Catalysts2016, 6(7), 94; doi:10.3390/catal6070094 (registering DOI) - published 25 June 2016 Show/Hide Abstract
Abstract: Metal-free transformations of organotrifluoroborates are advantageous since they avoid the use of frequently expensive and sensitive transition metals. Lewis acid-catalyzed reactions involving potassium trifluoroborate salts have emerged as an alternative to metal-catalyzed protocols. However, the drawbacks to these methods are that they rely on the generation of unstable boron dihalide species, thereby resulting in low functional group tolerance. Recently, we discovered that in the presence of a Brønsted acid, trifluoroborate salts react rapidly with in situ generated oxocarbenium ions. Here, we report Brønsted acid-catalyzed direct substitution of 2-ethoxytetrahydrofuran using potassium trifluoroborate salts. The reaction occurs when tetrafluoroboric acid is used as a catalyst to afford functionalized furans in moderate to excellent yields. A variety of alkenyl- and alkynyltrifluoroborate salts readily participate in this transformation.
Abstract: In industry, one of the main catalysts typically employed for the selective oxidation of methanol to formaldehyde is a multi-component oxide containing both bulk Fe2(MoO4)3 and excess MoO3. It is thought that the excess MoO3 primarily acts to replace any molybdenum lost through sublimation at elevated temperatures, therefore preventing the formation of an unselective Fe2O3 phase. With both oxide phases present however, debate has arisen regarding the active component of the catalyst. Work here highlights how catalyst surfaces are significantly different from bulk structures, a difference crucial for catalyst performance. Specifically, Mo has been isolated at the surface as the active surface species. This leaves the role of the Fe in the catalyst enigmatic, with many theories postulated for its requirement. It has been suggested that the supporting Fe molybdate phase enables lattice oxygen transfer to the surface, to help prevent the selectivity loss which would occur in the resulting oxygen deficit environment. To assess this phenomenon in further detail, anaerobic reaction with methanol has been adopted to evaluate the performance of the catalyst under reducing conditions.
Abstract: Soft sensors are used for fault detection and prediction of the process variables in chemical processing units, for which the online measurement is difficult. The present study addresses soft sensor design and identification for deactivation of zeolite catalyst in an industrial-scale fixed bed reactor based on the process data. The two main reactions are disproportionation (DP) and transalkylation (TA), which change toluene and C9 aromatics into xylenes and benzene. Two models are considered based on the mass conservation around the reactor. The model parameters are estimated by data-based modeling (DBM) philosophy and state dependent parameter (SDP) method. In the SDP method, the parameters are assumed to be a function of the system states. The results show that the catalyst activity during the period under study has approximately a monotonic trend. Identification of the system clearly shows that the xylene concentration has a determining role in the conversion of reactions. The activation energies for both DP and TA reactions are found to be 43.8 and 18 kJ/mol, respectively. The model prediction is in good agreement with the observed industrial data.
Abstract: This study aimed to investigate TiO2 photocatalytic degradation of synthetically-prepared greywater samples with differing compositional contents of organic matter (OM), anion concentration, and microbiological consortium. Treatment efficiency was followed through removal of organic matter content in terms of dissolved organic carbon (DOC), specific spectroscopic parameters, and bacterial inactivation. Photocatalytic degradation kinetics were expressed by pseudo first-order kinetic modeling. The best DOC removal rates were attained for greywater samples containing OM with lower molecular size fractions. In addition, either enhancing or reducing the effect of common anions as radical scavengers were observed depending on the composition and concentration of variables in the greywater matrix. Moreover, possibility of a photocatalytic disinfection process was found to be of a bacteria type specific in OM-loaded synthetic greywater samples. Photocatalytic destruction of fecal streptococci required longer irradiation periods under all conditions. Bacterial removal rates were found to be in the order of total coliform > fecal coliform > fecal streptococci, for low organic load greywater, and fecal coliform > total coliform > fecal streptococci, for high organic load greywater.
Abstract: Organic and inorganic compounds utilised at different stages of various industrial processes are lost into effluent water and eventually find their way into fresh water sources where they cause devastating effects on the ecosystem due to their stability, toxicity, and non-biodegradable nature. Semiconductor photocatalysis has been highlighted as a promising technology for the treatment of water laden with organic, inorganic, and microbial pollutants. However, these semiconductor photocatalysts are applied in powdered form, which makes separation and recycling after treatment extremely difficult. This not only leads to loss of the photocatalyst but also to secondary pollution by the photocatalyst particles. The introduction of various magnetic nanoparticles such as magnetite, maghemite, ferrites, etc. into the photocatalyst matrix has recently become an area of intense research because it allows for the easy separation of the photocatalyst from the treated water using an external magnetic field. Herein, we discuss the recent developments in terms of synthesis and photocatalytic properties of magnetically separable nanocomposites towards water treatment. The influence of the magnetic nanoparticles in the optical properties, charge transfer mechanism, and overall photocatalytic activity is deliberated based on selected results. We conclude the review by providing summary remarks on the successes of magnetic photocatalysts and present some of the future challenges regarding the exploitation of these materials in water treatment.
Abstract: New gold catalysts supported on CeO2, ZrO2 and TiO2 were synthesized by two different techniques: deposition-precipitation and colloidal method. The role of the surfactant (PVA, PVP, THPC) was also investigated. The catalysts were tested in the oxidation of glucose to gluconic acid, in aqueous environment and under mild conditions (60 °C and atmospheric pressure). TEM and SEM analyses have shown that the small size of gold nanoparticles is a necessary condition, but not sufficient for a good conversion. In fact, for an active sample, we have verified that the excess of surfactant must be removed because it would coat the surface of the catalyst. The surfactant, however, should not be completely eliminated, since it has the fundamental role of stabilizing the sample preventing nanoparticles from aggregation. It was evidenced that both the synthetic approach and the kind of support affect the catalysts’ activity. In fact, by focusing on the three different supports, with all the preparation methods, the ceria has proved to be the best support. This is due to its ability to obtain small gold nanoparticles and to its ability to accumulate oxygen. The most appropriate synthesis methodology proved to be the colloidal method with PVA. Recyclability issue was investigated too.