Large diesel engines require emissions control strategies to meet the standards that are present across the globe. The low temperature exhaust temperature associated with these engines create uniquely challenging conditions to meet these standards, and thus significant research is being pursued into approaches that can reduce the emissions of NOx and hydrocarbon (HC) criteria pollutants. This effort investigates the ability of two zeolite-based materials that have demonstrated the ability to store NOx and HCs, Pd/LTA and Pd/SSZ-13. Research was performed in controlled conditions of a flow reactor to repeatedly probe the ability of these materials to store NOx and representative HCs under industrially relevant conditions. After the 30-minute storage, the NOx/HC release and reactivity were evaluated as the materials were heated to 600 °C under oxidizing conditions. Both qualitative and quantitative differences for the two types of materials are evident. It is seen that while NO capture using Pd/SSZ-13 was ~1.6x higher than Pd/LTA, the latter stored ~2.6-2.7x higher decane, releasing it primarily when the bed warmed to >200 °C. In each case the NOx storage behavior decreases with repeated adsorption/desorption cycles, while the HC storage behavior is stable. Using a range of characterization techniques our research focused on identifying different adsorption sites on the materials to explain the varying behavior to help guide development of new more robust materials.

Reducing pollutant emissions from heavy-duty (HD) diesel engines is critical due to their significant environmental impact, particularly concerning NOx emissions. Understanding and optimizing modern diesel oxidation catalyst (DOC) and selective catalytic reduction (SCR) performance is essential for improving exhaust aftertreatment (EAT) system efficiency to meet stringent emissions regulations. The oxidation of nitric oxide (NO) to nitrogen dioxide (NO2) in DOC plays a key role in improving SCR efficiency in reducing NOx. This study investigates the DOC performance in oxidizing NO to NO2 and its impact on the SCR efficiency of a 2021 MY Navistar E39 HD diesel engine. The influence of engine speed, load, exhaust gas temperature, and composition on DOC efficiency is experimentally investigated. The relationships between DOC inlet temperature, oxygen availability and NO2/NOx ratio at the DOC inlet are examined to better understand their effects on the overall DOC efficiency. The results indicate that DOC NO oxidation efficiency is highly dependent on exhaust temperature, with optimal oxidation occurring within a specific temperature range (275-350 degrees C). Below this threshold, the chemical reactions are kinetically limited, while at higher temperatures, thermodynamic constraints reduce the efficiency of DOC in oxidizing NO to NO2. The experimental data further reveal that the NO2/NOx ratio peaks at medium loads before declining at higher loads due to reduced residence time and mass transfer effects. Additionally, the SCR NOx conversion efficiency is significantly influenced by the NO2/NOx ratio, achieving peak performance when the NO2/NOx ratio approaches 0.5. A DOC chemistry model was developed and validated against the experimental data to predict DOC oxidation behavior under various operating conditions. The findings of this study provide insights into the interdependencies between DOC and SCR performance, contributing to the optimization of SCR systems for optimized NOx reduction.

Nanoparticle-supported Pt and Pd catalysts are employed industrially to convert CO and hydrocarbon residue from incomplete diesel fuel combustion into more environmentally-benign products. However, these catalysts deactivate over time due to sintering, especially for Pt nanoparticles which readily generate volatile species under high operating temperatures. Here, we turned the detrimental vapor-mediated sintering of Pt into an advantage by using a physical mixture of Pt and Pd catalysts prepared using a raspberry-colloid-templating (RCT) method. The RCT method produced Pt/Al2O3 and Pd/Al2O3 catalysts with partially embedded NPs to inhibit surface-mediated sintering pathways. As validated using an industry-defined emission control test protocol, aging a physical mixture of Pt/Al2O3 and Pd/Al2O3 at high temperature produced an alloyed PtPd/Al2O3 catalyst that outperformed the fresh catalyst mixture and both individual catalysts for hydrocarbon conversion, while exhibiting high catalytic stability and resistance to sintering and to SO2 poisoning. X-ray photoelectron spectroscopy revealed that in the aged catalyst mixture, half of the Pd content existed in the more active metallic state, compared to the less active oxide forms in the fresh mixture and both individual catalysts, explaining the unusual activity enhancement. Our results represent a practical approach to producing active and stable PtPd/Al2O3 diesel oxidation catalysts for emission control applications.

Developing robust Pt/CeO2-based three-way catalysts (TWCs) with enhanced oxygen buffering capability and low-temperature activity is highly desirable. In this study, a new TWC family, Pt/(1 - x)CeO2(core)@xZrO2(shell) (where x = 0-0.5), was prepared and evaluated at degreened (DG) and hydrothermally aged (HTA) states. Incorporation of 0.1 molar concentration of ZrO2 resulted in a decreased temperature that 50% (T50) (CO: 167 degrees C, THCs: 218 degrees C, NO: 228 degrees C) and 90% (T90) (CO: 207 degrees C, THCs: 237 degrees C, NO: 244 degrees C) conversions achieved over HTA 1.8 wt% Pt/0.9CeO2@0.1ZrO2 compared to the HTA 1.8 wt% Pt/CeO2 sphere (CO: T50,90 = 179, 222 degrees C, THCs: 234, 252 degrees C, NOx: 240, 260 degrees C). An enhanced oxygen storage capacity and oxygen release rate were observed over Pt/0.9CeO2@0.1ZrO2 compared to the Pt/CeO2 sphere. Increasing the ZrO2 molar concentration to values greater than 0.2 resulted in increased T50s (224, 265 274 degrees C) and T90s (251, 289, 292 degrees C) for CO, THCs, and NOx, respectively, over 1.8 wt.% Pt/0.5CeO2@0.5ZrO2. Overall, this work highlights the potential of forming a ZrO2 shell on CeO2 spheres as a support for TWC applications.

Sorbent stability poses significant impacts on long-term performance of direct air capture (DAC) of CO2 and levelized cost of capture (LCOC). We report the DAC performance degradation of amine-infused fiber sorbents based on poly-(ethylenimine) (PEI), mesoporous SiO2, and cellulose acetate (CA) over CO2 cyclic sorption cycles in a nonoxidative environment. Infrared and nuclear magnetic resonance spectra indicate that the aminolysis reactions between CA ester moieties and PEI amine sites lead to the formation of acetamides and hence lower CO2 affinities of the sorbents. This stability issue can be remedied by hydrolysis treatment of the CA fiber sorbents before PEI impregnation or replacing CA with poly-(ether sulfone). This study underscores the importance of selecting proper support or additive materials of DAC contactors that are compatible with active species of CO2 capture.

In the past few decades, tremendous attention has been devoted to enhancing the activity of oxygen evolution reaction (OER) catalysts for hydrogen production, while the cost and long-term stability of catalysts, which can play an even more important role in industrialization, have been much less emphasized. Herein, we engineered an OER electrode from abundant stainless steel (SS) via facile approaches, and the obtained electrode consists of a Ni-rich oxide surface layer with a Fe-rich metal substrate. An outstanding activity was observed with an overpotential of 316 mV at 100 mA cm-2 in 1 M KOH electrolyte. Additionally, an electrode self-replenishing concept is proposed in which a Ni-rich catalyst layer can be regenerated from a metallic substrate due to the difference in diffusion and dissolution rates of metal oxides/hydroxides, and this regeneration is validated by various characterizations. A recorded degradation rate of 0.012 was observed at 1000 mA cm-2 for 1000 h. The facile engineering of OER electrodes from SS combined with the self-replenishing catalyst can potentially address the cost, activity, and long-term stability barriers.

Pd/BEA is chosen as a model passive NOx adsorber (PNA) to elucidate the effect of the feed gas composition on the NOx adsorption/desorption behavior. The Br & oslash;nsted acid and the partially hydrolyzed framework Al (P-HAl(OH)) sites in HBEA adsorb NO and NO2 under dry conditions. Moreover, the performance of HBEA is not affected by CO, while CO inhibits nitrate formation and promotes NO adsorption via the Pd(NO)(CO) complexes formation over Pd/BEA. H2O inhibits NO adsorption over the Br & oslash;nsted acid and P-HAl(OH) sites, and ionic Pd is the only active site for NOx adsorption under wet conditions. Furthermore, NO adsorption over hydrated Pd (Pd2+(OH)(NO)(H2O)(3)) is weaker than NO adsorption over bare ionic Pd (Z(2)[Pd2+(NO)], Z[Pd2+(OH)(NO)]). Dehydration of Pd2+(OH)(NO)(H2O)(3) forms more stable Z[Pd2+(OH)(NO)] during desorption. The NO adsorption capacity of Pd/BEA improves in the presence of CO under both dry and wet conditions by forming a stable carbonyl-nitrosyl complex.

PdO/gamma-Al2O3 catalysts suffer from gradual and irreversible catalyst deactivation under lean CH4 oxidation conditions, especially in a wet feed. Time-resolved CO chemisorption DRIFTS measurements are conducted systematically on a series of PdO/gamma-Al2O3 catalysts to probe the surface reactivity of PdO nanoparticles after various in situ pretreatments. At 80 degrees C, CO barely adsorbs on fully oxidized PdO surfaces but interacts with coordinatively unsaturated Pd sites, causing gradual reduction of the PdO surfaces. This results in the formation of characteristic IR bands on various metallic Pd-0 sites. By monitoring and comparing the formation kinetics of these IR bands on samples before and after CH4 oxidation, we theorize that the irreversible catalyst deactivation during CH4 oxidation is caused by PdO surface reconstruction, in which coordinatively unsaturated Pd sites gradually become fully coordinated by oxygen. Effectively, the surface reconstruction leads to the formation of a passivation layer on the PdO nanoparticles, which hinders their ability in activating CH4, and hence the subsequent oxidation reaction. Temperature-programmed reduction with CO as the reductant (CO-TPR) reveals that the passivation layer formed during CH4 oxidation is significant enough to increase the reduction temperature of PdO nanoparticles of the 3.0% PdO/gamma-Al2O3 samples, although such an effect is less obvious for the 0.4% PdO/gamma-Al2O3 samples. On the other hand, it is also discovered that the passivation layer is not completely inert. Under certain reaction conditions, with some being relatively mild, such as low-temperature CO oxidation in a net lean atmosphere and in the presence of H2O, the passivation layer can undergo structure change which results in regeneration or even activation of CH4 oxidation activity of an already deactivated catalyst. Additionally, it is discovered that the fully coordinated Pd-O surface is a metastable phase under CH4 oxidation conditions. In the presence of H2O and at ambient temperatures, surfaces with coordinatively unsaturated Pd sites are thermodynamically more favorable.

A PtPd/Al2O3 catalyst developed for the complete oxidation of methane from the ventilation air of underground coal mines is compared against a model PdO/Al2O3 catalyst. Although the PtPd/Al2O3 catalyst is substantially more active and stable than the model catalyst, the nature of active sites between the two catalysts is deemed to be fundamentally the same based on their response to different feed gas compositions and the evolution of surface CO adsorption complexes during time-resolved CO adsorption DRIFTS experiment. For both catalysts, coordinatively unsaturated Pd sites are considered the active centers for methane activation and the subsequent oxidation reaction. H2O competes with CH4 for the same active sites, resulting in severe inhibition. Additionally, the CH4 oxidation reaction also causes self-inhibition. Taking both inhibition effects into consideration, a relatively simple kinetic model is developed. The model provides a good fit of the 72 sets of kinetic data collected on the PtPd/Al2O3 catalyst under practically relevant reaction conditions with CH4 concentration in the range of 0.05–0.4%, H2O concentration of 1.0–5.0%, and reaction temperatures of 450–700 °C. Kinetic parameters based on the model suggest that the CH4 activation energy on the PtPd/Al2O3 catalyst is 96.7 kJ/mol, and the H2O adsorption energy is −31.0 kJ/mol. Both values are consistent with the parameters reported in the literature. The model can be used to develop catalyst sizing guidelines and be incorporated into the control algorithm of the catalytic system.

Boron-containing compounds are one of the lubricant additive options due to their suitable properties for additives and have been used as commercial lubricant additives. In the present study, the impact of a boron-containing lubricant oil additive, AR9100 (BR), on Pd/Rh-based three-way catalyst (TWC) performance is investigated, and the results are compared with the baseline no-additive (NA) case and the industry standard zinc dialkyl-dithiophosphate (ZDDP) results. Accelerated engine aging is performed using a genset to expose the catalysts to lubricant additives at high temperatures. All aged TWC samples are investigated for reactivity in a bench-flow reactor and characterized using a variety of analytical techniques. Compared with the no-additive case, the temperatures of 90% conversion (T90) of NO, CO, C3H6, and C3H8 for the ZDDP-aged TWC sample increased by 34, 30, 37, and 48 °C. However, the T90 of all gas species for the BR-aged TWC sample are similar to the NA-aged TWC sample. Additionally, a significant decrease in water–gas shift reactivity and oxygen storage capacity is observed in the ZDDP-aged sample, but not in the BR-aged sample. Inductively coupled plasma-optical emission spectrometry (ICP-OES) analysis and electron probe microanalysis (EPMA) maps of accelerated engine aging samples show the presence of phosphorus and boron in ZDDP- and BR-aged TWC samples, respectively. However, no boron-related peaks are observed in the X-ray diffraction (XRD) pattern of the BR-aged TWC sample, which may exist in the form of an amorphous phase.

In this study, the diesel oxidation performance of degreened (DG) and hydrothermally aged monometallic and bimetallic Pd/Pt/SiO2(core)@Zr(shell) catalysts with varying Pd/Pt molar ratios from 3/1-1/3 was evaluated. Pd/Pt(3/1)/SiO2 @Zr (DG) achieved 50% and 90% conversion of CO at 166 degrees C (T50), 169 degrees C (T90) and total hydrocarbons (THCs) at 198 degrees C (T50), 244 degrees C (T90). Decreasing the Pd/Pt molar ratio led to a decrease in the T50,90's, with Pd/Pt(1/3)/SiO2 @Zr (DG) achieving T50,90's at 153, 156 degrees C for CO and 171, 200 degrees C for THCs, respectively. Moreover, Pd/Pt(1/3)/SiO2@Zr showed enhanced hydrothermal stability. XRD and TEM showed that in the hydrothermally aged bimetallic catalysts, the fraction of Pd present as a Pt-Pd metallic alloy increased with Pt content. The enhanced low temperature performance of Pd/Pt(1/3)/SiO2@Zr compared to the other studied catalysts was attributed to Pd being primarily present in metallic form, despite being subjected to severe oxidizing conditions.

Cu is a unique metal that catalyzes carbon monoxide/carbon dioxide (CO/CO2) to form high-order hydrocarbons and oxygenates through the CO/CO2 reduction reaction (CO/CO2RR) at decent selectivity and productivity.

To understand how the composition of novel lubricant additives and their ash interact with gasoline particulate filters (GPFs), an accelerated aging protocol was conducted using three lubricant additive formulations and two GPF types. The additive packages (adpaks) consisted of Ca+Mg detergent in a 3:1 or 0:1 ratio and an anti-wear component—either zinc dialkyl dithiophosphate (ZDDP) or a novel phosphonium-phosphinate ionic liquid (IL) substitute. The particulate sampling captured amount/compositions of particulate matter (PM) generated, total particulate number, and size distribution. Five ash loadings were completed. GPF position and adpak composition affected the backpressure, ash composition, ash morphology, and captured mass. The particulate sampling indicated that the ash component consisted primarily of particles less than 50 nm in size and that the Mg-only adpak resulted in more particulate of 50–400 nm in size. Postmortem materials characterization indicated GPFs in the underfloor position had deeper penetration of ash into the walls compared to the close-coupled position. Additionally, the Mg-only adpak had a higher filter collection efficiency (>90%) and the ash particles consisted of a higher concentration of dense ash material. In contrast, four of the 3:1 Ca:Mg lubricant adpaks resulted in a collection efficiency of only 40–50%. Although the collection efficiency was higher with the Mg-only adpak, the ash layer in the GPF was not thicker, nor was the penetration into the wall more significant, and surprisingly the full useful life (FUL) backpressure was lower than with Ca:Mg adpaks. The higher density of the Mg-derived ash was the only detectable difference. A possible explanation of this observation is that Mg ash has a lower melting point and is more susceptible to densification during combustion or GPF regeneration. The substitution of IL in place of the ZDDP did not lead to any notable changes in collection efficiency or location of the ash.

With increasing concerns about global warming, the push for sustainable and eco-friendly fuels is accelerating. Propane, recognized as liquefied petroleum gas or LPG, has garnered research interest as an alternative fuel due to its notable advantages, including a high-octane rating, reduced greenhouse gas emissions, and potential cost-effectiveness. However, to realize its full potential as an alternative fuel it is essential to develop catalysts that efficiently handle emissions at low temperatures. In our research, we investigated three distinct palladium (Pd)-based three-way catalyst (TWC) formulations (PdRh, Pd-only, and Pd-OSC) to investigate the influence of typical TWC components rhodium (Rh) and oxygen storage components (OSC) in exhaust scenarios relevant to propane-fueled engines. Among these, the formulation containing oxygen storage components (Pd-OSC) showed the highest reactivity for both NO and C3H8 while minimizing performance degradation from hydrothermal aging (HTA). Notably, the temperature of 50% conversion (T50) for propane in the Pd-OSC fresh and HTA sample was lower by 30 °C and 13 °C, respectively, compared to the Pd-only sample, highlighting the role of oxygen storage materials in enhancing catalyst performance, even without dithering. Additionally, N2 physisorption showed that the Pd-OSC sample has a higher surface area and increased pore volume. This underscores the idea that OSC materials not only augment the catalyst’s porosity but also optimize reactant accessibility to active sites, thus elevating catalytic efficiency. In addition to evaluating performance, we further explored the performance and characteristics of the catalysts using catalytic probe reactions, such as water–gas shift and steam reforming reactions.

A bifunctional catalyst for converting CO2 to dimethyl ether in a single process can improve energy utilization efficiency and reduce capital and operational costs. To overcome the major challenge of catalyst deactivation caused by metal sintering and detrimental interactions among the catalytic components, we developed a layer structured bifunctional monolith catalyst concept, in which a CuO/ZnO/ZrO2 component for methanol synthesis using CO2 as feedstock and a Ferrierite zeolite component for the subsequent dehydration reaction are washcoated on a metallic monolith substrate as two separate layers. The monolith catalyst significantly improves the synergistic effects of the two components, resulting in a 20% increase in the productivity for dimethyl ether at 240 °C as compared to the conventional catalysts. More remarkably, the layer structured design minimizes the undesirable interaction between the two components and drastically improves the on-stream durability of the catalyst. No activity decline was observed in a 146-hour performance test.

Designing Rh-free, especially Pt-only, three-way catalysts with improved low-temperature activity/stability is highly desirable. Herein, we demonstrate that ultrastable Pt/CeO2-Al2O3 nanosheet catalysts can be obtained based on a Sabatier principle of metal-support interaction. Tuning the surface coverage of penta-site rich γ-Al2O3 nanosheets (AlNS, weak adhesion to Pt) by CeO2 “nano-islands” (strong adhesion to Pt) can lead to the synthesis of Pt/60 wt.%CeO2-AlNS that have lower light-off temperatures for CO, hydrocarbons, and NO compared to conventional Pt/CeO2 and Pt/Al2O3 catalysts by 100-200 oC and a similar performance with the state-of-the-art Rh-based catalyst. Incorporating CeO2 on the surface of AlNS can retard the sintering of CeO2 and Pt during harsh redox hydrothermal aging. The improved activity/stability of Pt/CeO2-AlNS catalysts can be attributed to tuning of the Pt detachment and migration from and back to the CeO2 nanoislands, respectively, that keeps Pt as nanoclusters on CeO2, the most active species for three-way catalyst applications.

Catalytic oxidation of CH4 over nonprecious Ni/CeO2 catalysts has attracted wide attention. Controlling the morphology of a CeO2 support can enhance the CH4 oxidation activity without changing the catalyst composition. Herein, a series of 2 wt % Ni/CeO2 nanocatalysts with different CeO2 support morphologies (nanoparticles (P), rods (R), cubes (C)) and synthetic procedures (precipitation, sol-gel (SG)) were evaluated for their CH4 oxidation performance. The redox properties of CeO2 supports and corresponding Ni loaded catalysts were characterized by H2-temperature-programmed reduction and oxygen storage capacity (OSC) measurements. The relationship among the CeO2 morphologies, surface areas, redox properties, and CH4 oxidation activity for both CeO2 supports and Ni/CeO2 catalysts was established. The findings suggest that CeO2-R has a greater amount of surface oxygen vacancies as well as an improved OSC and CH4 oxidation activity compared to CeO2-P and CeO2-C supports. The same CH4 oxidation activity pattern was observed for the Ni containing catalysts (Ni/CeO2-R > Ni/CeO2-P > Ni/CeO2-C). Increasing the CeO2 surface area by using a solgel synthesis method (CeO2-SG) improved the amount of surface oxygen vacancies and CH4 oxidation performance of CeO2-SG and Ni/CeO2-SG compared to CeO2-R and Ni/CeO2-R, respectively. Finally, all studied Ni/CeO2 nanocatalysts showed improved hydrothermal stability compared to conventional Pd/Al2O3.

A three-way catalyst (TWC) and a TWC with a NOx storage component (NS-TWC) were evaluated on a lean spark ignition (SI) engine platform to reduce the fuel consumption and emissions of a passive selective catalytic reduction (pSCR) emission control system. The pSCR system is an approach for controlling NOx emissions from lean SI engines. It relies on onboard NH3 generation over a TWC during brief periods of fuel-rich operation. The NH3 is then stored on a downstream SCR catalyst and is available for NOx reduction during subsequent periods of lean engine operation. The NS-TWC addition enabled longer lean operation and more efficient NH3 use, which lowered fuel penalty of the pSCR system. Over a pseudo-transient drive cycle, the lean SI engine with pSCR that included NS-TWC demonstrated a 8.3% reduction in gasoline consumption over stoichiometric-only engine operation, and the NOx and non-CH4 organic gas emissions were consistent with Environmental Protection Agency (EPA) Tier 3 levels. The CO emissions, primarily from rich operation, exceeded the EPA Tier 3 levels. A cleanup catalyst (CUC) with high oxygen storage capacity was used to oxidize tailpipe CO during rich excursions by using the stored oxygen from the preceding lean operation. Although the CUC decreased CO emissions and reduced NH3 slip, some of the NH3 was converted back to NOx. Furthermore, rich CO control remains challenging. The results of this work demonstrate significant improvement in fuel consumption and emissions with a modified pSCR system architecture.

Designing Rh-free, especially Pt-only, three-way catalysts with improved low-temperature activity/stability is highly desirable. Herein, we demonstrate that ultrastable Pt/CeO2-Al2O3 nanosheet catalysts can be obtained based on a Sabatier principle of metal-support interaction. Tuning the surface coverage of penta-site rich gamma-Al2O3 nanosheets (AlNS, weak adhesion to Pt) by CeO2 "nano-islands" (strong adhesion to Pt) can lead to the synthesis of Pt/60 wt.%CeO2-AlNS that have lower light-off temperatures for CO, hydrocarbons, and NO compared to conventional Pt/CeO2 and Pt/Al2O3 catalysts by 100-200 degrees C and a similar performance with the state-of-the-art Rh-based catalyst. Incorporating CeO2 on the surface of AlNS can retard the sintering of CeO2 during harsh redox hydrothermal aging, associate with the strong interaction between CeO2 "nano-island" and penta-site rich gamma-Al2O3 nanosheets. Moreover, the improved activity/stability of Pt/CeO2-AlNS catalysts can be attributed to tuning of the Pt detachment and migration from and back to the CeO2 "nano-islands", respectively, that keeps Pt as nanoclusters on CeO2, the most active species for three-way catalyst applications.