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Cu/SSZ-13 catalysts not only exhibit superior SCR performance but also possess excellent selective catalytic oxidation (SCO) ability to remove NH 3 escaped from engine exhaust gas fueled by NH 3. To elucidate the effect of Cu loading on Cu/SSZ-13 catalysts, a series of Cu/SSZ-13 catalysts were prepared through wet impregnation method to remove high-concentration NH 3 (5000 ppm). The SCO activity test results showed that when Cu loading increased from 1% to 10%, there was an obvious improvement effect on NH 3 conversion performance at low temperature. Cu 10 /SSZ-13 catalyst reached a high NH 3 conversion of 96% at 250 °C, and N 2 selectivity was higher than 86% in the whole temperature range. However, when further increasing Cu loading from 10% to 20%, there was no distinctive difference in NH 3 conversion and N 2 selectivity. The characterization results indicated that there were abundant active species, adsorbed oxygen species, and acid sites on the surface of Cu 10 /SSZ-13 catalyst. The [Cu(OH)]+ and isolated Cu2+ species in zeolite channels of Cu 10 /SSZ-13 catalyst rather than CuO species on the surface played a key role in NH 3 -SCO reactions. Since 20% Cu loading would result in a significant decrease in isolated Cu2+ species, it resulted in both [Cu(OH)]+ species in zeolite channels and superfluous Cu species on zeolite surface being main active species in NH 3 -SCO reactions. In-situ DRIFTS experiments suggested that NH 3 -SCO reactions over Cu/SSZ-13 catalysts followed the internal selective catalytic reduction (i-SCR) mechanism. [Display omitted] [ABSTRACT FROM AUTHOR]

Two series of Cu/SSZ-13 catalysts were synthesized via aqueous solution and solid-state ion exchange using SSZ-13 supports of varying Si/Al ratios. The isolated and multinuclear Cu content of these catalysts were determined by H 2 temperature programmed reduction (H 2 -TPR). Multinuclear Cu in these catalysts, including in situ Cu-dimers formed from ZCuIIOH coupling and permanent CuO clusters, are active species for dry NO oxidation. NH 3 oxidation on these catalysts follows an internal SCR (i-SCR) mechanism, i.e., a portion of NH 3 is first oxidized to NO, then NO is selectively reduced by the remaining NH 3 to N 2. NH 3 oxidation displays distinct kinetic behavior below ∼300 °C and above ∼400 °C. At low temperature the results indicate that NH 3 -solvated mobile Cu-ions are the active centers. CuO clusters, when present, also contribute to the low temperature activity by catalyzing NH 3 oxidation to NO. At high temperature, in situ Cu-dimers and CuO clusters catalyze NH 3 oxidation to NO, and isolated Cu-ions catalyze SCR to realize the cascade turnovers. For both NO and NH 3 oxidation, Cu-dimers balanced by framework charges of close proximity appear to be more active than Cu-dimers balanced by distant framework charges. However, the former Cu-dimers are less stable than the latter and tend to split into monomers in the presence of vicinal Brønsted acid sites. Via density functional theory (DFT) calculations, the i-SCR mechanism for low temperature NH 3 oxidation, i.e., the energetic favorability for the involvement of the NO intermediate, is justified. The DFT results also agree with experimental data that the formation of Cu-dimers from ZCuIIOH dimerization is essential for NH 3 oxidation at high temperature. [Display omitted] • NO and NH 3 oxidation on Cu-SSZ-13 occurs on multinuclear Cu sites, including in situ Cu-dimers and permanent CuO clusters. • NH 3 oxidation follows an internal SCR mechanism, which displays distinct kinetic behavior below 300 °C and above 400 °C. • Solvated CuII(NH 3) 3 OH species oxidize NH 3 at low-temperature and catalyze further reduction of produced NO to N 2 and H 2 O. • Permanent CuO clusters catalyze NH 3 oxidation to NO at low temperatures, clarifying a synergy with isolated Cu-ions. • At high temperature, multinuclear Cu sites sustain NH 3 oxidation, and immobilized & isolated Cu-ions sustain NO reduction. [ABSTRACT FROM AUTHOR]

• Alkali metal ions result in weak hydrothermal stability of Cu/SSZ-13. • Na+ and K+ show similar deactivation mechanism on hydrothermal stability. • K+ causes lower activity due to small hydrated diameter and strong binding ability. Cu/SSZ-13 has considered being a good candidate for NH 3 -SCR catalysts. However, in real world, Cu/SSZ-13 inevitably expose to alkali metals deposit and hydrothermal aging, and hence, the role of alkali ions (Na+ and K+) poisoning on the hydrothermal stability of Cu/SSZ-13 was investigated in this work. The Cu/SSZ-13 catalyst was treated with different loadings of alkali content at 600 °C or different hydrothermal temperatures at low alkali metal loading. Different from non-poisoned Cu/SSZ-13 catalysts under hydrothermal aging, the introduced alkali ions weaken the hydrothermal stability of Cu/SSZ-13 and make poisoned catalysts have inferior SCR performance. H 2 -TPR results demonstrate the presence of alkali ions lead to more copper ions transform to copper oxides species and the extents of transformation increase as the alkali contents and aging temperature increasing. Moreover, XRD results prove that the CHA framework collapse and, simultaneously, SiO 2 and CuAlO x species form under high contents of alkali ions or high aging temperature. Besides, potassium invariably shows the severe deactivation because of a small hydrated diameter and strong binding ability. Our study reveals that diesel should pay attention to control the contents of alkali ions, especially for K+, in automotive products and the operating temperature in after-treatment applications. [ABSTRACT FROM AUTHOR]

To improve the alkali metal resistance of commercial catalyst Cu/SSZ-13 for ammonia selective catalytic reduction (NH3-SCR) reaction, a simple method to synthesize Cu/SSZ-13 with a core–shell like structure was developed. Compared with smaller-sized counterparts, Cu/SSZ-13 with a crystal size of 2.3 μm exhibited excellent resistance to Na poisoning. To reveal the influence of the crystal size on Cu/SSZ-13, physical structure characterization (XRD, BET, SEM, NMR) and chemical acidic distribution (H2-TPR, UV-Vis, Diethylamine-TPD, pyridine-DRIFTs, EDS) were investigated. It was found that the larger the crystal size of the molecular sieve, the more Cu is distributed in the crystal core, and the less likely it was to be replaced by Na to generate CuO. Therefore, a 2.3 μm sized Cu/SSZ-13 well-controlled the reactivity of the side reaction NH3 oxidation and the generation of N2O. The result was helpful to guide the extension of the service life of Cu/SSZ-13.

• Alkali co-cations Na+ and K+ stabilize SSZ-13 during hydrothermal aging. • Alkaline earth co-cation Ca2+ destabilizes SSZ-13 during hydrothermal aging. • Repulsive interactions between Cu ions and co-cations prevents Cu overloading. • At optimized co-cation and Cu ratios, both SCR performance and catalyst stability improve substantially. Cu,M/SSZ-13 (M = Na+, K+ and Ca2+) selective catalytic reduction (SCR) catalysts with Si/Al = 6 and M/Cu ratios varying from 0.1 to 1.0 are prepared by solution ion exchange, followed by slurry drying and hydrothermal aging at 800 °C. The catalysts are characterized with X-ray diffraction and N 2 adsorption isotherms to probe their textural properties; 27Al and 29Si nuclear magnetic resonance and NH 3 temperature-programmed desorption to probe their acidity properties and levels of dealumination; and electron paramagnetic resonance and H 2 temperature-programmed reduction to quantitatively explore the nature of Cu moieties in the catalysts. These studies are followed by density functional theory calculations to elucidate Cu and co-cation interactions at an atomic level and SCR reaction tests to reveal correlations between the chemical and physical properties of the catalysts and their SCR performance. Through these comprehensive investigations, it is discovered that alkali metal co-cation addition can be used for the synthesis of highly stable, and highly active and selective Cu/SSZ-13 catalysts with relatively high Al content. In catalysts with optimal alkali incorporation, dealumination of the SSZ-13 substrate is largely inhibited, allowing high concentrations of SCR-active isolated Cu ions. At the same time, repulsive interactions between Cu ions and alkali metal co-cations preclude excessively high isolated Cu-ion loadings. Interplay between and optimization of these two factors is considered the underlying origin for this successful catalyst synthesis strategy. On the other hand, the alkaline earth co-cation Ca2+ fails to demonstrate any beneficial effects, since it destabilizes isolated Cu ions via site competition. [ABSTRACT FROM AUTHOR]

• Short perspective on the new science of commercial Cu/SSZ-13 SCR catalysts. • Brief historical context on catalytic vehicle emission control also provided. • Short discussion of future challenges for the vehicle emission control community. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Strong phosphorus-copper interaction was observed on the P-poisoned Cu-SSZ-13. • P-poisoning was more severe on NH 3 and NO oxidation than on ammonia-SCR. • Phosphorus-zeolite framework interaction was observed on P-poisoned Cu-SSZ-13. • Phosphorus decreased the hydrothermal stability of Cu-SSZ-13. Abstract Automotive catalysts are continuously exposed to different poisons and to high temperature, which result in hydrothermal aging. Phosphorus is one of the poisons that the catalyst could be exposed to and it originates from the lubricant oil. In this work, we study the influence of phosphorus poisoning on the catalytic performance and the deactivation mechanism in the hydrothermal aging of Cu-SSZ-13 catalysts. Phosphorus poisoning was performed by impregnating the Cu-SSZ-13 catalysts with (NH 4) 2 HPO 4 solution using the incipient wetness impregnation method, which allowed us to precisely control the amount of phosphorus poison on the catalyst. XPS results show that phosphorus oxide (P 2 O 5), metaphosphate (PO 3 –) and phosphate (PO 4 3–) are formed on the surface of phosphorus-poisoned catalysts, and metaphosphate is the main compound among those species. Phosphorus tends to interact with copper sites and strongly impacts the electronic and reduction property of Cu, as disclosed using EDX mapping, UV–vis DRS and H 2 -TPR. Results of catalytic activities show that phosphorus poisoning is more severe on ammonia and NO oxidation reactions than on standard ammonia-SCR. This is possibly due to the formation of copper phosphates in the large cages, as revealed using H 2 -TPR, which reduces the oxidation capacity. Moreover, results of XRD and 27Al and 31P solid-state NMR reveal that phosphorus not only interacts with copper by forming a P O Cu linkage but also partially inserts into the zeolite framework by forming a localized AlPO 4 phase. Both non-poisoned and P-poisoned catalysts lose their active sites and chabazite structures due to dealumination after successively aging in hydrothermal conditions (8 vol.% O 2 , 5 vol.% H 2 O in Ar) at different temperatures (800, 850, and 900 °C), which results in a large decrease in SCR performance. Specifically, the P-poisoned catalysts degrade faster than the non-poisoned catalysts. Results demonstrate that phosphorus induces the extensive formation of AlPO 4 that accelerates the dealumination during hydrothermal aging. This work provides new insight into understanding the deactivation mechanism in Cu-SSZ-13 from the perspectives of phosphorus-poisoning and hydrothermal aging, and it clearly shows that it is crucial to examine poisoning and hydrothermal aging simultaneously. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Kinetic model for SCR coated filter, including soot oxidation and SCR reactions. • Random pore model for soot oxidation in order to describe the fast oxidation. • Ammonia inhibits soot oxidation due to formation of amines/amides on soot. • Free edge site mechanism important for describing the ammonia effect. • Model could well describe soot oxidation and SCR reactions over Cu/SSZ-13. Abstract SCR coated filters have recently been introduced. These combine soot capture through diesel particulate filters (DPF) and NO x removal through ammonia selective catalytic reduction (NH 3 SCR). This study investigates the impact of soot on the reactions being important for the SCR process on Cu/SSZ-13, as well as the impact of different gases on soot oxidation using flow reactor measurements. A limited impact of soot on the SCR reactions and a clear inhibiting effect of NH 3 on soot oxidation, is found. Ammonia TPD, in-situ DRIFT, and XPS experiments are used to investigate the interaction between soot and ammonia. Amines/amides are found on the soot when exposed to NH 3 and H 2 O. The results are used to develop a kinetic model for soot oxidation over DPF and a soot coated Cu/SSZ-13 catalyst using diesel soot generated from an engine bench. It is found that it is important to incorporate a random pore model and a free edge site mechanism through which ammonia block these free edge carbons. The model describes well soot oxidation in the presence of NH 3 over DPF, as well as soot oxidation and the SCR mechanism over soot loaded Cu/SSZ-13. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The cyclic lean/rich aging at around 600 °C has led to a severe deterioration of NO conversion over Cu/SSZ-13 in high temperature region. • The accelerated NO formation during NH 3 oxidation associated with CuOx formation was a primary reason for the deactivation of Cu/SSZ-13. • The lean/rich-aged Cu/SSZ-13 could partially be regenerated by the post-treatment at 700 °C due to the re-dispersion of CuOx into Cu2+ ions. • Cu/LTA showed far better tolerance to rich feeds than Cu/SSZ-13 due to less reducible nature of Cu ion on LTA suppressing CuOx formation. Abstract Selective catalytic reduction of NOx by urea (urea/SCR) and Lean NOx Trap (LNT) are two leading technologies for NOx reduction under lean condition. To quickly warm up SCR catalysts, considerable efforts have been made in integrating SCR onto a diesel particulate filter, so called SDPF. With the fact that the real driving emission test has taken effect, SDPF coupled with LNT might be one of most viable solutions to meet stringent emission regulations. However, desulfation process for LNT may result in a severe deactivation of SDPF in downstream. Here, we investigated the tolerance of Cu/zeolite SCR catalysts against periodic lean/rich operation condition simulating desulfation over LNT in front of SDPF. The lean/rich aging at 620 °C has led a severe deterioration of NOx conversion over Cu/SSZ-13 hydrothermally aged 800 °C, especially in high-temperature region above 400 °C. The accelerated NH 3 oxidation to NO was the primary cause for the poor NOx removal activity, originated from the alteration of Cu state. Cu ions turned out to be converted to CuOx cluster upon their exposure to rich condition, which could partly be re-dispersed as Cu2+ ion after the post-treatment at 700 °C under lean condition. Cu/SSZ-13 with low Cu content revealed better activity maintenance under the high-temperature rich condition compared to higher Cu loading counterpart. Cu/LTA recently developed showed superior tolerance against rich feed due to less reducible nature of Cu+ ion therein compared to that in Cu/SSZ-13 leading to less CuOx formation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Controllable preparation of Cu/SSZ-13 with various particle sizes was realized by adjusting seeds amounts and pH values; • The morphology and physiochemical properties of Cu/SSZ-13 are not affected by particle size; • The NH 3 -SCR reaction over Cu/SSZ-13 is not controlled by intracrystalline diffusion limitation. Abstract In this work, we report a facile technique to prepare crystalline Cu/SSZ-13 particles with uniform and controllable sizes. Samples with varying particles sizes (0.4–2 µm) with 1–2 wt% Cu were synthesized by carefully controlling the amount of zeolite seeds and by adjusting the pH values, with larger seed amounts and higher pH values resulting in smaller particle sizes. Various techniques (SEM, XRD, BET, H 2 -TPR etc.) were used to characterize these samples and the results confirm that despite the varying particle sizes, these Cu/SSZ-13 catalysts have similar Si/Al ratio, acidity and Cu distributions. Hence, these catalysts provided the perfect sample sets to probe the role of intra-crystalline diffusion in NH 3 SCR reactions. The kinetic experiment results indicate that turnover frequencies (TOFs) of the catalysts with different particle sizes and copper loadings are identical, therefore NH 3 -SCR reaction rate over Cu/SSZ-13 catalysts is not limited by intra-crystalline diffusion. [ABSTRACT FROM AUTHOR]

The impacts of Pd poisoning to the activity, selectivity, and hydrothermal stability of Cu/SSZ-13 selective catalytic reduction (SCR) catalysts are reported. Pd lowers DeNOx efficiency of Cu/SSZ-13 via two mechanisms: (1) displacing SCR active sites in the form of isolated Pd-ions, and (2) catalyzing non-selective NH 3 oxidation in the form of PdO. The first mechanism works by the diffusion of isolated Pd-ions into chabazite cages to displace ZCuIIOH SCR active species, and it occurs on Cu/SSZ-13 catalysts with and without external surface CuO clusters in similar fashion. In contrast, the second mechanism works differently with and without external surface CuO clusters. For Cu/SSZ-13 catalyst without external CuO clusters (i.e., primarily isolated Cu-ions), PdO leads to significant decrease of DeNOx efficiency at reaction temperatures above ∼400 °C due to its non-selective NH 3 oxidation activity at high temperatures. However, this poisoning effect becomes much less impactful on Cu/SSZ-13 catalyst containing CuO clusters. This is due to the formation of CuO-PdO solid solution via interactions between CuO and PdO, which reduces non-selective NH 3 oxidation potential. Furthermore, this solid solution formation even mitigates adverse effects caused by hydrothermal aging. Hence, the poisoning effects of Pd are closely related to Cu speciation and spatial distribution of a Cu/SSZ-13 catalyst. Finally, this study suggests a strategy in eliminating Pd poisoning, that is, the introduction of an oxide phase that effectively traps PdO but does not adversely influence SCR. [Display omitted] • Pd-ions poison Cu/SSZ-13 catalysts by displacing Cu active sites. • PdO facilitates NH 3 oxidation to NOx and thus deteriorates SCR activity. • CuO-PdO solid solution formation mitigates the negative impacts of PdO. [ABSTRACT FROM AUTHOR]

Lean nitric oxide (NOx)-trap (LNT) and selective catalytic reduction (SCR) are efficient systems for the abatement of NOx. The combination of LNT and SCR catalysts improves overall NOx removal, but there is a risk that the SCR catalyst will be exposed to high temperatures and rich exhaust during the LNTs sulfur regeneration. Therefore, the effect of exposure to various rich conditions and temperatures on the subsequent SCR activity of a Cu-exchanged chabazite catalyst was studied. CO, H2, C3H6, and the combination of CO + H2 were used to simulate rich conditions. Aging was performed at 800 °C, 700 °C, and, in the case of CO, 600 °C, in a plug-flow reactor. Investigation of the nature of Cu sites was performed with NH3-temperature-programed desorption (TPD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) of probe molecules (NH3 and NO). The combination of CO and H2 was especially detrimental to SCR activity and to NH3 oxidation. Rich aging with low reductant concentrations resulted in a significantly larger deactivation compared to lean conditions. Aging in CO at 800 °C caused SCR deactivation but promoted high-temperature NH3 oxidation. Rich conditions greatly enhanced the loss of Brønsted and Lewis acid sites at 800 °C, indicating dealumination and Cu migration. However, at 700 °C, mainly Brønsted sites disappeared during aging. DRIFT spectroscopy analysis revealed that CO aging modified the Cu2+/CuOH+ ratio in favor of the monovalent CuOH+ species, as opposed to lean aging. To summarize, we propose that the reason for the increased deactivation observed for mild rich conditions is the transformation of the Cu species from Z2Cu to ZCuOH, possibly in combination with the formation of Cu clusters.

This study focuses on the effect of gas composition during SO 2 poisoning over Cu/SSZ-13 for NH 3 -SCR application and was performed by conducting SO 2 -TPD experiments in a variety of lean gas compositions. In addition, the poisoned monoliths were characterized in detail using ICP-SFMS, UV–vis and XPS. During SO 2 poisoning under dry and lean conditions, two different sulfur species were found, which were assigned to weakly bound SO 2 and copper sulfate like species. Moreover, a significantly larger amount of copper sulfates was present in humid environment. The presence of NH 3 during the poisoning resulted in the formation of ammonium sulfate species which were decomposed at the same temperature independently if the poisoning with SO 2 was conducted in ammonia oxidation conditions or under standard or fast SCR conditions. Moreover, if the temperature ramp was conducted with O 2 and H 2 O compared to Ar alone, more stable sulfate species were formed. In addition, SO 2 poisoning under standard SCR conditions resulted in mostly ammonium sulfate formation at 200 °C, whereas copper sulfates were predominant after poisoning at 400 °C. After hydrothermal aging at 800 °C, more reducible copper species were noticeable and UV–vis showed that copper oxides had been formed. Sulfur poisoning of the hydrothermally aged sample resulted in the additional formation of copper sulfates during poisoning at 200 °C, which was not the case for poisoning of the fresh catalyst. Thus, the copper oxide species enhanced the copper sulfate formation. [ABSTRACT FROM AUTHOR]

The influence of phosphorus on Cu-SSZ-13 NH 3 -SCR catalysts was investigated in order to reveal the deactivation behavior of Cu-SSZ-13 in the presence of phosphorus-containing poisons in the exhaust of diesel engines. The phosphorus-poisoning was simulated by treating the Cu-SSZ-13 catalysts with (NH 4 ) 2 HPO 4 aqueous solution using incipient wetness impregnation method. The focus of the study was the effect of phosphorous on the different reactions occurring on the SCR catalyst, including ammonia oxidation, NO oxidation and standard SCR using monolith catalysts. Moreover, characterization such as ICP-SFMS, N 2 -physisorption, and NH 3 -TPD were employed for the evaluation of the physical and chemical properties of the P-impregnated catalysts. Physically blocking of pores and poisoning of acidic sites were observed on the P-impregnated catalysts. In addition, we observed that phosphorus severely suppressed ammonia oxidation and NO oxidation, while its impact on standard SCR reaction was nearly negligible below 300 °C. Interestingly, a promotive effect was found at higher temperatures, likely due to the severely inhibiting effect on NH 3 oxidation caused by the formation of copper phosphates in the large cages (i.e. 8-membered rings) of Cu-SSZ-13. [ABSTRACT FROM AUTHOR]

To reveal the role of SO3 poisoning in Cu/SSZ-13 NH3-SCR catalysts, fresh and sulfated Cu/SSZ-13 catalysts were prepared in the presence or absence of SO3 flux. The deactivation mechanism is probed by the changes of structural, copper species, and selective catalytic reduction (SCR) activity. The variations concentrate on the changes of copper species as the Chabazite (CHA) framework of Cu/SSZ-13 catalysts could keep intact at high ratios of SO3/SOx. The thermal gravimetric analyzer (TGA) results reveal that the copper sulfate formed during sulfation and the amounts of sulfate species increased with an increase in the SO3/SOx ratio. In contrast to the changing trend of copper sulfate, temperature program reduction (H2-TPR), and electron paramagnetic resonance (EPR) results manifest that, since the number of active copper ions declines with an increase of the SO3/SOx ratio, the active sites transform to these inactive species during sulfation. Due to the combination of NH3-SCR activity and the kinetic tests, it is shown that the decreased number of active sites is responsible for the declined SCR activity at low temperature. As Cu/SSZ-13 catalysts show excellent acid-resistance ability, our study reveals that the Cu/SSZ-13 catalyst is a good candidate for NOx elimination, especially when SO3 exists.

To reveal the role of impregnated sodium (Na) ions in Cu/SSZ-13 catalysts, Cu/SSZ-13 catalysts with four Na-loading contents were prepared using an incipient wetness impregnation method and hydrothermally treated at 600 °C for 16 h. The physicochemical property and selective catalytic reduction (SCR) activity of these catalysts were studied to probe the deactivation mechanism. The impregnated Na exists as Na+ on catalysts and results in the loss of both Brönsted acid sites and Cu2+ ions. Moreover, the high loading of Na ions destroy the framework structure of Cu/SSZ-13 and forms new phases (SiO2/NaSiO3 and amorphous species) when Na loading was higher than 1.0 mmol/g. The decreased Cu2+ ions finally transformed into CuxO, CuO, and CuAlOx species. The inferior SCR activity of Na impregnated catalysts was mainly due to the reduced contents of Cu2+ ions at kinetic temperature region. The reduction in the amount of acid sites and Cu2+ ions, as well as copper oxide species (CuxO and CuO) formation, led to low SCR performance at high temperature. Our study also revealed that the existing problem of the Na ions’ effect should be well-considered, especially at high hydrothermal aging when diesel particulate filter (DPF) is applied in upstream of the SCR applications.

The purpose of this study is to attribute NH-TPD peaks observed over Cu/SSZ-13 catalysts to different catalytic sites. This is done by comparing a large number of copper loadings, especially below 40% ion exchange, to be able to see effects relevant to sites in both 6-membered and 8-membered rings. We found that intermediate (200-300 °C) and high (400-500 °C) temperature NH-TPD peaks followed similar trends to the copper species in 6-membered and 8-membered rings respectively, as seen by H-TPR and NO-DRIFTS. Thus we propose that these two TPD peaks represent ammonia stored on H and Cu sites in 6 and 8-membered rings, respectively. This assignment is further supported by the finding that the intermediate and high temperature NH-TPD peaks of samples with different Si/Al ratios also follow the same trend. Moreover, we observe that the activation energy for ammonia oxidation is significantly lower for Cu in 6MR compared to Cu in 8MR rings. Graphical Abstract: [ABSTRACT FROM AUTHOR]

For the first time, sub-micron Cu/SSZ-13, obtained by modifying an existing synthesis procedure, was shown to be an effective and stable catalyst for selective catalytic reduction of NO. Characterization of the materials with X-ray diffraction, N 2 -physisorption and 27 Al MAS NMR shows that hydrothermal aging, which simulates SCR reaction conditions, is more destructive for smaller particles in a sodium form. After Cu exchange, however, the catalytic performance and hydrothermal stability for Cu/SSZ-13 is independent of the particle size. In particular, a clear positive correlation is found between remaining tetrahedral framework Al and isolated Cu-ion concentrations in aged Cu/SSZ-13 catalysts of comparable Al and Cu contents. This indicates that (1) isolated Cu-ion and paired framework Al configurations display remarkable hydrothermal stabilities; and (2) paired-Al contents can be varied via modifying the synthesis procedures, which appear to have a more critical influence on stabilizing isolated Cu-ions during harsh hydrothermal aging than the particle size. This study is of high interest for applications in vehicular DeNOx technologies where high loadings of active species on wash coats can be achieved by using sub-micron Cu/SSZ-13. [ABSTRACT FROM AUTHOR]

Cu/SSZ-13 Selective Catalytic Reduction (SCR) catalysts have been extensively studied for the past five-plus years. New and exciting fundamental and applied science has appeared in the literature quite frequently over this time. In this short review, a few topics specifically focused on a molecular-level understanding of this catalyst are summarized: (1) The nature of the active sites and, in particular, their transformations under varying reaction conditions that include dehydration, the presence of the various SCR reactants and hydrothermal aging; (2) Discussions of standard and fast SCR reaction mechanisms. Considerable progress has been made, especially in the last couple of years, on standard SCR mechanisms. In contrast, mechanisms for fast SCR are much less understood. Possible reaction paths are hypothesized for this latter case to stimulate further investigations; (3) Discussions of rational catalyst design based on new knowledge obtained regarding catalyst stability, overall catalytic performance and mechanistic catalytic chemistry.

Elucidating aging mechanisms in real-world applications is a critical component for developing and maintaining Cu/SSZ-13 SCR catalysts. To reveal gaps between laboratory accelerated aging and real-world aging, herein we report thorough comparative studies between 6 representative catalysts. We apply a wide range of catalyst characterization methods to gain atomic-level knowledge on Cu transformation under different aging protocols, including surface area/porosity analysis, X-ray diffraction (XRD), H 2 -temperature programmed reduction, NH 3 -temperaure programmed desorption, solid-state nuclear magnetic resonance (NMR), in situ X-ray photoelectron (XPS) and electron paramagnetic resonance (EPR) spectroscopies. We then correlate such knowledge to SCR, NH 3 /NO oxidation kinetic behavior of the catalysts. We found that sulfur aging plays the most important role in interpreting catalyst degradation during real-world application, including direct sulfur poisoning of isolated CuII SCR active species to CuSO 4 -like species, the agglomeration of such species to multinuclear CuSO 4 clusters, and eventually, CuO formation during desulfation treatments. Such chemistries convert SCR active Cu to SCR inert Cu moieties without severely deteriorating catalyst support integrity. These characteristics are partially replicated by hydrothermal aging in the presence of SOx but are poorly mimicked by hydrothermal aging alone. [Display omitted] • Hydrothermal aging treatment has a minor influence on low-temperature SCR. • High-mileage samples undergo hydrothermal aging less severely than lab-aged samples. • SCR performance of high-milage samples is more adversely impacted by sulfur poisoning. • Formation of p -Z 2 CuII species is indicative of hydrothermal aging severity. • Formation of multinuclear CuSO 4 species is indicative of sulfur aging severity. [ABSTRACT FROM AUTHOR]

In this study, we have developed a multi-site kinetic model that describes the sulfur poisoning and gradual sulfur removal over Cu/SSZ-13 used for NH 3 -SCR. Sulfur poisoning was conducted under SCR conditions and thereafter, repeated SCR experiments were conducted to examine the effect of such poisoning and the subsequent gradual removal of sulfur. In addition, the effect of sulfur poisoning was examined on NH 3 TPD and ammonia oxidation experiments. The following sites were used in the kinetic model: copper in the six-membered rings as described by S1 Cu , copper in the larger cages with S2 and S3 as a site where physisorbed ammonia can attach. Further, ammonia was also adsorbed on the Brönsted sites, represented by S1 Brön in the model, but in order not to further complicate the model, small amounts of ammonia storage on Brönsted sites were also lumped into S2. In the model, SO 2 was adsorbed on the sites containing copper, which are S1 Cu and S2. It should be noted that S1 Cu and S2 represents hydrated copper sites. Interestingly, we observed experimentally that ammonia storage was larger after sulfur poisoning compared to before, which is why we added ammonia storage and desorption to the S1 Cu –SO 2 and S2–SO 2 sites. However, ammonia was already adsorbing on the copper site; thus, these steps did not result in increased storage. Consequently, reaction steps were added where additional ammonia was adsorbed to form S1 Cu –SO 2 –(NH 3 ) 2 and S2–SO 2 –(NH 3 ) 2 species, which could be interpreted as precursors to ammonium sulfates. Another aspect that must be addressed in the model is the observation in the literature that SO 2 is more easily desorbed in SO 2 + NH 3 + O 2 TPD than SO 2 + O 2 TPD. Reversible reaction steps were therefore added whereby the S1 Cu –SO 2 –NH 3 and S2–SO 2 -NH 3 species were decomposed to form SO 2. A final reaction step was incorporated into the model to describe the SCR reaction with ammonia attached to the sulfur sites. The developed model could well describe the sulfur poisoning and gradual regeneration during repeated SCR experiments. In addition, the model well described the NH 3 TPD and NH 3 oxidation before and after sulfur poisoning. [ABSTRACT FROM AUTHOR]

In this study, the ammonia-SCR process was investigated using 2.5 wt.% Cu/BEA, 2.6 wt.% Cu/SAPO-34 and 3.1 wt.% Cu/SSZ-13. Several reactions such as NO oxidation, ammonia oxidation, standard SCR, fast SCR and NO 2 SCR were studied to understand the effect of zeolite type. It was found that the small-pore zeolites/silicoaluminophosphates with CHA structure (Cu/SAPO-34 and Cu/SSZ-13) exhibited higher SCR activity at 150 °C and lower selectivity toward N 2 O formation during standard SCR conditions than Cu/BEA. However, formation of ammonium nitrate species during fast SCR conditions at 150 °C occurred over Cu/CHA catalysts, which resulted in a gradual decrease of the NO x conversion. Such blocking was also observed over Cu/BEA, albeit to a minor extent. The ammonium nitrate formation and its decomposition temperature regimes resulted in that the Cu/BEA was catalytically more active at lower temperature than either Cu/SAPO-34 or Cu/SSZ-13 during fast SCR conditions. Additionally, our results show that the ammonium nitrate species were more stable on the small-pore zeolites than on Cu/BEA. Comparing the two Cu/CHA catalysts, Cu/SAPO-34 and Cu/SSZ-13, it was found that ammonia oxidation at high temperatures and ammonia SCR at 150 °C was higher on Cu/SAPO-34. Further, TPR experiments showed that Cu in Cu/SAPO-34 is more easily reduced compared to Cu/SSZ-13. This can facilitate the redox processes and can thereby be a reason for the higher activity at 150 °C for Cu/SAPO-34. In addition, Cu/SAPO-34 forms less N 2 O and this might be a result of the formation of more stable ammonium nitrates. To conclude, the choice of the type of zeolite/silicoaluminophosphates affects the activity and selectivity of the different steps in the SCR process. [ABSTRACT FROM AUTHOR]

Cu/SSZ-13 catalysts with three Si/Al ratios of 6, 12 and 35 were synthesized with Cu incorporation via solution ion exchange. The implications of varying Si/Al ratios on the nature of the multiple Cu species that can be present in the SSZ-13 zeolite are a major focus of this work, as highlighted by the results of a variety of catalyst characterization and reaction kinetics measurements. Specifically, catalysts were characterized with surface area/pore volume measurements, temperature programmed reduction by H 2 (H 2 -TPR), NH 3 temperature programmed desorption (NH 3 -TPD), and DRIFTS and solid-state nuclear magnetic resonance (NMR) spectroscopies. Catalytic properties were examined using NO oxidation, ammonia oxidation, and standard ammonia selective catalytic reduction (NH 3 -SCR) reactions on selected catalysts under differential conditions. Besides indicating the possibility of multiple active Cu species for these reactions, the measurements are also used to untangle some of the complexities caused by the interplay between redox of Cu ion centers and Brønsted acidity. All three reactions appear to follow a redox reaction mechanism, yet the roles of Brønsted acidity are quite different. For NO oxidation, increasing Si/Al ratio lowers Cu redox barriers, thus enhancing reaction rates. Brønsted acidity appears to play essentially no role for this reaction. For standard NH 3 -SCR, residual Brønsted acidity plays a significant beneficial role at both low- and high-temperature regimes. For NH 3 oxidation, no clear trend is observed suggesting both Cu ion center redox and Brønsted acidity play important and perhaps competing roles. [ABSTRACT FROM AUTHOR]

In this study, we have developed a kinetic model for ammonia-SCR over a well-characterized Cu/SSZ-13 catalyst. It was found that a three-site model was needed in order to describe the ammonia temperature programmed desorption (TPD) with adsorption at 50 and 150 °C as well as ammonia oxidation, and NH 3 -SCR up to 600 °C. Based on literature studies, where detailed characterization of Cu/SSZ-13 have been conducted using several experimental techniques, we suggest the following physical interpretation of the S1 and S2 sites in the model. The S1 sites are associated with copper located in a six-membered ring, possibly slightly distorted due to interactions with water and ammonia while, the S2 sites represent copper in the large cages or Cu x O y species. In addition, ammonia is also stored on Brönsted acid sites, but in order not to complicate the model further, it was lumped together in the S1 and S2 sites. Finally, S3 sites have been added in order to describe the large amount of physisorbed ammonia at low temperature. This three-site model was capable of adequately describing the ammonia TPD experiments with the initial temperature of 50 and 150 °C. The heats of adsorption of ammonia on the S1 and S2 sites were determined using micro-calorimeter experiments. Further, the main SCR reaction in the model occurs on S1 sites and the main ammonia oxidation reaction on S2 sites. However, due to the complex behavior associated with ammonia oxidation, where the conversion slightly decreased when the temperature was increased from 350 to 400 °C, an ammonia oxidation reaction occurring at low temperature with low rate needed to be introduced on S1. In a similar way, an added step was needed for ammonia-SCR on S2, which occurred at high temperature where the ammonia coverage on S1 was low resulting in low conversion. To summarize, the three-site model developed was capable of well describing the ammonia storage and release, ammonia oxidation as well as SCR and N 2 O formation across a broad temperature interval (100–600 °C). [ABSTRACT FROM AUTHOR]

Cu/SSZ-13 catalysts with Si/Al = 6 and various Cu/Al ratios are synthesized with solution ion exchange. Catalysts are characterized with surface area/pore volume measurements, Temperature Programmed Reduction (TPR), and Electron Paramagnetic Resonance (EPR) spectroscopy. Catalytic properties are examined using NO oxidation, ammonia oxidation, and standard ammonia selective catalytic reduction (NH 3 -SCR) reactions. Prior to full dehydration of the zeolite catalysts, hydrated Cu 2+ ions are found to be very mobile as judged from EPR. NO oxidation is catalyzed by O-bridged Cu-dimer species that form at relatively high Cu loadings and in the presence of O 2 . For NH 3 oxidation on samples with low to intermediate Cu loadings, transient Cu-dimers are the low-temperature (⩽300 °C) active centers, while these dissociate to monomers at 350 °C and above and become active centers. For the much more complex standard SCR reaction, transient Cu-dimers are the active sites for reaction temperatures <250 °C at very low Cu loadings (Cu/Al ⩽ 0.016). Between ∼250 and 350 °C, these Cu-dimers become less stable causing SCR reaction rates to decrease. At temperatures ⩾350 °C, Cu 2+ monomers that had migrated to faces of 6-membered rings are the active sites. At intermediate Cu loadings, monomeric Cu 2+ ions are also active in SCR in the low-temperature regime; these are proposed to be located within CHA cages and next to 8-membered rings, likely in the form of [Cu(OH)] + . At high Cu loadings (i.e., more than one Cu 2+ ion in each unit cell), stable Cu-dimers form and these do not dissociate at temperatures above 350 °C. These moieties effectively occupy CHA cage space and block pore openings causing decreased efficiency of the catalysts. Also these moieties are highly active in catalyzing the NH 3 oxidation reaction thus causing SCR selectivities to decrease above ∼450 °C. Finally, our kinetics results strongly support a redox mechanism for standard SCR. [ABSTRACT FROM AUTHOR]

[Display omitted] • Methane-to-methanol reactions depend on zeolite crystal structure and Brønsted acid sites. • Different active Cu sites for methane-to-methanol and NH 3 -SCR were found. • [CuII(OH)]+ and Cu x O y cluster species are important active sites for methane-to-methanol. • Apparent differences of hydrothermal stability in methane-to-methanol and SCR reactions were revealed. This study investigated and compared the reactivities of NH 3 -SCR and methane-to-methanol reactions over the monolithic Cu/SSZ-13 catalysts with different zeolite crystal sizes before and after hydrothermal aging. It was found that the methanol yield decreases with the increase in crystal size in methane-to-methanol, and a severe deactivation was detected after aging. However, the NH 3 -SCR performance presents a higher thermal stability and even an enhanced low-temperature reactivity after aging. The fresh and aged catalysts were comprehensively characterized by XRD, SEM, N 2 physisorption, NH 3 -TPD, H 2 -TPR, XPS, UV–vis-NIR and in-situ DRIFTS measurements. The results indicate that the isolated Cu2+ species, including those that interacted with two Al in 6MR and [CuII(OH)]+ motifs, and acid sites are main active centers for NH 3 -SCR. While Cu x O y clusters, [CuII(OH)]+ motifs and Brønsted acid sites in the Cu-CHA frameworks could be important active sites for methane-to-methanol. Besides, the stable SCR performance is ascribed to the stable textural property, higher crystallinity of zeolite, increased NH 3 storage capacity and isolated Cu2+ active sites. The loss of the catalytic activity in methane-to-methanol is mainly attributed to the decrease of Brønsted acid sites and Cu x O y concentration and the break of zeolite crystal structure. This work concludes the differences in active sites and hydrothermal stability between NH 3 -SCR and methane-to-methanol reactions, it is very helpful to understand the two reactions. [ABSTRACT FROM AUTHOR]

In real-world application, Cu/SSZ-13 simultaneously suffers severe deactivation from hydrothermal aging and SO 2 poisoning during the periodic regeneration of diesel particulate filter (DPF). Herein, we first investigated the synergistic deactivation mechanism of hydrothermal aging and SO 2 poisoning on Cu/SSZ-13 under SCR condition. Hydrothermal aging alone induces more severe degradation of selective catalytic reduction (SCR) performance than SO 2 poisoning alone, while the presence of SO 2 during hydrothermal aging causes further worse SCR performance compared with hydrothermal aging alone. Hydrothermal aging not only damages Si-OH-Al sites, particularly in four-membered ring (4MR) of the CHA cage, but also brings the conversion of ZCuOH, leading to the formation of inactive CuO/CuAlO x species. By contrast, SO 2 poisoning alone is more prone to promote the transformation of ZCuOH to Z 2 Cu. Synergistic deactivation of hydrothermal aging and SO 2 poisoning would exacerbate the damage of Si-OH-Al sites and then the formation of CuO/CuAlO x species. These results are expected to assist the knowledge-based catalyst design for diesel aftertreatment applications.

To improve the alkali metal resistance of commercial catalyst Cu/SSZ-13 for ammonia selective catalytic reduction (NH3-SCR) reaction, a simple method to synthesize Cu/SSZ-13 with a core–shell like structure was developed. Compared with smaller-sized counterparts, Cu/SSZ-13 with a crystal size of 2.3 μm exhibited excellent resistance to Na poisoning. To reveal the influence of the crystal size on Cu/SSZ-13, physical structure characterization (XRD, BET, SEM, NMR) and chemical acidic distribution (H2-TPR, UV-Vis, Diethylamine-TPD, pyridine-DRIFTs, EDS) were investigated. It was found that the larger the crystal size of the molecular sieve, the more Cu is distributed in the crystal core, and the less likely it was to be replaced by Na to generate CuO. Therefore, a 2.3 μm sized Cu/SSZ-13 well-controlled the reactivity of the side reaction NH3 oxidation and the generation of N2O. The result was helpful to guide the extension of the service life of Cu/SSZ-13. [ABSTRACT FROM AUTHOR]

• The impact of sulfur poisoning and regeneration on Cu/SSZ-13. • Regeneration could not totally recover the efficiency of sulfured catalysts. • Different sulfate species formed on the main active sites of Cu/SSZ-13. • SO 2 was oxidized by Cu x O y species, and Si-O(H)-Al bond could not be poisoned without active metal species. • Active sites and nitrates/nitrites storage capacity decreased after sulfur poisoning. This study focuses on exploring the impact of sulfur poisoning and regeneration on the performance and active sites of Cu/SSZ-13 catalyst. It was found that sulfured samples had obviously lower conversion than fresh samples below 350 °C, and thermal regeneration at 550 °C could not totally remove sulfate species. These catalysts were also comprehensively characterized by H 2 -TPR, TPD, NH 3 -TPO, NO-TPO, and BET. SO 2 and NH 3 co-adsorbed on the Z 2 Cu sites to form ammonia sulfate species, however, they went through the two-step decomposition reaction during regeneration. SO 2 interacted more tightly with ZCuOH to form copper bisulfite species. SO 2 was oxidized by Cu x O y species to further form sulfate species. Si-O(H)-Al bond could be sulfur poisoned when Cu species in the catalysts. Additionally, sulfated species could block pores, but not lead to structure collapse. Furthermore, in situ DRIFTS results illustrated that active sites and nitrates/nitrites storage capacity decreased after sulfur poisoning. [ABSTRACT FROM AUTHOR]

• Cu/SSZ-13 catalysts with different [Cu(OH)]+ and Cu2+ sites were synthesized. • Poisoning of Cu2+ involves P 2 O 5 , but for [Cu(OH)]+, involving PO 3 − and PO 4 3−. • Phosphorus poisoning results in low hydrothermal stability. • Upon aging, [Cu(OH)]+−phosphate/ metaphosphate is easier to detach from the framework. • The formation of AlPO 4 has a linear relationship with [Cu(OH)]+/Cu2+ ratios. Non-poisoned and P-poisoned Cu/SSZ-13 catalysts with different types of Cu sites, i.e., [Cu(OH)]+ and Cu2+, were investigated for NH 3 -SCR. Phosphorus was found to interact more with [Cu(OH)]+ than Cu2+. Moreover, less phosphorus was required per Cu for poisoning in the samples with a high content of [Cu(OH)]+. We propose a phosphorus poisoning mechanism based on H 2 -TPR and XPS: poisoning of one Cu2+ involved two P atoms, i.e., P 2 O 5 , but for [Cu(OH)]+ contamination, only one P atom (PO 3 − or PO 4 3−) is needed. Furthermore, phosphorus poisoning resulted in a decline in NH 3 /NO oxidation and an improvement in SCR activity at high temperatures. Upon hydrothermal aging, [Cu(OH)]+−phosphate/metaphosphate complexes were likely easier detached from the framework than the Cu2+−P 2 O 5 species. This resulted in that the P-poisoned catalyst with high content [Cu(OH)]+ experienced more severe deactivation and dealumination than the non-poisoned catalyst. Additionally, 27Al-NMR suggested that the formation of AlPO 4 has a linear relationship with [Cu(OH)]+/Cu2+ ratios. [ABSTRACT FROM AUTHOR]

The Cu/SSZ-13 catalyst can provide multiple active sites for the ammonia selective catalytic oxidation (NH 3 -SCO), the influence of which can be tuned by varying the Si/Al ratio. The latter parameter was found to influence the surface acidic property and the Cu species distribution, which are critical for NH 3 adsorption and activation. It was found that both CuO and isolated Cu2+ ions coexist in Cu/SSZ-13 catalyst. The selected Si/Al-20 sample with the highest content of CuO species and abundant acidity exhibited the best NH 3 -SCO performance. Unlabelled Image • Acidic property and Cu2+ species of Cu/SSZ-13 are systemically tuned by varying Si/Al ratio. • Cu/SSZ-13 (Si/Al-20) shows excellent NH3-SCO activity due to the proper ratio of CuO and Cu2+ ions. • Cu/SSZ-13 with CuO and isolated Cu2+ ions acting as multiple active sites follows i-SCR mechanism. [ABSTRACT FROM AUTHOR]

Lean nitric oxide (NOx)-trap (LNT) and selective catalytic reduction (SCR) are efficient systems for the abatement of NOx. The combination of LNT and SCR catalysts improves overall NOx removal, but there is a risk that the SCR catalyst will be exposed to high temperatures and rich exhaust during the LNTs sulfur regeneration. Therefore, the effect of exposure to various rich conditions and temperatures on the subsequent SCR activity of a Cu-exchanged chabazite catalyst was studied. CO, H2, C3H6, and the combination of CO + H2 were used to simulate rich conditions. Aging was performed at 800 °C, 700 °C, and, in the case of CO, 600 °C, in a plug-flow reactor. Investigation of the nature of Cu sites was performed with NH3-temperature-programed desorption (TPD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) of probe molecules (NH3 and NO). The combination of CO and H2 was especially detrimental to SCR activity and to NH3 oxidation. Rich aging with low reductant concentrations resulted in a significantly larger deactivation compared to lean conditions. Aging in CO at 800 °C caused SCR deactivation but promoted high-temperature NH3 oxidation. Rich conditions greatly enhanced the loss of Brønsted and Lewis acid sites at 800 °C, indicating dealumination and Cu migration. However, at 700 °C, mainly Brønsted sites disappeared during aging. DRIFT spectroscopy analysis revealed that CO aging modified the Cu2+/CuOH+ ratio in favor of the monovalent CuOH+ species, as opposed to lean aging. To summarize, we propose that the reason for the increased deactivation observed for mild rich conditions is the transformation of the Cu species from Z2Cu to ZCuOH, possibly in combination with the formation of Cu clusters. [ABSTRACT FROM AUTHOR]

• Selective catalytic reduction of NO x with NH 3 over Cu/SSZ-13. • Catalysts are prepared by one-pot synthesis method with different Si/Al ratios. • Cu/SSZ-13-6.5 shows the best NH 3 -SCR performance and hydrothermal stability. • Increasing Si/Al deteriorates physical-chemical properties of aged catalysts. • Increasing Si/Al decreases active sites, nitrate species, acidity of aged catalysts. This study focuses on investigating the influence of Si/Al ratio on the performance of hydrothermally aged Cu/SSZ-13 catalysts prepared by in situ hydrothermal synthesis method. It was found that NH 3 -SCR performance and hydrothermal stability of Cu/SSZ-13 decreased with increasing Si/Al ratio. Fresh and hydrothermally aged Cu/SSZ-13 with Si/Al ratio of 6.5 showed the best SCR activity and N 2 selectivity in a broad temperature of 200–500 °C, in which more than 90% NO x was reduced with superior N 2 selectivity above 95%. The effect of Si/Al ratio on the properties of the physicochemical structure, the change of acidity intensity, and Cu species migration or transformation of the fresh and aged Cu/SSZ-13 catalysts were comprehensively characterized by NH 3 -TPO, NH 3 -TPD, H 2 -TPR, N 2 physisorption, XRD, ICP-AES, and XPS. The increase of the surface CuO species, the decrease of the amount of Cu2+ in active sites, the chemisorption NH 3 species, the specific surface area, the total pore volume, and the increase of average pore diameter, may be the main reasons for performance deterioration over high-Si/Al-ratio catalysts after hydrothermal aging. Furthermore, in situ DRIFTS indicate that, with the increasing Si/Al ratio, the zeolitic structure was easy to collapse, and that the surface acid sites, the active copper species, as well as the adsorbed surface nitrate, decreased after hydrothermally aged. After hydrothermal aging, the amount of isolated Cu2+ decreased, and more CuO species were aggregated, mainly coming from the conversion of the unstable isolated Cu2+ species in D6R or CHA cages. The decrease of isolated Cu2+ and CuO species aggregation were significant in Cu/SSZ-13 with high Si/Al ratios. The CuO leaded to the instability of the SSZ-13 skeleton structure and NH 3 oxidation promotion, resulting in catalysts deactivation. [ABSTRACT FROM AUTHOR]

To reveal the role of SO3 poisoning in Cu/SSZ-13 NH3-SCR catalysts, fresh and sulfated Cu/SSZ-13 catalysts were prepared in the presence or absence of SO3 flux. The deactivation mechanism is probed by the changes of structural, copper species, and selective catalytic reduction (SCR) activity. The variations concentrate on the changes of copper species as the Chabazite (CHA) framework of Cu/SSZ-13 catalysts could keep intact at high ratios of SO3/SOx. The thermal gravimetric analyzer (TGA) results reveal that the copper sulfate formed during sulfation and the amounts of sulfate species increased with an increase in the SO3/SOx ratio. In contrast to the changing trend of copper sulfate, temperature program reduction (H2-TPR), and electron paramagnetic resonance (EPR) results manifest that, since the number of active copper ions declines with an increase of the SO3/SOx ratio, the active sites transform to these inactive species during sulfation. Due to the combination of NH3-SCR activity and the kinetic tests, it is shown that the decreased number of active sites is responsible for the declined SCR activity at low temperature. As Cu/SSZ-13 catalysts show excellent acid-resistance ability, our study reveals that the Cu/SSZ-13 catalyst is a good candidate for NOx elimination, especially when SO3 exists. [ABSTRACT FROM AUTHOR]

To reveal the role of impregnated sodium (Na) ions in Cu/SSZ-13 catalysts, Cu/SSZ-13 catalysts with four Na-loading contents were prepared using an incipient wetness impregnation method and hydrothermally treated at 600 °C for 16 h. The physicochemical property and selective catalytic reduction (SCR) activity of these catalysts were studied to probe the deactivation mechanism. The impregnated Na exists as Na+ on catalysts and results in the loss of both Brönsted acid sites and Cu2+ ions. Moreover, the high loading of Na ions destroy the framework structure of Cu/SSZ-13 and forms new phases (SiO2/NaSiO3 and amorphous species) when Na loading was higher than 1.0 mmol/g. The decreased Cu2+ ions finally transformed into CuxO, CuO, and CuAlOx species. The inferior SCR activity of Na impregnated catalysts was mainly due to the reduced contents of Cu2+ ions at kinetic temperature region. The reduction in the amount of acid sites and Cu2+ ions, as well as copper oxide species (CuxO and CuO) formation, led to low SCR performance at high temperature. Our study also revealed that the existing problem of the Na ions' effect should be well-considered, especially at high hydrothermal aging when diesel particulate filter (DPF) is applied in upstream of the SCR applications. [ABSTRACT FROM AUTHOR]

Cu/SSZ-13 Selective Catalytic Reduction (SCR) catalysts have been extensively studied for the past five-plus years. New and exciting fundamental and applied science has appeared in the literature quite frequently over this time. In this short review, a few topics specifically focused on a molecular-level understanding of this catalyst are summarized: (1) The nature of the active sites and, in particular, their transformations under varying reaction conditions that include dehydration, the presence of the various SCR reactants and hydrothermal aging; (2) Discussions of standard and fast SCR reaction mechanisms. Considerable progress has been made, especially in the last couple of years, on standard SCR mechanisms. In contrast, mechanisms for fast SCR are much less understood. Possible reaction paths are hypothesized for this latter case to stimulate further investigations; (3) Discussions of rational catalyst design based on new knowledge obtained regarding catalyst stability, overall catalytic performance and mechanistic catalytic chemistry. [ABSTRACT FROM AUTHOR]