Exhaust Catalysts Research Articles

WAYS OF UTILIZATION OF SPENT PETROCHEMICAL MOLYBDENUM CATALYSTS

The article gives an overview of diff erent recycling technologies for exhaust catalysts. The quantitative indexes of extraction ratio of molybdenum are given. The reasons for the decline of molybdenum extraction rate from spent catalysts of pyrometallurgical and hydrometallurgical technologies are indicated. The advantages and disadvantages of technology of direct steel alloying by spent catalyst through the slag phase are described. The general scheme of tailings recycling of hydrometallurgical and pyrometallurgical refi ning of spent catalysts were proposed, implying their use as components of the solid slag mixtures. The optimal ways of complex catalysts processing and waste-free scheme for spent catalysts processing are described. The use of calcium molybdate was proposed as ligature at the stage of steel processing at ladle furnace.

Pd model catalysts: Effect of aging duration on lean redispersion

An automotive three-way catalyst (TWC) deteriorates as a function of temperature, time and aging environment. While much effort has gone into formulating durable exhaust catalysts, relatively little attention has been paid to controlling the aging environment on the vehicle with techniques currently in use to protect the catalyst and counteract the increasing demands for higher fuel economy (e.g., overfueling to reduce exhaust temperatures). New engine control methods that are designed to minimize aging may be possible that can reduce the extent of catalyst deactivation and provide a lean environment capable of redispersing many of the precious metal particles. To develop improved engine control methods, detailed experimental information is needed to map the response of the catalyst to different aging conditions. In this report, we examine palladium-based model powder catalysts on ceria–zirconia, which were exposed to three different exhaust compositions, lean-only, rich-only and redox, each at 700°C for three different durations, 20min, 2h and 16h. Residual catalyst activity and metal-support interaction were probed with Water Gas Shift (WGS) reaction and Oxygen Storage Capacity (OSC) measurements. The Pd metal particle size and dispersion were estimated by H2 chemisorption and XRD line broadening. Lean catalyst treatments at 550°C and 700°C were applied to determine the effect on Pd size and catalyst activity. An infrared study of CO adsorption onto the catalysts was used to identify whether Pd crystallite facets were covered by the support after exposure to the redox aging environment then again after the lean treatments were applied. The aging temperature and reducing gas environment significantly deteriorated catalytic activity through a combination of metal oxidation state effects and support interactions, while the aging duration was linked to the extent of Pd sintering reversibility through lean treatments. These insights provide a basis to develop engine control and aftertreatment design strategies to avoid severe aging modes and determine how often to actively intervene to regenerate the catalyst.

Extending the potential of x-ray free-electron lasers to industrial applications—an initiatory attempt at coherent diffractive imaging on car-related nanomaterials

Recent advances in x-ray free-electron lasers (XFELs) open up new pathways for contributing to industrial research-and-development activities. In this article, we describe our initiatory attempt at using the SPring-8 Ångström compact free-electron laser (SACLA) for industrial applications. The attempt was conducted by the authors through the industry-academia partnership program initiated by RIKEN, aimed at examining the potential of XFELs for the analysis of car-related nanomaterials. Using the infrastructures developed at SACLA, we performed single-shot coherent diffractive imaging experiments on automotive exhaust catalysts and succeeded in obtaining the reconstructed images. This effort has paved the way for the future use of XFELs in the research-and-development activity of automotive exhaust catalysts.

ChemInform Abstract: Invited Review: Some Recent Developments in the Atomic‐Scale Characterization of Structural and Transport Properties of Ceria‐Based Catalysts and Ionic Conductors

AbstractReview: 107 refs.

Catalytic decomposition of methane to COx-free hydrogen and carbon nanotubes over Co–W/MgO catalysts

Bimetallic catalysts containing a series of Co/W at 40/10, 30/20, 20/30 and 10/40wt% supported on MgO with a total metal content of 50wt% were prepared and used for the catalytic decomposition of methane to COx-free hydrogen and multi-walled carbon nanotubes (MWCNTs). The solid fresh and exhausted catalysts were characterized structurally and chemically through XRD, TPR, BET, TGA, TEM and Raman spectroscopy. The 40%Co–10%W/MgO catalyst exhibited the highest activity for the production of both hydrogen and MWCNTs. The formation of a large amount of non-interacted Co3O4 species is considered as the main reason for the catalyst superiority in its activity. On the contrary, catalysts formulations of 20%Co–30%W and 10%Co–40%W demonstrated the formation of a large amount of hardly reducible CoWO4 and MgWO4 particles causing lower activity of these catalysts toward methane decomposition as evidenced through the XRD and TPR results.

The Application of High Surface Area Cordierite Synthesized from Kaolin as a Substrate for Auto Exhaust Catalysts

AbstractCordierite is often used as substrate for three way catalysts for the treatment of automobile exhaust gases, mainly because of its high stability. In this paper, different synthesis methods of cordierite are systematically investigated with the aim to improve functionalities and surface properties. Amongst them, the conventional sintering method from kaolin was paid attention to, due to economic reasons and the high yield of obtained cordierite phase. With the aim to improve the porosity, burnable additives were added to the precursor powder and acid leaching was applied to treat the surface of the substrates. The latter was found to be the most efficient method, especially when dolomite and industrial aluminum hydroxide were added in the precursors. Surface area of the cordierite sample reaches 139 m2/g with acceptable mechanical strength. The increase of the cordierite surface area resulted in a higher loading of MnO2‐Co3O4‐NiO catalytic active phases, leading to higher activity for the complete oxidation of CO. The deposition of an additional ψ‐Al2O3 support layer, which is normally done for these kinds of applications, becomes superfluous.

AUTOMOBILE CATALYSTS – THE MAIN RESERVE OF DOMESTIC AND WORLD PRODUCTION OF SECONDARY METALS-PLATINOIDS

The use of platinum group metals in the technique is steadily growing, the world production of primary metals does not allow to cover all the needs of the world market. Therefore, the issues related to the implementation of programs on recycled platinum and more sophisticated processing technologies securing minimal losses, become paramount. The article considers the current state and development trends of the world market of platinoids and secondary metals. In recent years , a number of major deposits in South Africa suffered depletion, the sales of platinum group metals from GOKHRAN Russia stockpiles dropped thus exacerbating the problems of the global platinoids market. The article draws attention to the following trends: increase of platinoids recycling and growing production of secondary met­als, substantial reserves provides extracting of platinum group metals from exhausted catalysts of the petrochemical industry and exhausted gases catalysts of cars. The creation of automobile catalysts processing industry allows to return annually up to 5 t of the secondary platinoids , cor­respondingly $250 mln, a substantial contribution to the Russian economy.

High-strength scaffolds for bone regeneration

Repair of large skeletal defects that are intrinsic to skeletal stability represents the greatest challenge for orthopaedic surgeons. 1 Despite extensive research to replicate the mechanical properties of bones in a synthetic alternative none are commercially available. This research reports a practical solution to this challenge by applying the extrusion process used for the production of ceramic exhaust catalysts to calcium phosphate bone graft substitutes. Clay-like hydroxyapatite (HA) pastes formed in a high-shear mixer were extruded through a complex die, dried and finally fired to form highly porous and strong monoliths. Five different samples were produced with differing wall thickness, cell pitch and porosity. The resulting HA monoliths had primary axis compressive strength of 142–265 MPa and compressive modulus of 3·9–4·4 GPa. These values well correspond to cortical bone and are exceptional given the bulk porosity of the samples varied from 54·4% to 63·1%. All samples supported the proliferation of MG63 cells with only a marginal difference between the samples. It is expected that calcium phosphate-based extruded monoliths will provide a possible commercial alternative to autograft and allograft for large structural bone defects.

Platinum group elements in the precipitation of the dry region of Xinjiang and factors affecting their deposition to land: the case of Changii City, China

Platinum group elements and their compounds are a class of incident allergens and some platinum group element compounds also have carcinogenic effects. They accumulate in city environment as a result of emissions from catalysts used for vehicle exhausts. In this study, sixteen precipitation samples were collected on the north campus of Changji University located in the center of Changji. They were analyzed for palladium (Pd), platinum (Pt), and rhodium (Rh) by inductively coupled plasma–mass spectrometry. The average concentrations of Pd, Pt, and Rh were found to be 26.73ng L-1 (range: 3.18–84.25ng L-1), 1.71ng L-1 (range: below the detection limit to 6.38ng L-1), and 1.49ng L-1 (range: below the detection limit to 3.53ng L-1), respectively. Pd deposition was most pronounced for single precipitation events, reaching 35.47ng m-2 (range: 1.27–101.10ng m-2), followed by Rh (max. 4.96ng m-2, range: 0–14.85ng m-2) and Pt (max. 1.38ng m-2, range: 0-7.66ng m-2). Both Pd and Pt were higher in winter than in other seasons in terms of their wet deposition amounts and their concentrations in precipitation, whereas Rh was lower in winter. Moreover, the results indicated that discharge from coal combustion in winter, the amount of precipitation, and the number of dry days before rainfall events all significantly affected the wet deposition amount and precipitation concentration of platinum group elements. Pd deposition flux was highest (reaching 5.47×103 ng m-2) corresponding to 18 and 16 times the Rh and Pt fluxes, respectively. Finally, vehicle exhaust catalyst emissions from motor vehicles were not the only source of atmospheric platinum group metals in the city environment; in fact, combustion of coal in winter was found to be the dominant contributor of Pt and Pd in the atmosphere.

Growth and surface modification of LaFeO3 thin films induced by reductive annealing

The mixed electronic and ionic conductivity of perovskite oxides has enabled their use in diverse applications such as automotive exhaust catalysts, solid oxide fuel cell cathodes, and visible light photocatalysts. The redox chemistry at the surface of perovskite oxides is largely dependent on the oxidation state of the metal cations as well as the oxide surface stoichiometry. In this study, LaFeO3 (LFO) thin films grown on yttria-stabilized zirconia (YSZ) was characterized using both bulk and surface sensitive techniques. A combination of in situ reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and Rutherford backscattering spectrometry (RBS) demonstrated that the film is primarily textured in the [100] direction and is stoichiometric. High-resolution transmission electron microscopy measurements show regions that are dominated by [100] oriented LFO grains that are oriented with respect to the substrates lattice. However, selected regions of the film show multiple domains of grains that are not [100] oriented. The film was annealed in an ultra-high vacuum chamber to simulate reducing conditions and studied by angle-resolved X-ray photoelectron spectroscopy (XPS). Iron was found to exist as Fe(0), Fe(II), and Fe(III) depending on the annealing conditions and the depth within the film. A decrease in the concentration of surface oxygen species was correlated with iron reduction. These results should help guide and enhance the design of LFO materials for catalytic applications.

Extraction of molybdenum and vanadium from the spent diesel exhaust catalyst by ammonia leaching method

Molybdenum (Mo) and vanadium (V) were effectively extracted from the spent diesel exhaust catalyst (V2O5–MoO3/TiO2) by using an ammonia leaching method. Meanwhile, the structure of the spent catalyst carrier (TiO2) was not destroyed and might be reused. The effects of ammonia (NH3·H2O) concentration, leaching temperature and time, concentration of hydrogen peroxide (H2O2) and liquid to solid ratio on the extraction of Mo and V were systematically investigated. It is shown that the extraction efficiency of Mo increased from 68.68% to 96.45% while the extraction efficiency of V remained stable at 27% with increasing ammonia concentration from 2.95 to 7.38mol/L, leaching temperature from 298.15 to 473.15K, and reaction time from 1 to 8h. With the concentration of H2O2 solution increasing from 1.0 to 2.5mol/L, the extraction efficiency of V increased from 26.87% to 39.73%. Under the optimum conditions (the ammonia concentration of 4.5mol/L, leaching temperature of 413.15K, reaction time of 2h, the H2O2 solution concentration of 1.0mol/L and the liquid to solid ratio of 20/1mL/g), the extraction efficiencies of Mo and V reached 95.13% and 46.25%. Moreover, the catalyst carrier TiO2 with anatase crystal phase was also obtained.

Activated interiors of clay nanotubes for agglomeration-tolerant automotive exhaust remediation

Naturally occurring clay nanotubes, halloysite, act as a high-performance exhaust catalyst when copper–nickel alloy nanoparticles are dispersed onto the interior surface.

Aging of Diesel Exhaust Catalysts in Use with Biofuels

Aging of Diesel Exhaust Catalysts in Use with Biofuels

An Assessment of CFD Applied to Steady Flow in a Planar Diffuser Upstream of an Automotive Catalyst Monolith

Flow maldistribution across automotive exhaust catalysts significantly affects their conversion efficiency. Flow behaviour can be predicted using computational fluid dynamics (CFD). This study investigates the application of CFD to modelling flow in a 2D system consisting of a catalyst monolith downstream of a wide-angled planar diffuser presented with steady flow. Two distinct approaches, porous medium and individual channels, are used to model monoliths of length 27 mm and 100 mm. Flow predictions are compared to particle image velocimetry (PIV) measurements made in the diffuser and hot wire anemometry (HWA) data taken downstream of the monolith. Both simulations compare favourably with PIV measurements, although the models underestimate the degree of mixing in the shear layer at the periphery of the emerging jet. Tangential velocities are predicted well in the central jet region but are overestimated elsewhere, especially at the closest measured distance, 2.5 mm from the monolith. The individual channels model is found to provide a more consistently accurate velocity profile downstream of the monolith. Maximum velocities, on the centre line and at the secondary peak near to the wall, are reasonably well matched for the cases where the flow is more maldistributed. Under these conditions, a porous medium model remains attractive because of low computational demand.

The trace metal signature of atmospheric aerosols sampled at a European regional background site (puy de Dôme, France)

Trace metal composition of atmospheric aerosols provides clues as to emission sources and history of air masses. Atmospheric trace metal concentrations measured between 2011 and 2013 at puy de Dome (1,465 m elevation, central France) are, on average, intermediate between low-altitude urban sites and Atlantic remote environment (115 ng/m3 Al, 0.55 ng/m3 Sr, 0.136 ng/m3 Ce, 1.34 ng/m3 Pb). Three main factors control trace metal variability: (1) the concentrations markedly decrease at night while the site is generally located in the free troposphere/nocturnal residual layer (average of 43 ng/m3 Al, 0.27 ng/m3 Sr, 0.052 ng/m3 Ce, 0.25 ng/m3 Pb during 2012 summer nights). The nocturnal depletion is greater for refractory crustal elements (Al, Fe, Ti and rare earth elements) than for B, Na and chalcophile/siderophile elements (e.g., Tl, In, Sb, Zn, Cd, Cu, Bi, Mo, Re, Pt and Pd), which probably partition into the gas phase and/or a fine mode fraction. (2) Cr, Ni, Mo, Ag, Pb and Pt record a greater influence of anthropogenic sources (combustion, iron/steel industry, and automobile exhaust catalysts) in winter, and/or in the continental air mass that most frequently influences the site during the cold season. (3) Air masses reaching the site have distinct trace element fingerprints depending on their origin. The African air has crustal like signatures (Al/Ti, La/Sm). The Atlantic air is enriched in B, Cu, Bi, Co, W, Re and Ag and depleted in Tl, Sb and Se relatively to Al. Continental air is enriched in Cr and Ni and depleted in Na. Local air (France) is enriched in chalcophile elements (Zn, Pb, Se, As, Sb, Tl) and to a lesser extent in alkalis and rare earth elements, likely due to limited activation and scavenging of primary particles during a short-history of transport.

A new monolithic Pt-Pd-Rh motorcycle exhaust catalyst to meet future emission standards

A new composite oxide material as support, CeO2-ZrO2-La2O3-PrO2-Al2O3, was synthesized by a co-precipitation method. Pd-Rh, Pt-Rh, and Pt-Pd-Rh supported on monolithic carrier catalysts were obtained by an impregnation route. The textural, structural, and reductive properties of the catalysts were characterized by N2 adsorption-desorption, temperature-programmed reduction, oxygen storage capacity measurements, and X-ray diffraction. The air-fuel-ratio (A/F), space velocity (SV), and temperature characteristics of the fresh and aged catalysts were investigated on a systematic basis. The results showed that among the three catalysts, Pt-Pd-Rh displayed the best performance. For an SV of 40000 h−1 in the case of fresh Pt-Pd-Rh, the light-off temperatures (T50) for C3H8, CO, and NO were 239, 187, and 191 °C, respectively, with corresponding ΔT (T90–T50) values of 21, 3, and 3 °C, respectively. After aging, the T50 for C3H8, CO, and NO were 298, 203, and 223 °C, respectively, and the ΔT values were 22, 5, and 13 °C, respectively. Moreover, the window widths for the A/F in the case of fresh and aged Pt-Pd-Rh catalysts were wide. Overall, the excellent performance for the Pt-Pd-Rh catalyst makes it suitable as a motorcycle exhaust catalyst, which can meet future emission standards.

The effect of loading on sintering and catalytic activity of Pt/SiO2 hybrid catalyst powders synthesized via spray pyrolysis

Platinum (Pt) is commonly used as a heterogeneous catalyst to effectively convert carbon monoxide (CO) from automobile exhaust gas into carbon dioxide (CO2). Platinum/silica (Pt/SiO2) hybrid catalyst powders with varying Pt content were synthesized via a spray pyrolysis process. The average particle size and specific surface area of the Pt nanoparticles on the Pt/SiO2 hybrid catalyst powders were characterized as-prepared and after heat treatment. As the Pt loading increased, the Pt nanoparticles grew on the surface of the SiO2 as a result of sintering, and the catalytic efficiency decreased. This work demonstrates that the Pt/SiO2 (4 wt% Pt) hybrid catalyst powder is suitable as a hightemperature automobile exhaust catalyst, compared with the Pt/SiO2 hybrid catalyst powder with high Pt loading (14 wt% Pt), indicating that metal nanoparticle loading is a key factor for determining catalytic activity.

Summary of Research on the Use of Intermediate Ethanol Blends in On-Road Vehicles

The paper summarizes research on the use of intermediate ethanol blends in the U. S. vehicle fleet. Intermediate ethanol blends, fuels with ethanol content above 10%, are just being introduced in the U. S. for use in conventional vehicles. Thirty published studies are covered including the extensive program conducted by the Coordinating Research Council. The individual studies are grouped by vehicle performance aspect: driveability, exhaust emissions, evaporative emissions, flexible-fuel vehicles, onboard diagnostics, and durability of engine, fuel, and emissions control systems. Within each performance aspect, data are examined for common trends and potential fuel impacts. In some cases, results from similar programs are combined and analyzed. A variety of ethanol impacts on vehicle performance and emissions are identified and described. Emphasis is placed on impact areas or potential failure modes that have been identified and tested. Differences in vehicle responses to increasing ethanol content are identified. Some of the studies concluded that intermediate ethanol blends have similar performance to gasoline or low level ethanol blends in a number of areas including short-term driveability and emissions and exhaust catalyst and evaporative control system durability in the post-2001 vehicles tested. However, there are areas where research has identified potential adverse impacts from intermediate ethanol blends including false illumination of Malfunction Indicator Lights and reduced engine and fuel system durability.

Low-temperature remediation of NO catalyzed by interleaved CuO nanoplates.

A copper(II)-oxide-based exhaust catalyst exhibits better activity than Pt- and Rh-nanoparticle catalysts in NO remediation at 175 °C. Following theoretical design, the CuO catalyst is rationally prepared; CuO nanoplates bearing a maximized amount of the active {001} facet are arranged in interleaved layers. A field test using a commercial gasoline engine demonstrates the ability of the catalyst to remove NO from the exhaust of small vehicles.

H2-assisted NH3-SCR over Ag/Al2O3: An engine-bench study

A combined catalyst system of Ag/Al2O3 and Fe-BEA was tested in a light-duty engine-bench for H2-assisted NH3-SCR. Ag/Al2O3 was used to provide a high low-temperature activity, while Fe-BEA can provide a high activity at higher temperatures without the need to co-feed H2. The catalysts were combined in a sequential dual-brick layout and compared to Ag/Al2O3 and Fe-BEA only. The aim of the study was to investigate the performance of the catalysts in real life exhaust in contrast to synthetic gas. The catalysts were both tested during stationary and transient conditions. Transient testing was carried out with the New European Driving Cycle (NEDC). Laboratory tests were performed to complement the results from engine tests. Ag/Al2O3 showed a lower NOx conversion in stationary engine tests than expected. This was investigated further in a laboratory test set-up and was attributed to deactivation by soot and/or Ag oxidation, low H2 levels and low specific catalyst loading. NO2 increased the catalytic activity at below 250 and above 300°C. For the combined systems, it was preferred to have Fe-BEA in an upstream position of Ag/Al2O3 compared to the opposite. The high engine out NO2/NOx ratio, giving fast-SCR over the Fe-BEA, was believed to be the reason. At low temperature, the activity over the combined systems was higher than that for the individual catalysts showing that there were synergy effects of combining Ag/Al2O3 and Fe-BEA. This was also seen in the transient tests. However, the overall cycle NOx conversion was low due to very demanding conditions with a lot of the NOx being emitted at below 150°C. The order of performance based on an overall conversion during the NEDC was dual-brick with Ag/Al2O3 upstream=Ag/Al2O3 only>dual-brick Fe-BEA upstream>Fe-BEA only. The Ag/Al2O3 containing layouts showed a noticeable NOx conversion from the start of the cycle, i.e. before any NH2 or H2 was dosed. We believe that the NOx conversion seen came from NOx storage on the Ag/Al2O3.