Deactivation Correlations of Pd/Rh Three-way Catalysts Designed for Euro IV Emission Limits:effect of Ageing Atmosphere, Temperature and Time

Abstract The aim of this thesis is the knowledge of the most relevant deactivation mechanisms of Pd/Rh three-way catalysts under different ageing conditions, the deactivation correlation of laboratory scale ageing and engine bench/vehicle ageings, and the evaluation of the deactivation correlation. In the literature review, the phenomena involved in the three-way catalyst operation and its deactivation are considered. In the experimental section, ageing-induced phenomena in the catalyst are studied and deactivation correlations between laboratory scale and engine bench/vehicle ageings are presented, based on the results of several surface characterization techniques. The effects of ageing atmosphere and temperature, and time are considered in particular. Fresh and aged catalysts used in this study were metallic monoliths designed for Euro IV emission limits. Thermal ageings were carried out in the reductive, oxidative and inert atmospheres in the temperature range of 800°C to 1200°C, and in the presence of water vapour (hydrothermal ageing). The engine ageing was carried out in the exhaust gas stream of a V8 engine during a 40 hour period. The ageing procedure composed of rich and stoichiometric air-to-fuel ratios carried out consecutively. The vehicle ageing was accomplished under real driving conditions (100 000 kilometres). According to the results, deactivation of a Pd/Rh monolith is a combination of several ageing phenomena. The most important deactivation mechanisms are the sintering of active phase, the collapse in surface area and ageing-induced solid-solid phase transitions in the bulk washcoat. Furthermore, poisoning is a relevant deactivation mechanism of the vehicle-aged catalyst. High ageing temperature, gas phase composition and exposure time are essential variables to the deactivation of a Pd/Rh three-way catalyst. This thesis presents an approach to discover the deactivation correlation between the laboratory scale ageing and under the vehicle's operation in an engine bench or on-road. Based on the characterization results, the accelerated laboratory scale air ageing does not correspond to the ageing-induced changes in the catalyst under the vehicle's operation. Therefore, there is a need for a modified ageing cycle and according to the results, a deactivation correlation between the laboratory scale ageing and the engine bench ageing can be presented as a function of ageing temperature and atmosphere, and time. Instead, after the vehicle operation, the deactivation correlation cannot be presented based solely on the studied variables because, after 100 000 kilometres of driving, the role of poisoning should be taken into account in the ageing cycle. The results of this thesis can be utilized and applied in the development of laboratory scale ageing cycles, which corresponds closely to the ageing-induced changes in the catalyst during the vehicle operation. This enables a rather fast testing of the catalyst's performance and reduces the cost during the manufacturing of catalysts

Catalytic effect of transition metals (copper, iron, and nickel) on the foaming and properties of sugar-based carbon foams

Abstract Recently, bio-based carbon foams have gained much interest in many chemical industry fields because of their unique structure and properties. This study provides new information on the effects of catalytic metals (iron, nickel, and copper) on the foaming process. Specifically, the effects of these catalysts on the density, foam growth, and cell size and then further on the pore size distribution and specific surface areas after the physical activation are considered. Furthermore, some of the activated sugar foams were used in adsorption tests using methylene blue as adsorbent. Results showed that the highest effect on foam density was obtained using the iron catalyst in the foaming process. In addition, increasing the iron amount, the development of micro-pores decreased from 95.2 to 60.3% after cabonization and activation of the foams. Nickel and iron had the highest and lowest effect on foam rise at 1375 and 500%, respectively. Interestingly, when the nickel catalyst was used, cell sizes and surface areas two times larger than those when the foams were prepared with the iron and copper catalysts was obtained. The specific surface area of activated sugar-based carbon foams changed significantly with the increased copper amount inside the foaming solution in compared with iron or nickel catalyst. Methylene blue adsorption capacity of additional series of activated sugar foams decreased from 28 to 9% when meso-pore amount decreased

Electrocoagulation sludge valorization:a review

Abstract In the field of electrocoagulation (EC), various studies on pollutant removal and on the use of different EC technologies have already been made. An EC process generates sludge, which is considered waste, resulting in increased operational costs that come from waste disposal. Sludge contains valuable materials, such as the nutrients or metals removed during water purification, along with metals, such as aluminum or iron, which come from the electrodes used in an EC system. Based on the principles of circular economy or based on existing legislations, reducing the production of valuable wastes, and increasing the valorization rate of as many materials as possible are important endeavors. This study is mainly a review of the existing sludge valorization studies. This review highlights the valorization of sludge as a fertilizer (mainly as struvite), pigment, construction material (mainly as blocks), adsorbent, and catalyst. While it has already been found that EC sludge is valorizable, more studies on EC sludge valorization and on the quality of sludge produced from the effluent of EC processes are warranted

Physical activation of wooden chips and the effect of particle size, initial humidity, and acetic acid extraction on the properties of activated carbons

Abstract In this research study, two different wooden biomasses (birch and pine) were thermally carbonized and steam-activated into activated carbons in a one-stage process. The effects of particle size and humidity (as received and oven-dried) on the properties, such as specific surface areas, pore volumes, and pore size distributions, of the final activated carbon characteristics were examined. Another set of biomasses (birch, spruce, and pine) was pre-treated before carbonization and the activation steps through an extractive process using a weak acetic acid in Soxhlet extractors. According to the results, the dried samples had a slightly lower surface area, while no difference was observed in the yields. For the extracted samples, there was a significant difference, especially in the pore size distributions, compared to the non-extracted samples. There appeared to be a shift from a meso-microporous distribution to a microporous distribution caused by the extractive pre-treatment

An overview of treatment approaches for octahydro-1, 3, 5, 7-tetranitro-1, 3, 5, 7-tetrazocine (HMX) explosive in soil, groundwater, and wastewater

Abstract Octahydro-1, 3, 5, 7-tetranitro-1, 3, 5, 7-tetrazocine (HMX) is extensively exploited in the manufacturing of explosives; therefore, a significant level of HMX contamination can be encountered near explosive production plants. For instance, up to 12 ppm HMX concentrations have been observed in the wastewater effluent of a munitions manufacturing facility, while up to 45,000 mg/kg of HMX has been found in a soil sample taken from a location close to a high-explosive production site. Owing to their immense demand for a variety of applications, the large-scale production of explosives has culminated in severe environmental issues. Soil and water contaminated with HMX can pose a detrimental impact on flora and fauna and hence, remediation of HMX is paramount. There is a rising demand to establish a sustainable technology for HMX abatement. Physiochemical and bioremediation approaches have been employed to treat HMX in the soil, groundwater, and wastewater. It has been revealed that treatment methods such as photo-peroxidation and photo-Fenton oxidation can eliminate approximately 98% of HMX from wastewater. Fenton’s reagents were found to be very effective at mineralizing HMX. In the photocatalytic degradation of HMX, approximately 59% TOC removal was achieved by using a TiO₂ photocatalyst, and a dextrose co-substrate was used in a bioremediation approach to accomplish 98.5% HMX degradation under anaerobic conditions. However, each technology has some pros and cons which need to be taken into consideration when choosing an HMX remediation approach. In this review, various physiochemical and bioremediation approaches are considered and the mechanism of HMX degradation is discussed. Further, the advantages and disadvantages of the technologies are also discussed along with the challenges of HMX treatment technologies, thus giving an overview of the HMX remediation strategies

Precipitation of silica from zinc process solution

Abstract Precipitation of silica in concentrated sulfuric acid solutions was studied with laboratory-scale batch experiments. The effects of initial silicic acid concentration, temperature, and sulfuric acid concentration were studied. It was observed also in this work that the high ionic strength of the leaching solution drastically decreased the solubility of silica. The solubility was also studied using Gibbs energy minimization method and Pitzer model using the ChemSheet program. Good agreement was obtained between the model and experimental results. The precipitation reaction of silica was observed to follow a pseudo-first-order rate law. Based on the rate law used, an activation energy of 61.7 kJ mol⁻¹ was estimated. This implies a reaction-controlled mechanism of precipitation

Removal of metals by sulphide precipitation using Na₂S and HS⁻-solution

Abstract Precipitation of metals as metal sulphides is a practical way to recover metals from mine water. Sulphide precipitation is useful since many metals are very sparingly soluble as sulphides. Precipitation is also pH dependent. This article investigates the precipitation of metals individually as sulphides and assesses which metals are precipitated as metal hydroxides by adjustment of the pH. The precipitation of different metals as sulphides was studied to determine the conditions under which the HS⁻ solution from the sulphate reduction reaction could be used for precipitation. H₂S gas and ionic HS⁻ produced during anaerobic treatment could be recycled from the process to precipitate metals in acidic mine drainage (AMD) prior to anaerobic treatment (Biological sulphate reduction), thereby recovering several metals. Precipitation of metals with HS⁻ was fast and produced fine precipitates. The pH of acid mine water is about 2–4, and it can be adjusted to pH 5.5 before sulphide precipitation, while the precipitation, on the other hand, requires a sulphide solution with pH at 8 and the sulphide in HS⁻ form. This prevents H₂S formation and mitigates the risk posed from the evaporation of toxic hydrogen sulphur gas. This is a lower increase than is required for hydroxide precipitation, in which pH is typically raised to approximately nine. After precipitation, metal concentrations ranged from 1 to 30 μg/L

Effect of calcination conditions on the dispersion of cobalt Over Re, Ru and Rh promoted Co/γ-Al₂O₃ catalysts

Abstract The effects of catalyst calcination conditions, such as calcination temperature and calcination atmosphere composition on the dispersion of cobalt particles over Co/γ-Al₂O₃ catalysts for Fischer–Tropsch conversion of synthesis gas are studied. A number of catalysts were prepared by incipient wetness impregnation of 20-wt% of cobalt onto γ-Al₂O₃ and promoted with 0.5 wt% ruthenium, rhenium, and rhodium. Metal dispersions of active metals were studied by chemisorption of carbon monoxide. The highest dispersion for Co/γ-Al₂O₃ catalyst was achieved by calcination at 400 °C in a flow of N₂. Co metal dispersion seem to be increased in the calcination steps if a flowing gas was used instead of static calcination conditions. The addition of promoter metals like Ru, Re or Rh enhances the dispersion of the active metal

Activated carbon from hydrolysis lignin:effect of activation method on carbon properties

Abstract This study presents the effects of different activation methods to produce activated carbon from the hydrolysis lignin. Pretreatment of the feedstock with common mineral acids (HCL, HNO₃, and H₃PO₄), different steam rates for physical activation, and different chemical activating agents (ZnCl₂, Na₂CO₃, and KOH) for chemical activation were investigated. The pretreated biomass was carbonized and activated in one-stage process and the surface characteristics, such as total pore volume, pore size distribution and specific surface area, were investigated. The results showed that the activated carbon surface properties were not greatly affected by acid pretreatment. Brunauer-Emmett-Teller (BET) surface areas as high as 616 m²/g could be achieved with physical activation and 2054 m²/g with chemical activation. Different steam rates in the selected interval (0.5–2 cm³/min) did not change the pore size distribution but had small positive effect on the specific surface area, while chemical activation with ZnCl₂ increased the mesoporosity, and activation with KOH increased the microporosity and oxygen groups in the form of ether and alcohol bonds