Influence of the Substrate Properties on the Performances of NH3-SCR Monolithic Catalysts for the Aftertreatment of Diesel Exhaust: An Experimental and Modeling Study

Effect of a Plasma Burner on NOx Reduction and Catalyst Regeneration in a Marine SCR System

The problem of environmental pollution by the combustion of fossil fuels in diesel engines, to which NOx emission is a dominant culprit, has accelerated global environmental pollution and global and local health problems such as lung disease, cancer, and acid rain. Among various De-NOx technologies, SCR (Selective Catalytic Reduction) systems are known to be the most effective technology for actively responding to environmental regulations set by the IMO (International Maritime Organization) in marine diesel applications. The ammonia mixes with the exhaust gas and reacts with the NOx molecules on the catalyst surface to form harmless N2 and H2O. However, since the denitrification efficiency of NOx can be rapidly changed depending on the operating temperature from 250 °C to 350 °C at 0.1% sur contents of the catalyst used in the SCR, a device capable of controlling the exhaust gas temperature is essential for the normal operation of the catalyst. In addition, when the catalyst is exposed to SOx in a low exhaust gas temperature environment, the catalyst is unable to reduce the oxidation reaction of the catalyst, thereby remarkably lowering the De-NOx efficiency. However, if the exhaust gas temperature is set to a high temperature of 360–410 °C, the poisoned catalyst can be regenerated through a reduction process, so that a burner capable of producing a high temperature condition is essential. In this study, a plasma burner system was applied to control the exhaust gas temperature, improving the De-NOx efficiency from the engine and regenerating catalysts from PM (Particulate Matter), SOOT and ABS (ammonia bisulfate), i.e., catalyst poisoning. Through the burner system, the optimum De-NOx performance was experimentally investigated by controlling the temperature to the operating region of the catalyst, and it was shown that the regeneration efficiency in each high temperature (360/410 °C) environment was about 95% or more as compared with the initial performance. From the results of this study, it can be concluded that this technology can positively contribute to the enhancement of catalyst durability and De-NOx performance.

Cu/ZSM5-Geopolymer 3D-Printed Monoliths for the NH3-SCR of NOx

Geopolymer-based monoliths manufactured by direct ink writing, containing up to 60% by weight of presynthesized ZSM5 with low Si/Al ratio, were investigated as structured catalysts for the NH3-SCR of NOx. Copper was introduced as the active metal by ion exchange after a preliminary acid treatment of the monoliths. Monolithic catalysts were characterized by morphological (XRD and SEM), textural (BET and pore size distribution), mechanical (compressive strength), chemical (ICP–MS), redox (H2-TPR) and surface (NH3-TPD) analyses, showing the preservation of Cu-exchanged zeolite features in the composite monoliths. NH3-SCR tests, carried out on both monolithic and powdered samples in the temperature range 70–550 °C, confirmed that composite monoliths provide a very good activity and a high selectivity to N2 over the whole range of temperatures explored due to the hierarchical structure of the materials, in addition to a good mechanical resistance—mostly related to the geopolymer matrix.

A Fundamental Investigation of Gas/Solid Heat and Mass Transfer in Structured Catalysts Based on Periodic Open Cellular Structures (POCS)

In this work, we investigate the gas-solid heat and mass transfer in catalytically activated periodic open cellular structures, which are considered a promising solution for intensification of catalytic processes limited by external transport, aiming at the derivation of suitable correlations. Computational fluid dynamics is employed to investigate the Tetrakaidekahedral and Diamond lattice structures. The influence of the morphological features and flow conditions on the external transport properties is assessed. The strut diameter is an adequate characteristic length for the formulation of heat and mass transfer correlations; accordingly, a power-law dependence of the Sherwood number to the Reynolds number between 0.33 and 0.67 was found according to the flow regimes in the range 1-128 of the Reynolds number. An additional -1.5-order dependence on the porosity is found. The formulated correlations are in good agreement with the simulation results and allow for the accurate evaluation of the external transfer coefficients for POCS.

CeO2 grafted with different heteropoly acids for selective catalytic reduction of NOx with NH3

The CeO₂ catalysts grafted with heteropoly acid (i.e., HPA) could enhance their catalytic performance for selective catalytic reduction of NO_x with NH₃ (NH₃-SCR). In comparison to HSiW/CeO₂, HPMo/CeO₂, and commercial V₂O₅-WO₃/TiO_x catalysts, HPW/CeO₂ catalysts showed the best SCR performance. XPS and DRIFTS demonstrated that the amount of HPA on HPW/CeO₂ was more than those on HSiW/CeO₂ and HPMo/CeO₂. H₂-TPR results indicated that reducibility of HPMo/CeO₂ was stronger than those of HSiW/CeO₂ and HPW/CeO₂, resulting in the high-temperature performance loss. According to kinetic results, below 250 °C, k_SCR-ER and k_SCR-LH of HPW/CeO₂ were higher than those of HSiW/CeO₂, meanwhile k_side of both HSiW/CeO₂ and HPW/CeO₂ were low. Therefore, HPW/CeO₂ had the better SCR performance than HSiW/CeO₂. As NH₃ was completely consumed, SCR activity depended on the ratio of SCR reaction in the consumption of NH₃. The selectivity of SCR reaction, NSCR reaction, and C-O reaction of HSiW/CeO₂ were almost the same as those of HPW/CeO₂ above 250 °C, resulting in the NO_x conversion of HPW/CeO₂ was basically the same as that of HSiW/CeO₂ above 250 °C. Due to the lowest k_SCR-ER and k_SCR-LH, and highest k_side, NO_x conversion of HPMo/CeO₂ was the worst compared to HSiW/CeO₂ and HPW/CeO₂ catalysts.

A new V2O5–MoO3–TiO2–SO42−nanostructured aerogel catalyst for diesel DeNOxtechnology

A new V₂O₅–MoO₃–TiO₂–SO₄²⁻nanostructured aerogel catalyst exhibits superior SCR activity compared to the V₂O₅–WO₃/TiO₂commercial catalyst (EUROCAT) at high temperatures (375–500 °C).

Development of cerium-based catalysts for selective catalytic reduction of nitrogen oxides: a review

Nitrogen oxides (NO_X) are major pollutants of the atmosphere, and selective catalytic reduction of nitrogen oxides using ammonia as a reductant (NH₃-SCR) is an effective method to remove nitrogen oxides.

Simulation of exotherms from the oxidation of accumulated carbonaceous species over a VSCR catalyst

A model is built to simulate the burn-off process of accumulated carbonaceous species over a VSCR catalyst.

Impact of Catalyst Geometry on Diffusion and Selective Catalytic Reduction Kinetics under Elevated Pressures

In marine diesel engine applications, selective catalytic reduction (SCR) upstream of the turbocharger may become the preferred technology when dealing with high sulfur fuels and low exhaust gas temperatures. The target nitrogen oxide reductions in combination with minimum ammonia slip and reduced gas diffusion rates under elevated pressures require understanding of the impact of catalyst geometry on the SCR kinetics. The extent, trends, and sources for this observation are elucidated in this work by systematic testing of catalysts with equal geometry and/or intrinsic activity.

Effect of CeO2 for a high-efficiency CeO2/WO3–TiO2 catalyst on N2O formation in NH3-SCR: a kinetic study

The effect of CeO₂ for a high-efficiency CeO₂/WO₃–TiO₂ catalyst on N₂O formation in NH₃-SCR reaction was investigated using a kinetic method.