Optimizing Active Sites for High CO Selectivity during CO2 Hydrogenation over Supported Nickel Catalysts.

Controlling the selectivity of CO2 hydrogenation catalysts is a fundamental challenge. In this study, the selectivity of supported Ni catalysts prepared by the traditional impregnation method was found to change after a first CO2 hydrogenation reaction cycle from 100 to 800 °C. The usually high CH4 formation was suppressed leading to full selectivity toward CO. This behavior was also observed after the catalyst was treated under methane or propane atmospheres at elevated temperatures. In situ spectroscopic studies revealed that the accumulation of carbon species on the catalyst surface at high temperatures leads to a nickel carbide-like phase. The catalyst regains its high selectivity to CH4 production after carbon depletion from the surface of the Ni particles by oxidation. However, the selectivity readily shifts back toward CO formation after exposing the catalysts to a new temperature-programmed CO2 hydrogenation cycle. The fraction of weakly adsorbed CO species increases on the carbide-like surface when compared to a clean nickel surface, explaining the higher selectivity to CO. This easy protocol of changing the surface of a common Ni catalyst to gain selectivity represents an important step for the commercial use of CO2 hydrogenation to CO processes toward high-added-value products.

Structural and optical properties of europium- and titanium-doped Y2 O3 nanoparticles.

Luminescent nanoparticles of Y2 O3 doped with europium (Eu) and/or titanium (Ti) were synthesized using modified sol-gel routes. The crystalline cubic phase was confirmed using X-ray powder diffraction (XRD). Particle morphology and size were evaluated using scanning and transmission electron microscopy. High-resolution transmission electron microscopy showed that the synthesis method affected the average particle size and the Fourier transform of the images showed the lattice plane distances, indicating that the samples presented high crystallinity degree in accordance with the XRD pattern. The Ti valence was investigated using X-ray absorption near edge spectroscopy and the tetravalent form was the dominant oxidizing state in the samples, mainly in Eu and Ti co-doped Y2 O3 . Optical behaviour was investigated through X-ray excited optical luminescence and photoluminescence under ultraviolet-visible (UV-vis) and vacuum ultraviolet (VUV) excitation. Results indicated that Eu3+ is the emitting centre in samples doped with only Eu and with both Eu and Ti with the 5 D0 →7 F2 transition as the most intense, indicating Eu3+ in a noncentrosymmetric site. Finally, in the Eu,Ti-doped Y2 O3 system, Ti3+ (or TiIV ) excitation was observed but no Ti emission was present, indicating a very efficient energy transfer process from Ti to Eu3+ . These results can aid the development of efficient nanomaterials, activated using UV, VUV, or X-rays.

Is uvulopalatopharyngoplasty still an option for the treatment of obstructive sleep apnea?

Uvulopalatopharyngoplasty (UPPP) has been widely described as a surgical option for the treatment of obstructive sleep apnea syndrome. Several studies have demonstrated variable success rates, and different criteria have been used to define success of surgery. The aim of the present study was to assess the efficiency of UPPP by polysomnography and to correlate it to the clinical findings. Also, we correlated to the various studies dealing with this topic, considering the different criteria adopted in each of this. Sixty-four patients were included in the study. The efficiency of surgery for UPPP was analyzed to the variables such as body mass index, age, preoperative polysomnography results and follow-up period. Based on the criteria for postoperative cure, the success rate was 44 %. Younger patients presented a better success rate than older ones. No other correlation was found between clinical findings and UPPP success. UPPP can be curative in some patients, but combination with other treatment modalities must be considered. This should be mentioned to the patients, since in many cases the sites of airway collapse may be multiple and no clinical aspect (except for age) is indicative of good prognosis.

Unlocking the Catalytic Potential of TiO2-Supported Pt Single Atoms for the Reverse Water-Gas Shift Reaction by Altering Their Chemical Environment.

Single-atom catalysts (SACs) often exhibit dynamic responses to the reaction and pretreatment environment that affect their activity. The lack of understanding of these behaviors hinders the development of effective, stable SACs, and makes their investigations rather difficult. Here we report a reduction-oxidation cycle that induces nearly 5-fold activity enhancement on Pt/TiO2 SACs for the reverse water-gas shift (rWGS) reaction. We combine microscopy (STEM) and spectroscopy (XAS and IR) studies with kinetic measurements, to convincingly show that the low activity on the fresh SAC is a result of limited accessibility of Pt single atoms (Pt1) due to high Pt-O coordination. The reduction step mobilizes Pt1, forming small, amorphous, and unstable Pt aggregates. The reoxidation step redisperses Pt into Pt1, but in a new, less O-coordinated chemical environment that makes the single metal atoms more accessible and, consequently, more active. After the cycle, the SAC exhibits superior rWGS activity to nonatomically dispersed Pt/TiO2. During the rWGS, the activated Pt1 experience slow deactivation, but can be reactivated by mild oxidation. This work demonstrates a clear picture of how the structural evolution of Pt/TiO2 SACs leads to ultimate catalytic efficiency, offering desired understanding on the rarely explored dynamic chemical environment of supported single metal atoms and its catalytic consequences.

Avaliação da qualidade do tucupi comercializado na cidade de Castanhal- PA / Quality evaluation of marketed tucupi at Castanhal city

O tucupi é definido como um molho parcialmente fermentado e condimentado, derivado da mandioca. O presente trabalho teve como objetivo avaliar a qualidade do tucupi comercializado no município de Castanhal-PA, por meio de análises físico-químicas, com destaque para a determinação de cor (parâmetros L*, a* e b*). O estudo foi conduzido a partir de um delineamento em parcelas subdivididas de 27 amostras de tucupi, sendo os dados avaliados por análise de variância (p<0,05). Os resultados da pesquisa mostraram que houve diferença significativa para a acidez expressa em ácido lático, para o pH, para os açúcares totais e para todos os parâmetros da análise de cor. Conclui-se, portanto, que o tucupi comercializado no município de Castanhal-PA apresenta grande variação quanto as características do padrão de identidade e qualidade do produto, fazendo-se necessária uma maior atuação dos órgãos fiscalizadores sobre a produção e comercialização do tucupi.

Farofas de mandioca temperadas: avaliação microbiológica e da atividade de água / Cassava flour seasoned: microbiological evaluation and water activity

Produzida artesanalmente em casas de farinha, pode ser comercializada em feiras livres e supermercados. Este trabalho foi realizado com o objetivo de avaliar microbiologicamente duas amostras de farofas de mandioca temperadas e verificar o comportamento da atividade de água ao longo de um período de trinta e cinco dias de armazenamento sob temperatura constante de 30 ºC. A análise quanto a atividade de água foi realizada logo após o processamento e durante todo o período de armazenamento, com intervalos de sete dias. Com relação à análise microbiológica as amostras estavam dentro dos padrões estabelecidos pela legislação. A atividade de água diminuiu com a temperatura e com o tempo de armazenamento, porém, com valores inferiores a 0,6.

Predictors of uvulopalatopharyngoplasty success in the treatment of obstructive sleep apnea syndrome.

OBJECTIVE: Uvulopalatopharyngoplasty (UPPP) has been described as an option for treating obstructive sleep apnea syndrome (OSAS), with variable success rates. The main purpose of our study was to correlate UPPP success to craniofacial bony structure and orofacial muscles function. METHODS: Clinical variables, including body mass index (BMI), age, and preoperative apnea-hypopnea index (AHI); cephalometric measurements of the craniofacial region and hyoid bone position; and muscle function variables including clinical protocol and tongue strength measures were evaluated in 54 patients who underwent UPPP in the last 7years. The measurements were related to the success or failure of UPPP based on the results of preoperative and postoperative polysomnography (PSG). RESULTS: The variables BMI, preoperative AHI, and cephalometric measurements showed no influence on surgical success. The clinical muscle protocol also was similar between groups. However, the muscle strength of the anterior portion of the tongue was significantly greater in the group that showed surgical success compared to those with surgical failure. CONCLUSION: OSAS is a multifactorial disease and diagnostic symptom assessments should be individualized. In addition, special attention should be given to functional muscle alterations of the airways, as they might influence the evolution of the disease.

Propofol-induced sleep: polysomnographic evaluation of patients with obstructive sleep apnea and controls.

OBJECTIVE: The localization of upper airway obstruction in patients with obstructive sleep apnea (OSA) may optimize treatment. Nasoendoscopy during propofol sedation allows such an evaluation, but the effect of this drug on respiratory patterns and muscle relaxation is unknown. The objective of the present study was to determine through polysomnography whether propofol would change sleep parameters. STUDY DESIGN: Prospective study of subjects submitted to polysomnography under sedation with propofol. SETTING: Tertiary referral center. SUBJECTS AND METHODS: Fifteen non-obese subjects (4 controls/11 OSA patients) were submitted to two diurnal polysomnograms (90-120 minutes of sleep), with and without the use of propofol. The parameters presence of snoring, apnea-hypopnea index (AHI), oxygen desaturation, and sleep architecture were compared. RESULTS: The use of propofol did not induce snoring in the control subjects, whereas 100 percent of the OSA patients snored. AHI and mean oxygen saturation (SaO(2)) did not differ significantly between examinations with and without sedation. However, minimum SaO(2) differed significantly (P < 0.05) with sedation, being lower during propofol sedation. Propofol also significantly changed the sleep architecture, with a significant increase in N3 sleep (P < 0.005) and total abolishment of rapid eye movement sleep (P < 0.0005) during propofol sedation. CONCLUSIONS: These preliminary results allow us to infer that sedation with propofol changes sleep architecture but permits respiratory evaluation, because the main respiratory parameters evaluated in OSA are maintained. These preliminary results support the view that nasoendoscopy under propofol sedation is a promising examination for management of this disease.