Noble metal-exchanged small-pore molecular sieves withchabazite topology are promising materials for automotive cold-start NOxemission control applications. A combination offirst-principles thermody-namics and density functional theory was applied for the prediction ofmonomeric palladium, platinum, and ruthenium species formed in 1Al or 2Alsites of six-/eight-membered rings of the SSZ-13 framework in the presenceof SO2, NO, O2, and H2O at temperatures between 0 and 1100 K.Calculations using gradient-corrected Perdew-Burke-Ernzerhof (PBE)functional and hybrid Heyd-Scuseria-Ernzerhof (HSE06) functionalshowed that the binding energy of NO adsorbed on Pd, Pt, or Ru ions is astrong function of exchange-correlation functional. Use of the PBEfunctional overestimated the binding strengths of NO to Pd, Pt, or Ru ions compared to the HSE06 functional. While PBE ledto the adsorption of two NO per Pd, Pt, or Ru ion, HSE06 predicted the adsorption of a single NO. Isolated Pd, Pt, or Ru ions in 1Alsites tended to bind NO stronger than their counterparts in 2Al sites. Both functionals revealed that Pd and Pt ions have moresimilarities in terms of both NO adsorption and sulfur resistance compared to Ru ions. The results of this study are beneficial forfurther modeling of passive NOxadsorbers with improved properties to deliver cleaner tailpipe emissions during engine cold start

Biodiesel is a promising renewable fuel, which may help to limit our dependence on fossil fuels. However, the presence of contaminants in biodiesel can affect the Cu speciation of the Cu-SSZ-13 selective catalytic reduction (SCR) catalyst, resulting in its deactivation and decreased durability. In situ Cu K-edge X-ray absorption fine structure (XAFS) scanning during a temperature-programmed reduction in hydrogen (H-2-TPR) has been applied here for the analysis of Cu speciation in Cu-SSZ-13 catalysts aged using pure and contaminated biodiesel fuels. XAFS data were analyzed using the multivariate curve resolution alternating least-squares (MCR-ALS) method. While only reduction from Cu-II to Cu-I was observed at temperatures below 500 degrees C for the catalyst aged using pure biodiesel, a one-step reduction of Cu-II to Cu-0 at temperatures between 400 and 500 degrees C was found for the catalyst aged using P-doped biodiesel. The transformation of isolated CuII species to Cu-II clusters was suggested for the catalyst as a result of aging using P-doped biodiesel. The catalyst aged using S-doped biodiesel showed mainly the reduction of isolated Cu-II to Cu-I, which was inhibited as compared to that observed for the catalyst aged using pure biodiesel. The reduction of the catalyst aged using P+S-doped biodiesel led to the reduction of Cu-II to both Cu-I and Cu-0. The phosphorus was responsible for the formation of Cu-II clusters during aging of the catalyst using P+S-doped biodiesel. This study reveals that the presence of phosphorus in biofuels should be strictly regulated to avoid major changes in the Cu speciation of Cu-SSZ-13 catalysts.

Fresh and SO₂-poisoned Cu-SSZ-13 selective catalytic reduction (SCR) catalysts were studied using near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) in the presence of NH₃, O₂, and NO, as well as by in situ X-ray absorption spectroscopy (XAS) using H₂, He, and CO. In contrast to the fresh catalyst, inhibited reduction of Cu-species and the absence of Cu-metal nanoparticles was found in the SO₂-poisoned catalyst during heating/cooling in H₂ and CO. High structural disorder and differences in the formation of Cu-carbonyl species were seen for the SO₂-poisoned catalyst compared to the fresh catalyst. Suppressed oxidation-reduction and low mobility of Cu-species during exposure to NH₃-SCR-related gases were observed in the SO₂-poisoned catalyst, unlike in the fresh catalyst. These observations help explain catalyst deactivation during the standard NH₃-SCR reaction. The formation of Cu-metal nanoparticles in the fresh catalyst revealed another possible deactivation pathway for the SCR-catalyst in combined LNT-SCR systems during fuel-rich periods.

Two different SCR catalysts, V2O5-WO3/TiO2 and Cu-SSZ-13, were exposed to biodiesel exhausts generated by a diesel burner. The effect of phosphorus and sulfur on the SCR performance of these catalysts was investigated by doping the fuel with P-, S-, or P + S-containing compounds. Elemental analyses showed that both catalysts captured phosphorus while only Cu-SSZ-13 captured sulfur. High molar P/V ratios, up to almost 3, were observed for V2O5-WO3/TiO2, while the highest P/Cu ratios observed were slightly above 1 for the Cu-SSZ-13 catalyst. Although the V2O5-WO3/TiO2 catalyst captured more P than did the Cu-SSZ-13 catalyst, a higher degree of deactivation was observed for the latter, especially at low temperatures. For both catalysts, phosphorus exposure resulted in suppression of the SCR performance over the entire temperature range. Sulfur exposure, on the other hand, resulted in deactivation of the Cu-SSZ-13 catalyst mainly at temperatures below 300-350 °C. The use of an oxidation catalyst upstream of the SCR catalyst during the exhaust-exposure protects the SCR catalyst from phosphorus poisoning by capturing phosphorus. The results in this work will improve the understanding of chemical deactivation of SCR catalysts and aid in developing durable aftertreatment systems. 

A combination of first-principles thermodynamics and density functional theory (DFT) was applied for the prediction of sulfur-poisoned monomeric Cu/Fe species formed in the SSZ-13 catalyst framework under selective catalytic reduction (SCR)-relevant conditions in the presence of sulfur dioxide, ammonia, oxygen, and water. Differences in fresh and sulfur-poisoned species were found for Cu- and Fe-SSZ-13 catalysts containing one Al (1Al sites) or two Al (2Al sites) in 6-membered rings (6MRs) or 8-membered rings (8MRs). The impact of ammonia concentration during low-and high-temperature sulfur-poisoning on Cu- and Fe-speciation was also investigated. SCR-relevant concentrations of ammonia in the gas mixture led to the formation of ammonium sulfates over copper in 2Al and 1Al sites of Cu-SSZ-13, while bisulfate and sulfuric acid species were predicted at these copper sites either in the absence of ammonia or at negligible concentrations of ammonia during low- and high-temperature poisoning. The absence of ammonia in the gas mixture led to the formation of iron-bisulfates at 2Al sites of Fe-SSZ-13 during low- temperature poisoning, while the formation of ammonium sulfates was favorable under SCR-relevant conditions. In contrast to the facile formation of ammonium sulfates at copper sites of Cu-SSZ-13, only ammonium-free iron-sulfates formed at 1Al sites in Fe-SSZ-13 under realistic operational conditions. The regeneration of 2Al sites of Cu-SSZ-13 was predicted to occur at higher temperatures compared to 2Al sites in Fe-SSZ-13, whereas the opposite was predicted for 1Al sites. The analysis of fresh and regenerated Cu/Fe species was carried out as well. These theoretical results on model catalysts provide a first step in the understanding of sulfur-poisoning in Fe-SSZ-13 catalysts, supporting further experimental investigations to improve NH3-SCR catalysts for meeting future emission standards.

In situ Cu and S K-edge X-ray absorption spectroscopy (XAS) was used for the investigation of sulfur-poisoned and regenerated Cu-SSZ-13 selective catalytic reduction (SCR) catalysts. Highly dispersed sulfur in the oxidation state +6 was found in the catalysts. Even though a similar amount of sulfur was deposited in the catalysts poisoned at both 200 and 500 °C, a higher fraction of sulfur-free Cu species was seen for the catalyst poisoned at the higher temperature. Regeneration at 550 °C resulted in more sulfur-free Cu species in the catalyst poisoned at 500 °C, even though a higher amount of sulfur was detected in this catalyst compared to the regenerated catalyst poisoned at 200 °C. Inconsistencies between the amount of sulfur and the fraction of sulfur-free Cu species were attributed to the additional sulfur storage at sites that do not involve Cu. It was suggested that increased temperature of poisoning may facilitate the formation of Al sulfates along with Cu sulfates. These results provide the next step in detailed understanding of sulfur poisoning and regeneration of Cu-SSZ-13 catalysts.

Regeneration of a sulfur-poisoned Cu-SSZ-13 catalyst via a temperature ramp in an inert atmosphere with subsequent holding under oxidizing conditions at 500 degrees C restores significant activity for NOx conversion under standard, fast, and NO2-rich SCR conditions. The N2O selectivity of the regenerated catalyst is higher than for the fresh catalyst under NO2-rich SCR conditions at 280 degrees C, while the opposite was observed for the standard and fast SCR conditions. Analysis of copper speciation showed that sulfur-free Cu species have different conditiondependent behavior in the fresh and regenerated catalysts. Heating the poisoned catalyst in an oxidizing atmosphere transforms a portion of ammonium sulfates into stable metal sulfates, while heating under inert or reducing conditions leads to more effective desulfation without the formation of stable metal sulfates. Reducing conditions result in desulfation at lower temperatures compared to inert conditions. These results contribute to the further development of regeneration strategies for Cu-SSZ-13 catalysts.

The effect of phosphorus poisoning on the catalytic behavior of diesel oxidation catalysts was investigated over model and supplier monolith catalysts,i.e., Pd-Pt/Al2O3. The results of ICP and XPS from the vapor-phase poisoning over model catalysts suggested that the temperature of phosphorus poisoning affects both the overall content of phosphorus and the dispersion of phosphorus (i.e., inlet/outlet and surface/bulk). Phosphorus oxide (P2O5), metaphosphate (PO3-), and phosphate (PO43-) were identified in the poisoned model and supplier catalysts. The distribution of these species on poisoned model catalysts was highly dependent on the poisoning temperature,i.e., a higher temperature resulted in a higher concentration of PO43-. The outlets of the monoliths contained more PO(4)(3-)and less P(2)O(5)than the inlets. Both active sites and surface OH groups on model and supplier catalysts were contaminated upon phosphorus poisoning. It is found that PO(4)(3-)had a stronger influence on the active sites than P2O5. One significant finding in this study is that the vapor-phase phosphorus poisoning could be a practical and cost efficient approach to simulate an accelerated aging/poisoning process.

We have investigated how the exhaust gases from a heavy-duty Euro VI engine, powered with biogas impact a vanadium-based selective catalytic reduction (SCR) catalyst in terms of performance. A full Euro VI emission control system was used and the accumulation of catalyst poisons from the combustion was investigated for the up-stream particulate filter as well as the SCR catalyst. The NO(x)reduction performance in terms of standard, fast and NO2-rich SCR was evaluated before and after exposure to exhaust from a biogas-powered engine for 900 h. The SCR catalyst retains a significant part of its activity towards NO(x)reduction after exposure to biogas exhaust, likely due to capture of catalyst poisons on the up-stream components where the deactivation of the oxidation catalyst is especially profound. At lower temperatures some deactivation of the first part of the SCR catalyst was observed which could be explained by a considerably higher surface V4+/V(5+)ratio for this sample compared to the other samples. The higher value indicates that the reoxidation of V(4+)to V(5+)is partially hindered, blocking the redox cycle for parts of the active sites.

Catalytic emission control is used to reduce the negative impact of pollutants from diesel exhausts on our health and on the environment. For a heavy-duty truck, such a system consists of a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), a selective catalytic reduction (SCR) catalyst, and an ammonia slip catalyst (ASC). Due to greenhouse-gas induced global warming, it is necessary to decrease the emissions of such gases. Two strategies for this reduction are: 1) to produce engines that are more fuel efficient, 2) to use sustainably produced renewable fuels such as biodiesel and HVO. However, both these strategies may pose additional challenges for the emission control system: a colder exhaust due to the higher fuel-efficiency requires the use of highly active catalysts; catalyst deactivation related to impurities in biofuels, which requires very robust catalysts.   The objective of this thesis was to study the impact of biofuel as well as lubrication oil-related contaminants on the performance of emission control catalysts (DOC and SCR catalysts) for heavy-duty diesel engines. The main focus has been on the low-temperature performance of V2O5-WO3/TiO2 (VWTi) and Cu-SSZ-13 SCR catalysts.    Results from the project have shown that both Cu-SSZ-13 and VWTi catalysts capture and can be deactivated by phosphorus (P), while only the Cu-SSZ-13 is deactivated by sulfur (S). The degree of the P-related deactivation depends on the concentration in the catalyst, which depends on content of P in the exhaust and the exposure time, as well as the type of catalyst. S-deactivation of Cu-SSZ-13 is observed at low temperatures, where un-poisoned Cu-SSZ-13 are significantly more active than VWTi catalysts. As a contrast, the VWTi-performance can even be improved by sulfur; but alkali metals are severe poisons to VWTi catalysts. Partial performance-recovery of S-poisoned Cu-SSZ-13 can be obtained by exposing it to sulfur-free exhausts at elevated temperatures. The use of an upstream DOC, providing fast SCR conditions to the SCR catalyst, considerably improves the low-temperature performance of the VWTi, as well as sulfur-poisoned Cu-SSZ-13 catalysts. An upstream DOC also protects the SCR catalysts from phosphorus deactivation, as it can trap large amounts of P. However, if too much phosphorus is captured by the DOC, severe deactivation of this catalyst results, which lowers the overall performance of the exhaust treatment system.  Insights from this project will guide the development of robust exhaust treatment systems for various applications. Additionally, it could aid in developing more durable emission control catalysts.

Katalytisk avgasrening används för att minska de negativa hälso- och miljöeffekterna av dieselavgaser. För tunga lastbilar består detta avgasreningssystem av flera komponenter, dieseloxidationskatalysator (DOC), partikelfilter, SCR-katalysator och ammoniaköverskottskatalysator. I och med de klimatnegativa effekterna av växthusgaser, inkl. koldioxid, måste även emissionerna av dessa från tunga fordon minska. Två sätt att uppnå detta är att 1) producera mer bränsleeffektiva motorer, 2) använda förnybara bränslen såsom biodiesel och hydrerad växtolja (HVO). Båda dessa strategier kan dock medföra tuffa utmaningar för efterbehandlingssystemet – kallare avgaser respektive katalysatordeaktivering relaterad till kontamineringsämnen i biobränslena. Detta kräver att katalysatorerna är både aktiva och tåliga.  Syftet med detta doktorandprojekt har varit att studera effekten av biobränsle- och motoroljerelaterade kontamineringsämnens påverkan på avgasreningskatalysatorer för tunga dieselmotorer.  Huvudfokuset har varit påverkan på lågtemperaturegenskaperna hos två olika typer av SCR-katalysatorer, V2O5-WO3/TiO2 (VWTi) och Cu-SSZ. Resultat från projektet har visat att fosfor kan ackumuleras i både VWTi och Cu-SSZ-13 och deaktivera dessa, medan svavel endast deaktiverar Cu-SSZ-13. Denna deaktivering syns vid låga temperaturer där Cu-SSZ-13 annars har en betydligt bättre prestanda än VWTi. Prestandan för svavelförgiftad Cu-zeolit kan delvis fås tillbaka genom att öka temperaturen i avgaserna i svavelfri miljö. Närvaro av ammoniak i avgasen underlättar regenereringen. VWTi-katalysatorn är däremot inte känslig för svavel utan får snarare en något förbättrad prestanda. Däremot är alkalimetaller ett starkt gift för VWTi.  En uppströms DOC kan väsentligt förbättra lågtemperaturprestandan för VWTi och för svavelförgiftad Cu-SSZ-13 genom att förse dessa med NO2 så att snabb SCR kan uppnås. DOCn kan också skydda SCR-katalysatorer från fosforförgiftning genom att själv fånga upp fosfor. För mycket fosfor på DOCn resulterar dock i förgiftning även av denna, vilket påverkar resten av avgasbehandlingssystemet negativt. Resultaten från detta projekt kan användas för att utveckla robusta avgasbehandlingssystem för olika typer av tillämpningar, och kan bidra till utvecklandet av mer tåliga katalysatorer.