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Graphical abstract Highlights • Dry SO 2 streams poison Z 2 Cu and ZCuOH sites in Cu-SSZ-13. • SCR kinetics are consistent with 1:1 SO 2 poisoning of each Z 2 Cu site. • New H+ sites are formed after SO 2 poisoning of Z 2 Cu sites. • SO 2 -poisoned Cu sites are less mobile than NH 3 -solvated Cu sites. • Z 2 Cu sites are more resistant to SO 2 poisoning and easier to regenerate. Abstract The effects of sulfur poisoning on Cu-SSZ-13 zeolites, used commercially for the selective catalytic reduction (SCR) of nitrogen oxides (NO X) with ammonia, were studied by exposing model Cu-zeolite powder samples to dry SO 2 and O 2 streams at 473 and 673 K, and then analyzing the surface intermediates formed using spectroscopic and kinetic assessments. Model Cu-SSZ-13 zeolites were synthesized to contain distinct Cu active site types, predominantly either divalent Cu2+ ions exchanged at proximal framework Al (Z 2 Cu), or monovalent CuOH+ complexes exchanged at isolated framework Al (ZCuOH). SCR turnover rates (473 K, per Cu) decreased linearly with increasing S content to undetectable values at equimolar S:Cu ratios, consistent with poisoning of each Cu site with one SO 2 -derived intermediate. Cu and S K-edge X-ray absorption spectroscopy and density functional theory calculations were used to identify the structures and binding energies of different SO 2 -derived intermediates at Z 2 Cu and ZCuOH sites, revealing that bisulfates are particularly low in energy, and residual Brønsted protons are liberated at Z 2 Cu sites as bisulfates are formed. Molecular dynamics simulations also show that Cu sites bound to one HSO 4 − are immobile, but become liberated from the framework and more mobile when bound to two HSO 4 −. These findings indicate that Z 2 Cu sites are more resistant to SO 2 poisoning than ZCuOH sites, and are easier to regenerate once poisoned. [ABSTRACT FROM AUTHOR]

The influence of phosphorus on the catalytic properties, durability, sulfur resistance and kinetics of Cu-SSZ-13 for NO x reduction by ammonia selective catalytic reduction (NH 3 -SCR) were systematically investigated to obtain a deeper understanding of the deactivation of Cu-SSZ-13 in the presence of phosphorus-containing impurities in diesel exhaust. An enhanced effect on NO conversion at low phosphorus loading was found above 450 ℃, probably due to the reduction of copper oxides that promote NH 3 oxidation at high temperatures. As the phosphorus loading reached 0.4 mmol/g catal , the framework dealumination and decrease of the BET specific surface area, acidity, and isolated Cu 2+ ions accounted for the decrease in activity and hydrothermal stability over the entire temperature range. Simultaneously, the activity of phosphorus-impregnated samples tested in the presence of SO 2 indicates that phosphorus accelerates the deactivation of Cu-SSZ-13 in the presence of SO 2 at low temperatures, primarily due to the severe decrease of the Cu 2+ ion content and partial coverage of the acid sites and active sites by phosphate and sulfate species. Additionally, kinetic analysis further demonstrated that phosphorus has an inhibitory effect on the SCR reaction rates at low temperatures and high phosphorus addition changes the NH 3 -SCR reaction kinetic parameters. The data presented herein provide a comprehensive picture of the interaction between phosphorus and Cu-SSZ-13. [ABSTRACT FROM AUTHOR]

Abstract: 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. [ABSTRACT FROM AUTHOR]

Sb was used as the additive to enhance the NH 3 -SCR performance of MnTiO x catalyst. Experimental results revealed that MnSbTiO x -0.2 demonstrated outstanding NH 3 -SCR activity in a wide temperature window (100–400 ℃) and high resistance to SO 2 . Characterization results indicated the introduction of Sb into MnTiO x catalyst could improve the dispersity of active species and generate more surface acid sites, Mn 4+ and surface adsorbed oxygen species. In situ DRIFT spectra proved that the presence of Sb in MnSbTiO x -0.2 catalyst could form new Brønsted acid sites, along with the increased surface Lewis acidity. The improved adsorption of NH 3 and NO x species over MnSbTiO x -0.2 catalyst had a stimulating effect on the NH 3 -SCR reaction over it through Langmuir−Hinshelwood (L-H) route. Moreover, Sb species in MnSbTiO x -0.2 could improve the reactivities of ad-NH 3 and ad-NO x species in SCR reaction. All these factors contributed to the excellent performance of MnSbTiO x -0.2 catalyst. [ABSTRACT FROM AUTHOR]

Our previous studies suggested that the biomass tar derived from pyrolysis of distilled spirit lees (DSL) is an attractive agent for lowering NOx emission in the circulating fluidized bed decoupling combustion (CFBDC) process. The present work is furthered to evaluate the capabilities of other tar agents including sawdust (SD) tar and Xianfeng (XF) coal tar for NO reduction in a lab-scale drop-tube reactor. Additionally, five representative model tar compounds including phenol, benzene, acetic acid, methyl acetate and heptane were also tested to clarify the contribution of the main components in tar agents to NO reduction. The realized NO reduction efficiency by tar obviously varied with the reburning stoichiometric ratio (SR) and reaction temperature. At a specified mass feeding rate of reductant, say 0.15 g/min, the NO reduction realized by the SD tar is higher than that by the XF coal tar, and was even better than that by the DSL tar obtained in our previous study. Testing the NO reduction by model tar compounds revealed that phenol plays an important role in enabling its good NO reduction for the SD tar. The major understanding from the work is that the compounds containing at least an aromatic ring (e.g. phenol, benzene, etc.) are the major contributor for reducing NO in either biomass tar or coal tar. [ABSTRACT FROM AUTHOR]

Nitro aromatic waste water pollutants have become a serious issue, constituting a severe hazard to whole ecosystems and public health. Therefore, it is necessary to design high performance catalytic equipment for the reduction of nitroaromatic compounds from contaminated aqueous solutions. Herein, a robust and rapid method is developed to prepare a macroporous monolithic carbon foam with commercial melamine resin foam as the raw material. Then, the prepared monolithic carbon foam is exploited as an excellent 3D porous network to load Au NPs (MCF/Au). The as-prepared MCF/Au monolith can be innovatively utilized to construct a dynamic fixed-bed system. In addition, the as-obtained system exhibits exceptional catalytic reduction performance for 4-nitrophenol (4-NP). More importantly, the continuous flow reactor system shows excellent recyclability and can be reused for at least ten successive runs without apparent loss of activity. [ABSTRACT FROM AUTHOR]

The selective catalytic reduction (SCR) of NOx with C 3 H 6 in the presence of O 2 on silica sub-microtubes with platinum nanoparticles was studied in order to establish a possible reaction mechanism at different experimental conditions. This catalyst showed a high NO conversion with very high selectivity to N 2 at mild conditions in the presence of excess oxygen when using C 3 H 6 as reducing agent. The influence of both NO and C 3 H 6 concentrations on their conversions was analyzed at different space times. The obtained results suggest that the three reactants (C 3 H 6 , NO, and O 2 ) are adsorbed on Pt sites. The kinetic model proposed considers that both dissociative adsorption of NO and activation of the hydrocarbon can take place simultaneously. Nevertheless, the value of the parameters obtained by the resolution of the model equations indicates that the first one presents a major relevance. These results are in concordance with the high selectivity to N 2 observed, because the preponderance presence of dissociated NO avoids the formation of N 2 O by the reaction of molecular NO with N dissociated from NO. Furthermore, both NO reduction and C 3 H 6 oxidation conversions are represented reasonably well by the model presented. [ABSTRACT FROM AUTHOR]

Ti-Bearing blast furnace slag has been found to be suitable as the support of the selective catalytic reduction (SCR) catalysts. Mn–Ce–M (M = Fe, Co, Ag)/Slag catalysts prepared using a solution impregnation method for the low-temperature selective catalytic reduction (SCR) of NO with NH3 under the influence of transition metals were investigated in this study. The experiments suggested that the addition of Co can greatly enhance the SCR activity and the addition of Fe can broaden the SCR temperature range (NO conversion ＞90%), while the addition of Ag reduced the SCR activity. The XRD and SEM analyses revealed that for the Co and Fe doped catalysts, the active components were well dispersed, while the Ag doped catalyst had agglomeration and sintering. The XPS results revealed that the Fe and Co doped catalysts had relatively higher ratios of Mn4+/Mn3+, Ce3+/Ce4+ and Oα/Oα + Oβ. TPR results showed that the redox properties were enhanced after adding Co and Fe. NH3-TPD was also studied to investigate the acid sites over the surface of the catalysts. And the addition of Co and Fe increased strong acid sites on the surface of the catalyst. However, the strength of acid sites over the surface of the Ag doped catalyst was too high to cause the desorption of NH3. [ABSTRACT FROM AUTHOR]

Catalytic performance of CeO 2 -MO x (0.25) (M = Mn, Fe and Cu) mixed oxide nanocatalysts were investigated in NO + CO reduction. Sol-gel method was used to synthesize nanocrystalline mixed oxides. Catalysts were characterized by XRD, BET, SEM, TEM and H 2 -TPR analysis. The Ce-Cu mixed oxide catalyst showed superior activity than other catalysts (with 80% NO and 72% CO conversions), due to its better reduction properties. To model and optimize the NO and CO conversions, a neuro-genetic approach was employed. This approach established by combining an artificial neural network with a genetic algorithm. The results showed that the ANN model is accurate with R 2 = 0.991, 0.979 and 0.960 for training, validation and testing, respectively. Catalyst design factors (Cu/Ce molar ratio, citric acid/nitrate and calcination temperature) were optimized by GA. The optimum values were 0.49, 0.98 and 500 °C. For Cu/Ce molar ratio, citric acid/nitrate and calcination temperature, correspondingly. NO conversion predicted through ANN-GA system and obtained via experimental at 300 °C were 91% and 90%, respectively. [ABSTRACT FROM AUTHOR]

In this study, the concept of fast SCR for NO reduction with NH as reducing agent is realized via the combination of nonthermal plasma (NTP) with Mn-based catalyst. Experimental results indicate that 10% wt. Mn-Ce-Ni/TiO possesses better physical and chemical properties of surface, resulting in higher NO removal efficiency if compared with 10% wt. Mn-Ce/TiO and 10% wt. Mn-Ce-Cu/TiO. Mn-Ce-Ni/TiO of 10% wt. achieves 100% NO conversion at 150 °C, while 10% wt. Mn-Ce/TiO and 10% wt. Mn-Ce-Cu/TiO need to be operated at a temperature above 200 °C for 100% NO conversion. However, NO conversion achieved with 10% wt. Mn-Ce-Ni/TiO is significantly reduced as HO and SO are introduced into the SCR system simultaneously. Further, two-stage system (SCR with DBD) is compared with the catalyst-alone for NO conversion and N selectivity. The results indicate that 100% NO conversion can be achieved with two-stage system at 100 °C, while N selectivity reaches 80%. Importantly, NO conversion achieved with two-stage system could maintain >95% in the presence of CH, CO, SO, and HO, indicating that two-stage system has better tolerance for complicated gas composition. Overall, this study demonstrates that combining NTP with Mn-based catalyst is effective in reducing NO emission at a low temperature (≤200 °C) and has good potential for industrial application. [ABSTRACT FROM AUTHOR]

Hexavalent chromium is a water-soluble pollutant, the mobility of which can be controlled by reduction of Cr(VI) to less soluble, environmentally benign Cr(III). Iron(II/III)-bearing clay minerals are widespread potential reductants of Cr(VI), but the kinetics and pathways of Cr(VI) reduction by such clay minerals are poorly understood. We reacted aqueous Cr(VI) with two abiotically reduced clay minerals: an Fe-poor montmorillonite and an Fe-rich nontronite. The effects of ionic strength, pH, total Fe content, and the fraction of reduced structural Fe(II) [Fe(II)/Fe(total)] were examined. The last variable had the largest effect on Cr(VI) reduction kinetics: for both clay minerals, the rate constant of Cr(VI) reduction varies by more than 3 orders of magnitude with Fe(II)/Fe(total) and is described by a linear free energy relationship. Under all conditions examined, Cr and Fe K-edge X-ray absorption near-edge structure spectra show that the main Cr-bearing product is a Cr(III)-hydroxide and that Fe remains in the clay structure after reacting with Cr(VI). This study helps to quantify our understanding of the kinetics of Cr(VI) reduction by Fe(II/III)-bearing clay minerals and may improve predictions of Cr(VI) behavior in subsurface environments. [ABSTRACT FROM AUTHOR]

The SCR performances of CaO poisoning CeO 2 –WO 3 and V 2 O 5 –WO 3 /TiO 2 catalysts were prepared and compared for selective catalytic reduction of NO with NH 3 (NH 3 –SCR). It was found that the CeO 2 –WO 3 catalyst showed better calcium resistance than V 2 O 5 –WO 3 /TiO 2 catalyst even when the CaO mass percentage reached up to 5 wt%. In order to further understand the resistance mechanism, XRD, Raman, XPS, H 2 -TPR, NH 3 -TPD and in situ DRIFTS were used to analyze and explore the changes of CeO 2 –WO 3 catalysts before and after the CaO deactivation. The results manifested that the introduction of Ca species not only affected CeO 2 lattice but also led to CaWO 4 formation on the surface. Additionally, although CaO increased the surface chemisorbed oxygen and Ce 4+ species, the reducibility and Lewis acid sites, NH 3 chemisorbed amount and Brønsted acid sites were greatly inhibited after deactivation. Furthermore, the enhanced NO 2 adsorption capacity after the alkaline Ca species introduction could partially offset the negative effect in the loss of acid sites over the catalyst surface, which might be the primary reason for stronger CaO resistance of CW catalyst than traditional V 2 O 5 –WO 3 /TiO 2 catalyst. [ABSTRACT FROM AUTHOR]

The embodiment of the NOx selective catalytic reduction (SCR) functionality in a diesel particulate filter (DPF), so-called SCR-on-Filter (SCRoF), is investigated through numerical modeling with SCR kinetics corresponding to Cu-Chabazite and Fe-ZSM5 catalysts. The results of the simulations of the SCR activity, performed in the absence and presence of soot, indicate that the presence of soot negligibly affects the NOx conversion efficiency, given the slow dynamics of passive regeneration. Conversely, the reduction in cake thickness by soot passive oxidation is significantly different in the absence of SCR activity (uncatalyzed DPF) compared to that in its presence (SCRoF). In fact, in the SCRoF only 60-80% of the original soot consumption obtained in the absence of SCR reaction over 1 h can be achieved. Individual Cu-Chabazite and Fe-ZSM5 catalysts, as well as in-series layers of the two catalysts, are investigated to devise the widest temperature window for SCRoF. © 2016 American Institute of Chemical Engineers AIChE J, 63: 238-248, 2017 [ABSTRACT FROM AUTHOR]

Zero-valent iron (ZVI) reductive dechlorination is a promising approach for the abatement of chlorinated organic pollutants in the environment. In this study, ZVI and Ni/Fe bimetal nanoparticles were synthesized and applied for the treatment of chloronitrobenzenes (CNBs) in water. The pre- and post-reaction nanoparticles samples were characterized by SEM and XRD respectively. Here we show that ZVI nanoparticles can effectively perform the selective reduction of p -CNB to p -chloroaniline ( p -CAN) with a selectivity of ca. 100% in 10 min without dechlorination throughout the research. Catalytic reduction of p -CNB over Ni/Fe nanoparticles could be divided into two sequential processes: the first is the conversion of p -CNB to p -CAN, and the second is the reductive hydrodechlorination of p -CAN with aniline formation. Direct catalytic hydrodechlorination of p -CNB as a side route was also observed. Results indicate that ZVI initiates the electron transfer process for the reduction of p -CNB to p -CAN, whereas Ni catalyst is in favor of hydrogen transfer as the dominant pathway for the dechlorination reactions. The complete reduction mechanisms of p -CNB over ZVI and Ni/Fe nanoparticles were discussed, and the kinetics of dechlorination of CNBs were found to be pseudo-first order. The effects of different experimental parameters, such as solution pH, dosage of Ni/Fe nanoparticles, initial concentration of p -CNB and the Ni loading on the catalytic reduction of p -CNB were carefully investigated. Under the several reaction conditions tested, a complete dechlorination could be attained in 2 h. The dechlorination reactivity for mono-CNBs decreases in the order: p -CNB > o -CNB > m -CNB. The energy gap between HOMO and LUMO is firstly indicated as a descriptor to evaluate the dechlorination reactivity of mono-CNBs, which may provide a new insight in predicting the dechlorination reactivity for other organic chlorides. [ABSTRACT FROM AUTHOR]

WO role in NO reduction over VO-WO/TiO was studied by comparing the kinetic parameters of the selective catalytic reduction (SCR) reaction, the non selective catalytic reduction (NSCR) reaction and the C-O reaction. The results show that the SCR reaction over VO/TiO was promoted after WO incorporation, while the NSCR reaction and the C-O reaction were both restrained. Graphical Abstract: [ABSTRACT FROM AUTHOR]

Methoxychlor [or 4,4′-(2,2,2-trichloroethane-1,1-diyl)bis(methoxybenzene)], a common environmental pollutant, has been catalytically reduced with nickel(I) salen electrogenerated in situ at carbon cathodes in dimethylformamide (DMF) containing 0.050 M tetra- n -butylammonium tetrafluoroborate (TBABF 4 ). Cyclic voltammograms for reduction of nickel(II) salen in the presence of various concentrations of methoxychlor provide evidence for catalytic reduction. Cathodic peak currents for the nickel(II) salen–nickel(I) salen redox couple increase in proportion to the concentration of methoxychlor, whereas the anodic peak current associated with reoxidation of nickel(I) salen diminishes; in addition, a cathodic prepeak appears at higher concentrations of methoxychlor. Controlled-potential (bulk) electrolyses of nickel(II) salen at reticulated vitreous carbon cathodes in the presence of methoxychlor allowed the n value for reduction of methoxychlor to be determined. With the aid of gas chromatography–mass spectrometry, major electrolysis products have been identified as 4,4′-(2-chloroethene-1,1-diyl)bis(methoxybenzene) and 4,4′-(ethene-1,1-diyl)bis(methoxybenzene), and the product distribution was determined by means of gas chromatography. Adducts arising from the combination of fragments derived from methoxychlor and DMF have also been detected and confirmed, and a mechanistic scheme is proposed to account for the various products. [ABSTRACT FROM AUTHOR]

Thenonselective catalytic reduction (NSCR) reaction and the catalyticoxidation of NH3to NO (C–O reaction) simultaneouslyhappened during the selective catalytic reduction (SCR) of NO withNH3over V2O5–WO3/TiO2, especially at higher temperatures. There was anexcellent linear relationship between the SCR reaction rate and gaseousNO concentration, and the intercept and slope can be used to describethe rate constant of NO reduction through the Langmuir–Hinshelwoodmechanism and that through the Eley–Rideal mechanism, respectively.However, the NSCR reaction rate was nearly independent of gaseousNO concentration, and the reaction order of the C–O reactionwith respect to gaseous NO concentration was much less than zero.According to the kinetic study, the relationship of the SCR performance(i.e., SCR activity and N2selectivity) with the key factors(for example V2O5content, H2O effect,and reactant concentration) was built, which can be used to predictthe SCR performance. [ABSTRACT FROM AUTHOR]

The catalytic activity of palladium (Pd) nanostructures highly relies on their size and morphology, especially enclosed with high-index facets, which provide more active sites so as to enhance their catalytic performance comparing with their low-index facet counterparts. Herein, Pd concave nanocubes enclosed with {730} facets by a one-pot scalable liquid method, with various high-index facets are synthesized via tuning reduction kinetics. Due to their high-index facets, the Pd concave nanocubes exhibit much higher electrocatalytic activity and stability for methanol oxidation than the Pd nanocubes enclosed by {100} facets and commercial Pd/C. Furthermore, we scale up synthesis of Pd concave nanocubes by expanding the volume of all species to fifty times with high-yield production. [ABSTRACT FROM AUTHOR]