N2 Yield Research Articles

Simulation of Denitrification of Vehicle Exhaust over Cu-CHA Bazite Catalyst for a Monolith Reactor

A CFD model with chemical reaction kinetic and heat and mass transfer for a monolith reactor is established by COMSOL Multiphysics to investigate the influence of different operating conditions and water on denitrification efficiency for Cu-CHA. At the low temperature range, water has little effect on the denitrification efficiency over the Cu-CHA catalyst while NO conversion is increased by about 30% at the medium temperature. The concentration of O2 (CO2) has no significant effect on the performance of Cu-CHA catalyst. The best ratio of NO2 to NOx in feed gases may be 1/2, which improves the denitrification efficiency and the yield of N2 but it produces relatively little N2O. The optimal ammonia-nitrogen ratio is 1.1, where Cu-CHA catalyst has fairly great denitrification efficiency and low NH3 leakage. Increasing inlet flow velocity and cross area of channels have negative effect on NO conversion, while longer channels and thicker substrate have the opposite effect.

Nitrogen migration in sewage sludge chemical looping gasification using copper slag modified by NiO as an oxygen carrier

In view of the high cost and failure of resource utilization of waste copper slag, the copper slag modified by NiO is used as an oxygen carrier in the chemical looping gasification, where the sewage sludge is converted into syngas through the oxidation of copper slag. Additionally, current studies on nitrogen migration in chemical looping are limited to the detection of nitrogen compounds in gas products, and there is little research on nitrogen migration from raw materials to solid-liquid-gas products. Therefore, under different oxygen equivalent coefficients (Ω), steam contents, reaction times, and cycle number, the nitrogen changes in gas (Gas-N), tar (Tar-N) and char (Char-N) were investigated in this paper. With increasing of Ω (0–0.78), the oxidation and catalytic cracking reactions of the NOx precursors, Char-N and Tar-N were promoted, and the yield of N2 increased from 52.49% to 91.98%. The addition of steam would lead to a significant increase in the yield of NOx precursors. The release of NH3 and HCN was mainly concentrated in the first 5 min. As the numbers of cycle increased, NH3-N and HCN-N both gradually decreased. Based on the above results, the distribution and migration mechanism of nitrogen species were also summarized.

Biological N2 fixation and yield performance of soybean inoculated with Bradyrhizobium

Biological N2 fixation and yield performance of soybean inoculated with Bradyrhizobium

Surface acid etching for efficient anchoring of potassium on 3DOM La0.8Sr0.2MnO3 catalyst: An integration strategy for boosting soot and NOx simultaneous elimination

The emission of soot and NOx is one of the most severe environmental issues, and the key factor is the development of catalysts in after-treatment systems. In this study, an innovative non-noble metal catalyst, named HKLSM, was fabricated by etching 3DOM La0.8Sr0.2MnO3 with citric acid and synchronously anchoring potassium salt, for soot and NOx simultaneous removal. The citric acid could not only slightly erode the 3DOM skeleton, thereby beneficial to the dispersion of potassium, but also react with high-valence state Mn to generate abundant coordination unsaturated Mn3+ sites, which could produce more active oxygen species. Moreover, HKLSM showed a higher NOx adsorption capability than the samples that were not subjected to acid etching. This adsorbed NOx could be stored as NO3− species, which could facilitate soot combustion. Among all the as-prepared catalysts, HKLSM demonstrated a competitive soot combustion activity with a T50 value of 368 °C, a TOF value of 3.24 × 10−4 s−1, a reaction rate of 1.87 × 10−7 molg−1s−1, a total NOx to N2 yield of 42.0% and favorable reusability and water-resistance. This integration strategy can rationalize an alternative protocol to soot and NOx simultaneous elimination or even other catalysis systems.

Electroplating of surfactant-modified tin catalyst over a nickel foam electrode (Sn/Ni) for selective N2 yield from nitrate reduction as affected by Sn(200) and Sn(101) crystal facets

The crystal habit of metallic tin (Sn) on a nickel foam electrode (Sn/Ni) was manipulated by cationic surfactants in order to assess the selective conversion of NO3−. The Sn electroplating additive included benzethonium chloride (BZT), cetylpyridinium chloride (CPC), cetyltrimethylammonium chloride (CTAC), and hexyltrimethylammonium bromide (C6TAB). Characterization showed that FSn(200) (= Sn(200)/[Sn(200) + Sn(101)]), which indicated that the preference of the Sn(200) facet was modified by the surfactants. FSn(200) was in the following order: BZT > CPC > CTAC > C6TAB-Sn/Ni. As FSn(200) increased, a positive correlation between selectivity of N2 (SN2) and FSn(200) existed. The highest amount of SN2 (as high as 65 %) was obtained at FSn(200) = 0.95. The consecutive kinetics was derived to define the formation rate of the nitrogen compound in the constant current mode. NO3- and NO2- adsorption determined the effectiveness of nitrate reduction on the Sn(200) surface, which efficiently mediated H species formation.

Physical interpretation of a pulsed atmospheric pressure plasma jet following parametric study of the UV–to–NIR emission

In the present report, an atmospheric pressure plasma jet is sustained in a helium channel by high square wave unipolar voltage. The gas flow rate and the square wave features (amplitude, frequency, and duty cycle) are varied over a wide range, while the plasma ultraviolet to near infrared emission is recorded. The plasma emission pattern, the propagation dynamics of the involved ionization fronts, the relative density of critical excited species, and the rotational and vibrational temperatures of neutral and ionic species are measured. An optimum operational window is found corresponding to a helium flow rate of 2 slm, a pulse amplitude of 7.5 kV, a pulse repetition rate of 10 kHz, and a pulse duty cycle of 5%–7%. Under these conditions, a plasma jet length close to 45 mm and a gas temperature close to 325 K are obtained, while a high yield of OH, N2(SPS), N2+(FNS), N2(FPS), He*, O*, and NOγ is achieved. The results are found to be in good agreement with the bibliography and motivate a consideration on the involved physical mechanisms. The plasma jet propagation with respect to the reactive species production is discussed based on the local electric field variation over the high voltage pulse width.

Physiological stabilization, community characterization, and nitrogen degradation dynamics in an anammox consortium from estuarine sediments.

Anammox is a cost-effective and sustainable process for nitrogen removal; however, the production of a physiologically stable inoculum is a critical point in the start-up process. In this work, estuarine sediments were used as incubation seeds to obtain cultures with stable anammox activity. Assays were performed in batch cultures fed with stoichiometric amounts of ammonium and nitrite, analyzing physiological response variables and the microbial community. Estuarine sediments showed a stable anammox process after 90days, consuming ammonium and nitrite simultaneously with concomitant generation of N2 and nitrate in stoichiometric amounts. In kinetic assays, substrates were fully consumed after 210hr, exhibiting N2 and nitrate yields of 0.85 and 0.10, respectively. The microbial community analysis using PCR-DGGE indicated the presence of uncultured anammox bacteria and members of the genus Candidatus Jettenia. The results evidenced the achievement of anammox cultures, although their start-up and kinetic characteristics were less favorable than those recorded in man-made systems. PRACTITIONER POINTS: Estuarine sediments were used as incubation seeds to obtain cultures with stable anammox activity. The sediments were fed with stoichiometric amounts of ammonium and nitrite, analyzing the physiological response variables and the microbial community. Sediments showed a stable anammox process after 90days, converting the substrates into N2 and nitrate according to stoichiometry. Anammox cultures were achieved although their start-up and kinetic characteristics were less favorable than those recorded in man-made systems. Microbial community analysis using PCR-DGGE indicated the presence of uncultured anaerobic ammonia-oxidizing bacterium and members of genus Candidatus Jettenia.

Contrasted response to climate change of winter and spring grain legumes in southwestern France

Abstract Climate change could undermine grain legumes ability to fix atmospheric nitrogen and their contribution to increase cropping systems sustainability. Pea (Pisum sativum L.) and faba bean (Vicia faba L.) are the two most widely grown grain legumes in Europe, yet the potential impact of climate change on their performances has not been quantified. We calibrated and evaluated the STICS soil-crop model for spring pea, winter pea and winter faba bean using experimental data from southwestern France and explored the effect of contrasting climate change scenarios. After calibration, STICS accurately simulated grain yield and amount of N2 fixed for the experimental growing seasons. Assuming no change in crop management, mean and inter-annual variability of grain yield and fixed N2 were assessed for historical (1995−2015), mid-term (2020−2040) and long-term (2060−2080) periods in one location in southwestern France. We considered projections from three climate models and two Representative [CO2] Pathways (RCP 4.5 and RCP 8.5). The climate models spanned a wide range of changes in temperature (+0.3 to +4.1 °C) and rainfall (−15% to +8%) depending on time horizon and RCP. Simulated grain yield increased over the long term in most scenarios (+1 to +25%), and spring pea tended to benefit less than winter pea and winter faba bean. Nevertheless, for the climate scenario with a decrease in rainfall and the strongest increase in temperature, simulated spring pea grain yield decreased by 28% while winter legumes yields were less affected (−14% for pea and no decrease for faba bean). Simulated changes in the amount of N2 fixed followed the grain yield response. Temperature rise caused a shortening in crop cycle duration. Simulated temperature stress significantly increased for spring and winter pea in most climate change scenarios while winter faba bean was rather unaffected due to greater upper temperature thresholds. N2 fixation of spring pea was reduced by above-optimal temperature during its vegetative growth in spring while N2 fixation of winter legumes was enhanced by the increase in temperature during their vegetative growth in winter. Simulated drought stress only increased in the climate scenario predicting a decrease in rainfall. Overall, [CO2] increase would allow offsetting negative effects of temperature and drought on grain yield and N2 fixation, except for climate scenarios involving a decrease in rainfall and the strong increase in temperature. The contrasted simulated response of winter and spring grain legumes to climate change in southwestern France points to the opportunity to tap grain legume diversity and cultivar choice as an adaptation strategy.

Study on the performance of magnetic Co3O4/γ-Fe2O3 catalyst in NO + CO reaction

In this study, a series of catalysts, supported by γ-Fe2O3 and with different concentrations of Co3O4 as active components, were prepared by impregnation method for selective catalytic reduction (SCR) of NO by CO. The catalysts were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), H2 temperature programmed reduction (H2-TPR), vibrating sample magnetometer (VSM), in situ infrared diffuse reflectance spectroscopy (in situ DRIFTS). The possible mechanism of catalysts in NO + CO reaction was proposed. The results show when the molar ratio of Co3O4 to γ-Fe2O3 is 20:45, the catalyst has the best N2 yield in NO + CO reaction, it is because the two metal oxides have the strongest interaction at this ratio and can produce more oxygen vacancies on the surface and improve the oxygen storage capacity. After a period of magnetization, it showed better catalytic performance than before, because the magnetized catalyst can absorb additional paramagnetic gas like NO. Finally, based on the results of in-situ infrared spectroscopy, a possible mechanism is proposed, showing that the reaction conforms to the L-H mechanism.

Scandium and copper co-doping effect on stability and activity to the NO direct decomposition of Ba3Y4O9

Direct decomposition of NO on Ba3Y4O9 doped with Cu and Sc was studied and it was found that co-doping of Sc and Cu into Ba3Y4O9 was effective for increasing both lattice stability and NO decomposition activity. In particular, Ba3Y3Sc0.6Cu0.4O9 (10 % Cu and 15 % Sc doping) catalyst showed N2 and O2 yield of 90 % and 99 %, respectively, in NO decomposition reaction at 700 ℃. Comparing with the pristine and single-metal doped system, the optimized catalyst showed superior long-term stability and increased activity under O2, and water vapor co-existence conditions because of the increased stability of crystal structure, improved lattice oxygen mobility and weakened oxygen adsorption on the surface. TPD and in-situ FT-IR results suggested that the co-doping effect was assigned to the easier removal of surface NO2− or NO3− species which blocks the active site to NO decomposition.

Manipulating the crystalline morphology and facet orientation of copper and copper-palladium nanocatalysts supported on stainless steel mesh with the aid of cationic surfactant to improve the electrochemical reduction of nitrate and N2 selectivity

Surfactants, namely, cetyltrimethylammonium chloride, polydiallyldimethylammonium chloride, and benzethonium chloride were used to control the crystal growth of metallic Cu nanoparticles supported on stainless steel mesh electrodes as to improve the selective electrochemical conversion of NO3− to non-toxic N2. Results showed that the Cu(200)/Cu(111) ratio controlled the selectivity of N2, NO2−, and NH4+. The Kd value increased from 10% to 30% when the Cu(200)/Cu(111) intensity ratio was decreased 60% to 30%, meaning increase Cu(111) increased N2 production. Furthermore, the presence of a second metal, namely, Pd increased the N2 selectivity. The best N2 yield (XN2 = 22%), occurring on monometallic Cu, synthesized with BZT at 1-time CMC was further increased to XN2 = 65% over bimetallic Pd0.27Cu0.73/SS. The selectivity of nitrite (SNO2-) and ammonium (SNH4+) on Cu/SS were 33.1 and 43.5%, respectively, which were decreased to 0.30 and 34.0%, respectively, on bimetallic Pd0.27Cu0.73/SS.

Effect of burner diameter and diluents on the extinction strain rate of syngas-air non-premixed Tsuji-type flames

The present study focuses on the experimental determination of the global extinction strain rate (ag) for different syngas-air combinations using the Tsuji type configuration. To study the effect of porous burner diameter (D), ag values were obtained for four values of D at atmospheric pressure. The experimentally obtained ag for a given fuel-oxidizer combination decreases with an increase in burner diameter (D). This trend is consistent with the limited data available in the literature for hydrocarbon fuels. Other geometric and flow-field effects namely, (1) plug flow, (2) flow-field blocking by the burner, and (3) heat loss by the flame to sidewalls that can affect ag were also experimentally quantified. The results from this study show that the plug flow boundary condition is always satisfied for oxidizer inlet distance > 2 times the largest porous burner diameter. Burner diameter less than 1/4 times side wall length (as is the case for all burners used in this study) does not significantly modify the flow. Hence, these two flow-field modifications do not affect ag. However, heat loss from the flame to the ambient through the side walls can cause a 4–9 % decrease in ag. Experiments showed that, CO/H2 mixtures diluted with N2 yield 1.6–2.25 times higher ag in comparison to CO/H2 mixtures diluted with CO2. Increasing H2 from 1 to 5 % leads to 2.5–3.8 times increase in ag, compared to 5 to 10 % increase in H2 which leads to only 1.3–1.7 times increase in ag for 70 % of N2 (v/v) in fuel mixture. Global extinction strain rate (ag) increases by 1.5–2.4 times with 10 % increase in CO for fuel mixtures consisting of H2 (1 and 5 % by v/v), CO2 (50, 60 and 70 % by v/v) and N2 (50, 60, 70 and 80 % by v/v). The change in overall reactivity (ωo) due to different diluents is used to quantitatively explain the variation of ag for different fuel compositions. These effects are also qualitatively explained using OH radical concentration change with H2 % in the fuel mixtures.

Core-shell structure effect on CeO2 and TiO2 supported WO3 for the NH3-SCR process

A series of CeTi samples (CeO2/TiO2, TiO2@CeO2, TiO2/CeO2, and CeO2@TiO2) was prepared and modified by tungsten. The 5 %WO3/TiO2@CeO2 (W/Ti@Ce) catalyst exhibited the best NH3-SCR performance (NO conversion and N2 yield above 95 % at 250–500 ºC) due to the synergistic effect of redox ability and acidity. The techniques of XPS, H2-TPR, and NH3-TPD were introduced to reveal the effect of Ce3+ atom contents, redox properties and acidity on catalytic performance. W/Ti@Ce shows good redox ability, which is conducive to the low-temperature selective catalytic reduction (SCR) reaction. NH3-TPD results show that W/Ti@Ce have a large amount of medium- and strong-strength acids, which are conducive to high-temperature SCR reaction. Therefore, the core-shell catalyst has the optimal synergistic effect of redox property and acidity, which is in favor of the excellent NH3-SCR performance. Furthermore, the W/Ti@Ce with a core-shell structure displayed better SO2 resistance due to the stronger interaction between Ce and Ti.

Optimizing the dual-layer Pt/Al2O3 + Cu/SSZ-13 washcoated monolith: Selective oxidation of NH3 to N2

The state-of-the-art Ammonia Slip Catalyst (ASC) has a dual-layer washcoat architecture with a bottom layer of Pt/Al2O3 and a top layer of Cu/SSZ-13. A trade-off between the NH3 conversion and N2 selectivity presents a challenge in the ASC design. While a sufficiently thick and active zeolitic top layer increases the N2 selectivity, it also imposes a diffusion barrier to the reacting species in reaching the bottom Pt layer, lowering NH3 conversion. Here we describe a systematic study to identify the ASC architecture and composition that optimizes the trade-off. The in-house synthesized ASC samples span the single layer Pt/Al2O3, conventional dual-layer Pt/Al2O3 + Cu/SSZ-13, uniform single layer of mixed Pt/Al2O3 + Cu/SSZ-13, and a hybrid design comprising a bottom layer of mixed Pt/Al2O3 + Cu/SSZ-13 and a thin top layer of Cu/SSZ-13. The overall Pt and Cu loadings are fixed across the series of samples with the Cu distributed between the two layers. The best results are obtained with the combination of a base mixed layer that provides for effective coupling between Pt and Cu active sites and a top Cu/SSZ-13 layer of an intermediate thickness and nominally half of the total Cu loading. This design has sufficient oxidation activity to convert the NH3 and reduction activity to limit NOx slippage. A 1 + 1 dimensional model which follows from our recent work [3] is effective in predicting most of the data and assists in converging on the best composition and architecture. The hybrid design exhibits a linearly decreasing dependence of the NH3 conversion and logarithmically increasing dependence of the N2 selectivity on the top layer Cu loading. The intersection of the two functions is shown to provide a good balance between the two opposing performance variables. The model is used to identify the combination of Pt loading and Cu loading distribution giving the maximum N2 yield for a specified temperature and space velocity.

Selective catalytic oxidation of ammonia over LaMAl11O19−δ (M = Fe, Cu, Co, and Mn) hexaaluminates catalysts at high temperatures in the Claus process

A method for selective catalytic oxidation of ammonia at high temperature was proposed to remove the ammonia impurity in the Claus process. Cu substituted hexaaluminate catalysts achieved the highest N2 yield at around 520 °C and the reaction followed the i-SCR mechanism.

Reaction properties of ruthenium over Ru/TiO2 for selective catalytic oxidation of ammonia to nitrogen

The objective of this study was to investigate reaction characteristics of selective catalytic oxidation of ammonia to nitrogen (NH3-SCO) using ruthenium-based catalysts. Ruthenium was compared with platinum, a metal generally used as an NH3 oxidation catalyst. Experiment was carried out by depositing active metal onto TiO2. 1Ru/TiO2 was superior to 1Pt/TiO2 in NH3 conversion and N2 yield. Therefore, various analyses were conducted to determine the influence of catalytic properties of 1Ru/TiO2 on reaction activity. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Field Emission-Transmission Electron Microscope (FE-TEM) analyses confirmed that ruthenium was present in RuO2. Such a structure was confirmed to be excellent for adsorption ability of NH3 and oxygen through analysis of NH3-TPD, NH3-TPO, H2-TPR, and O2-chemisorption. In addition, in situ diffuse reflectance infrared Fourier transform spectroscopy (DIRFTS) analysis suggested that Ru/TiO2 had excellent ability to convert NH3 to NO. The converted NO then reacted with adsorbed NH3 to generate N2. Based on results of NH3 injection at various concentrations, it was found that the rate at which NH3 was converted to NO from the Ru/TiO2 surface affected N2 selectivity.

Mechanistic insight into the methanol selective catalytic reduction of NO reaction over Cu-containing perovskites

The selective catalytic reduction (SCR) of NO by methanol was studied on LaFe0.8Cu0.2O3, and compared with that on an Ag/Al2O3 reference catalyst. A detailed characterization of the catalyst’s physicochemical properties was carried out by X-ray diffraction, N2 physisorption, H2 temperature-programmed reduction, isotopic exchange experiments, NOads + O2ads temperature-programmed desorption, and X-ray photoelectron spectroscopy. Materials reactivity was investigated in the CH3OH-SCR of NO. The LaFe0.8Cu0.2O3 catalytic system, modified using reactive grinding (Cu-RG), exhibits the best catalytic performance in terms of both NO conversion (95% at 450 °C) and N2 yield (YN2 ≈ 93%). Activity is related to low-temperature Cu2+ redox activation, and a strong improvement of structural Fe3+ reducibility occurs with substitution of the structure. In contrast, Ag/Al2O3 was confirmed to be close to inactive in the studied temperature range. To elucidate the main reaction pathways over the two catalysts, in situ diffuse reflectance infrared Fourier transform spectroscopy was performed to determine the nature of the adsorbed species and surface intermediates involved. Over Cu-containing perovskite, CH3OH is observed to form methoxy species (OCH3). The surface adNOx species observed over Cu-RG are mainly reactive nitrite/nitrate species, which further reacted with OCH3 species to form formohydroxamic acid and carboxylate. In the case of Ag/Al2O3, nitrate species continuously accumulated over the alumina surface, on which dehydration of CH3OH indubitably occurs. Therefore, no enolic intermediate of SCR can be observed over Ag/Al2O3. A reaction mechanism over LaFe0.8Cu0.2O3 was finally proposed, supported by density functional theory calculations, in which CN bond coupling accompanied by the first H transfer step is identified as the crucial step for N2 production in the CH3OH-SCR process over Cu-containing perovskites.

Efficiency of Phosphotungstic Acid Modified Mn-Based Catalysts to Promote Activity and N2 Formation for Selective Catalytic Reduction of NO with Ammonia

Abstract In this work, the modified Mn-based NH3-SCR (NH3 low-temperature selective catalytic reduction) catalysts with excellent NO conversion and N2 selectivity be designed. N2 yield was hardly more than 75 % over MnOx/TiO2 for NH3-SCR reaction, whereas the NH3-SCR performance has been significantly improved by using 50 wt.% HPW (H3PW12O40)-MnOx/TiO2. 100 % NO conversion and more than 95 % N2 yield was obtained in wide operating temperature window (150–400°C), suggesting that the addition of HPW could effectively improve the NO reduction conversion. After that, the catalysts were further characterized by XRD, H2-TPR, XPS and in situ DRIFT. DRIFT analysis implied that the introduction of HPW significantly improve the capacity of NH4 + species adsorbed on Brønsted acid sites accompanied with inhibiting the formation and consumption of nitrite species. It proved that the non-selective catalytic reduction reaction over HPW-MnOx/TiO2 catalysts are restrained. HPW could accelerate the formation and consumption of NH4 + species adsorbed on Brønsted acid sites with deactivation of nitrate species. In addition, NH3(ad) could be hardly oxidized to NH species and then reacted with nitrate species (L-H mechanism) and gaseous NO (E-R mechanism). More importantly, the oxidation of NH3 was also suppressed, which plays a dominate role to form N2O above 300°C. Besides, the deactivation of potassium poisoning on the SCR activity significantly weakened for modified samples compared to parent catalyst.

Effects of strain induced by Au dispersion in Ba and Ni doped Y2O3 on direct decomposition of NO

NO direct decomposition on Y2O3 based oxide was studied and it was found that doping Ba and Ni simultaneously in Y2O3 is effective for achieving the high NO decomposition activity. The optimized amount for Ni and Ba doping is 5 and 0.5–1 mol%, respectively and on this Y2O3 based catalyst showed almost 100% N2 yield at 800 °C and high N2 yield was sustained under co-existence of oxygen. Effects of tensile strain caused by Au dispersion was further studied for increasing low temperature NO decomposition activity and it was found that NO decomposition activity around 500 °C was much increased by dispersion of 1 mol% Au which induced a tensile strain.

Morphology-Oriented ZrO2-Supported Vanadium Oxide for the NH3-SCR Process: Importance of Structural and Textural Properties.

ZrO2 supports, with diverse morphologies (hollow sphere, star, rod, mesoporous), were produced using hydrothermal and evaporation-induced self-assembly methods. Zirconia-supported vanadium oxide catalysts were prepared by wet impregnation and used for the low-temperature selective catalytic reduction (SCR) of NO with ammonia. Characterization of catalysts includes N2 physisorption, elementary analysis, X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction by H2, and temperature-programmed desorption of NH3. Significant differences in terms of activity are measured. 3 wt % V2O5 supported on mesoporous ZrO2 (V/MZ) presents excellent N2 yields (>90%, in the 200-400 °C interval), with a wide operating temperature window (NO conversion > 95%, in the 225-425 °C interval), and less interesting performances were obtained when vanadium oxide is supported over stars, hollow spheres, and rods. Surface characterization showed a content of tetravalent vanadium ion, when supported, decreasing in the order of mesoporous > hollow sphere > star > rod. This order is in perfect agreement with the order of performance of the catalyst in the NH3-SCR reaction. The impact of tetravalent ion's presence on the surface is confirmed by diffuse reflectance infrared Fourier transform spectroscopy analysis, Brønsted acid sites generated on the surface, and the V4+-OH species involved in the reaction. The production of more important nitrite species over the tetragonal supported vanadium oxide catalyst could be another reason for the excellent NH3-SCR performance displayed by the V/MZ catalyst. When supported over monoclinic zirconia, like vanadium oxide over star-type morphology, the adsorbed NH3 species (NH4+ and coordinated NH3) reacted with NO x adsorption species (nitrate) to form ammonium nitrate. Ammonium nitrate can be decomposed to N2 and N2O (or NO2). Thus, NO conversion curves and N2 yield curves over tetragonal zirconia (MZ) at lower temperature were ahead of those over V/star ZrO2 because of the higher V4+ surface content and more active B acid sites associated with an easy formation of the nitrito intermediate.