NH3-SCR Reaction Mechanism Research Articles

Enhanced NOx reduction on CePO4 catalysts: Cu-loading, phosphotungstic acid, and insights from In-situ DRIFTs and DFT

This study investigates the effects of varying Cu/Ce doping ratios on the NH3-SCR denitrification efficiency using Cu-HPW/CePO4 catalysts, where CePO4 serves as the support and copper-doped phosphotungstic acid (HPW) acts as the active phase. The NH3-SCR reaction mechanism was studied by In-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (In-situ DRIFTs) and Density Functional Theory (DFT). In-situ DRIFTs were employed to delve into the intricacies of adsorption and transformation dynamics at the surface sites of catalysts. This approach furnished a robust theoretical foundation aimed at augmenting the efficacy of low-temperature denitrification catalysts. DFT calculations were used to systematically investigate the reaction pathways, intermediates, transition states, and energy barriers over the HPW structure model to complete the NH3-SCR reaction. Empirical evidence suggests that modifying the catalysts with copper substantially enhances their denitrification efficacy and extends their operational temperature spectrum. A notable initial increase in denitrification efficiency was observed with increasing levels of copper modification, followed by a decline. Within the HPW-O15H site, the NH3-SCR reaction advances through both the E-R and L-H mechanisms, encompassing processes such as NH3 adsorption, intermediate formation and transformation, and product release.

Combined Experimental and Density Functional Theory Study on the Mechanism of the Selective Catalytic Reduction of NO with NH3 over Metal-Free Carbon-Based Catalysts.

Metal-free carbon-based catalysts are attracting much attention in the low-temperature selective catalytic reduction of NOx with NH3 (NH3-SCR). However, the mechanism of the NH3-SCR reaction on carbon-based catalysts is still controversial, which severely limits the development of carbon-based SCR catalysts. Herein, we successfully reconstructed carbon-based catalysts through oxidation treatment with nitric acid, thereby enhancing their low-temperature activity in NH3-SCR. Combining experimental results and density functional theory (DFT) calculations, we proposed a previously unreported NH3-SCR reaction mechanism over carbon-based catalysts. We demonstrated that C-OH and C-O-C groups not only effectively activate NH3 but also remarkedly promote the decomposition of intermediate NH2NO. This study enhances the understanding of the NH3-SCR mechanism on carbon-based catalysts and paves the way to develop low-temperature metal-free SCR catalysts.

Orchestrating dual adsorption sites and unravelling Ce-Mn interaction and reaction mechanisms for efficient NH3-SCR

Mechanism insight is suggested to be one of the most challenging issues in selective catalytic reduction of NO with NH3 (NH3-SCR), and the development of efficient NH3-SCR catalysts for industrial application needs a deep understanding of the catalytically active sites, reaction pathways and rate-determining steps. Herein, we study the NH3-SCR reaction mechanism on CeMn oxide catalyst. Mn3+ ions enter the CeO2 lattice to generate a Mn-O-Ce structure with a strong interaction, and Ce can synergize Mn species to orchestrate co-adsorption and accelerate the reaction rate. Theoretical studies verify that Ce and Mn sites act as double adsorption sites for NH3 and NOx, respectively. The proposed two reaction pathways including NH3 with NO and NH3 with NO2 may occur simultaneously owing to the same rate-determining step and the similar energy barriers. More interesting, the simulation results suggest that oxygen vacancies can automatically generate and supplement during the NH3-SCR reaction. This present work highlights the importance of elaborately modulating the double adsorption sites for NH3 and NOx and proposes the possible reaction mechanisms.

Effect of migration of ZCu(OH) to Z2Cu upon hydrothermal aging on the NH3-SCR reaction mechanism over a Cu-CHA catalyst

In this study, the experiments combined with activity tests and characterizations were conducted to investigate the influence of hydrothermal aging (HTA) on the reactivity of NH3-SCR over a Cu-CHA catalyst. The results showed that the NOx conversion efficiency can reach more than 80% below 225 ℃ in the reaction between NH3 and NO+O2 after hydrothermal aging, but it increases the N2O production. The wave spectrum of in-situ DRIFTs confirmed the notable differences in the NH3-SCR mechanism between Cu species of ZCu(OH) and Z2Cu at the same reaction conditions. The NH3-SCR reaction occurring on ZCu(OH) followed the ‘Langmuir-Hinshelwood’ (L-H) mechanism, where NH3 combined with products that oxidize NO to NO2 via dimerization and disproportionation reactions to produce the key intermediates as NH4NO2 and HONO. However, the entire NH3-SCR on Z2Cu followed the ‘Eley-Rideal’ (E-R) mechanism, in which adsorbed NH3 effectively reacted with gas-phase NO to form H2NNO and then produced N2.

Advancements in low-temperature NH3-SCR of NOx using Ba-based catalysts: a critical review of preparation, mechanisms, and challenges.

Presently, selective catalytic reduction (SCR), with either carbon monoxide, urea, hydrocarbons, hydrogen, or ammonia as a reductant, has become a nitrogen oxide (NOx) removal technology (NOx conversion) of many catalytic companies and diesel engine exhaust gas. Although, there exists a serious threat of low-temperature limitations. So far, certain scientists have shown that barium-based (Ba-based) catalysts have the potential to be highly effective at SCR of NOx at low temperatures when ammonia is used as the reducing agent. The process of NOx storage and reduction which alternate SCR is known as the Lean NOx trap. Herein, we give the condensed advancements and production of the catalysts that involve BaO in low-temperature NH3-SCR of NOx, the advantages of BaO catalysts compared to the recently hot electrocatalysis, the stability of BaO catalyst materials, and the condensed advancements and production of the catalysts that involve BaO in low-temperature NH3-SCR of NOx. These catalysts are viewed in the light of their preparation method, particulate, and posture in mixed oxides. Also, the characteristic features of Ba-based catalysts are carefully considered and briefed under the following areas: preparation method and precursor, crystallinity, calcination temperature, morphology, acid sites, the specific surface area for reaction, redox property, and activation energy of catalysts. More to these are the discussions on Eley-Rideal [E-R] and Langmuir-Hinshelwood [L-H] mechanisms, the H2O/SO2 and O2 permissiveness, and the NH3-SCR reaction mechanism over Ba-based catalysts highlighting their possible effects. Finally, we proposed the prospect and the likely future research plan for the low-temperature NH3-SCR of NOx.

Influence of Solvent on Selective Catalytic Reduction of Nitrogen Oxides with Ammonia over Cu-CHA Zeolite.

The copper-exchanged zeolite Cu-CHA has received considerable attention in recent years, owing to its application in the selective catalytic reduction (SCR) of NOx species. Here, we study the NH3-SCR reaction mechanism on Cu-CHA using the hybrid quantum mechanical/molecular mechanical (QM/MM) technique and investigate the effects of solvent on the reactivity of active Cu species. To this end, a comparison is made between water- and ammonia-solvated and bare Cu species. The results show the promoting effect of solvent on the oxidation component of the NH3-SCR cycle since the formation of important nitrate species is found to be energetically more favorable on the solvated Cu sites than in the absence of solvent molecules. Conversely, both solvent molecules are predicted to inhibit the reduction component of the NH3-SCR cycle. Diffuse reflectance infrared fourier-transform spectroscopy (DRIFTS) experiments exploiting (concentration) modulation excitation spectroscopy (MES) and phase-sensitive detection (PSD) identified spectroscopic signatures of Cu-nitrate and Cu-nitrosamine (H2NNO), important species which had not been previously observed experimentally. This is further supported by the QM/MM-calculated harmonic vibrational analysis. Additional insights are provided into the reactivity of solvated active sites and the formation of key intermediates including their formation energies and vibrational spectroscopic signatures, allowing the development of a detailed understanding of the reaction mechanism. We demonstrate the role of solvated active sites and their influence on the energetics of important species that must be explicitly considered for an accurate understanding of NH3-SCR kinetics.

Research Progress on Sulfur Deactivation and Regeneration over Cu-CHA Zeolite Catalyst

Benefiting from the exceptional selective catalytic reduction of NOx with ammonia (NH3-SCR) activity, excellent N2 selectivity, and superior hydrothermal durability, the Cu2+-exchanged zeolite catalyst with a chabazite structure (Cu-CHA) has been considered the predominant SCR catalyst in nitrogen oxide (NOx) abatement. However, sulfur poisoning remains one of the most significant deterrents to the catalyst in real applications. This review summarizes the NH3-SCR reaction mechanism on Cu-CHA, including the active sites and the nature of hydrothermal aging resistance. On the basis of the NH3-SCR reaction mechanism, the review gives a comprehensive summary of sulfate species, sulfate loading, emitted gaseous composition, and the impact of exposure temperature/time on Cu-CHA. The nature of the regeneration of sulfated catalysts is also covered in this review. The review gives a valuable summary of new insights into the matching between the design of NH3-SCR activity and sulfur resistance, highlighting the opportunities and challenges presented by Cu-CHA. Guidance for future sulfur poisoning diagnosis, effective regeneration strategies, and a design for an efficient catalyst for the aftertreatment system (ATS) are proposed to minimize the deterioration of NOx abatement in the future. Finally, we call for more attention to be paid to the effects of PO43- and metal co-cations with sulfur in the ATS.

Effects of Nb-modified CeVO4 to form surface Ce-O-Nb bonds on improving low-temperature NH3-SCR deNOx activity and resistance to SO2 & H2O

A series of novel ternary CeVO4 modified with different Nb contents (CeNbVO) catalysts were synthesized via alkali-assisted hydrothermal method, and applied for selective catalytic reduction (SCR) of NOx with NH3. The as-prepared CeNbVO catalysts show enhanced NH3-SCR performance compared with the CeVO catalyst. Especially, the optimal CeNbVO-2 with appropriate Nb amount displays the superior NH3-SCR activity with above 90 % NO conversion in the range of 210–420 °C with 5 %vol·H2O and excellent resistance to H2O/SO2. Effects of Nb-modified CeVO4 to form surface Ce-O-Nb bonds on improving low-temperature NH3-SCR activity and resistance to SO2 & H2O were investigated by using various characterization methods, including XRD, Raman spectroscopy, N2 physical adsorption, TEM, H2-TPR, NH3-TPD, O2-TPD, NO-TPD, XPS, kinetic tests and in-situ DRIFTS. Different phases can be obtained with the different Nb amount doping, leading to different SCR activity. The pure CeVO4 phase with the short-range ordered Nbn+–O2–-Cen+ bond is formed by adding a small amount of Nb in CeNbVO-2. The superior catalytic performance of CeNbVO-2 can be ascribed to its improved acidity and suitable oxidation ability, which may counteract the negative effects of nonselective NH3 oxidation to N2O. It is found that the formation of Nbn+–O2–-Cen+ bonds can significantly increase the surface active oxygen species and oxygen vacancy of the catalyst. Additionally, the NH3-SCR reaction mechanism is revealed using in-situ DRIFTS and kinetic studies.

Promotional mechanism of enhanced denitration activity with Cu modification in a Ce/TiO2-ZrO2 catalyst for a low temperature NH3-SCR system.

This study aims to investigate the enhanced low temperature denitration activity and promotional mechanism of a cerium-based catalyst through copper modification. In this paper, copper and cerium oxides were supported on TiO2–ZrO2 by an impregnation method, their catalytic activity tests of selective catalytic reduction (SCR) of NO with NH3 were carried out and their physicochemical properties were characterized. The CuCe/TiO2–ZrO2 catalyst shows obviously enhanced NH3-SCR activity at low temperature (<300 °C), which is associated with the well dispersed active ingredients and the synergistic effect between copper and cerium species (Cu2+ + Ce3+ ↔ Cu+ + Ce4+), and the increased ratios of surface chemisorbed oxygen and Cu+/Cu2+ lead to the enhanced low-temperature SCR activity. The denitration reaction mechanism over the CuCe/TiO2–ZrO2 catalyst was investigated by in situ DRIFTS and DFT studies. Results illustrate that the NH3 is inclined to adsorb on the Cu acidic sites (Lewis acid sites), and the NH2 and NH2NO species are the key intermediates in the low-temperature NH3-SCR process, which can explain the promotional effect of Cu modification on denitration activity of Ce/TiO2–ZrO2 at the molecular level. Finally, we have reasonably concluded a NH3-SCR catalytic cycle involving the Eley–Rideal mechanism and Langmuir–Hinshelwood mechanism, and the former mechanism dominates in the NH3-SCR reaction.

Enhancing the K-poisoning resistance of CeO2-SnO2 catalyst by hydrothermal method for NH3-SCR reaction

It is a very challenging task to improve the anti-alkali metal poisoning ability of non-vanadium-based denitration catalysts. To address this issue, we attempt to synthesize CeO2-SnO2 catalyst by hydrothermal method (denoted as CS-HT), which uses high temperature and high pressure environment of hydrothermal processto promote the distribution of Sn4+ in CeO2 lattice and enhance the interaction between each component. For comparison, CeO2-SnO2 catalyst was also prepared by co-precipitation method (denoted as CS-CP). The denitration activity and resistance to K-poisoning performance of these prepared catalysts for the selective catalytic reduction of nitrogen oxides by ammonia (NH3-SCR) were studied. The results showed that CS-HT catalyst had better denitration activity and anti-K poisoning performance than CS-CP catalyst. The physicochemical properties of these catalysts were characterized by XRD, Raman, XPS, H2-TPR, NH3-TPD. Experimental results indicated that the enhancement of anti-K poisoning ability of CS-HT catalyst was related to the good distribution of Sn4+, excellent redox performance and surface acidity. Moreover, the Sn-O bonds could combine with the introduced K more easily, which protected the Ce-O active sites. Finally, the possible NH3-SCR reaction mechanism and K-poisoning reasons on CeO2-SnO2 catalyst were analyzed by in-situ DRIFTS experiments.

Insight into the reaction mechanism over PMoA for low temperature NH3-SCR: A combined In-situ DRIFTs and DFT transition state calculations

Phosphomolybdic acid catalyst (PMoA/TiO2) is a promising catalyst for selective catalytic reduction of NOx with NH3 (NH3-SCR) due to its strong acidity and excellent redox property. This work presents the NH3-SCR reaction mechanism by In-situ diffuse reflectance Infrared Fourier Transform Spectroscopy (In-situ DRIFTs) and density functional theory (DFT). In-situ DRIFTs results indicated that the NH3-SCR performance over PMoA/TiO2 followed both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. The reaction pathway, intermediate, transition state and energy barrier over PMoA to complete NH3-SCR reaction were calculated by DFT. The results showed that the catalytic cycle includes foundational reaction (NH3 + NO reaction) and regenerative reaction (NH3 + NO2 reaction). NH2, NH2NO, HNNOH and HO2NNH species were the key intermediates. In the foundational reactions, NO2 played an important role in the removal of remaining H atoms. The NH3 dissociation on Lewis acid site, the internal hydrogen transfer on Brønsted acid site and the formation of HO2NNH species were the rate-controlling steps. The catalytic cycle of NH3-SCR over PMoA consists of standard SCR and fast SCR.

Promotional Effects on NH3-SCR Performance of CeO2–SnO2 Catalysts Doped by TiO2: A Mechanism Study

A novel Ti-doped Ce– Sn mixed oxide (Ce–Sn–Ti) catalysts were developed for the selective catalytic reduction (SCR) of NOx with NH3. The addition of titanium could improve SCR activity at a low-temperature window. By optimizing the element proportions, the NOx conversion of Ce0.6Sn2.4Ti2 catalysts could reach more than 90% in a wide-operating temperature window (200 –450 °C). The appropriate doping Ti formed Sn–O-Ti, Sn–O-Ce and Ti–O-Ce structures, which could increase the content of Ce3+ through electrons transfer from Sn or Ti to Ce (Ce3+ + Ti4+ ↔ Ce4+ + Ti3+ and 2Ce4+ + Sn2+ ↔ 2Ce3+ + Sn4+). The solid solution structure increased specific surface areas, active sites (Ce3+), and Lewis acid sites over the Ce0.6Sn2.4Ti2 catalysts. According to DRIFTS results, only bidentate nitrate could react with adsorbed NH3 species. However, adsorbed NH3 species could quickly react with the gaseous NO. The NH3-SCR reaction mechanism over Ce0.6Sn2.4Ti2 catalysts mainly followed the Eley –Rideal mechanism. The electron transfer between tin, cerium, and titanium elements led to generate more active sites (Ce3+) used for NH3 and NOx activation/oxidation, which improved SCR activity. The NH3-SCR reaction mechanism over Ce0.6Sn2.4Ti2 catalyst mainly followed the Eley−Rideal mechanism, in which adsorbed NH3 species could quickly react with the gaseous NO to generate N2 and H2O.

Recent Progress on Improving Low-Temperature Activity of Vanadia-Based Catalysts for the Selective Catalytic Reduction of NOx with Ammonia

Selective catalytic reduction of NOx with NH3 (NH3-SCR) has been successfully applied to abate NOx from diesel engines and coal-fired industries on a large scale. Although V2O5-WO3(MoO3)/TiO2 catalysts have been utilized in commercial applications, novel vanadia-based catalysts have been recently developed to meet the increasing requirements for low-temperature catalytic activity. In this article, recent progress on the improvement of the low-temperature activity of vanadia-based catalysts is reviewed, including modification with metal oxides and nonmetal elements and the use of novel supports, different synthesis methods, metal vanadates and specific structures. Investigation of the NH3-SCR reaction mechanism, especially at low temperatures, is also emphasized. Finally, for low-temperature NH3-SCR, some suggestions are given regarding the opportunities and challenges of vanadia-based catalysts in future research.

Insight into SO2 poisoning over Cu-SAPO-18 used for NH3-SCR

Abstract The impact of SO2 poisoning on Cu-SAPO-18 physicochemical properties and its NH3-SCR reaction mechanism was investigated. After exposing Cu-SAPO-18 to SO2+O2 for 40 min, the sulfite and sulfate species were detected on Cu-SAPO-18 surface, which caused a small decrease in BET surface area and micropore volume, the increase in NH3 storage and the deactivation of some isolated Cu2+ sites. These could be interpreted by the slight micropore blocking, interaction between sulfates and NH3 forming new NH4+ species and the formation of Cu-sulfate, respectively. Additionally, it was observed that isolated Cu2+ ions in pear-shaped cavity of AEI structure, which are beneficial to good low-temperature deNOx activity, were more severely poisoned by SO2 than Cu2+ in the double 6-membered ring (D6R). Accordingly, the NH3-SCR activity below 350 °C was restrained by SO2. Moreover, the in-situ DRIFTS results indicate that Cu-SAPO-18 catalyzed NH3-SCR reaction predominantly proceeds through Langmuir−Hinshelwood (L−H) mechanism at low temperature. SO2 poisoning inhibited the adsorption of NO + O2 and NH3 on Cu2+ sites, thereby decreasing the formation of Cu−NOx and Cu−NH3 intermediates, evidently, the L−H mechanism was suppressed by SO2. Interestingly, the deactivated Cu-SAPO-18 could be regenerated under SCR gas at 550 °C and resumed at least most NH3-SCR activity.

Selective catalytic reduction of NOx with NH3 over TiO2 supported metal sulfate catalysts prepared via a sol–gel protocol

Metal sulfate catalysts exhibited high SO2 tolerance in the NH3-SCR reaction. The NH3-SCR reaction mechanism on metal sulfate catalysts should follow the Eley–Rideal mechanism.

Recent advances in the selective catalytic reduction of NO&amp;lt;sub&amp;gt;&amp;lt;italic&amp;gt;x&amp;lt;/italic&amp;gt;&amp;lt;/sub&amp;gt; by NH&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; over small-pore zeolite catalysts

Selective catalytic reduction of NO x by NH3 (NH3-SCR) is one of the most effective methods for the removal of NO x . Small-pore zeolite catalysts, such as Cu/SSZ-13 and Cu/SAPO-34, have attracted more and more attention for the NH3-SCR of NO x due to the high activity and hydrothermal stability. The recent advances of NH3-SCR of NO x over small-pore zeolite catalysts (especially Cu-based zeolite) are reviewed. Special attention is laid on the catalytic performance, influence factors and the NH3-SCR reaction mechanism. Finally, future research on the small-pore zeolite catalysts for NH3-SCR of NO x is proposed.

The effect of copper loading and silicon content on catalytic activity and hydrothermal stability of Cu-SAPO-18 catalyst for NH3-SCR

The effect of Cu loading and Si content on catalytic activity and hydrothermal stability of Cu-SAPO-18 catalysts prepared by incipient wetness impregnation method was investigated in ammonia selective catalytic reduction (NH3-SCR) reaction. The Cu-SAPO-18 catalyst with Cu loading of 2.49 wt.% shows superior NH3-SCR performance and hydrothermal stability due to the presence of more isolated Cu2+ species and the less amount of CuO species. What’s more, the Cu-SAPO-18 catalysts with different Si content exhibit distinct NH3-SCR performance, though they contain similar Cu loading. The NH3-TPD, H2-TPR and EPR results indicate that the number of acid sites and isolated Cu2+ ions over Cu-SAPO-18 catalysts rises with increasing Si content from 0.084 to 0.173, but decreases with the highest Si content of 0.204. Consequently, the Cu-SAPO-18 (0.173) catalyst shows the best NH3-SCR performance. After hydrothermal treatment, the Cu-SAPO-18 (0.173) catalyst exhibits excellent NO reduction efficiency which attributes to its stable framework and the most amount of acid sites and isolated Cu2+ ions. Additionally, the NH3-SCR kinetic analysis over Cu-SAPO-18 catalyst was also performed and suggesting that Cu loading and Si content do not influence the NH3-SCR reaction mechanism.

A skeletal reaction scheme for selective catalytic reduction of NOx with NH3 over CeO2/TiO2 catalyst

CeO2/TiO2 has been regarded as the promising catalyst used for the selective catalytic reduction (SCR) of NOx with NH3. The complete NH3-SCR reaction mechanism of NO over CeO2/TiO2 catalyst was systemically investigated using density functional theory (DFT) calculations. Based on the DFT-derived energetics, a skeletal reaction scheme including 20 elementary reaction steps was proposed for NH3-SCR reaction of NO over CeO2/TiO2 catalyst. The results indicate that NH3, NO, O2, and NO2 adsorption on CeO2/TiO2(110) surface is dominated by the chemisorption mechanism. The successive dehydrogenation process of NH3 is cleaved by NH2 dehydrogenation step. NH2 derived from NH3 dehydrogenation step can stably exist on CeO2/TiO2 catalyst surface and serve as a key intermediate in NH3-SCR reaction. The activation energy barrier of N2O formation is higher than that of N2 formation, which is responsible for the excellent N2 selectivity of CeO2/TiO2 catalyst. NO2 formation under the typical low-temperature SCR conditions can make a contribution to NO reduction over CeO2/TiO2 catalyst. Reaction pathway analysis illustrates that the dominant reaction pathway of NO reduction by NH3 over CeO2/TiO2 catalyst is a three-step process: (1) NH2 formation from NH3 dehydrogenation, (2) N-N coupling reaction, and (3) NH2NO decomposition. During NO reduction, NH2 formation from NH3 dehydrogenation is the rate-determining step of N2 formation.

Iron oxide-based catalysts for low-temperature selective catalytic reduction of NOxwith NH3

AbstractSelective catalytic reduction (SCR) is now an established NOxremoval technology for industrial flue gas as well as for diesel engine exhaust gas. However, it is still a big challenge to develop a novel low-temperature catalyst for NH3-SCR of NOx, especially at a temperature below 200°C. In the past few years, many studies have demonstrated the potential of iron (Fe)-based catalysts as low-temperature catalysts for NH3-SCR of NOx. Herein, we summarize the recent progress and performance of Fe-based catalysts for low-temperature NH3-SCR of NOx. Catalysts are divided into three categories: single FexOy, Fe-based multimetal oxide, and Fe-based multimetal oxide with support catalysts. The catalytic activity and selectivity of Fe-based catalysts are systematically analyzed and summarized in light of some key factors such as activation energy, specific surface area, morphology, crystallinity, preparation method and precursor, acid sites, calcination temperature, other metal dopant/substitute, and redox property of catalysts. In addition, H2O/SO2tolerance and the NH3-SCR reaction mechanism over Fe-based catalysts, including Eley-Rideal and Langmuir-Hinshelwood mechanism, are emphasized. Lastly, the perspectives and future research directions of low-temperature NH3-SCR of NOxare also proposed.

The enhanced resistance to K deactivation of Ce/TiO2 catalyst for NH3-SCR reaction by the modification with P

The deactivation of SCR catalyst caused by K species contained in the fly ash would suppress its DeNOx performance. In this study, it was manifested that the modification of Ce/TiO2 catalyst with P could enhance its K tolerance. To understand the promotion mechanism, the fresh and poisoned catalyst samples were subjected to the characterization techniques including BET, XRD, XPS, H2-TPR, NH3-TPD and in situ DRIFT. The results elucidated that the introduction of P species could increase the reducibility of Ce species and generate more surface chemisorbed oxygen, along with the strengthened surface acidity for NH3 adsorption. It seemed that the NH3-SCR reaction mechanism over Ce/TiO2 catalyst was a combination of L-H mechanism (<200 °C) and E-R mechanism (≥200 °C). After the addition of P species, the NO oxidation over Ce/TiO2 catalyst was also accelerated, accompanied by the broadened temperature window for the NH3-SCR reaction under the control of L-H mechanism. The promoted NH3 species adsorption and the generated more NO2 over P-Ce/TiO2 catalyst were conducive to the NH3-SCR reaction through L-H pathway, which might be the primary reason for its good K resistance.