observed to promote the catalytic reduction of NO most efficiently, while Pd/Ba/Al2O3 exhibited the highest activity for the oxidations of CO and C3H6. The present data suggest that the optimal metal additive for a Pd-based TWC will be determined by the specific application. The selection of such metals should take into account not only the stability but also the promotional effect during the exhaust purification process.

Non-thermal plasma in honeycomb catalyst for the high-throughput removal of dilute styrene from air

This study focused on the removal of styrene using a metal-coated monolith (MCM) catalyst integrated with non-thermal plasma. The MCM catalyst was prepared by depositing a ZSM-5 support impregnated with a combination of three metals (Co, Pd, La) on a practical-scale honeycomb monolith. A comparative study with a commercial metal-coated monolith (CMCM) of the same dimensions was conducted to evaluate the effectiveness of the MCM with respect to styrene removal. The plasma discharge in the monolith was characterized by measuring the voltage and current waveforms and optical emission spectroscopy (OES). The electric power of the plasma discharge largely depended on the metal loading, flow rate, and humidity of the feed gas. The removal efficiency of styrene (inlet concentration: 20 parts per million, volumetric (ppm)) was examined using both plasma catalytic oxidation (PCO) and thermal catalytic oxidation (TCO), to enable the effect of plasma to be clearly assessed. PCO with the MCM catalyst achieved styrene removal efficiency of nearly 100% at a specific energy input (SEI) of 40 J/L, whereas the CMCM catalyst achieved 92% removal for identical SEI. In comparison, TCO with the MCM and CMCM catalysts required high temperatures of 420 °C and 480 °C, respectively, for the complete removal of styrene. In addition, the CO2 selectivity of the MCM catalyst was higher at 83% compared with 75% for the CMCM at SEI of 40 J/L. The optimal silica binder content for the deposition of a robust washcoat layer was found to be approximately 5%.

Removal of ethyl acetate in air by using different types of corona discharges generated in a honeycomb monolith structure coated with Pd/γ-alumina

A method based on the corona discharge produced by high voltage alternating current (AC) and direct current (DC) over a Pd/γ-Al2O3 catalyst supported on a honeycomb structure monolith was developed to eliminate ethyl acetate (EA) from the air at atmospheric pressure. The characteristics of the AC and DC corona discharge generated inside the honeycomb structure monolith were investigated by varying the humidity, gas hourly space velocity (GHSV), and temperature. The results showed that the DC corona discharge is more stable and easily operated at different operating conditions such as humidity, GHSV, and gas temperature compared to the AC discharge. At a given applied voltage, the EA conversion in the DC honeycomb catalyst discharge is, therefore, higher compared with that in the AC honeycomb catalyst discharge (e.g., 96% of EA conversion compared with approximately 68%, respectively, at 11.2 kV). These new results can open opportunities for wide applications of DC corona discharge combined with honeycomb catalysts to VOC treatment.

NOx Reduction Using Pilot-Scale SCR Under Oxyfuel Conditions

This paper presents a comprehensive experimental study of selective catalytic reduction (SCR) of nitrogen oxides formed in the oxyfuel combustion of lignite coal in a 500 kWth pilot-scale bubbling fluidized bed (BFB) boiler using the V2O5 over TiO2 honeycomb catalyst and the ammonia as the reducing agent. The study also compares the performance of the SCR between oxyfuel and air combustion modes. The SCR unit is placed in the tail-end position of the flue gas processing scheme after the cyclone particle separator. Experiments were realized both in air- and oxyfuel combustion regime, evaluating the impact of relevant process conditions on the NOx reduction. The dependence of the NOx reduction efficiency on the catalyst temperature and on the normalized stoichiometric ratio (NSR) of the reducing agent molar flow to the molar flow of NOx were studied. The efficiency of the NOx reduction was evaluated based on the NOx concentration measured simultaneously before and after the SCR unit. In the off-gas, the concentration of unreacted reducing agent (ammonia slip) was measured as well. For evaluation of real NSR, ammonia and flue gas flow rates were measured during each experiment. The catalyst temperature was regulated within the experiments in the range of 260 to 300 °C and the NSR was chosen in the range of 0 to 1.2. From this experimental setup, the correlations of the NOx reduction efficiency related to the different NSR and catalyst temperature were evaluated. The results show the fundamental information about the differences between air and oxyfuel conditions in a real combustion environment. In general, the NOx conversion efficiency was significantly higher during air combustion. In order to get similar results of maximum NOx conversion as reached during air combustion, it was necessary to increase NSR up to 1.8 and more, however at the cost of significantly increased ammonia slip. Although the SCR performance is lower in oxyfuel combustion, it was possible to decrease NOX under 100 ppmv with NSR about 1 and without any significant ammonia slip, which is important prior to further CO2 treatment.

High-Throughput NOx Removal by Two-Stage Plasma Honeycomb Monolith Catalyst.

A two-stage plasma catalyst system for high-throughput NOx removal was investigated. Herein, the plasma stage involved the large-volume plasma discharge of humidified gas and was carried out in a sandwich-type honeycomb monolith reactor consisting of a commercial honeycomb catalyst (50 mm high; 93 mm in diameter) located between two parallel perforated disks that formed the electrodes. The results demonstrated that, in the plasma stage, the reduction of NOx did not occur at room temperature; instead, NO was only oxidized to NO2 and n-heptane to oxygenated hydrocarbons. The oxidation of NO and n-heptane in the honeycomb plasma discharge state was largely affected by the humidity of the feed gas. Furthermore, the oxidation of NO to NO2 occurs preferably to that of n-heptane with a tendency of the NO oxidation to decrease with increasing feed gas humidity. The reason is that the generation of O3 decreases as the amount of water vapor in the feed gas increases. Compared to the catalyst alone, the two-stage plasma catalyst system increased NOx removal by 29% at a temperature of 200 °C and an energy density of 25 J/L.

Effective practical removal of acetaldehyde by a sandwich-type plasma-in-honeycomb reactor under surrounding ambient conditions

The effective removal of acetaldehyde by humidified air plasma was investigated with a high throughput of contaminated gas in a sandwiched honeycomb catalyst reactor at surrounding ambient temperature. Here, acetaldehyde at the level of a few ppm was successfully oxidized by the honeycomb plasma discharge despite the harsh condition of large water content in the feed gas. The conversion rate of acetaldehyde increased significantly with the presence of catalysts coating on the surface channels. The increased conversion rate was also obtained with a high specific energy input (SEI) and total flow rate. Interestingly, the conversion changed negligibly under the acetaldehyde concentration range from 5 to 20 ppm. However, the conversion rate decreased toward increased water amount in the feed gas. Notably, about 60% of acetaldehyde in the feed was oxidized under SEI of 40 J/L at water amounts ≤ 2.5%, approximately 0.5 g/kWh for acetaldehyde removal. Also, the plasma-catalyst reaction was superior to the thermal reactive catalyst for acetaldehyde removal in airborne pollutants. In comparison with other plasma-catalyst sources for acetaldehyde removal, the energy efficiency under the condition is comparable. Moreover, the honeycomb plasma discharge features high throughput, avoiding pressure drop, and straightforward reactor configuration, suggesting potential practical applications.

Application of Pt-Loaded Honeycomb Catalysts in Air Detritiation

In nuclear fusion reactor facilities, the multi-confinement system and the air detritiation system (ADS) are very important to prevent tritium leaking to the environment. A high-performance tritium oxidation catalyst is strongly required in the ADS. In this study, the air resistance and catalytic performance of honeycomb detritiation catalysts are investigated. Then, the honeycomb catalysts are applied in a glove-box detritiation system as well as in an ADS, and the detritiation performance is tested with tritium. Honeycomb catalysts have a much lower air resistance and an excellent scale-up effect due to the behavior of laminar flow. Thus, the honeycomb catalyst increases the reaction space velocity by nearly 100 times without decreasing the conversion rate of H2. Even at an extremely low tritium concentration, the honeycomb catalyst transforms tritium over 95% into tritiated water. In short, Pt-loaded honeycomb catalysts have a huge advantage in and broad potential for air detritiation.

Nonthermal plasma in practical-scale honeycomb catalysts for the removal of toluene

Nonthermal plasma combined with a practical-scale honeycomb catalyst of 5.0 cm in height and 9.3 cm in diameter was investigated for the removal of toluene. The creation of plasma in the honeycomb catalyst greatly depended on the humidity of the feed gas and the presence of metals on the honeycomb surface. Compared to the bare ceramic honeycomb, the metal-loaded one gave higher toluene removal efficiency because the decomposition of toluene by the plasma-generated reactive species occurred not only homogeneously in the gas phase but also heterogeneously on the catalyst surface. The present plasma-catalytic reactor was able to successfully remove about 80% of dilute toluene (15 ppm in air) at a large flow rate of 60 L/min with a specific energy input of 58 J/L. The honeycomb-based plasma-catalytic reactor system is promising for practical applications since it can overcome such problems as high-pressure drop and difficulty in scale-up encountered in packed-bed reactors.