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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.

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.

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 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.