Nitrate Species Research Articles

Destruction of Per- and Polyfluoroalkyl Substances in Reverse Osmosis Concentrate Using UV-Advanced Reduction Processes.

UV-advanced reduction processes (UV-ARP), characterized by the strongly reducing aqueous electron (eaq -), have been shown to degrade perfluoroalkyl and polyfluoroalkyl substances (PFAS). Due to the high cost of PFAS destruction technologies, concentrated waste streams derived from physical treatment processes, such as ion exchange or membrane concentrates, are promising targets for implementation of these technologies. However, there are limited studies on the application of UV-ARP for PFAS destruction in concentrated waste streams. This study evaluates the effectiveness of the UV/sulfite ARP in reverse osmosis concentrate (ROC) containing high concentrations of dissolved organic carbon (DOC), nitrate, and carbonate species, spiked with mg/L concentrations of perfluorooctanesulfonic acid, perfluorobutanesulfonic acid, perfluorooctanoic acid, and perfluorobutanoic acid. We demonstrate that hardness removal and preoxidation of ROC with UV/persulfate enables >90% PFAS defluorination within 24 h of subsequent UV/sulfite treatment, a 3-fold enhancement in defluorination % compared to UV/sulfite treatment without preoxidation. This enhancement is shown to result from abatement of the light shielding and eaq - scavenging capacity of DOC during UV/persulfate oxidation. Collectively, these results demonstrate that appropriate pretreatment steps increase the effectiveness of PFAS destruction using UV-ARP, supporting the application of UV-ARP for PFAS destruction in ROC and other concentrated waste streams.

Headspace-single drop microextraction based visual colorimetry for non-chromatographic speciation analysis of nitrite and nitrate in environmental water sample

In this work, a visual colorimetric method based on headspace-single drop microextraction (HS-SDME) was developed for the non-chromatographic speciation analysis of nitrite and nitrate. The method adequately exploited the individual chemical vapor conditions of nitrite and nitrate that were converted to NO by specific reductants. Gaseous NO underwent a diazotization reaction with chromogenic reagent through the HS-SDME process to change from colorless to purplish-red. Instead of using large, time-consuming and relatively complicated chromatographic equipment for separation, the species of nitrite and nitrate could be analyzed by simply changing the reagents. Meanwhile, the extraction method effectively mitigated the matrix interference of solution and improved the sensitivity of method, with intuitive discrimination of color by the naked eye. The limits of detection were 0.07 μg/mL for nitrite and 0.2 μg/mL for nitrate, respectively. This method has been applied to analysis of real environmental water samples, which also effectively extended the application scope of HS-SDME device.

Decomposition and Growth Pathways for Ammonium Nitrate Clusters and Nanoparticles.

Understanding the formation and decomposition mechanisms of aerosolized ammonium nitrate species will lead to improvements in modeling the thermodynamics and kinetics of aerosol haze formation. Studying the sputtered mass spectra of cation and anion ammonium nitrate clusters can provide insights as to which growth and evaporation pathways are favored in the earliest stages of nucleation and thereby guide the development and use of accurate models for intermolecular forces for these systems. Simulated annealing Monte Carlo optimization followed by density functional theory optimizations can be used reliably to predict minimum-energy structures and interaction energies for the cation and anion clusters observed in mass spectra as well as for neutral nanoparticles. A combination of translational and rotational mag-walking and sawtooth simulated annealing methods was used to find optimum structures of the various heterogeneous clusters identifiable in the mass spectra. Following these optimizations with ωB97X-D3 density functional theory calculations made it possible to rationalize the pattern of peaks in the mass spectra through computation of the binding energies of clusters involved in various growth and dissociation pathways. Testing these calculations against CCSD(T) and MP2 predictions of the structures and binding energies for small clusters demonstrates the accuracy of the chosen model chemistry. For the first time, the peaks corresponding with all detectable species in both the positive and negative ion mass spectra of ammonium nitrate are identified with their corresponding structures. Thermodynamic control of particle growth and decomposition of ions due to loss of ammonia or nitric acid molecules is indicated. Structures and interaction energies for larger (NH4NO3)n nanoparticles are also presented, including the prediction of new particle morphologies with trigonal pyramidal character.

A new explanation for the synergistic promoted mechanism of nitrate and nitrite anion species for the high performance MgO adsorbent

The mechanism of CO2 capture on the nitrate and nitrite anion species synergistic promoted MgO has been rarely studied and still not fully understood. Herein we report a systematic investigation on the CO2 adsorption performance of molten salts-promoted MgO adsorbent to deeply reveal the synergistic promoted mechanism of nitrate and nitrite. A series of MgO-based solid adsorbents were synthesized and applied for CO2 capture using NaNO2/KNO3 as promoters. The addition of mixed nitrate and nitrite promoters greatly enhances the adsorption capacity of MgO, exhibiting CO2 capture up to 10.25 mmol·g−1 under optimal conditions. The MgO-based adsorbent in the form of nanosheets has faster adsorption kinetics and better stability, and the possible reaction mechanism of MgO modified by nitrate and nitrite was proposed. Firstly, NO3– interacts with the lattice oxygen (O12-) of MgO to form NO2– and O22–. Secondly, Mg2+ interacts with the free NO2– to form [Mg···NO2]+ and further overcomes the energy barrier to generate [Mg2+···O2–] ion pairs. O22– is not stable and prone to side reaction. However, NO2– can be converted into O2–, and O2– is further generated to O22–, facilitating regeneration of NO3–. The introduction of molten salt can significantly reduce the reaction energy barrier, and the energy barrier required to generate [Mg2+···O2–] ion pairs is reduced from 6.86 eV to 3.50 eV. Adsorption kinetics studies reveal that the nano-flake MgO facilitates the full contact with the promoter and has faster reaction kinetics in the surface reaction control stage. These insights into the synergistic promoted mechanism of nitrate and nitrite anion species is expected to provide guidance for the further design of the high performance MgO-based CO2 adsorbent.

Low-Temperature Reduction of NOx by NH3 with Unity Conversion on Nanofilament MnO2/Activated Semi-Coke Catalyst.

Selective catalytic reduction of nitrogen oxides with NH3 at low temperatures remains a crucial goal for industrial applications. However, effective catalysts operating at 70-90 °C are rarely reported, limiting SCR scenarios to high-temperature conditions. Herein, we report a unique MnO2 nanofilament catalyst grown on activated semi-coke synthesized via a one-step in situ hydrothermal approach, which exhibits a stable and marked 100 % conversion rate of NO to N2 with 100 % selectivity at 90 °C, superior to the other prepared structures (nanowires, nanorods, and nanotubes). Temperature-programmed desorption shows a large number of acid sites on MnO2(NFs)/ASC, benefiting the formation of NH4 + ions. Meanwhile, diffuse reflectance infrared Fourier transform spectroscopy reveals the activation of NO with O2 to form bidentate nitrate/bridging nitrate NO2 intermediates via bidentate nitrate species, triggering the Fast SCR with NH3 at low temperatures. Such an effective, easy-to-prepare, and low-cost catalyst paves a new pathway for low-temperature SCR for a wide range of application scenarios.

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.

Seasonal variation and origins of C1–C5 alkyl nitrates: A year-long study at a Hong Kong coastal site

Alkyl nitrates (RONO₂) are key reactive nitrogen compounds with significant impacts on local and regional air quality. The concentrations of alkyl nitrates can vary significantly across different regions, especially in areas with varying levels of human activity. Long-term observation of alkyl nitrates is necessary to assess the intensity of photochemical reactions and the contributions from different sources. In this study, we present the first continuous year-long monitoring results of eight alkyl nitrates via whole air sample collection and GC-MSD/ECD analysis at a coastal site in Hong Kong. Source apportionment analysis via positive matrix factorization (PMF) revealed distinctive seasonal variations in the source contributions for the eight alkyl nitrate species. Furthermore, increased contributions from biomass combustion were found in autumn and winter, while marine emissions primarily influenced methyl nitrate levels during summer. Our study highlights the significant impact of biomass burning from inland areas on photochemical pollutants in Hong Kong. Cross-regional cooperation in the Greater Bay Area (GBA) is necessary for more comprehensive management of secondary photochemical pollution.

Reaction mechanism of 1,2-dichlorobenzene oxidation over MnOX-CeO2 and the effect of simultaneous NO selective reduction

MnOX-CeO2 formulation has been studied for the catalytic oxidation of 1,2-dichlorobenzene. Among the samples with different Mn and Ce content, the most active was 85%mol Mn and 15%mol Ce, due to its better morphological properties and the synergy achieved between the two phases composing it (mixed oxide phase and segregated Mn oxide). Deactivation was monitored at low temperature and a transient change in the oxidative capability at high temperature because of active sites with different oxidative capability. Based on in-situ FTIR results, oxidation reaction pathway is proposed. Active sites with different oxidative capability causes some reaction steps to occur faster than others as a function of temperature, which modifies the distribution of intermediate species. In the reduction of NO, its adsorption leads to nitrate species contributing to a faster re-oxidation of active sites and the presence of NH3 promotes the removal of adsorbed Cl.

A comparative study on the activity and adsorption of bimetallic MOF-derived Me-Cu/TiO2 (Me=Fe, Co, Ni) for low-temperature selective catalytic reduction of NO by CO

The catalytic activity, adsorption and synergistic effect over bimetallic MOF derivatives with different dopant metal were systemically compared. A series of Me-Cu/TiO2 (Me=Fe, Co, Ni) derived from bimetallic Me/Cu-BTC MOFs were fabricated via a sacrificing template method and applied for CO-SCR. Among the bimetallic catalysts, Fe-Cu/TiO2 presented the best low-temperature of nearly 100% NO conversion from 150 °C to 350 °C with good NO selectivity. For Me-Cu/TiO2 (Me=Fe, Co, Ni), the productions of crucial Cu+ intermediate were determined to be 51.17%, 50.45%,49.4% by XPS, which were consistent with their catalytic activity results. The superior redox behavior of Fe-Cu/TiO2 can be attributed to its higher Oβ / (Oα +Oβ) ratio of 32.90% and the higher Me2+ / Me3+ ratio of 1.79. In situ infrared analysis revealed that the Fe doping not only improved the formation and stability of nitrate species, but also enhanced the quantity of Lewis acid sites by forming Cu+-CO. Furthermore, a possible low-temperature Langmuir-Hinshelwood (L-H) mechanism over Me-Cu /TiO2 (Me=Fe, Co, Ni) was proposed.

Catalytic Ozonation of Low Concentration Toluene over MnFeOx-USY Catalyst: Effects of Interactions between Catalytic Components and Introduction of Gas Phase NOx.

A series of Mn and Fe metal oxide catalysts loaded onto USY, as well as single metal oxides, were prepared and characterized. The effects of interactions between the catalytic components and the introduction of gas phase NO on the catalytic ozonation of toluene were investigated. Characterization showed that there existed strong interactions between MnOx, FeOx, and USY, which enhanced the content of oxygen vacancies and acid sites of the catalysts and thus boosted the generation of reactive oxygen species and the adsorption of toluene. The MnFeOx-USY catalyst with MnOx and FeOx dimetallic oxides exhibited the most excellent performance of catalytic ozonation of toluene. On the other hand, the presence of NOx in reaction gas mixtures significantly promoted both toluene conversion and mineralization, which was attributed to the formation of nitrate species on the catalysts surface and thus the increase of both acid sites and toluene oxidation sites. Meanwhile, the reaction mechanism between O3 and C7H8 was modified in which the strong interactions between MnOx, FeOx, and USY accelerated the reaction progress based on the L-H route. In addition, the formation of the surface nitrate species not only promoted reaction progress following the L-H route but also resulted in the occurrence of the reaction via the E-R route.

A Reduced-Symmetry Pd2L4 Cage from a Heterotopic Dipyridyl Ligand.

Two dipyridyl ligands, L3,3 and L3,4, have been used in combination with palladium(II) in the construction of metallosupramolecular species that show anion-dependent behavior in solution. A rare example of a low-symmetry (C2h) lantern-type cage is formed in one instance, [Pd2(L3,3)4]4+, while the isomeric ligand yields a larger double-walled square complex, [Pd4(L3,4)8]8+. [Pd2(L3,3)4](NO3)4 was isolated in crystalline form revealing two anions within the interior of the C2h-symmetry cage. The cage itself is held together by hydrogen bonding between "head-to-tail" pairs of ligands that reinforces the symmetry generated by the ditopic ligands. In solution, the cage with NO3- has sharp 1H nuclear magnetic resonance (NMR) signals at room temperature, while the BF4- analogue has broad signals that sharpen at higher temperatures or upon addition of (Bu4N)(NO3), highlighting the importance of the anion in templating or otherwise influencing self-assembly in solution. Altering the substitution position of one of the pyridyl rings yields a more "open" complex, with [Pd4(L3,4)8](NO3)8 being isolated as a crystalline solid. The double-walled square complex has a greater Pd···Pd separation due to the increased angle that the pyridyl groups subtend at the core of the ligand. NMR spectroscopy and mass spectrometry studies suggest a single species in the presence of nitrate but multiple species with tetrafluoroborate.

The specificity of endogenous fatty acid nitration: only conjugated substrates support the in vivo formation of nitro-fatty acids

Through multiple pathways, nitrogen dioxide (•NO2) is the main species involved in endogenous nitration reactions. Early studies in the field primarily explored tyrosine nitration, a dominant reaction in the field. It was later shown that lipids are also nitration targets and generate an array of reaction products. Conjugated fatty acids are the preferential substrates of lipid nitration in vivo, generating electrophilic nitro-fatty acids (NO2–FAs), which serve as pleiotropic signaling modulators. In contrast, exposure of bisallylic fatty acids, including linoleic, linolenic and arachidonic acid, to •NO2 does not lead, under biological conditions, to the formation of nitrated species. This review focuses on the reaction mechanisms and products of lipid nitration and substrate specificity, focusing on the differential reactivity of conjugated dienes and bisallylic alkenes.

Mechanistic insights and application potentials for CeO2-Al2O3 passive NOx adsorber (PNA) materials

A series of CeO2/Al2O3 with Ce loading from 0.5 to 5.0 wt% were studied as PNA materials for low temperature NOx abatement. Via XRD, TEM imaging and UV–vis spectroscopy studies, it was demonstrated that CeO2 is present as nanoparticles on the Al2O3 support, and the particle size increases with increasing Ce loading. PNA performance of these materials was investigated by NOx trapping followed by TPD. The PNA chemistry was further probed with in situ NO-DRIFT spectroscopy. PNA chemistry involves a rapid direct NO trapping route that leads to surface nitrite formation, and a slower NO2 trapping route that leads to surface nitrate species. Surface nitrite decomposition releases NO at 200–300 °C, suitable for PNA application. Based on NO yields during TPD, the atomic efficiency of surface Ce was calculated, which demonstrates that dispersing CeO2 on high surface area supports is a viable strategy for improving PNA efficiency of CeO2-based materials.

Catalytic performance and mechanism of PtxVW catalyst for selective catalytic oxidation of high-concentration NH3

It is foreseeable that a high-concentration NH3 may exist in exhaust gas of NH3-fuel engines, which may result in some negative damages to ecological environment. Herein, a series of PtxVW catalysts with extremely low Pt doping amounts were synthesized with the aim to remove high-concentration NH3 efficiently via selective catalytic oxidation (SCO) method. The results showed that, Pt0.04VW catalyst (0.04 wt% Pt) achieved a complete NH3 conversion at 250 ºC. Both catalytic activity and N2 selectivity of Pt0.04VW catalyst were much superior over Pt/Al2O3 catalyst (1 wt% Pt) in a wide temperature range of 250–450 ºC. XPS, Raman and H2-TPR results indicated that Pt existed in the lattice of VOx and formed Pt-V bimetallic oxides. The interaction between Pt and V played a key role in the NH3-SCO reactions. DFT calculation demonstrated that dual electron transfer pathways between Pt and V atoms in PtxVW catalysts were beneficial for NH3 coordination on Lewis acid sites, then enhancing NH3-SCO reactions. In-situ DRIFTS and NH3-TPD product analysis suggested that NH3-SCO reactions on Pt0.04VW catalyst surface abide by internal selective catalytic reduction (i-SCR) and hydrazine mechanisms. Moreover, coordinated NH3 species on Lewis acid sites, bidentate nitrate species were the main intermediates in NH3-SCO reactions over Pt0.04VW catalyst.

The effect of Fe2O3 doping on a Pt/Co3O4 catalyst for CO oxidation: Improvement of thermal stability and catalytic activity

Although Pt/Co3O4 is an active catalyst for CO oxidation, its low thermal stability may impede its application. The thermal stability and catalytic performance of Pt/Co3O4 were considerably enhanced by Fe2O3 doping. Fe2O3 doping stabilized the mesostructured material during the high-temperature treatment, and the Fe2O3-doped samples retained a larger specific surface area. The characterization results revealed that Fe2O3 doping inhibited catalyst crystallization and decomposition and the growth of catalyst grains during high-temperature calcination. The Fe2O3 doping reduced the Co-O bond strength in the surface Co3O4 lattice, increased the Co3+ ratio, and generated highly active surface oxygen species. Fe2O3 doping also facilitates CO2 desorption, which improves CO adsorption and oxidation. SO2 and NO impede CO oxidation on Pt/Fe2O3/Co3O4. This negative impact was caused by the inert species formed when SO2 or NO reacted with O2 on the catalyst, such as SO42-, HSO4-, or nitrate species, which covered the active sites.

The underestimated role of manganese in modulating the nutrient structure in a eutrophic seasonally-stratified reservoir

Accumulation and subsequent release of nutrients have great potential to trigger algal blooms in lakes and reservoirs. We conducted high vertical resolution (2 m interval) monitoring at ∼monthly intervals over a year for hydrological parameters, Chl-a, ammonium (NH4+), nitrate (NO3−) and different species of phosphorus (P) and manganese (Mn) in a 40-meter-deep subtropical reservoir (Shanmei Reservoir) in Fujian, southern China. In this seasonally stratified reservoir featured with high nutrient loading, the consistent trend in the ratio of dissolved inorganic nitrogen (DIN) to dissolved inorganic phosphorus (DIP) between the euphotic zone and the hypolimnion, coupled with its mirrored correlation with Chl-a concentration indicates that upward flux from the hypolimnion affects phytoplankton growth in the euphotic zone. The monthly variation of the depth-integrated multiple species of N and P indicates that during the stratification period in the hypoxic hypolimnion, approximately 80% of the DIP is removed, leading to a remarkable decoupling phenomenon between NH4+ and DIP. This process effectively increases the ratio of DIN to DIP in the hypolimnion, thereby significantly reducing the potential of algal blooms caused by the upward flux. A robust positive linear correlation between iron-manganese bound phosphorus (CBD-P) and particulate Mn was observed during stratification period implying that DIP was scavenged by sediment-released Mn throughout the water column. Vertical profiles during stratification showed that upward diffusion of Mn2+ facilitated the formation of Mn oxide zones near the oxycline. The most significant decrease in DIP inventory occurs when Mn oxide zones migrate either upwards from the bottom or downwards from the oxycline, indicating that the migration of Mn oxides on the vertical profile is a key factor in the decoupling of NH4+and DIP.Our findings underscore the importance of Mn cycling as an underappreciated DIP self-immobilization process in the water column of reservoirs characterized by high nutrient loading. Furthermore, we propose that denitrification and Mn cycling establish a consecutive feedback mechanism, preventing excessive nutrient accumulation in low oxygen bottom water. In the context of global changes, we anticipate a heightened prominence of this feedback mechanism.

Protein nitration in the artery wall: A contributor to cardiovascular disease?

Nitration is a well-established post-translational modification of selected free amino acids, as well as proteins, lipids and nucleic acids. Considerable evidence is now available for the formation of long-lived species containing an added –NO2 function on the aromatic rings of tyrosine (Tyr) and tryptophan (Trp) residues (both free and on proteins), to purine nucleobases (and particularly guanine), and to unsaturated lipids within biological systems. Multiple potential mechanisms that give rise to these nitrated species have been identified including reactions of the potent oxidant and nitrating species peroxynitrous acid/peroxynitrite (ONOOH/ONOO−) and via oxidative reactions of heme proteins/enzymes (e.g. peroxidases) with the biologically-relevant anion nitrite (NO2−). •NO2 is likely to be a key intermediate, though involvement of HNO2, NO2+ and NO2Cl has also been proposed. The resulting nitrated products have been widely employed as qualitative or quantitative biomarkers of nitration events in vitro and in vivo. Increasing evidence suggests that at least some of these products are not benign species, with evidence for pro-inflammatory actions. In this article the mechanisms and role of nitration, and particularly that on proteins within the artery wall, in cardiovascular disease is discussed, together with emerging data suggesting that low levels of nitration occur within biological systems in the absence of added oxidants. Both stimulated and endogenous nitration may play a role in modulating cell signaling, alter the structure and function of both cellular- and extracellular proteins, and contribute to various inflammatory pathologies, including atherosclerosis.

Revealing the two distinctive roles of HY zeolite in enhancing the activity and durability of manganese oxide-zeolite hybrid catalysts for low-temperature NH3-SCR

Recently, metal oxide-zeolite hybrid systems have shown promise in enhancing catalytic performance in low-temperature selective catalytic reduction (SCR), but not much is known as to mechanistic details. The purpose of this study is to examine fluctuations in low-temperature activity contingent upon the presence or absence of zeolite and to elucidate a dual functional mechanism of mixed zeolite in improving the catalytic performance of MnOx, which is closely related to inter-particle diffusion of nitrite and nitrate species from MnOx to zeolite. Firstly, strong Brønsted acid sites on zeolite demonstrate a significantly faster reduction of diffused nitrite species compared to Brønsted/Lewis acid sites on MnOx. More importantly, we discovered that zeolite prevents ammonium nitrate deposition by absorbing and decomposing diffused nitrate species from MnOx. Such distinct interaction between zeolite and both nitrite and nitrate species clarified here will be of great promise in designing future hybrid catalytic materials for low-temperature NH3-SCR reactions.

Effect of sulfation on the catalytic performance of Mn-Co composite oxide catalyst for the selective catalytic reduction of NOx by NH3

The effect of sulfation on the catalytic performance of Mn-Co composite oxide catalyst for the selective catalytic reduction of NOx by NH3 (NH3-SCR) has been investigated. Different concentrations of SO2 have been used to sulfate Mn-Co composite oxide catalyst. The catalyst sulfated with 30 ppm SO2 showed the widest activity temperature window, over which 80% NOx conversion was obtained in the temperature range of 80–350 °C. The sulfation leads to the appropriate redox property of Mn-Co composite oxide, thus improving the N2 selectivity. Meanwhile, the sulfation contributes to the generation of more Brønsted acid sites, which is crucial for the enhanced activity. In situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS) demonstrated that the adsorbed NH3 species on both Lewis acid and Brønsted acid sites, monodentate nitrite, bidentate nitrate and cis-nitrite species are the reactive intermediates in the NH3-SCR reaction. This study provides an idea for the regulating the activity temperature window of NH3-SCR catalyst to adapt to its practical application.

Revealing the roles of Zr on enhanced H2-SCR performances on Pt/TiO2 catalyst

The development of Hydrogen Internal Combustion Engine (H2-ICEs) to replace conventional fuel engines is expected to be an effective way to reduce CO2 emissions, but some NOx emitted from the H2-ICEs still should be eliminated by the selective catalytic reduction of NOx with H2 (H2-SCR). Large amount of platinum oxide existed on Pt/TiO2 leads to its low H2-SCR activity. In contrast, the Zr-modified Pt/TiO2 catalysts exhibit a higher NOx conversion and N2 selectivity in a wider temperature window (100–180 °C) than those of Pt/TiO2. The appropriately weakened strong interaction between Pt and TiO2 by Zr induces more Pt0 species, which are active sites for the activation of NOx and H2 in H2-SCR reaction. More oxygen vacancies caused by the formation of Zr-Ov-Ti3+ bands involve in the activation of NOx and the adsorption of nitrates (NOx−) species. Furthermore, in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTs) demonstrates that Pt/ZrxTi1-x catalysts possess more adsorbed NOx− species and a faster reduction rate for them. Monodentate and bridged nitrates are considered to be more reactive with H2 than bidentate nitrates at relatively low temperatures. This work provides directions for the development of high-performance H2-SCR catalysts and the modulation of the conversion temperature.