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Simultaneous poisoning of sulfur + phosphorus on a platinum-based diesel oxidation catalyst was studied to gain a deeper understanding on the catalyst deactivation. Compared to a single poisoning (sulfur or phosphorus), the simultaneous poisoning had a severe effect on the catalyst activation: light-off temperature for 90% conversion of propene was not reached, this of carbon monoxide was much higher than expected, and the maximum conversion of nitrogen monoxide collapsed. With very comprehensive structural characterization by various methods (e.g. STEM-EDS, XPS, DRIFTS) used, we achieved to conclude an explanation for this. In the case of the S + P-poisoning of the catalyst, formed aluminum phosphate was found to block adsorption sites for sulfur species on alumina and sulfur adsorbs mainly on cerium oxides. In addition, sulfur species remain with and in the vicinity of the platinum particles blocking active sites. publishedVersion

Natural gas is an alternative fuel to replace partly conventional liquid fuels like diesel or gasoline to improve fuel economy (less CO2) and decrease pollutants (particulates). Mixed stoichiometric–lean combustion has been introduced as a potential way to manage without secondary diesel fuel. This study focused on catalytic methods to oxidize methane, HCs, CO and NO in lean-stoichiometric NG and lean diesel–NG exhaust gases in heavy-duty applications. Lean methane oxidation is the most challenging condition and only methane oxidation catalyst (MOC) developed for lean conditions was able to reach low methane light-off temperatures. MOC was almost as good as three-way catalyst (TWC) in stoichiometric conditions but the heavier ageing and λ oscillating conditions cause problems for MOC (no oxygen storage materials). Diesel oxidation catalysts (DOC) were very poor in TWC reactions but Pt-rich DOC is important to reach in lean higher NO2 utilized in DPF regeneration and SCR. In TWC + MOC, DOC + MOC combinations, the MOC part dominated methane oxidations due to that significant difference in their base activity for methane oxidation. The combinatory systems showed also in deactivation–regeneration cycles promising and interesting results, which can be utilized in transient, heterogeneous exhaust conditions.

Natural gas as a fuel for heavy duty applications has advantages in terms of lower CO2 and PM compared to Diesel applications. This makes operating heavy duty applications on natural gas attractive. However, in terms of aftertreatment, the challenge becomes one of controlling methane emissions over a range of vehicle operating conditions. Methane light off occurs > 400 °C and requires highly loaded precious metal catalysts (Raj in Johnson Matthey Technol Rev 60:228–235, 2016). This temperature is manageable in stoichiometric applications. However, for lean operating applications, the exhaust temperature can be below this posing a significant challenge for CH4 control. When operating lean the NOx emissions also become a challenge hence the requirement for a dedicated NOx control system. As part of the EU funded HD GAS project, an aftertreatment system was developed to meet the challenges of both NOx and CH4 control for a lean operating natural gas heavy duty engine. Fundamental studies were performed by the academic partners focusing on CH4 and NOx control, with the implementation and calibration on the engine performed by the industrial partners. This paper will discuss the steps taken from fundamental catalyst characterisation and catalyst specification to full size catalyst implementation onto a newly developed natural gas engine in order to meet Euro VI emissions legislation.

Catalytic combustion of methane, the main component of natural gas, is a challenge under lean‐burn conditions and at low temperatures owing to sulfur poisoning of the Pd‐rich catalyst. This paper introduces a more sulfur‐resistant catalyst system that can be regenerated during operation. The developed catalyst system lowers the barrier that has restrained the use of liquefied natural gas as a fuel in energy production.

An increasing number of heavy-duty vehicles are using liquefied natural gas (LNG) as a fuel due to the expanding refuelling station network for LNG and lower overall emissions compared to diesel vehicles. The latest EURO VI regulation or natural gas fuelled vehicles set a limit for NH3 of 10 ppm, and N2O exhaust is expected to be restricted in Europe in the near future. Poisonous and corrosive NH3 and the greenhouse gas N2O are formed as by-products in a three-way catalyst used to minimize the emissions of stoichiometric heavy-duty engines. In this work, we studied how high temperature NH3 and N2O formed in modern, fresh and aged bimetallic Pd/Rh three-way catalysts in simulated exhaust gas. More precisely, the exhaust gas composition and temperature were examined. Decreases in NO concentration and increases in temperature lowered the formation of NH3 and N2O, whereas a decrease in CH4 concentration reduced only NH3 formation. According to Raman and powder X-ray diffraction experiments, the structure of the catalyst changed during the ageing, and this reputedly affected the function of cerium-zirconium mixed oxides and thus the formation of NH3 and N2O. Temperature programmed reduction (H2-TPR) measurements showed changes in cerium-zirconium mixed oxide performance after ageing supporting Raman spectroscopy findings. Catalyst ageing in oxidizing conditions increased the formation of N2O. This study showed that exhaust gas composition plays an important role in the formation of undesired NH3 and N2O emissions.

Sulfur deactivation and regeneration behavior of the Pd/Al2O3 catalyst has been investigated via experimental characterization and density functional theory (DFT) simulations. During the sulfur exposure, PdO crystallites grow slightly while bulk Al2(SO4)3 forms on the support. DFT calculations indicate that SOx species interact strongly with the catalyst surface making it chemically inactive in agreement with the experimental results. During the regeneration treatment (CH4 conditions), PdO particles reduce, Al2(SO4)3 is partially removed, and the activity for CH4 conversion is increased. No full recovery can be observed due to remaining Al2(SO4)3, the formation of encapsulating sulfur species, and the partial reduction of PdO particles. To reoxidize Pd, the catalyst is further regenerated (O2 conditions). The resulting CH4 conversion is at the same level than with the regenerated catalyst. Thus, a small amount of Al2(SO4)3 appears to have a stronger effect on the performance than the state of Pd.

The impact of sulphur, phosphorus and water and their co-exposure on a monolith-type Pt/SiO 2 -ZrO 2 diesel oxidation catalyst was investigated. The accelerated laboratory-scale sulphur treatments for Pt/SiO 2 -ZrO 2 were done with and without water (S- and SW-treatments, respectively) at 400 °C. Similarly, the phosphorus treatment with water (PW-treatment) as well as the co-exposure of phosphorus, sulphur and water (PSW-treatment) were also done to find out the interactions between the impurities. The studied catalysts were characterized by using several techniques and the activity of the catalyst was tested in lean diesel exhaust gas conditions. Based on the XPS and the elemental analysis, more phosphorus was adsorbed on the Pt/SiO 2 -ZrO 2 catalyst than sulphur. Sulphur, in the presence and absence of water, was found to have a negligible effect on the CO and C 3 H 6 light-off temperatures (T 90 ) over the fresh Pt/SiO 2 -ZrO 2 , whereas the T 90 values of CO and C 3 H 6 increased by 30–45 °C as a result of the PW-treatment and by 15–35 °C after the PSW-treatment. Based on the Transmission electron microscope (TEM) analyses, no morphological changes on the Pt/SiO 2 -ZrO 2 surfaces were observed due to the phosphorus treatment. Therefore, the reason for the lower activity after the PW-treatment could be the formation of phosphates that are decreasing the specific surface area of the catalyst, blocking the accessibility of the reactants to the catalyst pores and active sites. However, it is worth noting that sulphur decreased the amount of adsorbed phosphorus and thus, inhibited the poisoning effect of phosphorus.

One way to lower CO2 and other harmful emissions of the transportation sector is the development of natural gas fueled vehicles. Availability of natural gas is good, and it is easy to apply to stoichiometric and lean-burn engines, which makes it ready-to-use technology. The main concern in the field is a sulfur poisoning of the exhaust gas after treatment system. We aim to clarify mechanisms of sulfur poisoning and regeneration of a lean-burn methane oxidation catalyst. Overall, it is concluded that sulfur itself is not the only reason for the deactivation of methane oxidation catalyst, but it is a joint effect of water vapor and sulfur species. The irreversible sulfur poisoning deteriorates oxygen mobility and hinders water desorption, which inhibits low temperature methane oxidation activity. The regeneration of sulfur poisoned catalyst takes place stepwise: PdSO4 → PdSO3 + 0.5O2 → Pd + SO2 + 0.5O2. The formation of metallic palladium makes the catalyst vulnerable for sintering, which leads to deactivation during long-term regeneration.

In order to meet stringent emission limits, after-treatment systems are increasingly utilized in natural gas engine applications. In this work, two catalyst systems were studied in order to clarify how the catalysts affect, e.g. hydrocarbons, NO x and particles present in natural gas engine exhaust. A passenger car engine modified to run with natural gas was used in a research facility with possibilities to modify the exhaust gas properties. High NO x reductions were observed when using selective catalytic reduction, although a clear decrease in the NO x reduction was recorded at higher temperatures. The relatively fresh methane oxidation catalyst was found to reach reductions greater than 50% when the exhaust temperature and the catalyst size were sufficient. Both the studied catalyst systems were found to have a significant effect on particulate emissions. The observed particle mass reduction was found to be due to a decrease in the amount of organics passing over the catalyst. However, especially at high exhaust temperatures, high nanoparticle concentrations were observed downstream of the catalysts together with higher sulphate concentrations in particles. This study contributes to understanding emissions from future natural gas engine applications with catalysts in use.

Structural changes of PtPd nanoparticles in a natural gas oxidation catalyst were studied at elevated temperatures in air and low-oxygen conditions and in situ using environmental transmission electron microscopy (ETEM). The fresh catalyst shows

The effect of sulphur and phosphorus on a Pt/SiO2–ZrO2 catalyst was studied. The laboratory accelerated sulphur (SW) or phosphorus (PW), and their co-exposure (PSW) treatments were done in gas phase for 5 h at 400 °C. The fresh and treated catalysts were characterized by XPS, FESEM-EDS, TEM-EDS, BET and BJH. The catalyst activity was tested in lean diesel exhaust gas conditions by using a gas FTIR. The value of the light-off temperature of CO and C3H6 over the studied catalysts was as follows: fresh ~ SW

Phosphorus is found to have a deactivating effect on the catalytic activity of the studied natural-gas-oxidation catalyst. Accelerated laboratory-scale phosphorus treatment was done to the PtPd/Al2O3 natural gas oxidation catalyst. The effect of phosphorus after low (0.065 M) and high (0.13 M) phosphorus concentration treatments was studied by using an inductively coupled plasma optical emission spectroscopy, N2 physisorption, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. In addition, the behavior of the catalyst was studied by a Gasmet FT-IR gas analyzer. Based on the received results it can be concluded that phosphorus was adsorbed on the surface by chemical bonds forming phosphates (PO4). In addition, the partial transformation of PdO to Pd was observed. Due to the phosphorus adsorption both the CO and CH4 oxidation activities were lower after the phosphorus treatments compared with the fresh catalyst.

The formation of hydrogen sulfide in car exhaust is undesirable due to unpleasant odor and toxicity of H2S gas. H2S release can be suppressed by the addition of a NiO scavenger to a three-way catalyst (TWC). In this work, Pd–Ni bimetallic catalysts were prepared by the co-addition of Pd and Ni to γ-Al2O3 or Al2O3-La2O3 support, by the impregnation method. Different concentrations of a propionic acid aqueous solution were used as the impregnation solvent. The structure of prepared catalysts was characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), and temperature-programmed reduction (TPR) techniques. Catalyst poisoning by SO2 was simulated under lean conditions and H2S release under rich conditions. XRD and TPR measurements revealed the effect of the impregnation solvent concentration on the ratio between NiO and NiAl2O4 spinel species and the reducibility of Ni species. Co-addition of Pd with Ni was proven to be beneficial for H2S suppression. Prepared bimetallic catalysts released considerably less H2S compared to physical mixtures of Pd/Al2O3 with NiO. The presence of bulk and well dispersed NiO on Pd–Ni catalysts assisted in sulfur release in the form of sulfur oxides rather than H2S. Bimetallic catalysts supported on Al2O3-La2O3 were found to release more H2S compared to catalysts on γ-Al2O3. The use of diluted solvent in bimetallic catalysts preparation decreased H2S release from Pd–Ni catalysts.

The effects of phosphorus poisoning on the activity of PtPd and Pt diesel oxidation catalysts and on the activity of the support material were investigated using the gas phase laboratory-scale-aging procedure. The catalysts were treated using two different phosphorus concentrations (0.065 and 0.13 mol/L (NH4)2HPO). The deactivation was studied by inductively coupled plasma optical emission spectroscopy, electron microscopy, X-ray diffractometry, X-ray photoelectron spectrometry and Fourier-transform infrared reflectance, N2-physisorption, and activity measurements with CO, C3H6 and NO. The amount of accumulated phosphorus was higher on the Pt catalyst surface than on the PtPd catalyst and significantly higher on the surface of the bare support material. Phosphorus concentration was uniform throughout the support layer (down to the 10 μm), and phosphorus was found as phosphate, although it can also form compounds like AlPO4 with the support. The treatment with low phosphorus concentration was found to have a clear deactivation effect only for C3H6 oxidation activity on PtPd catalysts above 200 °C. The treatment with high phosphorus concentration significantly decreased the activity of both the PtPd and Pt catalysts. In particular, the C3H6 and NO oxidation activities of the fresh and P-treated Pt catalysts were higher than those of the PtPd catalysts for the entire temperature range.

Ni additive in the three-way catalyst (TWC) has been known for its high activity in H 2 S suppression. However, the effect of Ni on the activity of TWC in stoichiometric exhaust gas conversion is less studied. In the present work characterization of bimetallic Pd–Ni catalysts supported on γ-Al 2 O 3 or γ-Al 2 O 3 –La 2 O 3 for potential TWC application was performed. The catalysts were prepared by wet co-impregnation and impregnation-evaporation methods. Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), temperature-programmed reduction (TPR), UV–vis diffuse reflectance spectrometry (UV–vis DRS), scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM) techniques were employed to confirm the effect of Ni addition on the catalysts structure. XRD, TPR, and STEM characterization was employed in order to evaluate the presence of Pd–Ni interaction. The activity of the catalysts was tested in the oxidation reaction of CO and C 3 H 6 under stoichiometric conditions. Based on the obtained results, we confirmed the structure of prepared catalysts and the effect of Pd–Ni interaction on the catalytic activity of Pd–Ni catalysts in CO and C 3 H 6 oxidation. XRD and TPR characterization suggested that Pd and Ni are competing for the support sites. The observed competition affected Pd-support and Ni-support interactions and consequently activity. Fresh bimetallic catalysts had higher catalytic activity compared to monometallic ones due to higher active metal loading and the presence of NiO phase. It was concluded that the catalytic activity of aged bimetallic catalysts is not affected by the addition of Ni. For that reason, addition of Ni as a second metal to Pd-based catalysts for TWC reactions can be considered in the future studies.

Emission regulations and legislation inside the European Union (EU) have a target to reduce tailpipe emissions in the transportation sector. Exhaust gas aftertreatment systems play a key role in low emission vehicles, particularly when natural gas or bio-methane is used as the fuel. The main question for methane operating vehicles is the durability of the palladium-rich aftertreatment system. To improve the durability of the catalysts, a regeneration method involving an efficient removal of sulfur species needs to be developed and implemented on the vehicle. This paper tackles the topic and its issues from a fundamental point of view. This study showed that Al2(SO4)3 over Al2O3 support material inhibits re-oxidation of Pd to PdO, and thus hinders the formation of the low-temperature active phase, PdOx. The presence of Al2(SO4)3 increases light-off temperature, which may be due to a blocking of active sites. Overall, this study showed that research should also focus on support material development, not only active phase inspection. An active catalyst can always be developed, but the catalyst should have the ability to be regenerated.

The activity of sulphur–water- and water-treated PtPd/Al2O3- and Pt/Al2O3-based monolith catalysts was investigated. The catalysts were characterized by X-ray photoelectron fluorescence, X-ray photoelectron spectroscopy, transmission electron microscopy and BET–BJH. The sulphur poisoning had a diminishing effect on the catalyst activity. The correlation between the laboratory-poisoned and engine-bench-aged catalyst activity was detected and found to have a relatively good correspondence.

The ageing conditions were analyzed with gasoline, diesel and natural gas (NG) catalysts to find the simplified, rapid thermal and chemical (sulfur) ageing methods for catalyst development. Rich-stoichiometric conditions prevented the deactivation of TWCs in gasoline and NG applications. Active metals and support are sintered thermally during short lean periods by increasing deactivation as a function of oxygen concentration. Air ageing for 3–10 h is an appropriate rapid ageing method for TWCs. Active regeneration conditions for DPF with a higher carbon concentration deactivated DOCs less than normal diesel exhaust conditions at 700 °C. Natural gas oxidation catalysts were sulfated in use conditions but almost complete recovery was possible above 600 °C with higher methane feeds at lean. In addition to sulfur, other chemical poisoning was also included in the rapid ageing methods by fittings to the diesel and NG field aged catalysts.

The behavior of a commercial Ce–Zr promoted Pd-Rh/Al2O3 catalyst for the abatement of methane from the exhausts of natural gas vehicles (NGVs) is studied in presence of large amounts of water under both stationary conditions and by periodically switching from lean to rich feed. Under stationary conditions with both stoichiometric (λ = 1.00) and lean (λ = 1.02) feed catalyst deactivation is observed after prolonged exposure to the reaction mixture. Periodic rich pulses in a constant lean feed gas result in the stabilization of catalytic performances. A higher methane conversion than those obtained with stoichiometric and lean feed mixtures is observed under rich conditions, during an experiment carried out by performing lean pulses (λ = 1.02) in a constant rich feed gas (λ = 0.98). The analysis of reactants conversion and products distribution suggests that different chemistries are involved under lean and rich conditions. Only reactions of complete oxidation of H2, CO, CH4 and NO occur under excess of oxygen, whereas under rich conditions NO reduction, CH4 steam reforming and water gas shift also occur. The effect of symmetric oscillation of the exhausts composition around stoichiometry is also addressed by periodically switching from slightly rich to slightly lean composition with different oscillation amplitudes (Δλ = ±0.01, ±0.02 and ±0.03). Higher and more stable methane conversion performances are obtained than those observed under constant λ operations. The presence of a more active PdO/Pd0 state is suggested to explain the enhancement of catalytic performances.

Sulphur, sulphur-water, and water pretreatments were done to find out the effect of these compounds on a diesel oxidation Pd/β-zeolite catalyst and β-zeolite washcoat. After pretreatments, the samples were analysed by BET, XRF, TEM-SEM, and XPS. In addition, the activity of fresh and pretreated Pd/β-zeolite catalysts was studied utilizing the by Gasmet FT-IR in production gas analysis. Sulphur compounds (SO2 or −SO4) were found to have a deactivating effect on the activity of the studied Pd/β-zeolite catalyst.

A fresh powder-like Pt/Al2O3 diesel oxidation catalyst was treated with sulphur (S–), sulphur–water (SW–), calcium–water (Ca–), sulphur–calcium–water (SCa–), and water (W–). BET, TEM–EDS, XPS, ICP-OES, AAS analyses and catalytic activity tests were used to find the effect of sulphur, calcium and water on the Pt/Al2O3 catalyst and its performance. Based on the ICP-OES and EDS results, sulphur was found to accumulate on the surface, whenever it was used in the pretreatments. Calcium was found in a very small amount on the Ca- and SCa-treated Pt/Al2O3 catalysts according to AAS and EDS results. For all the cases, the specific surface area was decreased after pretreatment. As expected, for the S- and SW-treated Pt/Al2O3 catalysts the light-off temperatures for CO and propene were higher compared to the corresponding fresh catalyst. Ca-, SCa-, and W-treated Pt/Al2O3 catalysts had almost the same light-off temperatures of CO and C3H6 than the fresh catalyst, instead. Based on the TEM–EDS results, the particle size of Pt and alumina washcoat microstructure was found to be unchanged after all the pretreatments. The pronounced deactivation is explained with sulphates formation on the active sites and with a decrease in the specific surface area.

Palladium precursors and solvents were studied for their effects on the activities of alumina-based palladium catalysts in methane combustion and the resistance of the catalysts to thermal aging. The properties of the catalysts were compared with those of a commercial reference. The palladium precursors were Pd(propionate) 2 , Pd(acetate) 2 and Pd(acetyl acetonate) 2 and the solvents were acetone, acetic acid, propionic acid and toluene. Catalysts were prepared by the wet impregnation method. Catalysts were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). The surface areas were measured by Brunauer–Emmett–Teller method (BET). Acidity of the alumina support was measured by NH 3 desorption. Activities of the catalysts in methane oxidation were screened under lean burn conditions. In methane oxidation with fresh catalyst, the best performance was obtained with a combination of Pd(acetate) 2 and acetic or propionic acid. The light-off temperatures of the fresh catalysts (562 K and 557 K, respectively) were slightly lower than the light-off temperature (567 K) of the commercial reference. Differences between the light-off temperatures of the aged and fresh catalysts were least when the catalysts were prepared with Pd(acetyl acetonate) 2 as Pd precursor and in acetic or propionic acid as solvent: +12 K and +18 K, respectively. The corresponding value for the reference was +64 K. For several of the fresh catalysts, conversion in methane oxidation at 623 K was over 90%. A comparison of methane combustion and NH 3 desorption results indicated that acidity of the support material affects catalysts activity.

Pd/CeO2 and Pd/Zr-CeO2 diesel oxidation catalysts were treated with sulphur, sulphur–water and water. According to the BET, TEM-EDS, XPS, ICP-OES analyses and catalytic activity tests, both studied catalysts were deactivated by sulphur due to formation of sulphates. Water treatment was found to have a promoting effect on the oxidation of CO and C3H6.

Pd/Al2O3, Pd/CeO2 and Pd/ZrO2 diesel oxidation catalysts and their washcoat materials were studied after sulphur treatment. The catalytic activities were analysed in simplified diesel exhaust gas composition by FT-IR technique. ICP-OES or XRF, physisorption and CO chemisorption was used to catalyst characterisation. The result shows that the sulphur treatment clearly deactivates the studied catalysts.

Phosphorus poisoning and its effect on the diesel oxidation catalysts morphology was studied by transmission electron microscopy (TEM). The studied catalyst samples were PtPd or Pt supported on the alumina-based washcoat including additives. The laboratory-scale phosphorus exposures were carried out with two different phosphorus concentrations. The cross-sectional TEM samples were prepared from the fresh and phosphorus-treated catalysts. After phosphorus exposures, significant structural changes were observed compared to the fresh catalysts. The shape of the noble metal particles had changed from irregular to more spherical-shaped particles. In addition, phosphorus was detected throughout the catalyst TEM samples but the amount varied depending on the local composition of the support. Phosphorus accumulated mainly in the alumina-containing areas of the support and indications of dense and amorphous aluminium phosphates were found. Based on the results gained, cross-sectional TEM characterization is essential to observe these kinds of morphological changes in the catalysts caused e.g. by phosphorus exposures. In addition, cross-sectional TEM samples are needed to study the effect of local variation in the support composition on the phosphorus accumulation. acceptedVersion

Barium, lanthanum, and praseodymium perovskites were prepared by malic acid complexation. Surface areas of the La and Pr perovskites were between 17.1 and 21.6 m2 g−1. The moderate low surface areas (5.7 m2 g−1) observed for corresponding barium perovskites were due to the high calcination temperatures. The calcination temperature also affected the shapes and sizes of the perovskite particles. According to SEM images the nanoparticles of the La and Pr perovskites were spherical, whereas those of barium perovskites were flakes. The conversion of methane increased in the order of A-site metal Ba

Lanthanum perovskites were synthesized by malic acid complexation and different amounts of palladium were added by dry-wet impregnation. Measurements of methane conversion on fresh and SO 2 -treated perovskite catalysts were made between 25 and 500 °C. Methane conversion on fresh catalysts commenced at ∼300 °C, and the best activities were achieved with low loadings of palladium. The B-site metal combinations Mn 0.4 Fe 0.6 and Mn 0.6 Fe 0.4 showed better conversion activity than Mn 0.5 Fe 0.5 and Fe. All fresh perovskite catalysts except those with 10% Pd gave 100% conversion of methane at 500 °C. The resistance of 10% Pd perovskite catalysts to sulfur was generally better than that of catalysts with low Pd loadings. This was due to the high Pd coverage on the perovskite surface. Fresh and SO 2 -treated LaMn 0.4 Fe 0.6 O 3 perovskite catalysts promoted with 2 and 2.5% of palladium exhibited the highest activities for methane conversion.

BaMn 0.6 Fe 0.4 O 3 , BaMn 0.4 Fe 0.6 O 3 , LaMn 0.6 Fe 0.4 O 3 , LaMn 0.4 Fe 0.6 O 3 , PrMn 0.6 Fe 0.4 O 3 , and PrMn 0.4 Fe 0.6 O 3 perovskites were synthesized via malic acid complexation and impregnated with 2% of palladium by dry-wet method. WGSR measurements were carried out in a stainless steel continuous flow reactor. The A-site metal increased the conversion of H 2 and CO 2 in the order Ba 0.4 Fe 0.6 than Mn 0.6 Fe 0.4 . The formation of carbonaceous surface species was observed. In measurements with a gas chromatograph, the oxidation of surface palladium was found to decrease in the order La > Pr > Ba. No correlation was observed between WGSR activity and oxidation of palladium.

In this work, a laboratory ageing cycle simulating the real engine ageing for three-way catalysts was developed. The laboratory cycle was created based on the rapid ageing hot (RAH) cycle used in the engine bench ageings. The simultaneous gas concentration and temperature changes were achieved by adjusting the IR-furnace and the gas flow parameters. The laboratory ageing cycle was verified by testing different samples after different ageings with the laboratory and the engine tests. In addition, some characterization methods: specific surface area (BET-method), dispersion (CO-chemisorption), particle size (CO-chemisorption) and oxygen storage capacity (with CO–O2 exchange experiments), were used to compare the effect of the different ageings on the catalyst samples.

Effect of thermal, engine bench, and vehicle ageings on catalytic activity and support properties was evaluated mainly by XRD on a real catalytic system. The solid–solid phase transitions in the bulk material are of particular importance to catalyst behaviour after ageings. It was observed that the ageing atmosphere either accelerated or inhibited the phase transitions. The formation of aluminates was observed after ageings in inert and reducing atmospheres as well as after engine and vehicle ageings. The formation of aluminates is associated with the loss of specific surface areas that remained higher after reducing and inert ageings. The formation of cerium and lanthanum aluminates prevents the formation of low surface area α-Al 2 O 3 that is responsible for the decrease in the total surface area. Catalytic activities also remained higher after reducing and inert ageings than after oxidizing ageing. Furthermore, laboratory ageing in reducing atmosphere seems to correlate best with the real vehicle ageing from the textural point of view.

Deactivation of Pd/Rh monoliths is considered. Based on the results of different characterization techniques, a deactivation correlation between laboratory scale ageing, engine bench ageing, and vehicle ageing is proposed.

The reactivity of (μ-H)2Ru3(CO)9(μ3-η2-C8H12) (1) and (μ-H)Ru3(CO)9(μ3-η3-C12H19) (2) with hydrogen and carbon monoxide was studied at elevated temperatures. Also the catalytic activity of 1 in homogeneous hydrogenation of 1-hexene was studied. At the lower carbon monoxide pressures compounds 1 and 2 converted to Ru3(CO)12 while at higher pressures they tend to fragmentate to the other ruthenium carbonyl compounds. Under a hydrogen atmosphere 1 and 2 converted to H4Ru4(CO)12 and at higher pressures tend to fragmentate to insoluble black precipitate. Complex 1 has a moderate activity in homogeneous hydrogenation of 1-hexene. Its activity is dependent on the temperature: activity increases when the temperature goes up.

The reactions of H4Ru4(CO)12 with cyclic triazaligands result in the formation of [LH]+[H3Ru4(CO)12]− salts, (L = 1,4,7-triazacyclononane (1), 1,4,7-trimethyl-1,4,7-triaza-cyclononane (2), 1,5,9-triazacyclododecane (3) and 1,5,9-trimethyl-1,5,9-triazacyclododecane (4)). The compounds were synthesized by refluxing H4Ru4(CO)12 in hexane followed by precipitation with the corresponding ligand. This is a convenient direct single-step synthetic route to produce [H3Ru4(CO)12]−-ion with a high yield. The compounds have been characterized by elemental analysis and spectroscopic measurements. In the 1H NMR spectra they showed a fluxional behavior. Reactivity towards CO at elevated temperature, and the catalytic activity of the new compounds in the water—gas shift reaction (WGSR) and in the carbonylation of methanol, have been discussed.

The enhancement of methane oxidation performances under periodic operation over a commercial Pd–Rh based three way catalyst (TWC) is investigated at different temperatures. Results confirm that under conditions with periodic oscillating feed around stoichiometry (λ = 1 ± 0.02), higher and more stable CH4 conversion are obtained than under conditions with constant stoichiometric feed. In particular higher CH4 conversion is obtained in the rich part of the cycle than in the lean one, the difference being more pronounced at high temperature. A narrow turning point for the TWC activity is finally observed under slightly rich conditions, which is characterised by a marked increase of CH4 conversion, paralleled by total consumption of O2 and NO and formation of small amounts of CO, H2 and NH3. Results suggest that the oxidation state of palladium plays a key role in the observed enhancement of catalyst performances.

Deactivation of the natural-gas-vehicle-aged Pt/Pd oxidation catalyst supported on γ-alumina-based washcoat was studied by electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, and catalytic activity measurements. Significant structural changes were detected in the used catalyst compared to the fresh one. Grain size of the washcoat had grown but its structure had remained the same, γ-alumina, as in the fresh catalyst. Sintering of the noble metal particles had occurred, particle sizes varied from ~5 up to ~100 nm. Decomposition of palladium oxide and platinum oxide to metallic Pd and Pt occurred followed by the formation of the bimetallic Pt/Pd crystals. Also reformation of palladium oxide was detected. In addition, the inlet part of the used catalyst was totally covered by a poisoning layer. Due to these structural changes and poisoning, the activity of the vehicle-aged catalyst had decreased significantly compared to the fresh one. All the changes were stronger in the inlet than in the outlet part of the used catalyst indicating higher operating temperature and more extensive thermal deactivation and poisoning in the inlet than in the outlet part of the converter.

The reaction between Ru 3 (CO) 12 and a cyclic olefin ( cis -cyclooctene or trans -cyclododecene) at 100 °C for several hours gives the title compounds ( μ -H) 2 RU 3 (CO) 9 ( μ 3 - η 2 -C 8 H 12 ) ( 1 ), and ( μ -H)RU 3 (CO) 9 ( μ 3 - η 3 -C 12 H 19 ) ( 2 ), both of which have been characterized by X-ray diffraction studies, IR and NMR spectral measurements and elemental analysis. The prolonged reaction between Ru 3 (CO) 12 and cis -cyclooctene gives compound HRu 3 (CO) 9 (C 8 H 11 ) ( 3 ). Compound 3 has been characterized with IR and NMR spectral analyses. In 1 the cyclooctene ring is linked via a μ 3 - η 2 -alkyne type of bonding to the face of the Ru 3 cluster. It is formally σ-bonded to two of the three Ru atoms and π-bonded to the third Ru. The two hydrides in 1 are bridging RuRu bonds. In 2 the cyclododecene ring is bonded to the Ru 3 face via the μ 3 - η 3 -CCHC linkage. There are two formal σ-bonds from the allyl part to the hydrido-bridged Ru atoms and the η 3 -allyl linkage to the third Ru atom.

Homogeneous hydrogenation of 1-hexene to hexane was studied using a triruthenium cluster containing a face-capping ligand, HRu3(CO)9(μ3-η3-1,3-dithiacyclohexane) (1), as a catalyst precursor. The catalytic activity of 1 was studied as a function of temperature (98–140°C), H2 pressure (10–60 bar) and catalyst concentration. The highest hydrogenation rate of 0.085 mol/h was measured at 141°C and 60 bar of H2 pressure. A linear dependence between the catalytic activity of 1 and the H2 pressure was observed in the pressure range of 10–50 bar, but equalizing at higher pressures (> 50 bar). A rise in the temperature causes an increase in catalytic activity but at the same time enhances the fragmentation of 1 and the formation of a brown precipitate. The fragmentation product was not active in hydrogenation but shows moderate isomerization activity. A possible mechanism for the hydrogenation of 1-hexene by 1 is presented.

Cyclic polydentate thioether ligands 1,3-dithiacyclohexane, 1,3,5-trithiacyclohexane and 1,4,7-tri-thiacyclononane react with Ru3(CO)12 to give the carbonyl substitution products HRu3(CO)9(μ3-η3-1,3-dithiacyclohexane) (1), Ru3(CO)9(μ3-η3-1, 3,5-trithiacyclohexane) (2) and Ru3(CO)9(μ2-η3-1,4,7-trithiaheptane) (3) in moderate yields. The crystal structures of 1–3 have been determined. A different coordination mode is observed in each case. Carbon monoxide was found not to replace the cyclic thioethers in the ruthenium complexes, but complexes 1 and 3 react with H2 Thus complex 1 under a hydrogen atmosphere in chloroform gives the new cluster complex (μ2-H)2Ru3(CO)8Cl(μ3-η3-1,3-[S2CH(CH2)3]) (4) the crystal structure of which was determined. Correspondence to: Dr. S. Rossi.

The decahexacarbonylhexarhodium cluster [Rh 6 (CO) 16 ] reacts with dimethylsulfide to give a series of substituted clusters [Rh 6 (CO) 16− x (SMe 2 ) x ], x =1–4 ( 1–4 . The crystal structures of 1 and 4 have been determined. The SMe 2 ligands replace terminal carbonyls, otherwise the cluster structure is maintained. The four sulfide ligands in 4 replace four carbonyl groups at Rh atoms in the same plane of the Rh 6 octahedron, with the SMe 2 groups lying alternately above and below this plane. The di- and tri-substituted species have been characterized by ir spectroscopy and elemental analysis. The reactivity of [Rh 6 (CO) 12 (SMe 2 ) 4 ] toward hydrogen and carbon monoxide has been studied. Under CO it undergoes replacement of SMe 2 by carbon monoxide to afford [Rh 6 (CO) 16 ]. In a corresponding reaction with H 2 [Rh 6 (CO) 12 (SMe 2 ) 4 ] is converted into a mixture of 2–4 . Hydrogenation of 1-hexene using [Rh 6 (CO) 12 (SMe 2 ) 4 ] as a catalyst precursor was observed at 60°C with a highest rate of 2200 turnovers/h.

Demand for lower and lower emissions in road transportation has promoted the development of more efficient exhaust emission catalysts. On the same time the fight against the impact of transportation on climate change has opened the way for the use of biofuels, e.g. biodiesel. Deactivation of catalytic surfaces is a serious problem in the design of more efficient automotive exhaust catalysts. Deactivation of catalysts can be classified in three types: chemical (e.g. poisoning), mechanical (e.g. fouling) and thermal (e.g. ageing). In the long run these deactivation processes can cause nearly total loss of catalytic activity in the catalyst material. In biodiesel fuelled vehicles these processes can lead to notably different effects in catalyst efficiency compared to those of conventional diesel vehicles [1].

The effect of bulk BaO promoter on CO oxidation activity of palladium oxide phase was studied by density functional calculations. A series of BaO(100) supported Pd(x)O(y) thin layer models were constructed, and energy profiles for CO oxidation on the films were calculated and compared with corresponding profiles for the most stable PdO bulk surfaces PdO(100) and PdO(101). The most stable of the thin films typically exhibit the same PdO(100) and PdO(101) surface planes; the PdO(100) dominates already with double layer thickness. The supporting promoter improves the CO oxidation activity of the Pd(x)O(y) phase via a direct electronic effect and introduced structural strain and corrugation. Changes in CO adsorption strength are reflected in oxidation energy barriers, and the promoting effect of even 0.3 eV can be seen locally. Easier oxygen vacancy formation may partially facilitate the reaction.