Insights on copper, manganese, and nickel/ZSM-5 catalytic mechanisms for nitric oxides selective reduction with ammonia

The elucidation of the selective catalytic reduction mechanisms over state-of-the-art metal-promoted zeolites is essential for nitric oxides removal in automobile and stationary source applications. In this work, H/ZSM-5 catalysts modified with transition metals, including copper, manganese, and nickel, were prepared by using an incipient wetness impregnation method and were evaluated for the selective reduction of nitric oxides with ammonia. Results indicate that copper/ZSM-5 exhibits the highest catalytic activity, with > 90% nitric oxide conversion at a broad operation temperature window (221–445 °C). The nitric oxide conversion profiles of nickel/ZSM-5 shows two peaks that correspond to weak activity among the catalysts; the low-temperature peak (290 °C) was induced by nickel clusters dispersed on the ZSM-5 surface, while the high-temperature peak (460 °C) was assigned to the bulk nickel oxides. The size of granular nickel monoxide crystallites with an exposed (2 0 2) plane is 2–30 nm, as confirmed by Scanning electron microscopy, X-ray diffraction, and Transmission electron microscope measurements. Temperature-programmed reductions with hydrogen results testified that the copper and nickel cations, as the main species contributing to selective catalytic reduction, were reduced via Cu 2+/Cu +→Cu 0 and Ni 2+→Ni 0 for copper/ZSM-5 and nickel/ZSM-5, respectively, while for the manganese/ZSM-5, the Mn 3+ species in manganese clusters were reduced to Mn 2+ by hydrogen. Particularly, temperature-programmed desorption coupled with mass spectrometer (TPD-MS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were comprehensively used to reveal the relationship between zeolite structure and catalysts’ properties for improving selective catalytic reduction. These results confirm that the ammonia is adsorbed and activated on both Brønsted and Lewis acid sites. The nitrous oxide desorbs in two stages during nitric oxide-TPD-MS measurements, corresponding to the desorption of nitric oxide bounded to amorphous clusters and the nitric oxide strongly bounded to bulk metal oxides, respectively. The selective catalytic reduction process follows the L-H mechanism at low temperatures, in which nitric oxide and ammonia molecules were adsorbed and activated on the catalyst surface. The selective catalytic reduction rates reached the maximum value of 1.8 × 10 8 (218 °C), 6.4 × 10 7 (227 °C), and 3.9 × 10 7 s −1 (235 °C) for copper, manganese, and nickel /ZSM-5, respectively

Comparative study of MCe0.75Zr0.25Oy (M = Cu, Mn, Fe) catalysts for selective reduction of NO by CO: Activity and reaction pathways

Basic oxygen furnace steelmaking leads to the production of CO-rich off-gas. When CO and NO are combined in off-gas, selective catalytic reduction by CO (CO-SCR) effectively achieves the synergistic removal of both pollutants. In this paper, CuCe 0.75Zr 0.25O y, MnCe 0.75Zr 0.25O y, and FeCe 0.75Zr 0.25O y catalysts are prepared and evaluated for their CO-SCR activity, and the results show that the reaction system needs to be anaerobic; thus, the CO-SCR reaction can be dominant. The T 90 values of CuCe 0.75Zr 0.25O y and FeCe 0.75Zr 0.25O y are 200 °C and 223 °C, respectively. The activities of these two catalysts are higher than that of MnCe 0.75Zr 0.25O y (T 90 = 375 °C). Linear nitrate and bridged bidentate nitrate are the main intermediate species involved in NO conversion on the catalyst surface, and bidentate CO 3 2− coordination is the main intermediate species involved in CO conversion on the catalyst surface. CuCe 0.75Zr 0.25O y has high lattice oxygen mobility and is more likely to react with NO and CO. In the presence of oxygen, most CO is oxidized by O 2, which increases continuously to 100%, 100%, and 98% for CuCe 0.75Zr 0.25O y, FeCe 0.75Zr 0.25O y, and MnCe 0.75Zr 0.25O y, respectively; additionally, CO is oxidized by O 2, and the CO-SCR reaction cannot be carried out

Transient behavior and reaction mechanism of CO catalytic ignition over a CuO–CeO2 mixed oxide

As a key heterogeneous process, the catalytic oxidation of CO is essential not only for practical applications such as automotive exhaust purification and fuel cells but also as a model reaction to study the reaction mechanism and structure-reactivity correlation of catalysts. In this study, the variation in activity-controlling factors during CO catalytic ignition over a CuO-CeO 2 catalyst was investigated. The activity for CO combustion follows the decreasing order of CuO-CeO 2 > CuO > CeO 2. Except for inactive CeO 2, increasing temperature induces CO ignition to achieve self-sustained combustion over CuO and CuO-CeO 2. However, CuO provides enough copper sites to adsorb CO, and abundant active lattice oxygen, thus obtaining a higher hot zone temperature (208.3 °C) than that of CuO-CeO 2 (197.3 °C). Catalytic ignition triggers a kinetic transition from the low-rate steady-state regime to a high-rate steady-state regime. During the induction process, Raman, X-ray photoelectron spectroscopy, CO temperature-programmed desorption and IR spectroscopy results indicated that CO is preferentially adsorbed on oxygen vacancies (Cu +-[Ov]-Ce 3+) to yield Cu +-[C≡O]-Ce 3+ complexes. Because of the self-poisoning of CO, the adsorbed CO and traces of adsorbed oxygen react at a relative rate, which is entirely governed by the kinetics on the CO-covered surface and the heat transport until the pre-ignition regime. The Cu +-[C≡O]-Ce 3+ complex is a major contributor to CO ignition. The step-response runs and kinetic models showed that after ignition, a kinetic phase transition occurs from a CO-covered surface to an active lattice oxygen-covered surface. During CO self-sustained combustion, the rapid gas diffusivity and mass transfer is beneficial for handling the low coverage of CO. The active lattice oxygen of CuO takes part in CO oxidation

Simulating effects of fire disturbance and climate change on boreal forest productivity and evapotranspiration

We used a terrestrial ecosystem process model, BIOME-BGC, to investigate historical climate change and fire disturbance effects on regional carbon and water budgets within a 357,500 km2 portion of the Canadian boreal forest. Historical patterns of increasing atmospheric CO2, climate change, and regional fire activity were used as model drivers to evaluate the relative effects of these impacts to spatial patterns and temporal trends in forest net primary production (NPP) and evapotranspiration (ET). Historical trends of increasing atmospheric CO2 resulted in overall 13% and 5% increases in annual NPP and ET from 1994 to 1996, respectively. NPP was found to be relatively sensitive to changes in air temperature (Ta), while ET was more sensitive to precipitation (P) change within the ranges of observed climate variability (e.g., ± 2 °C for Ta and ± 20% for P). In addition, the potential effect of climate change related warming on NPP is exacerbated or offset depending on whether these changes are accompanied by respective decreases or increases in precipitation. Historical fire activity generally resulted in reductions of both NPP and ET, which consumed an average of approximately 6% of annual NPP from 1959 to 1996. Areas currently occupied by dry conifer forests were found to be subject to more frequent fire activity, which consumed approximately 8% of annual NPP. The results of this study show that the North American boreal ecosystem is sensitive to historical patterns of increasing atmospheric CO2, climate change and regional fire activity. The relative impacts of these disturbances on NPP and ET interact in complex ways and are spatially variable depending on regional land cover and climate gradients

Precise in-situ infrared spectra and kinetic analysis of gasification under the H2O or CO2 atmospheres

Studying the mechanisms of bagasse conversion into syngas is essential to sustain the growing use of biomass in energy economy production. In this work, the precise kinetics of bagasse gasification with various gasification agents was firstly investigated employing insitu infrared spectra with Coats-Redfern integration, combining qualitative infrared spectroscopy allowed for kinetic analysis, so as to explore how the intermediate species vary in each basic reaction. The results demonstrate that the CO2 agent reduces the activation energy of nitryl after amino oxidation, making the lignin involved in gasification more easily as well as causing higher gasification efficiency. On the one hand, steam serving as a gasification agent enhances the concentration of hydroxyl groups and produces H2-rich syngas. On the other hand, the strong oxidizing hydroxyl group reduces the energy barrier of carbonyl and carboxyl groups in cellulose, which facilitates the gasification process. Furthermore, this study compared the effects of gasification agent (H2O or CO2) on syngas composition, reactor temperature distribution, carbon conversion rate, gasification efficiency, as well as low calorific value, providing essential information for understanding the micro-reaction pathways and pathway regulation during bagasse gasification. (c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved

Intrinsic sodium occurrence in Zhundong coal: Experimental observations and molecular modeling

Detailed intrinsic sodium occurrence for future research on migration, release, and catalyst effect behavior of sodium is necessary. Complementary characterizations, such as C-13 CP/MAS NMR, FT-IR, Na-23 CP/MAS NMR, XPS, elemental composition analysis, and sequential extraction experiments, were employed to elucidate the actual compound form of sodium as well as Zhundong coal's structural features. Thus, a molecular occurrence model of sodium in Zhundong coal was constructed based on its structural characteristics via computational chemistry. The occurrence model of alkali metals in Zhundong coal, including their compound form, relative content, and distribution properties, was investigated at the microstructural level. Preliminary results show that the amorphous cell formula of Zhundong coal is (C2080H980O380N30S10Na) n. Organic oxygen in Zhundong coal was 67.7% hydroxyl (ethoxy), 15.5% carbonyl, and the remaining 16.8% was attributed to carboxyl. Combined with the Na-23 CP/MAS NMR and sequential extraction experiment, organic sodium accounts for 18.01% of the total. Most inorganic sodium (81.99%) is present as hydrated sodium ion (75.08%), while a small part is present as NaCl crystal phase (3.34%) insoluble-sodium account for 3.57%. Calculated C-13 NMR, FT-IR, and Na-23 NMR spectra of the proposed model agree well with the experimental spectra suggesting that the molecular occurrence model of sodium in Zhundong coal is a particularly convincing model at the approximate condition of statistical average. The highest negative electrostatic potential area is near the carboxyl group and may be attributed to organic sodium absorption sites; the hydroxy or phenoxy group nearby may form additional coordination bonds to sodium, indicating the reflection of the complexity of the Na chemical environment as concluded from Na-23 CP/MAS NMR

Simultaneous catalytic elimination of CO, toluene and NH₃ over multifunctional CuCeZr based catalysts

Catalytic oxidation technology is a promising strategy to eliminate carbon monoxide (CO), volatile organic compounds (VOC) and other emissions from industrial boilers and to address ammonia (NH3) escape. Herein, we demonstrate the potential of copper-cerium-zirconium mixed oxides or those supported on TiO(2 )or ZSM-5 substrates for the simultaneous catalytic removal of CO, toluene and NH3. Among them, CuCeZr/ZSM-5 exhibits the best co-processing ability for mixed gases. In situ infrared spectroscopy analyses suggest that there is a competitive adsorption among CO, toluene and NH3, and the inhibition is in descending order of toluene>CO> NH3. Based on the physical-chemical characterizations, the Cu-Ce interfacial structure plays an important role in CO ignition at low temperatures. More importantly, the abundant acidic sites on the ZSM-5 support can improve the stability of adsorbed NH3 at high temperatures, resulting in the best NH3 catalytic oxidation performance of CuCeZr/ZSM-5 with no secondary pollutants of NOx. This study provides a strategy for the catalyst design to eliminate multiple pollutants targeting the properties of pollutants

Self-sustained CO Combustion Induced by CuCe0.75Zr0.25Oy Catalysts with Different Pore-forming Methods

CO self-sustaining combustion, induced by a CuCe0.75Zr0.25Oy catalyst, has been confirmed experimentally as an effective strategy to reduce serious environmental pollution and energy waste, which is caused by direct combustion of conventional converter gas in the steelmaking industry. In this paper, the effects of CuCe0.75Zr0.25Oy catalysts prepared by a sol-gel method via three different pore-forming agents (oxalic acid, cellulose and thermal decomposition) were investigated for their catalytic activity of self-sustained CO combustion. Additionally, characterization methods were used to obtain the structural properties of each catalyst. The results obtained show that the CuCe0.75Zr0.25Oy catalyst, as a sol-gel pore-forming agent, prepared from cellulose exhibits the highest activity among the three catalysts. Under the condition of a reaction gas (3% CO+5% O-2/N-2), the T-10 (70 degrees C), T-50 (73 degrees C) and T-90 (78 degrees C) of the cellulose catalyst are obviously lower than those of the other catalysts, where T-10, T-50 and T-90 denote the reaction temperature corresponding to the CO conversion of 10%, 50% and 90%, respectively. The reason is that the cellulose pore-forming agent promotes the formation of a multistage porous structure, which strengthens the synergistic effect between the Cu and Ce catalysts and changes the redox property of the overall catalyst. On the one hand, the strong synergy between CuO and CeO2 adjusts the dispersion and chemical state of copper nanoparticles. On the other hand, the oxygen vacancies generated locate at the copper-cerium interface enhance the ability of oxygen storage and oxygen release of the catalyst

Improving continuity of MODIS terrestrial photosynthesis products using an interpolation scheme for cloudy pixels

The Moderate Imaging Spectroradiometer (MODIS) sensors onboard the NASA Terra and Aqua satellites provide the means for frequent measurement and monitoring of the status and seasonal variability in global vegetation phenology and productivity. However, while MODIS reflectance data are often interrupted by clouds, terrestrial processes like photosynthesis are continuous, so MODIS photosynthesis data must be able to cope with cloudy pixels. We developed cloud‐correction algorithms to improve retrievals of the MODIS photosynthesis product (PSNnet) corresponding to clear sky conditions by proposing four alternative cloud‐correction algorithms, which have different levels of complexity and correct errors associated with cloudy‐pixel surface reflectance. The cloud‐correction algorithms were applied at four weather stations, two fluxtower sites and the Pacific Northwest (PNW) region of the USA to test a range of cloud climatologies. Application of the cloud‐correction algorithms increased the magnitude of both daily and annual MODIS PSNnet results. Our results indicate that the proposed cloud correction methods improve the current MODIS PSNnet product considerably at both site and regional scales and weekly to annual time steps for areas subjected to frequent cloud cover. The corrections can be applied as a post‐processing interpolation of PSNnet, and do not require reprocessing of the MOD17A2 algorithm