RESUMO
Designing catalysts with high thermal stability and resistance to deactivation while simultaneously maintaining their catalytic activity and selectivity is of key importance in high-temperature reforming reactions. We prepared Pt nanoparticle catalysts supported on either mesoporous SiO2 or TiO2. Sandwich-type Pt core@shell catalysts (SiO2@Pt@SiO2 and SiO2@Pt@TiO2) were also synthesized from Pt nanoparticles deposited on SiO2 spheres, which were encapsulated by either mesoporous SiO2 or TiO2 shells. n-Hexane reforming was carried out over these four catalysts at 240-500 °C with a hexane/H2 ratio of 1:5 to investigate thermal stability and the role of the support. For the production of high-octane gasoline, branched C6 isomers are more highly desired than other cyclic, aromatic, and cracking products. Over Pt/TiO2 catalyst, production of 2-methylpentane and 3-methylpentane via isomerization was increased selectively up to 420 °C by charge transfer at Pt-TiO2 interfaces, as compared to Pt/SiO2. When thermal stability was compared between supported catalysts and sandwich-type core@shell catalysts, the Pt/SiO2 catalyst suffered sintering above 400 °C, whereas the SiO2@Pt@SiO2 catalyst preserved the Pt nanoparticle size and shape up to 500 °C. The SiO2@Pt@TiO2 catalyst led to Pt nanoparticle sintering due to incomplete protection of the TiO2 shells during the reaction at 500 °C. Interestingly, over the Pt/TiO2 catalyst, the average size of Pt nanoparticles was maintained even after 500 °C without sintering. In situ ambient pressure X-ray photoelectron spectroscopy demonstrated that the Pt/TiO2 catalyst did not exhibit TiO2 overgrowth on the Pt surface or deactivation by Pt sintering up to 600 °C. The extraordinarily high stability of the Pt/TiO2 catalyst promoted high reaction rates (2.0 µmol · g(-1) · s(-1)), which was 8 times greater than other catalysts and high isomer selectivity (53.0% of C6 isomers at 440 °C). By the strong metal-support interaction, the Pt/TiO2 was turned out as the best catalyst with great thermal stability as well as high reaction rate and product selectivity in high-temperature reforming reaction.
RESUMO
PURPOSE: The purpose of the study was to identify the adequacy of enteral feeding, and the reason and prevalence of under-nutrition, and to determine the relationships between caloric intake and resulting nutritional parameters among neurosurgical intensive care unit (ICU) patients. METHODS: The participants for this descriptive study were 47 neurosurgical ICU patients who had enteral feeding initiated after ICU admission. Data were collected from the initial day of enteral feeding for 7 days. Data related to enteral feeding, feeding interruptions or delay, prealbumin, and transferrin were collected. RESULTS: The mean age of the participants was 56.62 years. Twenty-six patients did not receive their feeding formula more than once during 7 days, and 11 had interruptions more than 6 times. The mean number of feeding interruptions was 3.23 (SD = 4.47). On the average, only 76.44% of the estimated energy requirement was provided by enteral feeding to the patients. The frequency of underfeeding was 52.17% with respect to enteral feeding. The most frequent reason for the feeding interruption was observation before and after intubation and extubation, which was unavoidable. The next most common reason was gastrointestinal bleeding, mostly due to old clots or trace, followed by residual volume less than 100 mL. Changes in prealbumin and transferrin levels for 7 days between the underfed and adequately fed groups were not statistically significant. CONCLUSION: The management of enteral feeding by nurses was overprotective because of the unpredictable nature of ICU patients in terms of their underlying disease process. The management of feeding intolerance needs to be evidence-based and nurses must consistently follow the protocol that has been supported as a useful measure.