RESUMEN
Tuning the strong metal-support interaction (SMSI) in metal catalysts is a promising strategy to improve their catalytic performance. In this article, we systematically investigated the influences of different alcohol/water mixtures on the evolution of the interfacial structure of Cu/ZnO catalysts in the reduction stage. A series of in situ characterization and theoretical simulation studies were performed to elucidate the various mechanisms of alcohol induced SMSI. It was found that when methanol/water is added to H2 during the reduction pretreatment, more oxygen vacancies are formed on the ZnO support, which facilitates the dissociation of H2 O and the hydroxylation of ZnO species. Such promotion eventually favors the SMSI between Cu and ZnO and increases the catalytic activity for the methanol steam reforming reaction. In contrast, the addition of ethanol/water and 1-propanol/water during reduction leads to a physical blockage of the catalyst by alcohol molecules, poisoning the active Cu sites and limiting the migration of ZnO species.
RESUMEN
PURPOSE: To explore the clinical effect of fluoride coating combined with pit and fissure sealing or preventive resin filling on prevention of young first permanent molars caries. METHODS: Three hundred suspicious first permanent molars caries in 90 children (6-8 years old) who received oral health examination in our hospital from February 2015 to January 2016 were included as the study subject, and randomly divided into group A, B, C, D and E. Group A received pit and fissure sealing, group B received preventive resin filling, group C received 0.5% fluoride coating combined with pit and fissure sealing, group D received 0.5% fluoride combined with preventive resin filling, group E as control group with nursing daily brushing. 6, 12 and 18 months after treatment, caries rate in each group was evaluated and preservation of pit and fissure sealing or resin filling in group A, B, C, D was examined. The data were analyzed using SPSS 21.0 software package. RESULTS: Six and 12 months after treatment, there was no significant difference (P>0.05) in the preservation rate of pit and fissure sealing or resin filling and caries rate in group A, B, C, D. Eighteen months after treatment, caries rate in group E was significantly higher than that of group A, B, C, D; there was significant difference between group A and group C, group B and group D (P<0.01); caries rate of group A, B was relatively high, the preservation rate was lower than that of group C and D, the differences were statistically significant (P<0.05). CONCLUSIONS: For suspected young permanent molars caries, fluoride coating combined with pit and fissure sealing or separate pit and fissure sealing has a certain effect on prevent dental caries, but the fluoride coating combined with preventive resin filling is better.