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•A detailed study of the composition effect on structural and textural properties in CexPr1-xO2-δ (0 < x < 1) was conducted.•The calcination temperature on the catalysts’ synthesis ...was explored, along with their catalytic activity for soot combustion.•Ceria-praseodymia mixed oxides show improved catalytic activities for soot combustion with respect to ceria.•Ce0.5Pr0.5O2-δ-500 exhibits the highest catalytic activity in soot combustion under NOx/O2 atmosphere, among those studied.
The effect of Ce/Pr ratio on ceria-praseodymia on structural and surface properties is studied. The catalytic activity towards soot combustion under NOx/O2 and O2/N2 atmospheres is also evaluated, together with the NO oxidation activity to NO2. CexPr1-xO2-δ compositions (x = 0.8, 0.5 and 0.2) have been prepared along with ceria and praseodymia. Catalysts were prepared by co-precipitation. The Ce0.5Pr0.5O2-δ composition, was also prepared by nitrate calcination. Ceria-praseodymia mixed oxides yield reduction profiles shifted to lower temperatures, higher NO oxidation activities to NO2 and improved catalytic activities for soot combustion with respect to pure ceria. Ce0.5Pr0.5O2-δ was the most active one. Under NOx/O2, it has greater soot combustion activity if it is prepared by nitrate calcination. However, under O2/N2, the co-precipitation method is more favorable because of the better dopant insertion achieved in the ceria lattice, which seems to lead better oxygen mobility on the surface and in the bulk oxide.
The ceria-catalyzed oxidation of soot by O2/NO takes place with ceria oxygen (directly and via NO oxidation to NO2), and gas-phase O2 fills up the oxygen vacancies created on the catalyst. Display ...omitted
► Ceria oxygen, and not gas-phase molecular oxygen, oxidizes NO to NO2. ► Ceria oxygen exchanges with gas-phase O2 and prevails with regard to NO oxidation. ► Ceria oxygen oxidizes soot directly (active oxygen) or mediated by NO2. ► Gas-phase O2 does not react with soot, but fills up oxygen vacancies on ceria.
The ceria-catalyzed soot oxidation mechanism has been studied by a pulse technique with labeled O2 in the absence and presence of NO, using ceria–soot mixtures prepared in the loose contact mode. In the absence of soot, the ceria-catalyzed oxidation of NO to NO2 takes place with ceria oxygen and not with gas-phase O2. However, the oxygen exchange process between gas-phase O2 and ceria oxygen (to yield back O2, but with oxygen atoms coming from ceria) prevailed with regard to the ceria-catalyzed oxidation of NO to NO2. Gas-phase O2 did not react directly with soot when pulsed to a soot–ceria loose contact mixture. Instead, ceria oxygen is transferred to soot (this step does not require gas-phase molecular oxygen to be present), and gas-phase O2 fills up the vacancies created on the oxide in a further step. The transfer of oxygen between ceria and soot occurred directly in the absence of NO. However, in the presence of NO, NO2 is expected to be additionally generated by ceria oxygen oxidation, which also reacts with soot. The main reaction products of the ceria-catalyzed soot oxidation reaction with NO/O2 were CO2 and NO. Additionally, evidence of the reduction of NOx to N2 was found.
Graphical abstract The ceria-catalyzed oxidation of soot by O2 /NO takes place with ceria oxygen (directly and via NO oxidation to NO2 ), and gas-phase O2 fills up the oxygen vacancies created on the ...catalyst. Display Omitted Highlights Ceria oxygen, and not gas-phase molecular oxygen, oxidizes NO to NO2 . Ceria oxygen exchanges with gas-phase O2 and prevails with regard to NO oxidation. Ceria oxygen oxidizes soot directly (active oxygen) or mediated by NO2 . Gas-phase O2 does not react with soot, but fills up oxygen vacancies on ceria. The ceria-catalyzed soot oxidation mechanism has been studied by a pulse technique with labeled O2 in the absence and presence of NO, using ceria-soot mixtures prepared in the loose contact mode. In the absence of soot, the ceria-catalyzed oxidation of NO to NO2 takes place with ceria oxygen and not with gas-phase O2 . However, the oxygen exchange process between gas-phase O2 and ceria oxygen (to yield back O2 , but with oxygen atoms coming from ceria) prevailed with regard to the ceria-catalyzed oxidation of NO to NO2 . Gas-phase O2 did not react directly with soot when pulsed to a soot-ceria loose contact mixture. Instead, ceria oxygen is transferred to soot (this step does not require gas-phase molecular oxygen to be present), and gas-phase O2 fills up the vacancies created on the oxide in a further step. The transfer of oxygen between ceria and soot occurred directly in the absence of NO. However, in the presence of NO, NO2 is expected to be additionally generated by ceria oxygen oxidation, which also reacts with soot. The main reaction products of the ceria-catalyzed soot oxidation reaction with NO/O2 were CO2 and NO. Additionally, evidence of the reduction of NO x to N2 was found. PUBLICATION ABSTRACT
Two microporous hectorites were prepared by conventional and microwave heating, and a delaminated mesoporous hectorite by an ultrasound-assisted synthesis. These three hectorites were impregnated ...with copper. The characterization techniques used were XRD, N2 adsorption, TEM and H2 reduction after selective surface copper oxidation by N2O (to determine copper dispersion). The catalytic activity for soot combustion of the copper-free and the copper-containing hectorites was tested under a gas mixture of 500ppm NOx/5% O2/N2 (and 5% O2/N2 in some cases), evaluating their stability through three consecutive soot combustion experiments.
The delaminated hectorite showed the highest surface area (353m2/g) allowing the highest dispersion of copper. This copper-containing catalyst was the most active for soot combustion among those prepared and tested in this study. We have also concluded that the Cu/hectorite-catalyzed soot combustion mechanism is based on the activation of the O2 molecule and not on the NO2-assisted soot combustion.
•Two microporous hectorites and a delaminated mesoporous hectorite were prepared.•Hectorites have been tested for the first time as soot combustion catalysts.•A Cu-containing delaminated mesoporous hectorite was the most active catalysts.
The active phase Ce
0.5
Pr
0.5
O
2
has been loaded on commercial substrates (SiC DPF and cordierite honeycomb monolith) to perform DPF regeneration experiments in the exhaust of a diesel engine. ...Also, a powder sample has been prepared to carry out soot combustion experiments at laboratory. Experiments performed in the real diesel exhaust demonstrated the catalytic activity of the Ce–Pr mixed oxide for the combustion of soot, lowering the DPF regeneration temperature with regard to a counterpart catalyst-free DPF. The temperature for active regeneration of the Ce
0.5
Pr
0.5
O
2
-containing DPF when the soot content is low is in the range of 500–550 °C. When the Ce
0.5
Pr
0.5
O
2
-containing DPF is saturated with a high amount of soot, pressure drop and soot load at the filter reach equilibrium at around 360 °C under steady state engine operation due to passive regeneration. The uncoated DPF reached this equilibrium at around 440 °C. Comparing results at real exhaust with those at laboratory allow concluding that the Ce
0.5
Pr
0.5
O
2
-catalysed soot combustion in the real exhaust is not based on the NO
2
-assisted mechanism but is most likely occurring by the active oxygen-based mechanism.
THREE-WAY CATALYSTS: PAST, PRESENT AND FUTURE N. GUILLÉN-HURTADO; V. RICO-PÉREZ; A. GARCÍA-GARCÍA ...
Dyna (Medellín, Colombia),
01/2012, Letnik:
79, Številka:
175
Journal Article
Recenzirano
Odprti dostop
En este artículo de revisión se discute el pasado, presente y futuro de los catalizadores de tres vías. Se presentan las principales reacciones químicas que tiene lugar en los motor de gasolina así ...como las reacciones que ocurren en los catalizadores de tres vías (CTV) colocados en el escape, concretamente la oxidación de monóxido de carbonos e hidrocarburos y la reducción de los óxidos de nitrógeno a nitrógeno molecular. También se describen los principales componentes de un CTV (sustratos, metals nobles y óxidos de cerio). Por último se discute el problema del control de las emisiones en motores diesel, analizando la tecnología disponible en la actualidad para estos vehículos.
To determine the changes in the pattern of death of patients with systemic sclerosis (SSc) throughout 20 years.
Data were collected from the Spanish Scleroderma Registry (RESCLE), retrospective ...multicentre database from 1990 to 2009. SSc-related and SSc-non related causes of death were assessed.
987 patients were recruited. Overall standardised mortality ratio (SMR) was 2.34 (2.24-2.44). SSc-related causes of death were responsible of 72% of all deaths of those patients diagnosed within 1990-99 vs. 48% within 2000-09 (p=0.006). Relative pulmonary death rate was stable over time (68.1% within 1990-99 vs. 63.9% within 2000-09, p=0.815). Relative renal death rate was decreasing over time (17% within 1990-99 vs. 5.5% within 2000-09, p=0.175). Heart distribution tripled its ratio (12.8% within 1990-99 vs. 30.6% within 2000-09, p=0.058).
SSc-related causes of death were decreasing over time and, among them, pulmonary involvement was the leading cause of death in both decades. The ratio of renal causes decreased since 1990 at the time that the ratio of cardiac causes increased.
In the context of COVID-19 pandemic, we aimed to analyze the epidemiology, clinical characteristics, risk factors for mortality and impact of COVID-19 on outcomes of solid organ transplant (SOT) ...recipients compared to a cohort of non transplant patients, evaluating if transplantation could be considered a risk factor for mortality. From March to May 2020, 261 hospitalized patients with COVID-19 pneumonia were evaluated, including 41 SOT recipients. Of these, thirty-two were kidney recipients, 4 liver, 3 heart and 2 combined kidney-liver transplants. Median time from transplantation to COVID-19 diagnosis was 6 years. Thirteen SOT recipients (32%) required Intensive Care Unit (ICU) admission and 5 patients died (12%). Using a propensity score match analysis, we found no significant differences between SOT recipients and non-transplant patients. Older age (OR 1.142; 95% CI 1.08-1.197) higher levels of C-reactive protein (OR 3.068; 95% CI 1.22-7.71) and levels of serum creatinine on admission (OR 3.048 95% CI 1.22-7.57) were associated with higher mortality. The clinical outcomes of SARS-CoV-2 infection in our cohort of SOT recipients appear to be similar to that observed in the non-transplant population. Older age, higher levels of C-reactive protein and serum creatinine were associated with higher mortality, whereas SOT was not associated with worse outcomes.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
To prepare a protocol for the treatment of retinopathy of prematurity (ROP) agreed by the majority of Spanish ophthalmologists dedicated to this topic.
A draft of the protocol was produced taking ...into account the experience of the participants and up to date publications. This draft was corrected by all the ophthalmologists participating in the project, and the final document was agreed by all of them.
We present general guidelines as an aid for the treatment of ROP, including treatment criteria, treatment methods, a calendar of action, and follow-up.
It is important to have a common working protocol for the treatment of ROP to improve care and to avoid mistakes. Although individual Hospitals may adapt the protocol to their daily activity, it is recommended that there is a minimal working protocol agreed by most of professionals dedicated to pediatric ophthalmology in Spain.
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