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The Cu/SSZ-13 catalyst with Si/Al ratio of 10 and Cu/Al ratio in the range of 0.005 to 0.5 was synthesized by ion exchange method. The effect of Cu/Al ratio on the performance, selectivity, and active center of the catalyst SCR was studied. The samples with too low Cu/Al ratio have low catalytic activity in the entire temperature range due to the small number of active sites. The samples with too high Cu/Al ratio have good performance in the low temperature range due to the large number of active sites. However, a large amount of copper that has not undergone ion exchange will generate CuO, which greatly enhances the oxidation of NH 3 at high temperatures, which in turn leads to a decrease in catalytic performance at high temperatures. XRD and BET experiments show that all catalyst samples have good CHA crystal structure and microporous structure, and the pore size is mostly about 2 nm. In situ DRIFTS analysis shows that when the Cu/Al ratio is low, the proportion of Z 2 Cu in the active sites is higher, and the stability of the catalyst is enhanced. When the copper-aluminum ratio is high, the proportion of ZCuOH increases, and the low-temperature activity of the catalyst is higher., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

In response to stricter emission regulations, lean‐burn engines have attracted more and more attention. However, lean burn engines would inevitably lead to the increase in NOx emissions. The researchers combined Three‐Way Catalyst (TWC) and Selective Catalytic Reduction (SCR) to propose "passive SCR", which makes the engine periodically switch between rich and lean burn. During rich combustion, ammonia is produced by the TWC catalyst, stored in the downstream SCR, and reacts with NOx during lean combustion, in which increasing the ammonia yield on the TWC catalyst is the key. In this study, the self‐propagating high‐temperature synthesis method was used to modify the catalyst by adding copper to improve the ammonia production efficiency. The conversion rate of catalysts with different copper doping ratios from NO to ammonia was measured. Through XRD, BET, H2‐TPR, TEM, HRTEM, XPS, in‐situ DRIFTS, etc. the improvement mechanism of copper doping was analysed. The results showed that Pt0.01Cu0.1Ce0.45Zr0.45Ox had the highest catalytic activity, the widest reaction temperature window (300–550 °C) with the conversion greater than 96 %. The characterization results showed that appropriate amount of copper doping can adjust the valence distribution, form more oxygen vacancies, and improve the distribution of active species. The in‐situ DRIFTS further demonstrated that the conversion from bridged to monodentate and bidentate nitrate may be the key factors on the catalyst surface. [ABSTRACT FROM AUTHOR]

Summary: Electrochemical ammonia synthesis is a promising alternative technique to traditional Haber‐Bosch process, capable of converting nitrogen to ammonia at ambient conditions and can be driven by intermittent energy. However, it generally requires high overpotential for nitrogen dissociation due to the stable triple bonds of nitrogen molecules, resulting in a poor ammonia yield rate. Tailoring the electrolyte‐ion composition is a promising approach to facilitate nitrogen dissociation by optimizing the local reaction environment near the electrode toward ammonia production. In this study, the effect of anions in the electrolyte composition on electrocatalytic nitrogen reduction to ammonia is investigated. It is found that a lower onset potential for nitrogen reduction (−0.2 V vs RHE) and a higher ammonia yield rate (6.69 × 10−11 mol cm−2 s−1) are achieved in the electrolyte containing OH− anions, compared to singly charged anions of Cl− and SCN− when using an electrode made of commercial Au/C electrocatalysts. In addition, current density contributed by nitrogen reduction achieved in the high‐pH electrolyte (pH ≥ 13) shows around 3‐fold increase compared to that in low‐pH electrolyte (11 ≤ pH ≤ 12). Such performance enhancement is possibly attributed to the appearance of hydronium ions (H3O+) in high‐pH electrolyte, which facilitates nitrogen dissociation by strengthening protonation(*N2+6H3O++6e−→*+2NH3·H2O+4H2O). [ABSTRACT FROM AUTHOR]

The passive ammonia SCR system has been considered as a novel after-treatment method to reduce the emission of NOx and produce ammonia for downstream SCR. A series of Pd0.01FexCe(1−x)/2Zr(1−x)/2Oy catalysts (x = 0, 0.1, 0.2, and 0.4) was synthesized through a solution combustion synthesis (SHS) method. Their catalytic activities were investigated by XRD, BET, Raman, H2-TPR, XPS, and in situ DRIFTS. The relationship between the reactivity and species composition, acidic properties, surface oxygen vacancies, and redox behavior of the Pd0.01FexCe(1−x)/2Zr(1−x)/2Oy catalysts was established. Results demonstrated that a moderate amount of Fe doping can markedly enhance the specific surface area, improve the surface oxygen vacancies, increase the surface acidic sites, and tune the valence distribution of surface elements. Pd0.01Fe0.1Ce0.45Zr0.45Ox showed the highest ammonia yield with a wide reaction-temperature window (250–400 °C) and >95% NO conversion and complete conversion from nitric oxide to ammonia at 300–400 °C. This may be due to the phenomenon that highly dispersed Fe2O3 enhanced the interaction among PdO, Fe2O3 and the Ce0.5Zr0.5O2 support, improved the displacement of active species on the catalyst surface, and increased the surface oxygen vacancies, thus improving the catalytic activity. [ABSTRACT FROM AUTHOR]

Abstract: This study focuses on investigating the effect of ignition temperature for the combustion synthesis (CS) on the selective catalytic reduction of NO x with NH3 over Ti0.9Ce0.05V0.05O2−δ nanocomposites serial catalysts prepared by the solution combustion method. Ti0.9Ce0.05V0.05O2−δ -350°C showed the best SCR activity and N2 selectivity in a broad temperature window of 150–400°C, in which more than 83% NO x was reduced with the superior N2 selectivity above 95%. The influence of the ignition temperature for CS on the physical and morphological properties, the crystalline phase, the microstructure, the redox behavior, the oxidation state, the reactants adsorption capability, and the evolution of the surface nitrate and acid sites after the adsorption of NO x and NH3 was extensively investigated in detail using comprehensive characterization techniques including N2 physisorption, XRD, SEM, TEM, FTIR, EPR, and XPS. The increase of the ignition temperature, the decrease of the specific surface area, the total desorption pore volume, the surface fractal dimension, and the concentration of the chemisorbed oxygen, and the increase of the average pore diameter and the particle size, which may be the main reasons for the decline of the NO x removal efficiency and the N2 selectivity. In addition, the NO x /NH3-TPD results suggest that the Ti0.9Ce0.05V0.05O2−δ catalysts prepared at lower ignition temperatures could provide more chemisorption NO x and NH3 species, and simultaneously enhance the activation of both species that result in the improvement of the SCR activity. Furthermore, the in situ DRIFTS results indicate that the active monodentate nitrate and bridging nitrate species come from the NO x adsorption and that the ionic NH4 + bound to the BrØnsted acid sites are active species and essential for the SCR process. The increase of the ignition temperature decreases the key surface nitrate species and acid sites, and thus the relevant NH3-SCR activity and selectivity. [Copyright &y& Elsevier]

Plasma-catalytic synthesis of ammonia has the potential to store hydrogen on a decentralized scale under mild conditions by consuming the distributed renewable energy power. Suitable catalyst supports can promote plasma-catalytic ammonia synthesis (PCAS). The impact of the support (Al 2 O 3 , Si-MCM-41 and SiO 2) on the performance of the Ni catalysts for PCAS was investigated under ambient pressure without heating under various N 2 :H 2 ratios, discharge powers, and flow rates. Results indicated that Ni/Al 2 O 3 (Ni–Al) had an energy yield of 0.47 g NH 3 /kWh at an NH 3 concentration of 13,670 ppm or 1.15 g NH 3 /kWh at an NH 3 concentration of 3086 ppm and Ni/Si-MCM-41 (Ni-SiM) had a highest ammonia production rate of 6311 μmol/(g cat ·h) with the NH 3 concentration and energy yield closed to those of Ni–Al. The performances of the Ni–Al and Ni-SiM catalysts were maintained for at least 50 h, and the structures of the catalysts undergoing the 50-h reaction did not change significantly. The role of the support was revealed via several characterizations, suggesting that the number of weak acid sites, Ni dispersion, and Ni-support interactions of the catalysts, which are vital for PCAS, can be affected by the type and structure of the support. In situ and ex situ spectral measurements for some important species in PCAS were performed to test the hypothesis that the reaction takes place over the catalyst and in the gas phase. According to the in-situ DRIFTS in the N 2 –H 2 plasma, ex-situ N 1s XPS, and NH 3 -TPD, it was speculated that the generated NH 3 absorbed on the weak acid site could desorb in a timely manner to accelerate the regeneration of the active sites of the catalyst in the N 2 –H 2 plasma, which resulted in a higher ammonia concentration for PCAS. • Plasma-catalytic ammonia synthesis using Ni catalysts provides a novel idea on hydrogen storage using renewable energy. •The type and structure of the support affect the performance of the catalysts for plasma-catalytic ammonia synthesis. •In situ and ex situ spectral measurements of some important species for plasma-catalytic ammonia synthesis were performed. •The performance of the Ni/Al 2 O 3 and Ni/Si-MCM-41 catalysts were maintained for at least 50 h.. [ABSTRACT FROM AUTHOR]

• A binder-free electrode is prepared for ambient ammonia synthesis. • Bismuth nanoparticles are in-situ formed on nickel foam by displacement reaction. • The ammonia production performance is investigated at electrode scale. Bismuth nanoparticles on nickel foam (BiNPs@NF) is prepared via a facile displacement reaction for ambient ammonia synthesis. [Display omitted] Bismuth has been regarded as a promising electrocatalyst for triggering nitrogen reduction to ammonia, due to the ease of nitrogen dissociation rendered by the strong interaction between Bi 6p band and the N 2p orbitals. However, the poor conductivity of bismuth limits the electron transfer for nitrogen reduction. In addition, the sluggish water dissociation on the bismuth surface leads to insufficient proton supply for the protonation step of *N 2 , causing inferior ammonia production performance. In this work, we prepare an integrated and binder-free bismuth nanoparticles@nickel foam electrode for ambient ammonia synthesis via a facile displacement reaction. Using nickel foam as the conductive substrate improves the electron transfer of bismuth for nitrogen reduction to ammonia. In addition, enhanced water dissociation on the nickel surface improves the protonation of *N 2 by supplying adequate protons via hydrogen spillover, thus boosting the ammonia production performance. This integrated electrode eliminates the use of polymer binders and reduces the contact resistance between the diffusion layer and catalyst layer, facilitating electron delivery and reducing cell resistance, thus requiring less energy input for ammonia production. The performance examination in an electrochemical H-type cell shows that an ammonia yield rate as high as of 9.3 × 10−11 mol s−1 cm−2 and a Faradaic efficiency of 6.3% are achieved. An ammonia yield rate of 8.19 × 10−11 mol s−1 cm−2 is observed after 6 cycles, with a retention rate of 88%. [ABSTRACT FROM AUTHOR]

• The ammonia decomposition activity of A/Ce x Zr 1-x O 2 (A = Ni or Co, Fe) catalysts are analyzed. • The ammonia decomposition activity is improved effectively with electric field assistance. • Ni-based catalysts have the highest activity, while Fe-based catalyst had the highest energy efficiency with electric field. • The synergistic effects of basicity enhancement and proton hopping increase the activity of catalysts. It is a good strategy to improve the combustion performance of ammonia in engines by onboard hydrogen mixing through ammonia decomposition. To utilize the exhaust heat from engines, a novel technology to decompose ammonia at low temperature (<350 °C) was studied, which is based on the synergistic effect between electric field and Ce-doped catalysts. A series of non-noble metals (Fe/Co/Ni) supported on Ce-doped ZrO 2 semiconductor (Ce x Zr 1-x O 2) were synthesized by solution combustion method to investigate the electric field-assisted catalytic activity. We achieved an ammonia conversion of 60% at 300 °C for Ni/Ce 0.25 Zr 0.75 O 2 catalyst and the maximum energy efficiency is close to 20% for Fe/Ce 0.25 Zr 0.75 O 2 catalyst with electric field. The synergistic effects of basicity enhancement and proton hopping between the electric field and Ce-doped catalysts were found by a series of characterizations. Electric field facilitated the generation of strong basic sites, which was beneficial to the recombinative desorption of nitrogen. And the proton hopping helped to reduce hydrogen poisoning. [ABSTRACT FROM AUTHOR]

Ammonia, one of the most produced chemicals, is mainly produced by the Haber Bosch process, under high-temperature, high-pressure, and energy-intensive conditions. Therefore, electrocatalytic nitrogen reduction is an attractive alternative method under ambient conditions. In this paper, two-dimensional carbon nanosheets (CNS) are firstly prepared by a modified Hummer method, and then Co and Ni bimetal load on CNS are prepared by a hydrothermal method to investigate their electrocatalytic nitrogen reduction reaction (NRR) properties. CNS has a porous sheet structure, and the NiCo oxide nanoflower structure with zigzag folding grows on the surface of CNS, which is beneficial to improve the contact area of the catalyst with N 2 , increasing the number of active sites, and better improve the performance of N 2 reduction NH 3 synthesis. At −0.34 V, the NH 3 yield reaches a maximum of 22.18 μg·h−1·mg−1, and the Faradaic efficiency (FE) is 4.50 %, both of which are about twice as high as that of pure CNS, which is superior to other metal-doped electrocatalysts used for N 2 reduction. This study provides an effective method for the design of electrocatalysts with high N 2 reduction performance for ammonia synthesis. The catalytic mechanism is further explored by the theoretical calculations of DFT. • CoNi bimetal was loaded onto two-dimensional carbon nanosheets by hydrothermal method. • The lamellar structure of CNS and the NiCo oxide nanoflower structure improve the contact area of the material. • The bimetallic synergy provides more redox reaction sites for the catalyst. • The CNS/Ni 5 Co 5 composite catalyst obtained high yields of FE and NH 3. [ABSTRACT FROM AUTHOR]

• The CuO x @SiO 2 catalyst with excellent performance by the FSP method. • The CuO x @SiO 2 catalyst has good thermal stability due to strong sintering resistance. • Catalytic ammonia oxidation over the CuO x @SiO 2 catalyst follows fast i-SCR mechanism. • Reaction path at low temperature is different from that at high temperature. Ammonia has a great application prospect to reach zero-carbon emissions in the combustion society. However, the poor ignition and combustion performance and NOx emissions of ammonia limit its utilization, and catalytic combustion may be a reliable way to utilize ammonia. In this study, the catalysts were prepared by the flame spray pyrolysis method (FSP), and the catalytic combustion performance of ammonia was investigated in a wide temperature range (100–1000 °C). The results indicated that CuO x and core–shell CuO x @SiO 2 had high catalytic activity and N 2 selectivity under different equivalence ratios compared with other catalysts (FeO x and MnO x), and the thermal stability of CuO x @SiO 2 were more prominent. These two catalysts before and after ammonia catalytic combustion tests were characterized to reveal their acting mechanism. At low temperature (<600 °C), the catalytic ammonia combustion over CuO x followed the internal-selective catalytic reduction (i-SCR) mechanism, while that on CuO x @SiO 2 followed the fast i-SCR mechanism, resulting in the outstanding N 2 selectivity of CuO x @SiO 2. At high temperature (600–1000 °C), CuO x @SiO 2 with a better thermal stability hardly sintered. Hydrogen was generated at high temperature and then reacted with oxygen under low equivalence ratio or with the lattice oxygen of the fresh catalyst under high equivalence ratio. The core–shell CuO x @SiO 2 catalyst synthesized by the FSP method provides a novel idea on the catalyst design for catalytic ammonia combustion. [ABSTRACT FROM AUTHOR]

• Sensing material FeCr 2 O 4 was prepared using the polymer precursor method for fabricating sensing electrodes of mixed potential type NH 3 sensors based on yttria-stabilized zirconia (YSZ). • Sensing performance of the NH 3 sensors was strongly affected by sensing electrode thickness and operating temperature. • The sensor attached by FeCr 2 O 4 sensing electrode with a thickness of 98.95 μm demonstrated the largest response potential and the most outstanding sensitivity (-65.835 mV/decade) to 10–50 ppm NH 3 at 425℃. And the mixed potential has a linear relationship with the logarithm of NH 3 concentration. • The FeCr 2 O 4 /YSZ/Ag sensor exhibited excellent selectivity to NH 3 with the interference deviations of CH 4 , CO, CO 2 , NO, and NO 2 within ±10 %, good stability against oxygen concentration fluctuation and water vapor concentration change, and good long-term stability for 180 h. • According to the mixed potential mechanism, the sensitivity of the sensor was determined by the anodic reaction of NH 3 , the cathodic reaction of O 2 , as well as the non-electrochemical gas–solid heterogeneous catalytic reaction of NH 3. Ammonia detection is of great significance for feedback control of urea injection in SCR system. In this paper, FeCr 2 O 4 sensing materials were prepared using the polymer precursor method used as the sensing electrode of mixed potential NH 3 sensors based on yttria-stabilized zirconia. The composition and structure of sensing electrodes were characterized using XRD and SEM. The effects of sensing electrode thickness and operating temperature on sensing performance were investigated. These related phenomena were ascribed to the adsorption and reactivity of NH 3 , as well as the competition between electrochemical catalytic reactions and gas–solid heterogeneous catalytic reactions. It was found that the sensor coated by FeCr 2 O 4 sensing materials with a thickness of 98.95 μm exhibited the largest response potential and the most outstanding sensitivity (-65.835 mV/decade) to 10–50 ppm NH 3 at 425℃. Furthermore, the sensor exhibited excellent selectivity to NH 3 with the interference deviations of CH 4 , CO, CO 2 , NO, and NO 2 within ±10 %, good stability against oxygen concentration fluctuation and water vapor concentration change, and good long-term stability for 180 h. Moreover, the sensing mechanism of the mixed potential sensor was discussed. [ABSTRACT FROM AUTHOR]

• LaCo 1-x Fe x O 3 sensing electrodes were applied to fabricate mixed potential type sensors for ammonia detection at 475 °C. • LaCo 1-x Fe x O 3 nanoparticles was prepared by flame spray pyrolysis, which is an efficient, one-step synthesizing method. • The sensor using LaCo 0.9 Fe 0.1 O 3 -SE displayed the highest sensitivity (87.22 mV/decade) towards 15–70 ppm NH 3. • The sensor with LaCo 0.9 Fe 0.1 O 3 -SE showed good selectivity, oxygen and water vapor insensitivity, and long-term stability. NH 3 detection is of great significance for precise control of the SCR system. In this paper, mixed potential type ammonia sensor using LaCo 1-x Fe x O 3 sensing electrode, YSZ electrolyte, and Pt reference electrode was developed. LaCo 1-x Fe x O 3 sensing materials were made by flame spray pyrolysis technique, and Fe B-site substitution was implemented to enhance the sensing performance. It was observed that in the concentration range of 20–70 ppm at 475 °C, the sensor using LaCo 0.9 Fe 0.1 O 3 as sensing electrode exhibited the highest sensing signal and sensitivity to ammonia among the LaCo 1-x Fe x O 3 -SE sensors (x = 0, 0.05, 0.1, 0.2, 0.3). A sectional linear relationship between the response value change(Δ V) of that sensor and the logarithm of ammonia concentration within the range of 2–15 ppm and 15–70 ppm was noticed, and the sensitivities were 17.52 and 87.22 mV/decade, respectively. Its lower detection limit reached 2 ppm at 475 °C. Its excellent sensing properties are ascribed to enriched oxygen vacancies and high electrocatalytic performance of the perovskite electrode. Moreover, the sensor exhibited good selectivity against CH 4 , CO, NO, NO 2 , and good stability against oxygen and water vapor concentration fluctuation. Besides, the sensing response to 50 ppm ammonia has been tested for 22 days and only a slight fluctuation within 7 % was observed. Furthermore, the mixed potential sensing mechanism of the sensor was discussed. [ABSTRACT FROM AUTHOR]

Due to concerns over pollutant emissions and ever-increasing energy crisis, ammonia is being considered as a promising alternative fuel to control soot particles and their precursors (polycyclic aromatic hydrocarbons, PAHs) emissions in combustion for diesel engines. This paper aims to investigate the chemical effects of NH 3 addition on PAH formation in n-heptane laminar premixed flames. The laser-induced fluorescence (LIF) technique was used to measure the relative PAH fluorescence intensities qualitatively. A kinetic modeling study was performed to predict PAH concentrations by comparing with the experimental results, and then clarify the underlying effects of NH 3 on PAH formation. Both experimental and numerical results revealed that PAH concentrations decreased monotonically as ammonia fraction increased, suggesting a PAHs-inhibiting role for NH 3 in n-heptane baseline flames. Reaction pathway analysis revealed that the suppression of NH 3 on PAH formation could be attributed to the competition for H, OH and O radicals in fuels' decomposition, and chemical interactions of amine radicals with the C 1 -C 2 species. For this reason, the NH 3 addition produced a relatively decreased C 2 H 2 , thereby inhibiting the formation of propargyl. As a result, benzene formation was inhibited through C 3 H 3 self-recombination reaction, resulting sequentially in the suppression of PAH formation and growth. Besides, the decreased C 2 H 2 yield in the post-flame region of NH 3 doping flames also inhibited the formation of PAHs through the hydrogen-abstraction-acetylene-addition (HACA) mechanism. Unlabelled Image • Co-firing ammonia with n-heptane proposed an alternative to improve emission and combustion properties. • PAH concentrations decreased monotonically as ammonia fraction increased. • NH 3 addition chemically inhibited benzene formation through C 2 H 2 → C 3 H 3 → C 6 H 6. • The decreased C 2 H 2 yield inhibited the PAH formation by the HACA mechanism. [ABSTRACT FROM AUTHOR]

Due to concerns over pollutant emissions and ever-increasing energy crisis, ammonia as a fuel additive is being considered an effective alternative to control polycyclic aromatic hydrocarbons (PAH) formation. In this study, the effects of NH 3 addition on PAH formation were investigated experimentally and numerically in laminar premixed ethylene flames. To investigate the chemical effects of NH 3 in flames, the equivalence ratios, dilution ratios, and maximum flame temperatures of all tested flames were kept nearly identical. The axial profiles of fluorescence intensities in all target flames were measured by using the laser-induced fluorescence (LIF) technique. The experimental results demonstrated a strong suppression in the fluorescence intensities of PAHs with the increase of NH 3 addition. The model study with a blending mechanism reasonably captured the reduced PAH tendencies with the addition of NH 3 in experimental measurements, which indicated that NH 3 chemically inhibits the PAH formation in the premixed ethylene flames. Chemical kinetic analysis revealed that the NH 3 addition leads to the reduced C 2 H 2 yield, by which inhibition chemical effects of NH 3 addition on PAH formation are realized through the route C 2 H 2 → C 3 H 4 –P and C 4 H 4 → C 3 H 3 → A 1 → PAHs. Reaction pathway analysis showed that although there was no direct interaction between C 2 H 4 and NH 3 , the C 2 H 4 and NH 3 chemistry interacted by the competition of H, OH, and O radical pools. Specifically, the relative higher H radical in NH 3 -doped flames chemically inhibited the C 4 H 4 and C 3 H 4 –P formation. Moreover, the reduced C 2 H 2 yield in the post-flame region inhibited the PAHs growth process via the HACA route. This study highlights the need for an improved model with detailed hydrocarbon-nitrogen interactions to predict PAH formation accurately in the NH 3 /hydrocarbon combustion. • The effects of ammonia addition on PAH formation in premixed ethylene flames were investigated. • The mitigation of PAH formation through ammonia addition proposed a new alternative to control PAH emissions. • The LIF and modeling results indicated that NH 3 chemically inhibits PAH formation. [ABSTRACT FROM AUTHOR]