Reoxidation dynamics of highly dispersed VO_x species supported on γ-alumina

The VOx/γ-Al2O3 catalyst VA-200, which was introduced in a previous article, is further characterized by XPS and visible Raman spectroscopy. The reoxidation of highly dispersed VOx species with gas phase oxygen is investigated in detail and is described by an empirical kinetic model. It is observed that the reoxidation of reduced VOx/γ-Al2O3 catalyst is strongly affected by the presence of water. The proposed kinetic model includes a distinct coverage of VOx species with water or hydroxyl groups in the investigated temperature range of 479–712 K. Hydrated surface species are oxidized under release of water. Best fits of the experimental data can be achieved with first order rate laws with respect to oxygen concentration. Experiments are performed in an ideally mixed Berty-type reactor using oxygen step-marking over the reduced catalyst. The evolution of oxygen concentration using the kinetic model is in agreement with the experimentally observed behaviour. The signal of water released during the reaction can be modeled only qualitatively, which (presumably) stems from its sorption behaviour on the acidic alumina support. The oxidation of VOx species furthermore depends on the reaction temperature. The oxidation of V+III to V+V cannot be completely achieved at temperatures below 673 K. However, the activation energy of this reaction is low, as suggested by the absence of strong variations of the response shapes with respect to temperature

Long-term sequelae of severe acute kidney injury in the critically Ill patient without comorbidity: A retrospective cohort study

Background and Objectives: Acute kidney injury (AKI) necessitating renal replacement therapy (RRT) is associated with high mortality and increased risk for end stage renal disease. However, it is unknown if this applies to patients with a preliminary unremarkable medical history. The purpose of this study was to describe overall and renal survival in critically ill patients with AKI necessitating RRT stratified by the presence of comorbidity. Design, Setting, Participants, and Measurements: A retrospective cohort study was performed, between 1994 and 2010, including all adult critically ill patients with AKI necessitating RRT, stratified by the presence of comorbidity. Logistic regression, survival curve and cox proportional hazards analyses were used to evaluate overall and renal survival. Standardized mortality rate (SMR) analysis was performed to compare long-term survival to the predicted survival in the Dutch population. Results: Of the 1067 patients included only 96(9.0%) had no comorbidity. Hospital mortality was 56.6% versus 43.8% in patients with and without comorbidity, respectively. In those who survived hospitalization 10-year survival was 45.0% and 86.0%, respectively. Adjusted for age, sex and year of treatment, absence of comorbidity was not associated with hospital mortality (OR=0.74, 95%-CI=0.47-1.15), while absence of comorbidity was associated with better long-term survival (adjusted HR=0.28, 95%-CI = 0.14-0.58). Compared to the Dutch population, patients without comorbidity had a similar mortality risk (SMR=1.6, 95%-CI=0.7-3.2), while this was increased in patients with comorbidity (SMR=4.8, 95%-CI=4.1-5.5). Regarding chronic dialysis dependency, 10-year renal survival rates were 76.0% and 92.9% in patients with and without comorbidity, respectively. Absence of comorbidity was associated with better renal survival (adjusted HR=0.24, 95%-CI=0.07-0.76). Conclusions: While hospital mortality remains excessively high, the absence of comorbidity in critically ill patients with RRT-requiring AKI is associated with a relative good long-term prognosis in those who survive hospitalization