Flow Reactor Tests Research Articles

Redox and Kinetic Properties of Composition-Dependent Active Sites in Copper-Exchanged Chabazite for Direct Methane-to-Methanol Oxidation.

The CH4 oxidation performance of Cu-chabazite zeolites characterized by distinct Si/Al ratios and Cu loadings has been studied and the observed variations in reactivity have been correlated to the differences in the nature of the formed active centers. Plug flow reactor tests, in situ Fourier-transform infrared, and X-ray absorption spectroscopy demonstrate that a decrease in Cu loading shifts the reactivity/redox profile to higher temperatures and increases the CH3OH selectivity and Cu-efficiency. In situ electron paramagnetic resonance, Raman, ultraviolet-visible, Fourier-transform infrared, and photoluminescence spectroscopies reveal that this behavior is associated with the presence of monomeric Cu active sites, including bare Cu2+ and [CuOH]+ present at low Si/Al ratio and Cu loading. Formation of two distinct [Cu2(μ-O)]2+ moieties at higher Si/Al ratio or Cu loading forces these trends into the opposite direction. Operando electron paramagnetic resonance and ultraviolet-visible spectroscopy show that the apparent activation energy of monomeric Cu active species decreases with increasing Si/Al ratio, whereas the one of dimeric centers is unaffected.

Sustainable synthesis of N-doped carbon to stabilize Ru species for CO2 hydrogenation to formic acid

In this study, we developed nitrogen-doped carbon supporting materials from biomass-derived fertilizers, offering a sustainable and eco-friendly approach to heterogeneous catalysis for CO2 hydrogenation. Three types of fertilizers (AA50, AA80, and FV), derived from different biomass sources, were evaluated there potential to prepare the N-doped carbon structure. The synthesis of fertilizer-based supporting materials resulted in an abundant amount and a specific structure of doped nitrogen, essential for immobilizing atomically dispersed Ru catalysts during CO2 hydrogenation. The catalytic performance of the Ru catalysts supported on optimized fertilizer-derived materials exhibited a turnover number of 2748 over two hours and maintaining 98 % stability across five recycling tests. Analysis of spent catalysts showed that our fertilizer-based supports effectively prevented the sintering and leaching of the Ru catalysts. Moreover, the capability for industrial application was validated through a continuous flow reactor test, achieving an average formate productivity of 697 mmol•gcat−1h−1 over 100 hours. These results highlight the synthesized Ru catalyst on fertilizer-derived carbon material as a promising solution for eco-friendly CO2 hydrogenation to formic acid.

Kinetic modeling of NH3-selective catalytic reduction (SCR) over a mildly hydrothermally aged commercial Cu-SSZ-13 catalyst

Cu-SSZ-13 is often studied as a selective catalytic reduction (SCR) of NOx catalyst for diesel after-treatment systems. Mild hydrothermal aging (HTA) is commonly known to cause changes in catalyst performance. In this study, a kinetic model of SCR over a Cu-SSZ-13 catalyst that includes mild HTA and its impact on the SCR reaction was developed. The migration of Cu species during HTA, and how this change in Cu distribution affects low-temperature and high-temperature NH3 oxidation and SCR reaction mechanisms, were considered. Flow reactor test results were used for parameter estimation and verification. Different characterization techniques, including H2 temperature-programmed reduction (H2-TPR), NO + NH3-TPR, NH3 temperature-programmed desorption (NH3-TPD), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), were used to characterize and quantify catalyst site densities. The model can simulate the migration of Cu species and the NOx reduction performance changes during mild hydrothermal aging as a function of aging temperature and time.

Catalytic Hydrogel Membrane Reactor for Treatment of Aqueous Contaminants.

Heterogeneous hydrogenation catalysis is a promising approach for treating oxidized contaminants in drinking water, but scale-up has been limited by the challenge of immobilization of the catalyst while maintaining efficient mass transport and reaction kinetics. We describe a new process that addresses this issue: the catalytic hydrogel membrane (CHM) reactor. The CHM consists of a gas-permeable hollow-fiber membrane coated with an alginate-based hydrogel containing catalyst nanoparticles. The CHM benefits from counter-diffusional transport within the hydrogel, where H2 diffuses from the interior of the membrane and contaminant species (e.g., NO2-, O2) diffuse from the bulk aqueous solution. The reduction of O2 and NO2- were investigated using CHMs with varying palladium catalyst densities, and mass transport of reactive species in the catalytic hydrogel was characterized using microsensors. The thickness of the "reactive zone" within the hydrogel affected the reaction rate and byproduct selectivity, and it was dependent on catalyst density. In acontinuously mixed flow reactor test using groundwater,the CHMactivitywas stable for a 3 day period. Outcomes of this study illustrate the potential of the CHM as a scalable process in the treatment of aqueous contaminants.

Nanoporous gold functionalized with praseodymia-titania mixed oxides as a stable catalyst for the water-gas shift reaction.

Dealloyed nanoporous metals hold great promise in the field of heterogeneous catalysis; however their tendency to coarsen at elevated temperatures or under catalytic reaction conditions sometimes limit further applications. Here, we report on a highly stable nanoporous gold catalyst (npAu) functionalized with praseodymia-titania mixed oxides as synthesized by a sol-gel method. Specifically, we used aberration-corrected transmission electron microscopy to study the morphology and the interface between the oxide deposits and the npAu substrate at the atomic level. Based on electron energy loss spectroscopy (EELS), it is concluded that Pr-TiOx mixed oxides form a solid solution. Flow reactor tests reveal that the Pr-TiOx functionalized nanoporous gold is not only highly active but also very stable for the water gas shift reaction in a large temperature range (180-400 °C). Our results demonstrate the potential of engineering the compositions of oxides coatings on npAu for advanced functional systems.

Trade-off between NOx storage capacity and sulfur tolerance on Al2O3/ZrO2/TiO2–based DeNOx catalysts

Al2O3/ZrO2/TiO2 (AZT) ternary mixed oxides functionalized with Pt and BaO were synthesized in powder and monolithic forms and were utilized in NOx Storage Reduction/Lean NOx Trap (NSR/LNT) catalysis as novel catalytic materials. Adsorption of NOx and SOx species and their interactions with the catalyst surfaces were systematically investigated via in-situ FTIR technique revealing different NOx coordination geometries governed by the presence and the loading of BaO in the powder catalyst formulation. While BaO-free Pt/AZT stored NOx as surface nitrates, BaO incorporation also led to the formation of bulk-like ionic nitrate species. NOx adsorption results obtained from the current Temperature Programmed Desorption (TPD) data indicated that NOx Storage Capacity (NSC) was enhanced due to BaO incorporation into the powder catalyst and NSC was found to increase in the following order: Pt/AZT < Pt/8BaO/AZT < Pt/20BaO/Al2O3 < Pt/20BaO/AZT. Increase in the NSC with increasing BaO loading was found to be at the expense of the formation of bulk-like sulfates after SOx exposures. These bulk-like sulfates were observed to require higher temperatures for complete regeneration with H2(g). Catalytic activity results at 473 K and 573 K obtained via flow reactor tests with monolithic catalysts suggested that Pt/AZT and Pt/8BaO/AZT catalysts with stronger surface acidity also revealed higher resistance against sulfur poisoning and superior SOx regeneration in spite of their relatively lower NSC. Monolithic Pt/20BaO/AZT catalyst revealed superior NSC with respect to the conventional Pt/20BaO/Al2O3 benchmark catalyst at 573 K after sulfur regeneration. On the other hand, this trend was reversed at high-temperatures (i.e. 673 K). Preliminary results were presented demonstrating the enhancement of the high-temperature NSC of AZT-based materials by exploiting multiple NOx-storage components where BaO functioned as the low/mid-temperature NOx-storage domain and K2O served as the high-temperature NOx storage domain. Enhancement in the high-temperature NOx-storage in the BaO-K2O multiple storage domain systems was attributed to the formation of additional thermally stable bulk-like nitrates upon K2O incorporation.

Optimizing Binding Energies of Key Intermediates for CO2 Hydrogenation to Methanol over Oxide-Supported Copper.

Rational optimization of catalytic performance has been one of the major challenges in catalysis. Here we report a bottom-up study on the ability of TiO2 and ZrO2 to optimize the CO2 conversion to methanol on Cu, using combined density functional theory (DFT) calculations, kinetic Monte Carlo (KMC) simulations, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements, and steady-state flow reactor tests. The theoretical results from DFT and KMC agree with in situ DRIFTS measurements, showing that both TiO2 and ZrO2 help to promote methanol synthesis on Cu via carboxyl intermediates and the reverse water-gas-shift (RWGS) pathway; the formate intermediates, on the other hand, likely act as a spectator eventually. The origin of the superior promoting effect of ZrO2 is associated with the fine-tuning capability of reduced Zr(3+) at the interface, being able to bind the key reaction intermediates, e.g. *CO2, *CO, *HCO, and *H2CO, moderately to facilitate methanol formation. This study demonstrates the importance of synergy between theory and experiments to elucidate the complex reaction mechanisms of CO2 hydrogenation for the realization of a better catalyst by design.

Evaluation of Scenario Uncertainties in Entrained Flow Reactor Tests through CFD Modeling: Devolatilization

A Computational Fluid Dynamic model of oxy-coal devolatilization experiments in a pilot-scale entrained flow reactor is proposed to gain insight into the thermal histories of the cloud of solid fuel particles and to investigate sources of uncertainties that may affect the analysis of devolatilization. Solid fuel particles experience different paths and are characterized by a temperature which is lower than the reactor nominal one at some of the sampling locations used for investigating devolatilization rates. Indeed, neglecting the quick heating up of the particles by assuming their temperature to be equal to the reactor one for calculating kinetics leads to an underestimation of devolatilization rates. A simple hypothesis on a linear dependence of the particle temperature on residence time through an average heating rate, with residence time and heating rate estimated from the numerical model, was found to largely improve the reliability of devolatilization kinetics even with a simple Single First Order ...

Acido-basicity of lanthana/alumina catalysts and their activity in ethanol conversion

Lanthana on alumina samples (0.2, 0.8 and 4.7 theoretical monolayers) were prepared by incipient wetness impregnation using γ-Al2O3 as support. Characterization has been performed by BET, XRD, skeletal FT-IR, DR-UVvis, XPS, HR-TEM, IR spectra of the surface OH, adsorbed pyridine and CO2, and isopropanol TPD. Ethanol conversion was investigated both in temperature-programmed surface reaction (TPSR) dynamic conditions as well as in steady-state flow reactor tests. Lanthanum addition stabilizes alumina with respect to sintering and loss of surface area and La- containing phases are observed only for the high-La loaded catalyst. La-alumina catalysts are less active in ethanol dehydration than alumina but more selective to diethyl ether at partial conversion. 5%La2O3/Al2O3 is also equally or more selective than alumina to ethylene at high conversion, producing less carbonaceous material during reaction. Thus, this catalytic system might be a good candidate for (bio)ethylene production through (bio)ethanol dehydration.

Enhanced biogas production by anaerobic co-digestion from a trinary mix substrate over a binary mix substrate.

The synergetic enhancement of mesophilic anaerobic co-digestion of trinary and binary mix of organic fraction of municipal solid waste (OFMSW) + primary sludge (PS) + thickened waste activated sludge (TWAS) as substrates was investigated through batch biological methane potential (BMP) and semi-continuous flow reactor tests. Cumulative biogas yield (CBY) yield for the binary mix of OFMSW:TWAS was 555, 580, and 660 mL/g volatile solids (VS)added for an OFMSW:TWAS ratio of 25:75, 50:50, and 75:25, respectively, which was 48, 78.5, and 140% higher than the calculated expected biogas (CEB) yield from the corresponding individual substrates. The trinary mixture of OFMSW:TWAS:PS at ratios of 25:37.5:375.5, 50:25:25 and 75:12.5:12.5 was able to produce 680, 710 and 780 mL/g VSadded, respectively, which was 25.5, 62.0 and 135.6% more biogas than the calculated expected biogas yield from the corresponding individual substrates. Cumulative methane yield (CMY) of trinary mixtures was also higher than the corresponding binary mixtures (20, 27, and 12 % increase for OFMSW:TWAS:PS at a ratio of 25:37.5:37.5, 50:25:25, and 75:12.5:12.5 compared to the binary mix of OFMSW:TWAS at a ratio of 25:75, 50:50, and 75:25, respectively). Methane content of the biogas varied from 54 to 57%. The results from semi-continuous flow anaerobic reactors under hydraulic retention times (HRT) of 15, 10 and 7 days supported the results of batch biological methane potential tests. The results were conclusive that enhancement in biogas production was noticeably higher from the co-digestion of trinary mix of organic fraction of municipal solid waste+ thickened waste activated sludge + primary sludge than the binary mix organic fraction of municipal solid waste+thickened waste activated sludge or thickened waste activated sludge+primary sludge with concomitant improvements in VS removal and biodegradability for tri-digestion of organic fraction of municipal solid waste, thickened waste activated sludge and primary sludge.

제어를 위한 Lean NOxTrap의 흡장 및 환원 모델링

A control oriented model of the Lean NOx trap (LNT) was developed to determine the timing of NOx regeneration. The LNT model consists of NOx storage and reduction model. Once NOx is stored (NOx storage model), at the right timing NOx should be released and then reduced (NOx reduction model) with reductants on the catalyst active sites, called regeneration. The NOx storage model simulates the degree of stored NOx in the LNT. It is structured by an instantaneous NOx storage efficiency and the NOx storage capacity model. The NOx storge capacity model was modeled to have a Gaussian distribution with a function of exhaust gas temperature. NOx release and reduction reactions for the NOx reduction model were modeled as Arrhenius equations. The parameter identification was optimally performed by the data of the bench flow reactor test results at space velocity 50,000/hr, 80,000/hr, and temperature of 250 - 500°C. The LNT model state, storage fraction indicates the degree of stored NO x in the LNT and thus, the timing of the regeneration can be determined based on it. For practical purpose, this model will be verified more completely by engine test data which simulate the NEDC transient mode.

GT-POWERTM를 이용한 Lean NOxTrap 촉매 성능 모델링

In this study we designed a lean <TEX>$NO_x$</TEX> trap (LNT) model with <TEX>$GT-POWER^{TM}$</TEX> program and then the LNT model was compared to the bench flow reactor test results. This model consists of 9 kinetic reactions to represent the main steps of NO oxidation, <TEX>$NO_x$</TEX> adsorption, <TEX>$NO_x$</TEX> release and then its reduction. The comparison was performed on the operating conditions at the space velocity of 50,000 1/hr and 80,000 1/hr with the temperature range of <TEX>$200^{\circ}C{\sim}500^{\circ}C$</TEX> with the even spaced temperature step of <TEX>$50^{\circ}C$</TEX>. The experimental results show that the <TEX>$NO_x$</TEX> conversion efficiency was enhanced by the temperature up to <TEX>$350^{\circ}C$</TEX> and then decayed at higher temperatures. The LNT model predicts the similar trend of the <TEX>$NO_x$</TEX> conversion efficiency to the experimental results below <TEX>$350^{\circ}C$</TEX>, but overestimates above <TEX>$350^{\circ}C$</TEX>. This overestimation comes from the higher reduction efficiency which was obtained by the different reduction gas composition such as <TEX>$C_3H_6$</TEX> in the model to replace <TEX>$CH_4$</TEX>, <TEX>$C_2H_4$</TEX> in the bench test.

COx Free Hydrogen Production From Ammonia Decomposition Over Platinum Based Siliceous Materials

Abstract Ammonia has become an important source for hydrogen especially for fuel cell applications that require COx free hydrogen. In this study, high surface area Pt incorporated mesoporous siliceous materials were prepared for ammonia decomposition reaction to produce clean hydrogen. The results of a fixed bed flow reactor tests, conducted using pure ammonia showed that Pt-SiO2 type catalysts which were prepared by a one-pot hydrothermal synthesis procedure were very active in ammonia decomposition, such as 72% conversion was reached at 500°C at a gas hourly space velocity of 5,100 ml/h.gcat over the catalyst prepared at Pt/Si mol ratio of 0.03. Activity of the synthesized catalysts increased with an increase in Pt loading. Platinum incorporated siliceous materials prepared by impregnation procedures were also tested in ammonia decomposition and highly promising results were obtained.

Effect of H2S on Chemical Looping Combustion of Coal-Derived Synthesis Gas over Fe–Mn Oxides Supported on Sepiolite, ZrO2, and Al2O3

The performance of Fe–Mn oxide oxygen carriers supported on sepiolite, ZrO2, and Al2O3 with simulated synthesis gas/air in a novel combustion technology known as chemical looping combustion (CLC) was evaluated. Thermogravimetric analyses (TGAs) and bench-scale low-pressure (10 psi) flow reactor tests were conducted to evaluate the performance. Multicycle tests were conducted in atmospheric TGA with oxygen carriers using simulated synthesis gas with and without H2S. The effect of H2S impurities on both stability and oxygen transport capacity was also evaluated. Multicycle CLC tests were conducted in the bench-scale flow reactor at 800 °C with selected samples as well. Chemical-phase composition was investigated by the X-ray diffraction (XRD) technique. Five-cycle TGA tests at 800–900 °C indicated that all oxygen carriers exhibited stable performance. It was interesting to note that there was complete reduction–oxidation of the oxygen carrier during the five-cycle test. Fractional reduction, fractional oxid...

Development of a Quasi-Two-Dimensional Model for Analysing Continuous Regeneration—Diesel Particulate Filter States during Continuous and Active Regeneration

A quasi-two-dimensional model for describing regeneration events in the continuous regeneration—diesel particulate filter (CR-DPF) is presented, in which computational grids of the diesel particulate filter are provided in the discretization of physical domains in the axial and wall thickness directions. In the model, gas and particle flows, pressures, temperatures, and soot distributions in the inlet/outlet channels and wall, together with both continuous regeneration and active regeneration reactions, are considered. Rate constants of the chemical reactions are calibrated using results of soot oxidation tests in a mini flow reactor and engine bench tests. The distributions of loaded soot mass, filter temperature, and pressure during both continuous and active regenerations have been analysed using this model. The analysis shows that the predicted pressure drop across the diesel particulate filter is in good agreement with the data obtained in an engine bench test. The processes of soot loading including the deep wall filtration phase and the subsequent soot cake layer formation phase have been successfully predicted by calculation based on the model. It is also shown that soot accumulates mainly in the upstream area in the filter wall and at the front and rear parts in the axial direction when the soot accumulation amount is small. The reason for this uneven accumulation is presumed to result from the large pressure differences between the inlet and outlet channels at these locations.

ChemInform Abstract: High-Temperature Oxidation Mechanisms of m- and p-Xylene

Mechanisms for the oxidation of m- and p-xylene were developed with the aid of atmospheric flow reactor tests at temperatures ranging from 1093 to 1199 K. The experimental data suggested that m-xylene is oxidized by sequential oxidation and removal of the methyl side chains while p-xylene reacts through simultaneous, as well as sequential, oxidation of the side chains. The formation of p-xylylene (3,6-bis(methylene)-1,4-cyclohexadiene), postulated to occur during the oxidation of p-xylene, opens up the simultaneous oxidation route and leads to the formation of p-phthalaldehyde

Regenerable Multifunctional Sorbent Development for Sulfur and Chloride Removal from Coal-Derived Synthesis Gas

A large number of components in coal form corrosive and toxic compounds during coal gasification processes. These contaminants have to be reduced to the parts-per-million range to use the fuel gas in an integrated gasification combined cycle. Even more stringent requirements are expected if the fuel gas is to be used in fuel cell or chemical production applications. Impurity removal may be even more cost-effective if multiple impurities can be removed in a minimum number of steps. To accomplish this goal, a regenerable sorbent capable of removing both hydrogen chloride (HCl) and hydrogen sulfide (H2S) was investigated. The results of the thermogravimetric analyzer tests and bench-scale fixed-bed flow reactor tests conducted with the sorbent to evaluate the feasibility of both H2S and HCl sorption will be discussed in this paper.

저온 디젤 연소에서 발생하는 탄화수소 종 분석

Low temperature diesel combustion was achieved via a combination of late injection timing ( CA BTDC to CA BTDC) and heavy exhaust gas recirculation (37% to 48%) with ultra low sulfur Swedish diesel fuel in a 1.7L common rail direct injection diesel engine. When injection timing is retarded at a certain exhaust gas recirculation rate, the particulate matter and nitrogen oxides decease simultaneously, while the hydrocarbon and carbon monoxide increase. Hydrocarbon speciation by gas chromatography using a flame ionization detector reveals that the ratio of partially burned hydrocarbon, i.e., mainly alkenes increase as the injection timing is retarded and exhaust gas recirculation is increased. The two most abundant hydrocarbon species are ethene which is a representative species of partially burned hydrocarbons, and n-undecane, which is a representative species of unburned hydrocarbons. They may be used as surrogate hydrocarbon species for performing a bench flow reactor test for catalyst development.

Chemical-Looping Combustion of Coal with Metal Oxide Oxygen Carriers

The combustion and reoxidation properties of direct coal chemical-looping combustion (CLC) over CuO, Fe2O3, Co3O4, NiO, and Mn2O3 were investigated using thermogravimetric analysis (TGA) and bench-scale fixed-bed flow reactor studies. When coal is heated in either nitrogen or carbon dioxide (CO2), 50% of weight loss was observed because of partial pyrolysis, consistent with the proximate analysis. Among various metal oxides evaluated, CuO showed the best reaction properties: CuO can initiate the reduction reaction as low as 500 °C and complete the full combustion at 700 °C. In addition, the reduced copper can be fully reoxidized by air at 700 °C. The combustion products formed during the CLC reaction of the coal/metal oxide mixture are CO2 and water, while no carbon monoxide was observed. Multicycle TGA tests and bench-scale fixed-bed flow reactor tests strongly supported the feasibility of CLC of coal by using CuO as an oxygen carrier. Scanning electron microscopy (SEM) images of solid reaction products indicated some changes in the surface morphology of a CuO−coal sample after reduction/oxidation reactions at 800 °C. However, significant surface sintering was not observed. The interactions of fly ash with metal oxides were investigated by X-ray diffraction and thermodynamic analysis. Overall, the results indicated that it is feasible to develop CLC with coal by metal oxides as oxygen carriers.

Performances of SOx traps derived from Cu/Al hydrotalcite for the protection of NOx traps from the deactivation by sulphur

The behavior of Cu/Al mixed oxides (Cu/Al ratio in the 1:2–1:5 range) have been studied as novel, noble-metal free SOx traps to protect NOx traps from the deactivation by sulphur. The investigation was made both in a thermobalance apparatus and in a flow reactor, the latter simulating the reaction conditions and space-velocities of exhaust gases from lean-burn or diesel engines. The analysis of the SO2 uptake curves as a function of the Cu/Al ratio and reaction temperature indicates that the reaction mechanism of SO2 uptake depends on two reversible surface processes (the chemisorption of SO2 and its oxidation by copper ions) and a nearly irreversible process (bulk diffusion of the sulphate species). The rate of these processes depends on (i) the Cu/Al ratio and nature of the surface copper species, (ii) the surface area of the catalyst, (iii) the reaction conditions, and (iv) the degree of sulphation. The SOx traps showing the best performances in thermogravimetric tests were found also to show the best behavior in flow reactor tests, confirming the validity of thermogravimetric tests, notwithstanding the different composition of the feed used. The SOx trap having a Cu/Al ratio of 1:2 shows better performances with respect to a reference “state-of-the-art” SOx trap containing 2% Pt.