Decomposition Of NH4NO3 Research Articles

Ag-modified CuO-Fe2O3 composite catalysts for low-temperature NH3-SCO

A series of CuFe and Ag-modified CuFe composite catalysts were prepared for low-temperature selective catalytic oxidation of ammonia (NH3-SCO). Significant synergistic effects existed between Cu and Fe oxides in the CuFe(7:12) catalyst for catalyzing NH3 oxidation. Loading 6 wt.% Ag over CuFe(7:12) further enhanced NH3 conversion and N2 selectivity. At 200 °C, NH3 conversion and N2 selectivity reached 97.1 % and 79.3 %, respectively, over 6Ag/CuFe(7:12). Besides the exceptional catalytic effects of Ag species, the increased surface area, formation of CuFe2O4, improved reducibility of Cu and Fe oxides, and increased acid sites due to the composite of Cu and Fe and modification with Ag contributed to the superior performance of the 6Ag/CuFe(7:12) catalyst in NH3-SCO. In-situ DRIFTS results showed that NH3 oxidation might follow the internal selective catalytic reduction mechanism: NH3 was dehydrogenated and oxidized to NOx and nitrate species, and the formed NOx and nitrate species were reduced by the remaining NH3, −NH2 and −NH species to N2 and H2O. Loading Ag over CuFe(7:12) suppressed the formation of NO and NO2 but promoted that of N2O during NH3 oxidation, which could be attributed to the enhanced formation and decomposition of NH4NO3 in the presence of Ag.

Influence of zeolite framework, copper speciation, and water on NO2 and N2O formation during NH3-SCR

The catalytic activity of Cu-zeolites of different topologies: BEA, MFI, MOR, FER, and CHA, prepared by impregnation or by solid-state ion exchange, were evaluated for NO2 and N2O formation during NH3-SCR reaction with or without H2O. All catalysts obtained by solid-state ion exchange were active in wider temperature windows and exhibited higher selectivity to N2, compared to those obtained by impregnation. Regardless of the method of copper introduction, the zeolites with 3D channels (BEA, MFI, CHA) were more active than those with the 2D channel frameworks (MOR and FER). The multimodal formation of NO2 and N2O results from several identified parallel-consecutive pathways, controlled primarily by copper speciation and the reaction temperature. Decomposition of NH4NO3 occurs via thermal dissociation, dehydration, and comproportionation with NO routes. The topology of the zeolites has less influence on the extent of decomposition of NH4NO3 into N2O vs. NO2 (the N2O/NO2 ratio of 3.2–3.5 was found for all zeolites), exerting a more distinct impact on the decomposition onset. For zeolites with the 3D channels, it starts at lower temperatures, and the N2O and NO2 pathways are more separated with the increasing temperature, compared to the 2D channel zeolites. The NH4NO3 dissociation pathway is essentially controlled by Brønsted acidity of the zeolites.

Probing the role of nanoconfinement in improving N2 selectivity of Mn-based catalysts during NH3-SCR

Mn-based catalysts are promising low-temperature NH3-SCR catalysts, yet their strong oxidative capability leads to excessive N2O production, contributing to global warming. This study explored titanium nanotubes supported MnOx catalysts for NH3-SCR. The optimal catalyst, 10%Mn/TN showed remarkable NOx conversion over 95 % at 150–400 °C, together with a N2 selectivity surpassing 95 % below 300 °C. In contrast, 10%Mn/Ti catalyst used for comparison had a N2 selectivity as low as 30 %. The active Mn species may predominantly locate within the inner regions of the titanium nanotubes, which effectively regulated the redox properties of 10%Mn/TN. Density Functional Theory (DFT) calculations showed that the decomposition of NH4NO3 formed on 10%Mn/TN into H2O and N2O was more difficult than that on 10%Mn/Ti. Furthermore, the NH3-SCR reaction on 10%Mn/TN mainly followed the Eley-Rideal mechanism and NH4NO3 decomposition was effectively inhibited, consequently leading to a significant improvement in N2 selectivity. These findings offer crucial insights for the design and development of Mn-based catalysts with superior activity and N2 selectivity in NH3-SCR applications.

Unravelling the multiple effects of H2O on the NH3-SCR over Mn2Cu1Al1Ox-LDO by transient kinetics and in situ DRIFTS

Understanding detrimental effects of water in the low-temperature NH3-SCR is very important for advancing the design of novel catalytic materials. Herein, the effects of 5 vol% H2O on the performance of NH3-SCR over Mn2Cu1Al1Ox-LDO were investigated through steady-state and transient kinetic analysis of step-gas switching experiments, in-situ DRIFTS and 15NO-SSITKA-DRIFTS operando. Water exhibited a significant negative activity effect at T<180 °C. Slightly positive activity (200–300 °C) and N2-selectvity (120–300 °C) effects were observed due to suppression of NH3 oxidation and NH4NO3 decomposition to N2O. The decline in activity at 140 °C by ∼ 45 % in the presence of water was found to be related to the decrease of the site activity (k) and not of surface coverage (θ) of active species formed in the NH3-SCR reaction paths of N2/N2O formation. An increase in the concentration of inactive NOx-s might also contribute to the inhibitive effect of water.

Physico-chemical Characteristics and Evolution of NR-PM1 in the Suburban Environment of Seoul

In South Korea, particulate matter (PM) is generated from various emission sources, including domestic air pollutants and long-range transport. Effective air quality policies require an understanding of the chemical characteristics of PM and differences between urban and non-urban areas (suburban and background areas). We analyzed the chemical characteristics of non-refractory submicron aerosols (NR-PM1) in Yongin City, a suburban area southeast of Seoul, using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) in spring/summer. In spring/summer, photochemical reactions resulted in the highest proportion of Organic Aerosol (OA) among NR-PM1. Positive matrix factorization (PMF) revealed four OA sources: Primary OA and Secondary OA (Oxidized Primary OA (OPOA), Less Oxidized Oxygenated OA (LO-OOA), and More Oxidized Oxygenated OA (MO-OOA)). OPOA was formed from the oxidation of emissions from biomass burning and coal combustion; LO-OOA and MO-OOA were correlated with inorganic compounds and influenced by long-range transport. The majority of OA was SOA (82%). High temperatures and humidity accelerated the conversion of SO2 to SO42−, resulting in the proportion of SO42−, second only to OA. Despite favorable conditions for nitrate formation in ammonium-rich conditions, the proportion of NO3− was relatively low due to the decomposition of NH4NO3 into gaseous NH3 and HNO3 at high temperatures. This indicated that while ammonium-rich conditions are conducive to NH4NO3 production, elevated temperatures lead to its decomposition, resulting in lower NO3− concentrations in spring/summer. In the case study, for the case associated with long-range transport, the PM concentration increased due to inorganic compounds such as NO3− and SO42−. Conversely, in cases of domestic air stagnation, the concentration of PM increased primarily due to the presence of OA. These findings provide crucial insights for air quality management in suburban areas and can guide policies to reduce PM levels in spring and summer.

Seasonal oxidative dynamics and isotopic fractionation of NOx and SO2 in Ostrava, Czech Republic: Insights from stable isotope analysis

The city of Ostrava, NE Czech Republic, is known for its industrial pollution. It has well-characterized emission sources and stable air movement patterns. These features are conveniently used to generalize on atmospheric NOx and SO2 oxidation processes. In 2021, we conducted a series of sampling campaigns to assess the isotopic fractionation conducive to NO3− and SO42− aerosols in PM10. These sampling campaigns were timed to capture varying atmospheric conditions, including climatic inversion periods, providing also insights into urban emission dynamics over the course of the year. Gaseous NOx and SO2 were collected on passive filters, while their oxidized forms, NO3− and SO42, were captured on PM10 particle filters, enabling us to analyze the transformation dynamics of these pollutants. Isotopic analyses distinguished the sources of NOx emissions—coal combustion (δ15N = −3‰) and vehicular emissions (δ15N = −7 ‰)—and allowed quantifying isotope fractionation during their conversion to NO3− (εNOx-NO3- = 11.5 ± 1.15 ‰). This fractionation, however, was influenced by seasonal variations, and appears to be notably affected by NH4NO3 decomposition during warmer months. The correlation of the NO3− to NOx ratio with PM10 and atmospheric moisture highlighted the interplay between particulate matter and humidity in relevant atmospheric transformations. Similarly, for SO2, primarily emitted from coal combustion (δ34S = −2‰), we identified distinct fractionation patterns during oxidation to SO42− encompassing both kinetic (εSO2-H2O = −1.3 ± 0.5‰) and equilibrium (εSO2- SO42- = 2.24 ± 0.67‰) effects. The SO42−/SO2 ratio was correlated with PM10 but showed no dependence on humidity. Significantly, atmospheric inversion conditions accelerated oxidation, modifying the fractionation patterns for both NOx (εNOx-NO3- = 7‰) and SO2 (εSO2- SO42-= −0.9 ± 0.3‰). Our methodology elucidates pivotal mechanisms in atmospheric pollution transformation, underlined by the tracing of NOx and SO2 to aerosol conversions via δ15N and δ34S isotopic analyses. The isotope fractionation underscores equilibrium processes in oxidation reactions, while the effect of PM10 and humidity reveals the complexity of these atmospheric oxidative transformations. The role of wet deposition in removing SO2 highlights an essential pathway in the atmospheric sulfur cycle.

Pollution Characteristics, Source Apportionment, and Meteorological Response of Water-soluble Ions in PM2.5 in Xinxiang, North China

Pollution variation, source characteristics, and meteorological effects of water-soluble inorganic ions (WSIIs) in PM2.5 were analyzed in Xinxiang city, Henan Province. PM2.5 samples and their chemical components were monitored online by using URG-9000 in four seasons:winter (January, 2022), spring (April, 2022), summer (July, 2022), and fall (October, 2022). The results showed that the TWSIIs had the same seasonal fluctuations as PM2.5. The average seasonal concentrations of WSIIs ranged from 19.62-72.15 μg·m-3, accounting for more than 60% of PM2.5, demonstrating that WSIIs were the major components of PM2.5. The annual concentration value of NO3-/SO42- was 2.11, which showed an increasing trend, suggesting predominantly mobile sources for secondary inorganic aerosols (SNA). Further, the molar concentration value [NH4+]/[NO3-] was 1.95, demonstrating that agriculture emissions were the dominant contributors to atmospheric nitrogen. Furthermore, the backward trajectory analysis showed that the concentrations of Ca2+ and Mg2+ were higher when the northeasterly wind prevailed and the wind speed was high. High values of SOR and NOR were correlated with low temperatures and high relative humidity (T < 8℃, RH > 60%), demonstrating that more gaseous precursors were converted into sulfate and nitrate. At high temperatures (T > 24℃), there was no apparent high NOR value like that for SOR, mainly due to the decomposition of NH4NO3 at high temperatures. Finally, backward trajectories associated with the PMF-resolved results were used to explore the regional transport characteristics. The results illustrated that dust sources in the study areas were mainly influenced by air trajectories originating from the northwest regions, whereas secondary sulfate, secondary nitrate, and biomass sources contributed more to WSIIs when wind speed and altitude air masses were low in the area surrounding the observation site.

Effect of NO2 on N2 O production and NOx emission reduction in NH3 Selective Catalytic Reduction.

With the introduction of increasingly strict emission regulations, reducing nitrogen oxide (NOx ) emissions and nitrous oxide (N2 O) production from diesel engines have become the focus of research. At high temperature, the reaction of NO2 in the catalyst generates the intermediate product NH4 NO3 , which first crystallizes below 300 °C. These crystals tend to block the pores and inhibit the reaction. Subsequently, N2 O is produced through the decomposition of NH4 NO3 , leading to additional pollution. Therefore, the concentration of NO2 has a direct impact on both the NOx conversion efficiency and the generation of N2 O, requiring consideration of the optimal proportion of NO2 in SCR. Considering these two factors, it is concluded that the optimal amount of NO2 varies with temperature. To improve the NOx conversion rate of the Cu-SSZ-13 catalyst at low temperatures and reduce N2 O generation, the optimal NO2 ratio of the Cu-SSZ-13 catalyst under various operating conditions is studied using numerical simulations. As the temperature rises, the optimal NO2 /NOx ratio first increases and then decreases. Under the optimal NO2 /NOx ratio, the NOx conversion rate significantly increases, while N2 O generation decreases considerably. The optimal NO2 /NOx ratio also provides suggestions for the optimization of the DOC-DPF-DCR system.

Seasonal and regional variations of atmospheric ammonia across the South Korean Peninsula

This study aimed to identify the factors causing NH3 emissions in the South Korean Peninsula and West Sea region. To analyze the trends of NH3 and other air pollutants, such as NOx, CO, and NR-PM1, we collected samples from six supersites across the peninsula, a roadside in Seoul, and the West Sea over different sampling periods, ranging from 1 month to 1 year. The highest NH3 concentrations were found at rural areas, ascribed to agricultural activities, particularly NH4NO3 decomposition at high summer temperatures. Areas with low population densities recorded the lowest NH3 concentrations, attributed to the lack of anthropogenic activities. A roadside field experiment confirmed the close link between ambient NH3 and vehicle emissions in urban regions by showing a strong correlation between CO and NOx concentrations and that of NH3. Moreover, we examined oceanic emissions near the eastern coast of South Korea in the West Sea. Long-range transportation studies confirmed that most of the pollutants (NH3, CO, and PM1) were transported by wind from the northeastern region of China. A maritime origin study showed that oceanic emissions and NH4NO3 decomposition in the atmosphere owing to high temperatures were the causing NH3 pollution. These findings provided valuable insights into the emission sources of NH3 in primary air pollutants in South Korea, highlighting the contributions of land-based and oceanic sources. Our study can help inform policymakers and stakeholders for developing effective regional air pollution control strategies.

Hydrotalcite-Modified Clinoptilolite as the Catalyst for Selective Catalytic Reduction of NO with Ammonia (NH3-SCR).

A series of clinoptilolite-supported catalysts, modified with hydrotalcite-like phase (HT) by co-precipitation, were prepared and tested in NH3-SCR reactions. It was found that deposition of HT on clinoptilolite increased conversion of NO within 250-450 °C, and that the positive impact on the catalytic activity was independent of HT loading. The promoting effect of clinoptilolite was attributed to Brönsted acid sites present in the zeolite, which facilitated adsorption and accumulation of ammonia during the catalytic process. Concentration of N2O in the post-reaction gas mixture reached its maximum at 300 °C and the by-product was most likely formed as a consequence of NH4NO3 decomposition or side reaction of NH3 oxidation in the high-temperature region. The gradual elimination of nitrous oxide, noticed as the material with the highest concentration of hydrotalcite phase, was attributed to the abundance of oligomeric iron species and the superior textural parameters of the material. UV-Vis experiments performed on the calcined samples indicated that Fe sites of higher nuclearity were generated by thermal decomposition of the hydrotalcite phase during the catalytic reaction. Therefore, calcination of the materials prior to the catalytic tests was not required to obtain satisfactory overall catalytic performance in NO reductions.

Mechanism-based kinetic modeling of N2O formation on SCR activity over Cu-SSZ-13 catalysts for diesel vehicle

A three-site SCR model including Z2Cu, ZCuOH and Brönsted acid sites has been developed for accurately describing SCR reactions and N2O formation over Cu-SSZ-13. The N2O formation mechanism proposed by recent works was adopted. Low-temperature N2O formation is attributed to NH4NO3 decomposition on ZCuOH and Brönsted acid sites with different NH4NO3 formation routes. High-temperature N2O formation is derived from NOx-assisted NH3 oxidation on different sites with different routes. NH3 storage, NH3 oxidation, NO oxidation, Standard SCR, Fast SCR, NO2 SCR, NH4NO3 formation and decomposition were included. The NH4NO3 inhibition on low-temperature NH3-SCR reactions and N2O formation due to its deposition on catalyst surface were considered. The model has been validated by different steady-state and transient experiments. The results indicate the model can accurately predict SCR reactions, as well as N2O formation under different conditions. The model can improve NOx and N2O cooperative emission control performance in diesel engine after-treatment system.

Ceria-Supported Gold Nanoparticles as a Superior Catalyst for Nitrous Oxide Production via Ammonia Oxidation.

The production of nitrous oxide, N2 O, via NH3 oxidation is not on a practical scale due to the lack of a suitable catalyst. Instead, it is produced via thermal decomposition of NH4 NO3 , rendering N2 O too costly and limiting its prospective uses. Herein, we report CeO2 -supported Au nanoparticles (2-3 nm) as a highly selective catalyst for low-temperature NH3 oxidation to N2 O, exhibiting two orders of magnitude higher space-time yield than the state-of-the-art Mn-Bi/α-Al2 O3 and remarkable stability over 70 h on stream. The reaction proceeds via a Mars-van Krevelen mechanism, with the density of interfacial Auδ+ species and the oxygen storage capacity of CeO2 identified as the key performance descriptors. The latter could be enhanced by cobalt doping, improving the catalytic activity and setting a new benchmark for N2 O productivity. These findings establish NH3 oxidation as an efficient process for N2 O manufacture and facilitate its broader utilization in selective oxidations.

Ceria‐Supported Gold Nanoparticles as a Superior Catalyst for Nitrous Oxide Production via Ammonia Oxidation

AbstractThe production of nitrous oxide, N2O, via NH3 oxidation is not on a practical scale due to the lack of a suitable catalyst. Instead, it is produced via thermal decomposition of NH4NO3, rendering N2O too costly and limiting its prospective uses. Herein, we report CeO2‐supported Au nanoparticles (2–3 nm) as a highly selective catalyst for low‐temperature NH3 oxidation to N2O, exhibiting two orders of magnitude higher space–time yield than the state‐of‐the‐art Mn−Bi/α‐Al2O3 and remarkable stability over 70 h on stream. The reaction proceeds via a Mars–van Krevelen mechanism, with the density of interfacial Auδ+ species and the oxygen storage capacity of CeO2 identified as the key performance descriptors. The latter could be enhanced by cobalt doping, improving the catalytic activity and setting a new benchmark for N2O productivity. These findings establish NH3 oxidation as an efficient process for N2O manufacture and facilitate its broader utilization in selective oxidations.

N2O Formation Mechanism During Low-Temperature NH3-SCR over Cu-SSZ-13 Catalysts with Different Cu Loadings

Based on the in situ DRIFTS studies, the mechanism of formation and decomposition of NH4NO3 (decomposition to N2O) over Cu-SSZ-13 with different Cu loadings was investigated. Under standard SCR conditions, NH4NO2 can form over all catalysts, which can be more easily oxidized to NH4NO3 over higher Cu content catalysts because of their stronger oxidative ability resulting from the elevation of Cu(OH)+. Hence, a higher Cu content leads to more low-temperature N2O formation, while N2O barely occurred over Cu-0 and Cu-0.7 catalysts. When NO2 exists, NO3– forms from the disproportionation reaction of NO2 first, then reacts with NH3 to form NH4NO3, leading to N2O formation over all catalysts. Nevertheless, Cu2+ is active for the reaction between NH4NO3 and NO. The increase of Cu2+ allows more NH4NO3 consumption, and the self-inhibition of NH4NO3 alleviates, which allows NH4NO3 to decompose to N2O at lower temperatures, and N2O formation peak shifts toward lower temperatures.

Effect of nanostructured ferrites MFe2O4 (M= Cu, Co, Mg, Zn) on the thermal decomposition of ammonium nitrate

Ammonium nitrate (NH4NO3) represents a cheap, chlorine-free alternative to ammonium perchlorate for use as an oxidant for solid propellants. But its poor ignitability and low burning rate are all disadvantages to achieve such purposes. For this reason, it is necessary to carry out studies to improve its combustion characteristics, seeking to combine it with catalysts or fuels. The present work explores the possibility of improving its combustion characteristics by adding ferrites as catalysts. Nanostructured ferrites MFe2O4 (M= Mg, Co, Cu, and Zn) synthesized by autocombustion method were tested as catalysts for the thermal decomposition reaction of ammonium nitrate under open, partially open or sealed conditions. The ferrites were characterized by XRD, SEM, UV-vis spectrophotometry and Mössbauer spectroscopy. All the MFe2O4 samples are single phased with a cubic spinel structure and average sizes, L, ranging from about 9 (CoFe2O4) to 25 nm (CuFe2O4). The catalytic effect of MFe2O4 on the thermal decomposition of NH4NO3 was investigated by thermogravimetric analysis and differential scanning calorimetry techniques. The process was also followed in a volumetric Sieverts type apparatus. The results indicate that only under sealed conditions the addition of these ferrites has influence in the decomposition process of AN. The incorporation of any of these ferrites decreases the onset temperature of the process manifested itself through an exothermic reaction, and also increases the amount of heat released in the reaction. The Co-ferrite showed the best efficiency causing the onset temperature to drop around 60 °C. The catalytic performance is correlated with the electronegativity of M2+ cations, which act as Lewis acid sites that interact with the gas molecules.

The Role of H+- and Cu+-Sites for N2O Formation during NH3-SCR over Cu-CHA

The mechanism for N2O formation over CHA and Cu-CHA zeolite catalysts during NH3-SCR is investigated using density functional theory calculations. Direct NH4NO3 decomposition, which is commonly regarded as the main source of N2O, is found to be associated with high barriers in the absence of Bronsted acid sites. Although Bronsted acid sites promote NH4NO3 decomposition, it is still a highly activated process. Low-temperature N2O formation is instead found to be connected with an NO + NH3 reaction over Cu-sites. In particular, N2O can be formed from H2NNO with a low barrier over Cu-OOH-Cu complexes, which are proposed intermediates in the catalytic cycle for NH3-SCR over Cu-CHA. This finding provides an explanation for the experimentally observed low-temperature N2O formation and the relation between Cu loading and N2O formation. The proposed mechanisms open up strategies to enhance the selectivity to N2 during NH3-SCR.

SO2-Tolerant Selective Catalytic Reduction of NO x over Meso-TiO2@Fe2O3@Al2O3 Metal-Based Monolith Catalysts.

It is an intractable issue to improve the low-temperature SO2-tolerant selective catalytic reduction (SCR) of NO x with NH3 because deposited sulfates are difficult to decompose below 300 °C. Herein, we established a low-temperature self-prevention mechanism of mesoporous-TiO2@Fe2O3 core-shell composites against sulfate deposition using experiments and density functional theory. The mesoporous TiO2-shell effectively restrained the deposition of FeSO4 and NH4HSO4 because of weak SO2 adsorption and promoted NH4HSO4 decomposition on the mesoporous-TiO2. The electron transfer at the Fe2O3 (core)-TiO2 (shell) interface accelerated the redox cycle, launching the "Fast SCR" reaction, which broadened the low-temperature window. Engineered from the nano- to macro-scale, we achieved one-pot self-installation of mesoporous-TiO2@Fe2O3 composites on the self-tailored AlOOH@Al-mesh monoliths. After the thermal treatment, the mesoporous-TiO2@Fe2O3@Al2O3 monolith catalyst delivered a broad window of 220-420 °C with NO conversion above 90% and had superior SO2 tolerance at 260 °C. The effective heat removal of Al-mesh monolithcatalysts restrained NH3 oxidation to NO and N2O while suppressing the decomposition of NH4NO3 to N2O, and this led to much better high-temperature activity and N2 selectivity. This work supplies a new point for the development of low-temperature SO2-tolerant monolithic SCR catalysts with high N2 selectivity, which is of great significance for both academic interests and practical applications.

Ammonium-Salt Formation and Catalyst Deactivation in the SCR System for a Marine Diesel Engine

Due to the low temperature and complex composition of the exhaust gas of the marine diesel engine, the working requirements of the selective catalytic reduction (SCR) catalyst cannot be met directly. Moreover, ammonium sulfate, ammonium nitrate, and other ammonium deposits are formed at low temperatures, which block the surface or the pore channels of the SCR catalyst, thereby resulting in its reduction or even its loss of activity. Considering the difficulty of the marine diesel engine bench test and the limitation of the catalyst sample test, a one-dimensional simulation model of the SCR system was built in this paper. In addition, the deactivation reaction process of the ammonium salt in the SCR system and its influencing factors were studied. Based on the gas phase and the surface reaction kinetics, the models of the urea decomposition, the surface denitrification, the nitrate deactivation, and the sulfate deactivation were both constructed and verified in terms of accuracy. Moreover, the formation/decomposition reaction pathway and the catalytic deactivation of ammonium nitrate and ammonium bisulfate, as well as the composition concentration and the exhaust gas temperature range were correspondingly clarified. The results showed that within a certain range, the increase of the NO2/NOx ratio was conducive to the fast SCR reaction and the NH4NO3 formation’s reaction. Increasing the exhaust gas temperature also raised the NO2/NOx ratio, which was beneficial to both the fast SCR reaction and the NH4NO3 decomposition reaction, respectively. Furthermore, the influence of the SO2 concentration on the denitrification efficiency decreased with the increase of the exhaust gas temperature because of increasing SCR reaction rate and reversibility of ammonia sulfate formation, and when the temperature of the exhaust gas was higher than 350 °C, the activity of the catalyst was almost unaffected by ammonia sulfate.

Enhanced activity of Ni/SiO2 catalyst in dry reforming of CH4 via a modified impregnation method

A modified impregnation method with the addition of NH4NO3 was employed to prepared the supported Ni catalyst (denoted as Ni/SiO2-N). And the obtained catalyst exhibited an improved catalytic activity and stability in DRM at 800°C with GHSV of 48 L⋅gcat.−1⋅h−1 and CH4/CO2/N2 = 9/9/2. The XRD and H2-TPR results showed that the Ni/SiO2-N catalyst was possessed with smaller Ni particles and stronger metal-support interaction than Ni/SiO2 catalyst prepared by the common impregnation method, leading to the better catalytic performance. It is the decomposition of NH4NO3 which can generate extra heat in a short time during the catalyst preparation process that make the change in structure and performance of catalyst.

The influence of nanoxide additives on the characteristics of thermal decomposition of ammonium nitrate

Thermal decomposition of ammonium nitrate (NH4NO3) containing 5% (by weight) of catalytic additives in the form of metal oxides (NiO, CuO, Co2O3) has been studied. The experiment was performed by thermogravimetric analysis at a heating rate of 5°C/min to a maximum temperature of 800°C in argon atmosphere. Based on the results of DTA, physical and kinetic characteristics of thermal decomposition we analytically assessed. The addition of catalytic agents was found to lead to a decrease of onset temperature of active NH4NO3 decomposition, which promotes the reaction shift to the low-temperature region. The effect of the initiation additive manifested in a significant reduction of sample residence time within preheating stage (Δti = 5.2 min). In presence of catalytic additives the total time of thermal decomposition tf was found to decrease. The greatest change of Δtf (2.8 minutes) was recorded for the sample modified by addition of Co3O4. The maximum decrease of the average activation energy (for decomposition of 5%Co3O4/NH4NO3) was 14.2 kJ/mol.