The facile fabrication of low-cost photocatalysts with enhanced activity and high atomic utilization is becoming increasingly necessary for solar energy usage and/or conversion. In this work, a series of mesoporous carbon nitride nanosheets with an enlarged specific surface area was synthesized via an inorganic acid-assisted exfoliation method without any soft or hard templates. An ultralow loading of downsized noble metal Pt was anchored on these porous nanosheets, exhibiting enhanced photocatalytic activity. The formation of mesoporous nanosheets in carbon nitride was expected to boost the mass transfer and shorten the charge carrier transfer route during the photocatalytic reaction. The characterization of samples revealed that the enhanced conductivity and photocurrent of the carbon nitride nanosheets also contributed to the enhanced H2 evolution activity. The maximum H2 production rates of 172.92 μmol h-1 and 321 μmol h-1 were achieved over the nanosheets derived from melamine and urea under visible light irradiation, which are 10.92- and 2.22-fold that of the corresponding bulk carbon nitride, respectively. This exfoliation method was demonstrated to be an efficient and universal method for the preparation of carbon nitride nanosheets with a mesoporous structure and high atom utilization of the co-catalyst for H2 evolution from water.

Cu-SSZ-13 catalysts are widely used for diesel aftertreatment applications for NOx (NO and NO2) abatement via selective catalytic reaction (SCR) due to their high conversion efficiency and excellent hydrothermal stability. Diesel engine exhaust contains small amounts of SOx due to the combustion of sulfur compounds in diesel fuel. The engine out SOx level mainly depends on the sulfur content in the diesel fuel. The presence of SOx from engine exhaust can deteriorate the SCR performance of Cu-SSZ-13 catalysts in real-world applications. This work is focused on the sulfur-induced deactivation process of a Cu-SSZ-13 catalyst under a range of simulated diesel engine operating conditions. Two catalyst deactivation modes, namely chemical poisoning and physical poisoning, are identified, primarily depending on the operating temperature. Chemical poisoning mainly results from the interaction between SOx and Cu species within the zeolite framework. Physical poisoning is a consequence of the accumulation of ammonium (bi) sulfate formed from the interaction between SOx and NH3, especially at low temperature conditions. Temperature programmed desorption (TPD) experiments were conducted to characterize the deactivated catalyst. In addition, a modeling approach was applied to quantify the deactivation process as well as the decomposition of the sulfur species on the poisoned catalyst to optimize the catalyst reactivation strategy.

Cu-SSZ-13 catalysts have been widely used for NOx reduction via SCR for diesel aftertreatment applications due to their high SCR efficiency. Hydrothermal aging and sulfur poisoning are two areas of research on Cu-SSZ-13 catalysts due to their significant relevance to real world applications. In addition to the effects of 650 degrees C hydrothermal aging, this work also investigates the corresponding sulfur poisoning effects upon aging. Hydrothermal aging results in decreasing SCR reactivity with constant activation energy. Upon sulfation at 400 degrees C, the catalyst displays decreasing SCR reactivity with lower activation energy. However, upon longer aging duration prior to sulfation, the decrease in SCR reactivity becomes less and the catalyst becomes more resistant toward sulfur poisoning with less sulfur loading. The enhanced sulfur poisoning resistance of Cu-SSZ-13 catalyst can be mainly ascribed to the gradual conversion of ZCuOH to Z(2)Cu upon aging as suggested by results from NH3 TPD and DRIFTS.

Filtration via a porous medium is a ubiquitous process where high-fidelity physical models are needed. The classical cell model oversimplifies the filtration medium and results in biased and inaccurate predictions of the filter performance. This paper presents the discrete framework of a polydisperse cell model that can incorporate any measured pore size distribution. A new equation connecting the polydisperse cell efficiencies and the medium efficiency is derived from first principles. For ceramic filters, the discrete model demonstrates a generic prediction capability of the filtration efficiency with a root-mean-squared difference of 5.4%, while the counterpart of the classical cell model is 26.4%. In addition, the discrete model eliminates the biased predictions of the classical cell model on sub-100 nm particles.

Engine particulate filters have been widely applied across the world to control engine exhaust particulate matter (or particulate number) emissions. With increasing vehicle mileage, ash accumulation deteriorates vehicle fuel economy and complicates on-board control. Extending filter service life with ash loading has significant economic and environmental impacts. Many studies have been conducted in characterizing ash accumulation and evaluating its impacts on filter performance. However, comprehensive reviews covering all the key issues in the field are rather rare. This paper reviews the extensive prior research on filter ash, and not only summarizes the experimental observations but also elucidates the fundamental mechanisms. The review covers the areas of ash origin, accumulation, transport, evolution, and artificial acceleration methods. The previously reported data of ash properties is compiled and analyzed. The advantages and disadvantages of ash acceleration approaches are also discussed in detail. Based on the cumulative understanding, a few potential ways to improve ash management are discussed in this paper. In short, the present work systematically reviews the previous observations and understanding of ash aging in particulate filters and identifies areas that need further research, which can be useful guidance for future studies.

Surface-modified Ni species derived from 2D Ni-MOFs were loaded on g-C3N4 with high dispersion by the in situ calcination method.

The nanocomposite preparation procedure plays an important role in achieving a well-established heterostructured junction, and hence, an optimized photocatalytic activity. In this study, a series of g-C3N4/ZnO nanocomposites were prepared through two distinct procedures of a low-cost, environmentally-friendly, in-situ fabrication process, with urea and zinc acetate being the only precursor materials. The physicochemical properties of synthesized g-C3N4/ZnO composites were mainly characterized by XRD, UV–VIS diffuse reflectance spectroscopy (DRS), N2 adsorption-desorption, FTIR, TEM, and SEM. These nanocomposites’ photocatalytic properties were evaluated in methylene blue (MB) dye photodecomposition under UV and sunlight irradiation. Interestingly, compared with ZnO nanorods, g-C3N4/ZnO nanocomposites (x:1, obtained from urea and ZnO nanorods) exhibited weak photocatalytic activity likely due to a “shading effect”, while nanocomposites (x:1 CN, made from g-C3N4 and zinc acetate) showed enhanced photocatalytic activity that can be ascribed to the effective establishment of heterojunctions. A kinetics study showed that a maximum reaction rate constant of 0.1862 min-1 can be achieved under solar light illumination, which is two times higher than that of bare ZnO nanorods. The photocatalytic mechanism was revealed by determining reactive species through adding a series of scavengers. It suggested that reactive ●O2− and h+ radicals played a major role in promoting dye photodegradation.

The hydrothermal stability of K-Ca-Si-O glass soot oxidation catalysts has been improved by substitution of Ce and Zr for Ca. This work demonstrates that glasses can be tailored to withstand the challenging diesel exhaust hydrothermal environment by considering the field strengths and partial molar free energies of the hydration reactions (ΔGi) of the cation species in the glass. The result is a glass that shows less formation of precipitates after 2 h hydrothermal exposure in air with 7% H2O at temperatures ranging from 300–700 °C. A K-Ca-Si-O glass with a soot T50 (the temperature when 50% of the soot is oxidized) of 394 °C was found to degrade to 468 °C after a 2 h, 700 °C hydrothermal exposure, whereas the improved K-Ce-Zr-Si-O glass only changed from 407 °C to 427 °C after the same treatment.

Potassium volatility and activity in a novel K-Ca-Si-O glass catalyst was investigated over extended periods of soot oxidation. Soot was continuously deposited and oxidized by maintaining a glass catalyst-coated filter at temperatures above the oxidation balance point to provide a soot mass equivalent to 100 000 miles of engine operation. Testing revealed the 52-SiO2, 35-K2O, and 13-CaO wt % glass catalysts show a significant improvement in soot oxidation performance over a Pt catalyst. The glass catalyst retains soot oxidation catalytic activity even after testing equivalent to 100 000 miles of use. Migration of potassium in the catalyzed filter from the inlet to the outlet channels was observed. Although potassium was detected on an uncoated downstream core after 50 h of testing, showing that some volatilization of K occurs, the catalyst retains remarkable activity. Surface analysis characterization shows K enrichment of the catalytic glass surface relative to the bulk, which supports the proposed mechanism that water vapor in the diesel exhaust draws K+ ions to the glass surface. The studies demonstrate that a glass designed to allow the catalyst surface to be replenished with K ions on a continuous basis can overcome previous concerns about the durability of soot catalysts relying on alkali metals.

Cummins has recently launched next-generation aftertreatment technology, the Single ModuleTM aftertreatment system, for medium-duty and heavy-duty engines used in on-highway and off-highway applications. Besides meeting EPA 2010+ and Euro VI regulations, the Single ModuleTM aftertreatment system offers 60% volume and 40% weight reductions compared to current aftertreatment systems. In this work, we present model-based approaches that were systematically adopted in the design and development of the Cummins Single ModuleTM aftertreatment system. Particularly, a variety of analytical and experimental component-level and system-level validation tools have been used to optimize DOC, DPF, SCR/ASC, as well as the DEF decomposition device. The highlights of this work can be summarized as follows: a). internal dosing is more efficient than external dosing to control HC slip; High CPSI DOCs show better HC oxidation performance at high SV due to enhanced mass transfer; b). the adopted advanced DPF technologies enable greater ash capacity for long maintenance intervals; c). SCR performance was optimized with the use of a hydrothermally robust Cu-Zeolite catalyst coated on high CPSI substrates.

K-containing soot oxidation catalysts are promising to reduce or replace noble metal usage in combustion engine emission abatement systems. In this paper, we introduce a facile approach for applying a K-containing glass catalyst onto structured wire mesh monoliths to achieve low temperature soot removal. A polyvinyl butyral (PVB) modified sol-gel process was developed to yield a crack-free thickness that is 6 times that of the conventional sol-gel process. An intermediate SiO2 barrier layer was found to be effective to insure stability of the glass catalyst over extended cycling periods. The catalytically coated wire mesh can lower the soot ignition temperature ((Tig)) to similar to 370 degrees C with O-2, and offers catalytic stability for long term combustion cycling. (C) 2018 Elsevier B.V. All rights reserved.

In diesel soot oxidation studies, both well-defined model soot and a reliable means to simulate realistic contact conditions with catalysts are crucial. This study is the first attempt in the field to establish a lab-scale continuous flame soot deposition method in simulating the “contact condition” of soot and a structured diesel particulate filter (DPF) catalyst. The properties of this flame soot were examined by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM) for structure analysis, Brunauer-Emmett-Teller (BET) for surface area analysis, and thermogravimetric analysis (TGA) for reactivity and kinetics analysis. For validation purposes, catalytic oxidation of Tiki® soot using the simulated contact condition was conducted to compare with the diesel particulates collected from a real diesel engine exhaust system. It was found that the flame soot is more uniform and controllable than similar samples of collected diesel particulates. The change in T50 due to the presence of the catalyst is very similar in both cases, implying that the flame deposit method is able to produce comparably realistic contact conditions to that resulting from the real exhaust system. Comparing against the expensive engine testing, this novel method allows researchers to quickly set up a procedure in the laboratory scale to reveal the catalytic soot oxidation properties in a comparable loose contact condition.

With ever-tightening emission regulations, particulate filters are critical for internal combustion engines to meet the stringent particulate matter emission standards. A fast way to predict the filter performance, instead of numerically solving the governing differential equations, is needed for filter design and selection, real-time control, malfunction detection, and deposit load sensing. Approximate analytical solutions for wall flow filters, considering asymmetric channels and arbitrary deposit amounts, are derived by a technique of successive approximation. The analytical predictions of filter pressure drop have been validated against both steady state and transient experimental measurements. Moreover, over a broad range of filter operating conditions, the accuracy of the second-order analytical solution is validated by comparisons with the numerical predictions. The derivation also provides analytical expressions for channel and wall velocity profiles along the filter length. This study reveals the necessity of considering the nonlinear term of the governing equations when the actual open widths of inlet and outlet channels are quite different.

One field-returned DPF loaded with a high amount of ash is examined using experimental and modeling approaches. The ash-related design factors are collected by coupling the inspection results from terahertz spectroscopy with a calibrated DPF model. The obtained ash packing density, ash layer permeability and ash distribution profile are then used in the simulation to assess the ash impact on DPF backpressure and regeneration behaviors. The following features have been observed during the simulation:1. The ash packing density, ash layer permeability and ash distribution profile should be collected at the same time to ensure the accurate prediction of ash impact on DPF backpressure. Missing one ash property could mislead the measurement of the other two parameters and thus affects the DPF backpressure estimation.2. The ash buildup would gradually increase the frequency for the backpressure-based active soot regeneration. However, the accumulated ash reduces the energy density during the regeneration event as well as adsorbing exotherm, lowering the thermal cracking risk.

K–Ca–Si–O glass was applied to metal supports for use as a catalyst for diesel soot combustion. Glasses were processed from the melt and by a sol–gel route. Catalyst activity for the oxidation of diesel exhaust soot and flame soot from an oil lamp was compared by thermogravimetric analysis (TGA). The results show that a K-based catalytic glass coating on metal substrates can reduce the temperature where half of the engine soot is oxidized (T50) to as low as 360°C under loose contact conditions, and offers catalytic stability for long term combustion cycling. Scanning electron microscopy observations show that sol–gel glass processing is effective for coating complex wire mesh shapes without pore clogging.

Potassium disilicate (K2Si2O5) glasses substituted with additions of Ca2+ and Al3+ have been prepared, characterized and tested as diesel soot oxidation catalysts. Ca and Al modify the silicate glass network, resulting in improved stability for catalyzing oxidation of diesel soot. TGA and water immersion studies showed that substituting K2O with CaO can improve the chemical stability with a small loss of catalytic activity. (K2O)0.5(CaO)0.5(SiO2)2 had a soot ignition temperature (Tig) around 410°C and also excellent catalytic stability with repeated soot oxidation cycling. Similarly, substituting with Al3+ gave improved stability, with (K2O)0.7(Al2O3)0.3(SiO2)2 exhibiting a Tig around 370°C and better stability than K2O·2Si2O2. The activity results are interpreted with insights gained from FTIR characterization.

A novel approach for catalyzing diesel soot oxidation with a potash glass is reported. A simple potash glass (35K2O:2SiO2:13CaO weight ratio) was synthesized and examined for activity for the combustion of diesel soot under various contact and atmospheric conditions by thermogravimetric analysis (TGA). The glass was found to be an effective soot oxidation catalyst. Leaching of potassium from the glass helps to mitigate the effect of potassium loss during combustion, offering an effective means to maintain the surface activity of the glass catalyst, as seen from repeated TGA cycling.