Hydrocarbon and soot oxidation over cerium and iron doped vanadium SCR catalysts

V$_{2}$O$_{5}$−WO$_{3}$/TiO$_{2}$ (VWTi) catalysts are widely employed for selective catalytic reduction (SCR) of NO$_{x}$. However, due to their poor thermal stability the application in diesel particulate filters (DPFs), i. e. 2‐way SCRonDPF is limited. In this study, the potential of Ce‐ and Fe‐doped VWTi systems for hydrocarbon and soot oxidation in addition to the SCR activity was systematically investigated for fresh and thermally aged samples. The formation of metal vanadates upon thermal aging, as identified by X‐ray diffraction, Raman and X‐ray adsorption spectroscopy, prevents drastic sintering of the support and maintains a high NO$_{x}$−SCR and hydrocarbon oxidation activity. Additionally, the doped VWTi catalysts show a slight increase of the CO$_{2}$ selectivity during hydrocarbon oxidation, which represents an important aspect for such multifunctional catalysts. Despite of the advantages, the formation of metal vanadates hinders the mobility of vanadium species and decreases the soot oxidation ability of the doped catalysts. Interestingly, a promising soot oxidation activity was identified for the VWTi−Fe sample after aging at 650 °C, which resulted in decomposition of the iron vanadate and generation of highly dispersed and mobile V$_{2}$O$_{5}$

A review on exhaust gas after-treatment of lean-burn natural gas engines – From fundamentals to application

Modern lean-operated internal combustion engines running on natural gas, biogas or methane produced from wind or solar energy are highly fuel-efficient and can greatly contribute to securing energy supply, e.g. by mitigating fluctuations in the power grid. Although only comparably low emission levels form during combustion, a highly optimized emission control system is required that converts pollutants over a wide range of operation conditions. In this context, this review article pinpoints the main challenges during methane and formaldehyde oxidation as well as selective catalytic reduction of nitric oxides. The impact of catalyst formulation and operation conditions on catalytic activity and selectivity as well as the combination of several technologies for emission abatement is critically discussed. Additionally, recent experimental and theory-based progress and developments are assessed, allowing coverage of all time and length scales relevant in emission control, i.e. ranging from mechanistic and fundamental insights including atomic-level phenomena to full-scale applications

Insights into the Structural Dynamics of Pt/CeO2_{2} Single-Site Catalysts during CO Oxidation

Despite their high atomic dispersion, single site catalysts with Pt supported on CeO$_{2}$ were found to have a low activity during oxidation reactions. In this study, we report the behavior of Pt/CeO$_{2}$ single site catalyst under more complex gas mixtures, including CO, C$_{3}$H$_{6}$ and CO/C$_{3}$H$_{6}$ oxidation in the absence or presence of water. Our systematic operando high-energy resolution-fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) spectroscopic study combined with multivariate curve resolution with alternating least squares (MCR-ALS) analysis identified five distinct states in the Pt single site structure during CO oxidation light-off. After desorption of oxygen and autoreduction of Pt$^{4+}$ to Pt$^{2+}$ due to the increase of temperature, CO adsorbs and reduces Pt$^{2+}$ to Pt$^{δ+}$ and assists its migration with final formation of Pt$_{x^Δ+}$ clusters. The derived structure–activity relationships indicate that partial reduction of Pt single sites is not sufficient to initiate the conversion of CO. The reaction proceeds only after the regrouping of several noble metal atoms in small clusters, as these entities are probably able to influence the mobility of the oxygen at the interface with ceria

INCAS BULLETIN, Volume 15, Issue 3/ 2023, pp. 31 – 46 (P) ISSN 2066-8201, (E) ISSN 2247-4528 Off-axis response and shear characterization of unidirectional ply-level hybrid carbon-fiber-reinforced polymer materials

Composite materials, among them Carbon Fiber Reinforced Polymers (CFRP), have become a key material in structural applications for lightweight structures such as spacecraft and aircraft. CFRP can be found under various quality grades and their mechanical performances increase with their cost and quality grade. In order to limit the costs of the material without degrading technical performances, hybridization could be of interest. However, assessing the conservation of quality standards of hybridized CFRP is crucial. This paper investigates the off-axis mechanical response of ply-level hybrid carbon composites, with varying thickness and material quality. Two types of carbon fiber prepregs were combined in the same laminate using symmetric and asymmetric stacking sequences. Monotonic quasi-static off-axis tests were performed to evaluate the non-linear stress-strain behavior of the laminates, with Digital Image Correlation used to measure strain. The apparent elastic modulus and the in-plane shear modulus were evaluated from the tensile tests at three off-axis angles. The results indicate that the hybrid laminates exhibit higher failure stress levels compared to simple laminates, with an intermediate failure strain. Overall, this study provides insights into the off-axis mechanical behavior of ply-level hybrid carbon fiber composites, with potential applications in the design of composite structures

Freisetzung von toxischem HCN bei der Stickoxidreduktion mittels NH₃‐SCR in mager betriebenen Erdgasmotoren

Die Reduzierung der Emissionen von Treibhausgasen und gesundheitsgefährdenden Schadstoffen ist eines der wichtigsten Ziele unserer Industriegesellschaft. Erdgasmotoren sind insbesondere bei magerem Betrieb attraktiv, da sie weniger CO$_{2}$ ausstoßen als Verbrennungsmotoren, die mit flüssigen Kraftstoffen betrieben werden. Sie benötigen allerdings ein katalytisches Kontrollsystem, um Stickoxide (NO$_{x}$) aus dem Abgas zu entfernen. Hier haben wir das Zusammenspiel der aktuellen Technologie zur Stickoxidreduktion, die selektive katalytische Reduktion (SCR) mittels NH$_{3}$, und Formaldehyd, einer schädlichen Emission in Erdgasmotoren, untersucht. Bei der NO$_{x}$ Entfernung werden beachtliche Mengen an toxischem Cyanwasserstoff (HCN) gebildet. Alle getesteten Katalysatoren wandeln Formaldehyd teilweise in HCOOH und CO um. Zusätzlich werden Sekundäremissionen von HCN über die katalytische Reaktion von Formaldehyd und dessen Oxidationsintermediaten mit NH$_{3}$ beobachtet. Da die HCN Emissionen mit den derzeitigen Komponenten nicht effizient in schadstofffreie Gase umgewandelt werden können, ist die Entwicklung von Katalysatoren mit einer gesteigerten Oxidationsaktivität nötig, um dieses kritische Problem zu lösen

Enhancement of Activity and Self-reactivation of NSR-catalysts by Temporary Formation of BaPtO3-perovskite

Calcination of a Pt/Ba/CeO2 catalyst at 700°C and subsequent reduction in hydrogen, carbon monoxide or propene at 350-550°C resulted in a considerable improvement of its NO x storage-reduction (NSR) properties compared to those of a freshly prepared Pt/Ba/CeO2 catalyst. This behavior is traced back to the temporary formation of BaPtO3 perovskite which leads after reduction to well-distributed Pt particles in intimate contact with the barium-containing phases. The oxidation and reduction of platinum is reversible which can be exploited for the design of "self-regenerating” NSR-catalysts under lean (>600°C) and rich (>400°C) reaction conditions. The formation of the BaPtO3-perovskite may not only be interesting for NSR-catalysis, but generally for Pt-based catalysts where a high dispersion of Pt is importan