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•Model soot (Printex U) oxidation by NO2 and O2 in the presence of H2O.•Soot oxidation initiated by NO2 at low Temperatures.•Synergistic effect between NO2 and O2 on soot ...combustion.•H2O promotion on soot oxidation.•Dependence of the kinetic parameters on carbon conversion.
The combustion of model soot (i.e. Printex U) by NO2 and O2 in the presence of water was investigated in a fixed bed micro reactor under isothermal conditions. A wide range of experimental conditions (e.g. 250–350°C, 0–5vol% O2, 0–500ppmv NO2, 0–5vol% H2O) were considered in order to investigate the role of NO2, O2 and H2O in the combustion process. It was found that the oxidation of soot is initiated by NO2 at temperatures where oxygen is unreactive. In addition, a synergistic effect between NO2 and O2 on soot combustion was observed in the presence of the NO2-O2 mixture. Both the direct reaction between soot and NO2 and also the contribution of gaseous oxygen on the combustion process appeared to rise with the increasing temperature and in the presence of water. Finally, the kinetic analysis of the experimental results showed a non-negligible dependence of the kinetic parameters on carbon conversion and in particular the poor accuracy of the shrinking-core model at low conversion degree.
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•NO can disproportionate to N2O over reduced metal sites.•N2O formation from NO is favored at low temperatures and with poorly reactive reducing agents.•Isocyanate species are ...involved in N2O formation.•Pt and Rh are the sites where N2O is formed.
In this paper mechanistic aspects involved in the formation of N2O over model Pt-Ba/Al2O3 and Rh-Ba/Al2O3 LNT catalysts are discussed. The reactivity of both gaseous NO and of stored NOx (nitrates) has been studied, with simultaneous surface characterization by operando FT-IR spectroscopy, using different reductants (i.e. H2, CO, CO + H2, CO + H2O) both under isothermal conditions and temperature programming. The results show that N2O formation may occur during both the lean/rich and rich/lean switches (primary and secondary N2O, respectively). In particular: i) primary N2O formation involves the presence of gas-phase NO and partially reduced metal sites; ii) N2O formation increases in the presence of CO because the reduction of the metal sites is slower, thus favoring N2O formation upon the lean/rich transition; iii) residual reducing species onto the surface (i.e. NCO−, CO) can react with NO giving the secondary N2O peak. A reaction pathway for N2O formation is suggested where metal sites (Pt or Rh) catalyse the NO dissociation reaction into N- and O-adatoms; N-species further interact with undissociated NO molecules leading to the formation of N2O (primary N2O). In additions, isocyanates formed during the NOx reduction in the presence of CO may participate in the N2O formation upon reaction with NO during the lean phase (secondary N2O).
Pt- and Rh-based catalysts show similar behavior even if Rh-based catalyst is less reactive than Pt-based sample likely due to the lower dispersion of the noble metal.
The paper presents the current status of the Maritime Aerosol Network (MAN), which has been developed as a component of the Aerosol Robotic Network (AERONET). MAN deploys Microtops handheld Sun ...photometers and utilizes the calibration procedure and data processing (Version 2) traceable to AERONET. A web site dedicated to the MAN activity is described. A brief historical perspective is given to aerosol optical depth (AOD) measurements over the oceans. A short summary of the existing data, collected on board ships of opportunity during the NASA Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies (SIMBIOS) Project is presented. Globally averaged oceanic aerosol optical depth (derived from island‐based AERONET measurements) at 500 nm is ∼0.11 and Angstrom parameter (computed within spectral range 440–870 nm) is calculated to be ∼0.6. First results from the cruises contributing to the Maritime Aerosol Network are shown. MAN ship‐based aerosol optical depth compares well to simultaneous island and near‐coastal AERONET site AOD.
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•The NOx release is not driven by the ads–des equilibrium of stored NOx.•15NO isotopic exchange allows decoupling NOx release from its further reduction.•15NO isotopic exchange is ...catalyzed by Pt.•Reduced Pt sites activate stored NOx that are destabilized and released as NO.
The release and reduction of NOx stored on Pt–Ba/Al2O3 is here investigated under nearly isothermal conditions. It is shown that the release driven by adsorption–desorption equilibrium of stored NOx is negligible. It is also shown that NO isotopic exchange between stored 14NOx and 15NO in absence of O2, which implies the release of stored NOx and has the potential to decouple NOx release from its further reduction, is catalyzed by Pt and is observed from temperatures well below that of the NOx thermal desorption. It is suggested that reduced Pt sites activate stored NOx that are destabilized and eventually released as NOx in the gas phase or adsorbed onto Pt. Therefore, under nearly isothermal conditions, the NOx release is a chemical reaction catalyzed by Pt occurring at the Pt/Ba interface. In the presence of reductants, the release of stored NOx and its further reduction cannot be decoupled. The higher is the reducing power the more effective is the reduction of Pt and activation of stored NOx by metal Pt that represent the first step of release and reduction of stored NOx.
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•The adsorption of NO/O2 over Pt- and Rh-containing catalysts leads to nitrites at low T and of nitrates at high T.•Pt-based catalysts shows superior NOx storage properties.•Pt-based ...catalysts shows superior NO oxidizing properties.•Pt-based catalysts are more active that Rh/Al2O3 in the reduction of stored NOx.•Rh- based catalysts show higher activity in the NH3 decomposition reaction and steam reforming of propylene.
In this work the reactivity of Pt-Rh NOx storage-reduction (NSR) catalysts in the reduction of NOx under lean conditions is investigated. It is found that significant amounts of NOx are stored on both Rh- and Pt-based samples at all the investigated temperatures (in the range 150–350 °C). Mostly chelating nitrites are adsorbed at the lowest investigated temperature (150 °C), while nitrates (both bidentate and ionic) at higher temperatures. However, at all temperatures nitrites prevail at the beginning of the storage phase, while nitrates represent the most abundant adsorbed species after prolonged contact. Pt-containing catalysts (either monometallic Pt or bimetallic Pt/Rh) show higher NOx storage capacity than the Rh monometallic sample, possibly due to the higher dispersion of Pt vs. Rh and/or to the higher oxidizing capability of Pt vs. Rh.
The stored NOx species show relevant thermal stability, and decompose to NOx and O2 upon heating. In particular, nitrites disproportionate to gaseous NO and nitrates; these latter then decompose to NOx and O2. On the Rh-Ba/Al2O3 catalyst the disproportionation reaction is observed with a higher temperature onset if compared to the Pt-based samples. The analysis of the reactivity of the stored NOx species (probed by isotopic labeling experiments and reduction with H2 and NH3) showed the lower reactivity of the Rh-Ba/Al2O3 sample; however Rh shows activity in the ammonia decomposition reaction to N2 and H2, unlike Pt. The lower reactivity of the Rh-Ba/Al2O3 sample is also pointed out by experiments under cyclic lean-rich conditions. However, the presence of Rh increases the reactivity of the catalyst in the steam reforming of hydrocarbons, especially at high temperature, and accordingly the reactivity of the bimetallic Pt/Rh sample at high temperatures is higher than that of the Pt and Rh monometallic catalysts.
In this study the pathways involved in N
2
O formation over a commercial LNT catalyst are addressed, when using H
2
as a reductant. For this purpose, flow microreactor experiments coupled with FT-IR ...under operando conditions are used. The results indicate that N
2
O formation occurs both at the lean-to-rich (primary N
2
O) and rich-to-lean (secondary N
2
O) transitions. Primary N
2
O originates at the reduction front due to the presence of partially reduced PGM sites that do not readily dissociates NO released from the stored NO
x
. Undissociated NO couples with N-adatoms leading to the formation of N
2
O. At variance, secondary N
2
O originates upon oxidation with NO/O
2
of reducing species left adsorbed on the catalyst surface (adsorbed CO, isocyanates and possibly NH
3
) during the rich phase, as pointed out by FT-IR spectroscopy. The concentration of such adsorbed species is however limited and hence the formation of secondary N
2
O is much smaller than that of primary N
2
O, when using H
2
as reducing agent. The emissions of N
2
O reduce upon increasing the temperature, and above 250 °C N
2
O formation is negligible. Finally the reactivity of N
2
O with adsorbed NO
x
species (nitrites) and with the actual reductants (H
2
and NH
3
) is also investigated, to provide further indications concerning the pathways leading to N
2
O emissions. It is found that N
2
O does not react with NO
x
species stored downstream the reduction front; at variance both H
2
and NH
3
may reduce N
2
O to N
2
and water at rather low temperatures. The role of this reaction on N
2
O emission is herein discussed.
The activity in the soot combustion of K- and Ba-based catalysts in “loose” and “full” contact is investigated in this study. Under loose contact systems (obtained by mechanically mixing the soot and ...catalysts), the K-containing samples are very active in the oxidation of soot, as opposite to the Ba-containing samples. Also, a synergistic effect in this reaction is seen between K and Pt for the case of the K-containing samples. Under full contact conditions (obtained by impregnation of the soot with aqueous metal solutions), the reactivity of soot increases; in these conditions the performance of the poorly reactive Ba-containing samples becomes similar to the very active K-based system. This result points out the key-role played by both the selected alkaline or alkaline earth metal oxides in the soot combustion, and suggests that the poor activity of Ba under loose conditions is possibly due to the low mobility of the Ba surface species. Finally, it is found that the presence of NO favors the soot oxidation under loose contact, specifically over noble metal-containing samples, due to the oxidation of NO to NO
2. However the presence of the alkaline and alkaline earth oxide also affects the soot oxidation activity in the presence of NO. This has been ascribed to the formation of Ba- and K-nitrite/nitrate species which participate in the soot combustion process by giving rise to NO
x
upon nitrite/nitrate decomposition and/or by directly reacting with soot.
In this work, we have investigated the release and reduction of NO
x
(nitrates) stored on Rh–Ba/Al
2
O
3
and Pt–Rh–Ba/Al
2
O
3
catalysts and compared with Pt–Ba/Al
2
O
3
. It is shown that the ...release occurs at the interface between the PGM sites and the storage sites, can be probed by isotopic exchange experiments and is governed by the rate of oxygen removal from the metallic PGM sites. Accordingly the presence of a reductant, that keeps the PGM sites in a reduced state by scavenging oxygen adatoms formed upon nitrate decomposition, greatly favors the release of NO and its subsequent reduction. In these steps, not much differences have been observed considering either Pt- or Rh-based samples.
There are limited data nationwide on the burden of systemic sclerosis (SSc)-related mortality. We aimed to determine recent trends in SSc and SSc-related pulmonary arterial hypertension (PAH) ...mortality overall and across population subgroups.
Using death certificate data from the National Center for Health Statistics, we computed the age-adjusted mortality rates of SSc and SSc-SSc−PAH, a lethal prevailing complication, across demographic groups, geographic regions and comorbid cardiorespiratory conditions, and used Joinpoint regression analysis to calculate the average annual percentage change (APC) in mortality.
From 2003 to 2016, 25 175 death records contained a code for SSc. Decedents were predominantly female (81%) and white (73%), with an average age of 66±14 years. The age-adjusted mortality rate decreased by 3% per year from 6.6 in 2003 to 4.3 per 1 000 000 population in 2016. Also, a decreasing trend was found when SSc was stratified by age, sex, race and geographic region. The prevalence of PAH was 23%. The odds of PAH were highest in female and black decedents, and in decedents with concomitant pulmonary embolism, cardiomyopathy and interstitial lung disease (ILD). SSc−PAH mortality remained stable from 2003 to 2008 then decreased by 3% per year from 2008 to 2016. In decedents with SSc−PAH, among all concomitant comorbidities, the mortality rate associated with ILD had the highest increase (average APC 6%, 95% CI 2%−10%).
The mortality rate from SSc decreased from 2003 to 2016. Decreases in mortality rates were similar across demographic groups and geographic regions. SSc−PAH-related mortality remained stable. The death rate for SSc−ILD and concomitant PAH increased during this period.
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