Synthesis and characterization of V, Mo and Nb incorporated micro-mesoporous MCM-41 materials

Highly microporous metal-MCM-41 ordered mesoporous structure catalysts having different metal/Si (V, Mo, Nb) atomic ratios and combinations of metal sources were hydrothermally synthesized. The structural properties estimated using different techniques were found to be in agreement with each other. Metals were successfully incorporated into MCM-41 without deteriorating the ordered hexagonal structure. The metal ions in the synthesis solutions probably settled on the hydrophilic end of the template hence the metal incorporation resulted improvements in the micropore structure. Low loading of metals caused an increase in the surface area and pore volume values of the catalysts. The highest total (1310 m(2) g(-1)) and micropore surface area values (1083 m(2) g(-1)) were obtained by Nb incorporation. The micro- and mesopore dimensions of MCM-41 increased from 0.5 to 1.1 nm and from 2.5 to 2.8 nm, respectively, with metal incorporation. Low V/Si ratios and presence of Nb in the starting solution enhanced narrow mesopore size distribution. The pore dimension and wall thickness values estimated from nitrogen adsorption and X-ray diffraction methods were consistent with the corresponding values obtained using transmission electron microscopy

Role of synthesis media on properties of tin and copper incorporated SBA-15 catalysts and their activity in selective oxidation of ethanol

Hydrothermal synthesis of metal/SBA-15 catalysts were performed by adding of metal sources before or after silica precursor, as powder or after dissolving in alcohol. Novel catalysts were developed carrying out synthesis in competitive (aluminum) ion media. XRD patterns and TEM images showed that uniform hexagonal arrays of SBA-15 support were not affected with metal loadings. Metal addition and dissolution in alcohol enhanced textural and ordered properties. Proposed ion attractions in highly charged media by presence of metals could explain wall thickness increase of SBA-15. Positive effects of aluminum environment on tin loading were supported by XRD, TEM, EDS and ICP-MS. Metal incorporation resulted in drastic changes in OH stretching region and remarkable increases in Bronsted and Lewis acid sites in FTIR spectrums. Aluminum and its quantity increase in synthesis solution enhanced surface acidity. The catalysts yielded conversion values reaching to 0.95 at moderate temperatures in oxidation of ethanol. The highest acetaldehyde-which was the major product- selectivity was observed as 0.58 at 300 degrees C. Distribution of species in the reactor outlet was tried to explain by Marsvan Krevelen adsorption/desorption surface mechanism of ethanol on the active sites

Activity Comparison of MCM-41 and V-MCM-4 Catalysts for Ethanol Selective Oxidation and DRIFTS Analysis

The activity of a V-MCM-41 catalyst with a V/Si molar ratio of 0.04 was compared with the activity of a pure MCM-41 catalyst and some DRIFTS studies were performed in order to understand the mechanism of selective oxidation of ethanol. V-MCM-41 was found to be much more active than pure MCM-41, favouring the formation of high amounts of ethylene over 300 degrees C. MCM-41, on the other hand, was found to favour the formation of acetaldehyde over ethylene at all studied temperatures. It was shown by reaction findings that over V-MCM-41, ethylene was produced mainly in the presence of gas phase oxygen whereas acetaldehyde was produced using the lattice oxygen even in the absence of gas phase oxygen. DRIFTS studies indicated the formation of acetaldehyde molecules from acetate-like surface species which were formed by the removal of a hydrogen atom from the beta-carbon of chemisorbed ethoxy species by the help of the lattice oxygen. On the other hand, removal of a hydrogen atom from the beta-carbon of the ethoxy species, in the presence of gas phase oxygen, resulted in the formation of vinyl-like surface species which then yielded ethylene molecules

Synthesis of boron nitride nanotubes from ammonia and a powder mixture of boron and iron oxide

Boron nitride nanotubes (BNNTs) were synthesized from the reaction of ammonia gas with a powder mixture of boron and iron oxide in a tubular reactor connected to a mass spectrometer for the on-line chemical analysis of the reactor outlet stream at different temperatures and inlet gas compositions. XRD results showed that hexagonal and rhombohedral boron nitrides, iron, boron oxide, and iron boride were the solid phases formed in these materials depending on the reaction temperature and gas composition. It was observed that the crystallinity of the product increased with an increase in temperature. The synthesized materials exhibited Type II isotherms. The chemical analysis revealed that the only reaction taking place in the gas phase was the decomposition reaction of the ammonia gas and BNNTs were produced by the reaction of nitrogen formed from the decomposition reaction with FexBy formed from the reaction of B with Fe2O3

Boron Oxide Production Kinetics Using Boric Acid as Raw Material

Boron oxide with a content of 99.93 wt.% from the dehydration of boric acid was synthesized. Conversion of boric acid to boron oxide was completed within 3 days at low temperature range (T 130 degrees C) for the isothermal dehydration reaction in the temperature range of 80 and 350 degrees C. Apparent activation energies were 65 and 28 kJ.mol(-1) for low and high temperature ranges, respectively. Thermogravimetric analysis (TGA) results showed that the reactions were nearly completed at around 330 degrees C, and activation energy for the first temperature region was found to be two-thirds of the isothermal value and the same for the second temperature region. Isothermal data analysis revealed that the apparent reaction order value was around 1.0 at low temperature range and decreased to 0.55 with temperature within the high temperature range

The prevalence and risk factors for urinary incontinence among inpatients, a multicenter study from Turkey

Objective: To determine the prevalence and the factors associated with urinary incontinence (UI) among inpatients in Turkey

Comprehensive geriatric assessment in older people : an umbrella review of health outcomes

Background: Comprehensive geriatric assessment (CGA) has been in use for the last three decades. However, some doubts remain regarding its clinical use. Therefore, we aimed to capture the breadth of outcomes reported and assess the strength of evidence of the use of comprehensive geriatric assessment (CGA) for health outcomes in older Methods: Umbrella review of systematic reviews of the use of CGA in older adults searching in Pubmed, Embase, Scopus, Cochrane library and CINHAL until 05 November 2021. All possible health outcomes were eligible. Two independent reviewers extracted key data. The grading of evidence was carried out using the GRADE for intervention studies, whilst data regarding systematic reviews were reported as narrative findings. Results: Among 1,683 papers, 31 systematic reviews (19 with meta-analysis) were considered, including 279,744 subjects. Overall, 13/53 outcomes were statistically significant (P < 0.05). There was high certainty of evidence that CGA reduces nursing home admission (risk ratio [RR] = 0.86; 95% confidence interval [CI]: 0.75–0.89), risk of falls (RR = 0.51; 95%CI: 0.29–0.89), and pressure sores (RR = 0.46; 95%CI: 0.24–0.89) in hospital medical setting; decreases the risk of delirium (OR = 0.71; 95%CI: 0.54–0.92) in hip fracture; decreases the risk of physical frailty in community-dwelling older adults (RR = 0.77; 95%CI: 0.64–0.93). Systematic reviews without meta-analysis indicate that CGA improves clinical outcomes in oncology, haematology, and in emergency department. Conclusions: CGA seems to be beneficial in the hospital medical setting for multiple health outcomes, with a high certainty of evidence. The evidence of benefits is less strong for the use of CGA in other settings