Design of regenerated TiNb2O7 with engineered local polarization effect for fast-charging applications prepared by waste SCR catalyst carriers.

This chapter gives an overview on the combined lean NOx trap (LNT) and selective catalytic reduction (SCR) catalysts. In particular, the focus is on the reaction pathways involved in such systems when different reducing agents are being used to accomplish the rich phase in the LNT system. In combined LNT–SCR systems, NH3 emitted from the LNT catalyst during the rich phase is captured onto a SCR catalyst placed downstream the LNT brick. The stored ammonia is then used as reactant in the SCR catalyst upon reaction with NO slipped from the LNT catalyst during the lean phase. This increases the NOx removal efficiency and reduces the emissions of unwanted ammonia. When using hydrocarbons as reducing agents, a non-NH3 SCR reaction pathway is also operating: in fact, HCs slipped through the LNT catalyst react with NO over the SCR catalyst, thus contributing to the overall NOx abatement. The overall system efficiency depends on several factors including the catalyst formulation (LNT and SCR), the operating conditions and the reducing agents used during the rich phase. In addition, the system architecture (dual layer vs dual bed) plays a role in determining the system efficiency.

Reduction of oxidized mercury over NOx selective catalytic reduction catalysts: A review

<div>Different aftertreatment systems consisting of a combination of selective catalytic reduction (SCR) and SCR catalyst on a diesel particulate filter (DPF) (SCR-F) are being developed to meet future oxides of nitrogen (NO<sub>x</sub>) emissions standards being set by the Environmental Protection Agency (EPA) and the California Air Resources Board (CARB). One such system consisting of a SCRF<sup>®</sup> with a downstream SCR was used in this research to determine the system NO<sub>x</sub> reduction performance using experimental data from a 2013 Cummins 6.7L ISB (Interact System B) diesel engine and model data. The contribution of the three SCR reactions on NO<sub>x</sub> reduction performance in the SCR-F and the SCR was determined based on the modeling work. The performance of a SCR was simulated with a one-dimensional (1D) SCR model. A NO<sub>2</sub>/NO<sub>x</sub> ratio of 0.5 was found to be optimum for maximizing the NO<sub>x</sub> reduction and minimizing NH<sub>3</sub> slip for the SCR for a given value of ammonia-to-NO<sub>x</sub> ratio (ANR). The SCRF<sup>®</sup> + SCR system was simulated using the 2D SCR-F + 1D SCR system model. For all the test conditions, the NO<sub>2</sub>/NO<sub>x</sub> ratio downstream of the SCRF<sup>®</sup> was found to be 0 due to NO<sub>2</sub> consumption by the NO<sub>2</sub> assisted particulate matter (PM) oxidation and the SCR reactions in the SCRF<sup>®</sup>. Due to this low NO<sub>2</sub>/NO<sub>x</sub> ratio, the NO<sub>x</sub> conversion performance of the downstream SCR was limited to a maximum of 70% and the system performance to a maximum of 97%. The low SCR performance is due to low fast SCR (<10%) and high standard SCR reaction (>85%) rates in the downstream SCR. Also, high NH<sub>3</sub> slip due to lower utilization by the SCR reactions was observed from the SCR. Improved NO<sub>2</sub>/NO<sub>x</sub> ratio at the SCRF<sup>®</sup> inlet results in NO<sub>2</sub> slip at the SCRF<sup>®</sup> outlet, which then leads to better NO<sub>x</sub> reduction performance of this system.</div>

The promoting/inhibiting effect of water vapor on the selective catalytic reduction of NOx

Selective catalytic reduction (SCR) catalyst is currently considered the most effective technology for high nitrogen oxides removal from exhaust gas of a diesel engine using ammonia as a reducing agent. To design an SCR catalyst, we require knowing the flow and reactive properties, geometric feature and thermal properties of the SCR catalyst. These properties can be described using partial differential equations (PDEs). PDEs can be solved by numerical methods. However, chemical reaction parameters from the reactive gases are unknown in PDEs. Therefore, the model cannot be solved unless the parameters are identified. Identification of reaction parameters in an SCR catalyst leads to a highly non-linear least squares problem. In this work, we solved this least squares problem for reaction parameters. Using these reaction parameters, the model was used to simulate the nitrogen oxides emission from an SCR catalyst.

Impacts of acid gases on mercury oxidation across SCR catalyst

The modern mobile aftertreatment systems (ATSs) include ammonia slip catalyst (ASC) located after the selective catalytic reduction (SCR) catalyst. Mainly copper, iron and vanadium SCR catalysts are applied commercially. SCR systems are mostly located after diesel particulate filter (DPF), which is thermally a demanding location for SCR and ASC. ASC properties are integrated to control strategy together with the SCR catalyst to reach NOx conversions above 95%. Reactions by Pt loading, Pt layer radial location (bottom, top, full layer) and feed conditions were simulated experimentally in synthetic gases on Cu, Fe and V based SCR catalysts in this study. NH3 slip after SCR unit was simulated in controlled (NH3/NO ≤ 1) or uncontrolled (NH3 only or NH3/NOx >> 1) conditions. The axial location of Pt relatively to the flow direction dominated to the radial location of Pt in reaction rates. The results showed significant differences in ammonia conversions and reaction selectivity (to N2, NO, N2O) by the Pt layer location (bottom or top) together with a thick SCR layer. The Pt loading was optimized to the range of 2–5 g/cft to keep a good selectivity to N2 as well as to avoid N2O/NOx formation and the Pt contamination effect on SCR. Pt-ASC was necessary to remove remaining NH3 and CO after SCR but the prevention of N2O formation is an essential part of design. Experimental simulations with 2-layer ASC with a Cu-chabazite (CHA) catalyst resulted in a complete mapping by the Pt loading as a function of space velocity and temperature as fresh and hydrothermally aged.

Porous oxygen-deficient TiNb2O7 spheres wrapped by MXene as high-rate and durable anodes for liquid and all-solid-state lithium-ion batteries

Tailored Alkali Resistance of DeNOx Catalysts by Improving Redox Properties and Activating Adsorbed Reactive Species

Diesel emission fluid (DEF) soaking and urea deposits on selective catalytic reduction (SCR) catalysts are critical issues for real diesel engine NH3-SCR systems. To investigate the impact of DEF soaking and urea deposits on SCR catalyst performance, fresh Cu-zeolite catalyst samples were drilled from a full-size SCR catalyst. Those samples were impregnated with DEF solutions and subsequently hydrothermally treated to simulate DEF soaking and urea deposits on real SCR catalysts during diesel engine operations. Their SCR performance was then evaluated in a flow reactor with a four-step test protocol. Test results show that the DEF soaking leached some Cu from the SCR catalysts and slightly reduced their Cu loadings. The loss of Cu and associated metal sites on the catalysts weakened their catalytic oxidation abilities and caused lower NO/NH3 oxidation and lower high-temperature N2O selectivity. Lower Cu loading also made the catalysts less active to the decomposition of surface ammonium nitrates and decreased low-temperature N2O selectivity. Cu loss during DEF impregnation released more acid sites on the surface of the catalysts and increased their acidities, and more NH3 was able to be adsorbed and involved in SCR reactions at medium and high temperatures. Due to lower NH3 oxidation and higher NH3 storage, the DEF-impregnated SCR catalyst samples showed higher NO x conversion above 400 °C compared with the non-soaked one. The negative impact of urea deposits during DEF impregnation was not clearly observed, because the high-temperature hydrothermal treatment helped to remove the urea deposits.

A noble-metal-free SCR-LNT coupled catalytic system used for high-concentration NOx reduction under lean-burn condition

Research progress on selective catalytic reduction (SCR) catalysts for NOx removal from coal-fired flue gas

Adsorption and Activation of NH3 during Selective Catalytic Reduction of NO by NH3

<div class="section abstract"><div class="htmlview paragraph">Significant reduction in Nitrogen Oxide (NOx) emissions will be required to meet LEV III Emissions Standards for Light Duty Diesel passenger vehicles (LDD). As such, Original Equipment Manufacturers (OEMs) are exploring all possible aftertreatment options to find the best balance between performance, robustness and cost. The primary technology adopted by OEMs in North America to achieve low NOx levels is Selective Catalytic Reduction (SCR) catalyst. The critical parameters needed for SCR to work properly are: an appropriate reductant such as ammonia (NH<sub>3</sub>) typically provided as urea, adequate operating temperatures, and optimum Nitrogen Dioxide (NO<sub>2</sub>) to NOx ratios (NO<sub>2</sub>/NOx). The NO<sub>2</sub>/NOx ratio is mostly influenced by Precious Group Metals (PGM) containing catalysts located upstream of the SCR catalyst. Different versions of zeolite based SCR technologies are available on the market today and these vary in their active metal type (iron, copper, vanadium), and/or zeolite type. To select an appropriate SCR type, the application’s operating conditions as well as environmental factors must be considered. To fundamentally understand these differences, a study was conducted where various SCR catalysts are evaluated in a laboratory environment in regards to, 1) PGM contamination 2) operating temperature and resulting thermal aging, 3) NO<sub>2</sub> levels from the system architecture, 4) the extent of reductant usage and overexposure, and 5) the impact of oxygen concentrations during the aging of catalysts. In this study, various types of copper SCR catalysts are evaluated using several unique and standard testing methods to expose them to conditions simulating lifetime exposure. Some non-ideal or “worst case scenarios” were explored regarding Diesel Emissions Fluid (DEF) usage, dosing quality and thermal exposure. Results highlight the advantages and disadvantages of various SCR and zeolite types available in the marketplace.</div></div>

Simultaneous soot combustion and NOx reduction over a vanadia-based selective catalytic reduction catalyst