Applying 3D X-ray Microscopy to Model Coated Gasoline Particulate Filters under Practical Driving Conditions.

Recent progress in 3D X-ray microscopy allows the analysis of coated gasoline particulate filters on a detailed pore-scale level. However, derivable detailed three-dimensional models for filter simulation are not applicable under transient driving conditions of automotive aftertreatment systems due to their inherent complexity. Here, we present a novel concept to utilize highly resolved 3D X-ray microscopy scans and their quantitative analysis for a macroscopic model of coated gasoline particulate filters intended to be applied in a driving cycle. A previously developed filtration model build on a 1D + 1D flow model on the channel scale of a filter is utilized. Accompanying measurements conducted on a dynamic engine test bench serve as validation for pressure drop and filtration characteristics. With the determined properties from 3D X-ray microscopy, the macroscopic model successfully replicates the measurements. Regarding the filter coating, the reduced porosity and a decrease of medium sized pores relative to an uncoated substrate reduce the filtration efficiency under steady-state as well as transient conditions.

Extended Model for Filtration in Gasoline Particulate Filters under Practical Driving Conditions.

In order to reliably predict the particle number filtration of gasoline particulate filters (GPF) under practical driving conditions, an extension to established filtration models is developed. For the validation of this approach and in order to close a gap of available measurement data at high space velocity in the literature, the particle-size-resolved fresh filtration efficiency of seven different cordierite filters is determined experimentally. Moreover, the experiments on a dynamic engine test bench focus on the impact of the pore-size distribution and the filter wall thickness under steady-state as well as transient, cold-start conditions. In order to model all trends observed, a new correlation for the particle collection due to inertial deposition is proposed and embedded in a heterogeneous multiscale model framework for a GPF. The presented approach can predict all trends observed in the measurements, including a stabilization of the filtration efficiency with increasing space velocities above a certain level. A comparison of several modeling approaches reveals the partly different behaviors at varying space velocities for the here presented model as well as for established filtration models.

Counting of oxygen defects versus metal surface sites in methanol synthesis catalysts by different probe molecules.

Different surface sites of solid catalysts are usually quantified by dedicated chemisorption techniques from the adsorption capacity of probe molecules, assuming they specifically react with unique sites. In case of methanol synthesis catalysts, the Cu surface area is one of the crucial parameters in catalyst design and was for over 25 years commonly determined using diluted N2O. To disentangle the influence of the catalyst components, different model catalysts were prepared and characterized using N2O, temperature programmed desorption of H2, and kinetic experiments. The presence of ZnO dramatically influences the N2O measurements. This effect can be explained by the presence of oxygen defect sites that are generated at the Cu-ZnO interface and can be used to easily quantify the intensity of Cu-Zn interaction. N2O in fact probes the Cu surface plus the oxygen vacancies, whereas the exposed Cu surface area can be accurately determined by H2.

Accumulation of Liquid Byproducts in an Electrolyte as a Critical Factor That Compromises Long-Term Functionality of CO2-to-C2H4 Electrolysis.

Electrochemical conversion of CO2 using Cu-based gas diffusion electrodes opens the way to green chemical production as an alternative to thermocatalytic processes and a storage solution for intermittent renewable electricity. However, diverse challenges, including short lifetimes, currently inhibit their industrial usage. Among well-studied determinants such as catalyst characteristics and electrode architecture, possible effects of byproduct accumulation in the electrolyte as an operational factor have not been elucidated. This work quantifies the influence of ethanol, n-propanol, and formate accumulation on selectivity, stability, and cell potential in a CO2-to-C2H4 electrolyzer. Alcohols accelerated flooding by degrading the hydrophobic electrode characteristics, undermining selective and stable ethylene formation. Furthermore, high alcohol concentrations triggered the catalyst layer's abrasion and structural disfigurements in the Nafion 117 membrane, leading to high cell potentials. Therefore, continuous removal of alcohols from the electrolyte medium or substantial modifications in the cell components must be considered to ensure long-term performing CO2-to-C2H4 electrolyzers.

Photo-DSC method for liquid samples used in vat photopolymerization.

The photo differential scanning calorimetry (photo-DSC) is an appropriate method to characterize photopolymers used in additive manufacturing (AM). Important process parameters such as optimal ultraviolet (UV) exposure time and reaction heat can be attained by this method. However, achieving reliable and meaningful results from photo-DSC experiments requires careful sample preparation, i.e. the selection of a suitable sample shape, sample mass and sample holder (crucible). The sample shapes drop and spread with 1.0 mg and 2.8 mg sample masses were investigated in this study. Three different times from sample preparation until the start of the measurement (0, 4 and 7 h) were tested, in order to investigate different surface effects such as oxygen-diffusion, prior UV-curing through ambient radiation and evaporation of volatile components. While the 1.0 mg spread sample shape offers the thinnest film thickness (40 µm) and thus the closest comparability to high resolution print jobs, the 2.8 mg drop shape offers a more robust sample preparation with minimized surface effects. To further reduce time-dependent surface effects, this study shows how a preexisting test protocol was shortened from 42 min to 24 min without losing measuring accuracy. Furthermore, to reduce evaporation, different covers were placed on different crucibles, which were tested over time in the device's automated sample changer (ASC) that enables automated and consecutive measurements. The combination of a cold pressed 85 µL crucible covered with a 300 µL Al2O3 crucible, which is removed shortly before the actual measurement, provides the best sample preparation for the ASC since mass loss remains below 1% for up to 10 h. Finally, two two-part resin systems, namely a methacrylate-urethane and an acrylate-epoxy based resin that are used in Digital Light Synthesis (DLS) are characterized part by part as well as in mixed state. Together with the investigation of different temperatures and atmospheres, it was possible to identify not only the part with the photoinitiator and the type of system (radical or cationic), but also a difference between methacrylates and acrylates with the aid of the photo-DSC method.