CONCLUSIONS AND OUTLOOK
We have presented an overview of the effect of computational model choice on the properties of octahedral transition metal complexes and emergent single atom catalyst (SAC) materials made from Fe centers in N-doped graphene. The octahedral transition metal complexes chosen mimic the ligand field environment observed in the SAC models but remain tractable for study with multi-reference wavefunction theory. Observations from the hexa-aqua and hexa-ammine complex studies revealed that spin state ordering of mid-row complexes could be sensitive both to the IPEA shift chosen and whether an extended active space was used, whereas late and early transition metals were far less sensitive. Then using these extended active space CASPT2 results as a benchmark, we observed that nearly all transition metal complexes benefitted from increased HF exchange. In fact, errors with respect to exchange fraction chosen monotonically decreased from 0 to 40% but with no improvement for higher exchange fractions. The 40% exchange hybrid results had comparable accuracy to the more computationally demanding double hybrid PBE0-DH.
To date, heterogeneous acid catalysts, such as ion exchange resins (Åkerman et al. 2011 ), zeolites (Singh et al. 2013 ), double-metal cyanide complexes (Kotwal et al. 2011 ), heteropolyacid-supported catalysts (Wee et al. 2013 ), hydrotalcite (Hamerski and Corazza 2014 ; Hamerski et al. 2016 ) and sulphated metal oxide catalysts (Kong et al. 2015 ), have been explored for catalytic glyc- erol esterification with OA. On the contrary, the drawbacks of homogeneous acid catalysts are dark product colour and burnt taste and require additional refining steps. Homog- enous acid catalyst can disperse into the reactants rapidly but resulted in poor product selectivity. In a recent study, it was demonstrated that the application of the Fe–Zn DMC complex is able to achieve GMO conversion with 63.4% and GMO selectivity of 67.3% under optimised conditions of 180 °C reaction temperature, 8 wt.% catalyst loading and 8 h of reaction time (Kotwal et al. 2011 ). Meanwhile, titanium silicate-type catalyst (Ti-SBA-16) featuring a hydrophobic surface attained a conversion of 72.8% at 180 °C, equimolar ratio, 3 wt % catalyst concentration and 3 h of operation time. The presence of catalyst sites in Ti-SBA-16 catalyst is not the only reason contributing to the excellent catalytic performance, but also the catalyst structure further helps in maximising the selectivity of the anticipated products. It was reported that the hydro- phobicity characteristic of Ti metal is able to enhance the glycerol esterification rate and selectivity. However, the high reaction temperature (180 °C) and long reaction time (10 h) are several of the limitations that could be improved to synthesise promising solid acid catalysts.
eﬀective for the degradation of refractory organic compounds, in cluding drugs [ 5 8 ]. AOPs are based on the generation of powerful and non selective oxidant species, such as hydroxyl radical ( • OH), that are capable to degrade organic compounds, transforming them into water (H2O) and carbon dioxide (CO2) as ultimate products. Homogeneous Fenton oxidation is one of the most appealing AOPs owing to: (i) the utilization of environmental friendly reagents (Fe 2+ and H2O2), (ii) its low energy consumption compared to other AOPs, (iii) its ability to destroy various organic compounds along with an improvement of biodegradability, and (iv) the simplicity of the required equipment al lowing an easy scale up from laboratory reactor to large scale process [ 9 11 ].
To date, heterogeneous acid catalysts, such as ion exchange resins (Åkerman et al. 2011), zeolites (Singh et al. 2013), double-metal cyanide complexes (Kotwal et al. 2011), heteropolyacid-supported catalysts (Wee et al. 2013), hydrotalcite (Hamerski and Corazza 2014; Hamerski et al. 2016) and sulphated metal oxide catalysts (Kong et al. 2015), have been explored for catalytic glyc- erol esterification with OA. On the contrary, the drawbacks of homogeneous acid catalysts are dark product colour and burnt taste and require additional refining steps. Homog- enous acid catalyst can disperse into the reactants rapidly but resulted in poor product selectivity. In a recent study, it was demonstrated that the application of the Fe–Zn DMC complex is able to achieve GMO conversion with 63.4% and GMO selectivity of 67.3% under optimised conditions of 180 °C reaction temperature, 8 wt.% catalyst loading and 8 h of reaction time (Kotwal et al. 2011). Meanwhile, titanium silicate-type catalyst (Ti-SBA-16) featuring a hydrophobic surface attained a conversion of 72.8% at 180 °C, equimolar ratio, 3 wt % catalyst concentration and 3 h of operation time. The presence of catalyst sites in Ti-SBA-16 catalyst is not the only reason contributing to the excellent catalytic performance, but also the catalyst structure further helps in maximising the selectivity of the anticipated products. It was reported that the hydro- phobicity characteristic of Ti metal is able to enhance the glycerol esterification rate and selectivity. However, the high reaction temperature (180 °C) and long reaction time (10 h) are several of the limitations that could be improved to synthesise promising solid acid catalysts.
therefore negligible competition e ﬀect for the active catalytic sites. In order to appreciate the contribution of free radicals with Fe MFI, a complementary experiment was carried out using methanol as radical scavenger (reaction rate constant with hydroxyl radical of 9.7 × 10 8 M 1 .s 1 [ 43 ]). Methanol concentration was set to 50 mM corresponding to 500 times the molar concentration of IBP and high Fe MFI loading condition (4.8 g/L) was selected to highlight the scavenging e ﬀect. Methanol was introduced after adsorption step (at the same time as H 2 O 2 ). From Fig. 1 , it can be seen that this addition signiﬁcantly re duced ﬁnal IBP removal yield from 88% to 23% although similar H 2 O 2 consumption of about 80% was still observed. This result pled for a main contribution of free radical mechanism. Note that complete inhibition of the reaction (no IBP removal) was observed in the homogeneous process.
This work investigated Fenton-based oxidation of ibuprofen, and reaction activation by ultrasound (US) irradiation and ultraviolet/visible light (UV/Vis) so as to lower the required concentration of dissolved iron catalyst or improve the activity of heterogeneous counterparts. To that purpose, the efficacy of individual homogeneous AOPs (sonolysis, photolysis, ultrasound/H 2 O 2 , light/H 2 O 2 , Fenton oxidation) was evaluated first, varying operating parameters such as light wavelength and ultrasound frequency. Then, their two-by-two and overall combinations (sonophotolysis, sono-Fenton, photo-Fenton and sono-photo-Fenton oxidation) were examined with emphasis on the identification of synergistic effects. In particular, combined US/Fenton and Vis/Fenton oxidation were found more effective than the sum of individual processes due to sono- and photo-regeneration of ferrous ions. These results also served as a reference for the assessment of heterogeneous systems. Among tested solids, iron-containing zeolite (Fe-ZSM5 type) was shown to be a promising catalyst for peroxide oxidation of ibuprofen due to high efficiency at natural pH and low iron leaching. However, in this case, no more than additive effects was observed between ultrasound/light irradiation andheterogeneous Fenton oxidation. Beside pollutant and Total Organic Carbon conversion, main degradation products were monitored for different processes and some plausible degradation pathways were proposed. Water matrix impact was also addressed using wastewater plant effluent, which resulted into hindered performance of all oxidation processes either due to alkaline buffer or light attenuation effect.
The functionalization of non-activated C-H bonds is one of the most studied topics in the current chemical research. 1 This strong interest is due to the numerous advantages of the direct functionalization of such non-reactive bonds leading to straightforward syntheses. 2 A plethora of homogeneous transition metal catalysts have been developed until now in the field of C-H activation. Heterogeneous catalysts, despite their advantages over homogeneous ones such as their higher robustness and easier recyclability, are generally less employed to activate C-H bonds on complex molecules. This fact is probably due to the challenge related to the modulation of heterogeneouscatalyst reactivity by organic ligands. 3 In contrast, for other types of important chemical reactions such as hydrogenations, the addition of ligands to influence the reactivity of heterogeneous catalysts has been known for decades. 4 In spite of the fact that N-heterocyclic carbenes (NHCs) are widely applied as ligands in homogeneous catalysis, 5 only recently, Glorius et al. reported their capability to tune the reactivity and selectivity of a heterogeneous Ru catalyst (Ru/K-Al 2 O 3 ). 6 In this example, the addition of
treatment, as is the case of photocatalysis since it can take advantage of solar light and may also lead to mineralization of the pollutant. Among the existing catalysts, the polyoxometalate decatungstate anion W 10 O 32 4- has proved to be an excellent photocatalyst in both homogeneousandheterogeneous media since its absorption band partially overlaps the solar spectrum providing the possibility of photo-assisted applications. As a result, the second part of the thesis aimed to test the photocatalytic activity of W 10 O 32 4- towards NAD degradation upon 365 nm irradiation. In homogeneous aqueous solutions NAD is efficiently degraded and mineralized into CO 2 and nitrate anions. The high solubility of W 10 O 32 4- is a drawback for application in water remediation due to problems of catalyst recovery. Consequently, it was necessary to immobilize the catalyst in a solid matrix, which was done by choosing layered double hydroxides (LDHs) materials as support. These materials present excellent anionic exchange properties, are easily synthesized, catalytically inert, and easily recovered from the reaction medium. The last part of this thesis consists in the synthesis of LDHs with different properties, intercalation of the W 10 O 32 4- on the as-prepared LDH and assessment of its photocatalytic activity towards NAD degradation under irradiation at 365 nm. Mg 2 Al-W 10 O 32 4- LDHs materials were synthesized using three different methods: (1) classical co-precipitation at constant pH, Mg 2 Al-W 10 O 32 4- LDH, (2) fast co-precipitation followed by supercritical CO 2 drying, SC-Mg 2 Al-W 10 O 32 4- LDH and (3) use of sacrificial polystyrene colloidal crystal template impregnation-coprecipitation to form three dimensionally ordered macroporous LDH, 3- DOM-Mg 2 Al-W 10 O 32 4- LDH. All the materials have been characterized by a variety of analytical techniques. The heterogeneous photocatalytic degradation of NAD in presence of the three catalysts at 365 nm was studied. Results show that NAD is efficiently degraded in the presence of the catalysts (2) and (3) with consequent mineralization and excellent recovery efficiency. The open structure and porosity presented by the catalyst (3) induces a more efficient light penetration in the LDH layers with consequent increase in the photocatalytic activity of W 10 O 32 4- . Therefore, the macroporous and supercritical LDH materials intercalated with decatungstate anion can be considered as promising catalysts for pollutant water treatment.
S1 Fig. Resolution of the ace-1 duplication structure. (A) Distribution of the paired-end (PE) insert size in the vicinity of the breakpoints (± 1 kb). For each strain, we recorded the insert size of each read and its paired read; for each 200 bp insert size class, we calculated the number of reads, which was then normalized relative to the 2R chromosome mean DOC (between 2 Mb and 5 Mb, excluding the duplicated region). Discordant PEs presented insert sizes distributed around 202 kb, and were identified only for the Acerduplikis (DD, mean insert size 250 bp) and AcerkisR 3 (R 3 R 3 , mean insert size 500 bp) strains. (B) Duplication breakpoints and junction resolution. The top figure shows the relative positions of the ampli- cons ( i.e. carrying the resistant R or susceptible S copy) of the DD strain duplication; the 5’ end of the amplified region is crosshatched in blue and the 3’ end is crosshatched in red. The bot- tom figure shows the expected mapping of the reads from DD strain onto the reference genomes: PE reads surrounding the duplication junction result in discordant pairs (i.e. pairs with reads mapping in opposite orientations, with an insert size different from the expected 250 bp); reads overlapping the duplication junction result in soft-clipped reads (i.e. partially mapped reads). These features were used to estimate the duplication length and to reconstitute the junction and breakpoint sequences. (C) Alignment of breakpoints and junction
reactants was used. This result was attributed to the strong acidity of Aquivion. A relatively low selectivity of GMO was obtained for Aquivion-catalyzed reaction (< 3%). This finding suggested that the superstrong acidity of Aquivion is suitable in producing large GTO molecules at the OA- to-glycerol molar ratio of 3:1. Further lowering the loading amount of Aquivion (optimisation of catalyst concentration) is necessary to attain high yield and selectivity of GMO. Superstrong acid potentially produces undesirable side reaction products, ∼50% by-product was attained in this experiment; the possible by-products would be glycerol oligomers, polyglycerol, alkenes, acrolein, or polyglycerol esters. A long reaction time is unadvisable for Aquivion- catalyzed reaction because the yield and GTO selectivity were reduced (Figure 12B).
included the explicit calculation of heat and mass transfer rates in a rigorous dynamic rate-based approach and the experiments on a batch distillation column showed good agreement with simulation results. Noeres et al. (2004) con- sidered a rigorous rate-based dynamic model for designing a batch heterogeneously catalyzed reactive distillation and good agreement was verified for compositions and temper- atures through the column after forced perturbations on reflux ratio. Singh et al. (2005) studied esterification reaction of acetic acid with n-butanol in a packed distillation col- umn with the commercial catalytic packing KATAPAK-S and non-catalytic wire gauze. A dynamic equilibrium stage model was developed to analyze the influence of various operating parameters and several trials were carried out; reasonably good agreement between the experimental and simulation results was said to be verified, but results were only shown for one representative attempt. Xu et al. (2005) developed a detailed three-phase non-equilibrium dynamic model for simulating batch and continuous catalytic distillation pro- cesses. The simulation results were in good agreement with the experimental data obtained from the production of diace- tone alcohol. Experiments were performed with the column under total reflux and the transient behavior was studied after a decrease of the reboiler duty. Finally, Völker et al.
Three sets of experiments were performed under optimized conditions in glycerol esterification with OA in the presence of different catalysts, namely, ZrO 2 -SiO 2 -Me&EtPhSO 3 H, Amberlyst 15 and Aquivion. Aquivion afforded the highest conversion, which was nearly 99% in 240 min reaction time (Figure 12A). Approximately 98% conversion was obtained within 120 min reaction time. The formation rates of GDO and GTO were the fastest for Aquivion (S GDO = 69% and S GTO = 30%), although an equimolar ratio of reactants was used. This result was attributed to the strong acidity of Aquivion. A relatively low selectivity of GMO was obtained for Aquivion-catalyzed reaction (< 3%). This finding suggested that the superstrong acidity of Aquivion is suitable in producing large GTO molecules at the OA- to-glycerol molar ratio of 3:1. Further lowering the loading amount of Aquivion (optimisation of catalyst concentration) is necessary to attain high yield and selectivity of GMO. Superstrong acid potentially produces undesirable side reaction products, ∼50% by-product was attained in this experiment; the possible by-products would be glycerol oligomers, polyglycerol, alkenes, acrolein, or polyglycerol esters. A long reaction time is unadvisable for Aquivion- catalyzed reaction because the yield and GTO selectivity were reduced (Figure 12B).
Yields in fatty acid methyl esters (FAMEs) and triacetin (TA) up to 90% and 70% respectively, were achieved after 4 h of reaction time at 483 K in the presence of 0.69 mol of SnO per mole of rapeseed oil using a methyl acetate to oil molar ratio of 40.
Quite interestingly, the catalyst performances improved when water was added to the reactions system. Moreover the same catalyst sample was used three consecutive times without observing any depletion of the catalytic activity.
Recyclability of the hybrid was investigated through sequential couplings of 1a and 2 using the same PdCNT cata- lyst sample. Briefly, a standard coupling experiment was set-up and after 4 h of reaction, the mixture was centrifuged, the liquid phase was collected, worked-up and the crude product was purified by column chromatography. In parallel, the catalyst-containing pellet was collected and reused for the coupling of fresh substrates 1a and 2. This was done over five consecutive cycles with no drop in catalytic activity (97 –98% yield for each run). TEM analysis of the catalyst recovered after 5 cycles showed no major changes in the mor- phology of the hybrid (Fig. S2a, ESI †). However, XPS analysis indicated that the recovered catalyst was mainly made of Pd metal (Fig. S2b, ESI †), indicating in situ reduction of the Pd oxide fraction during the catalytic cycle.
The air traffic management system is currently experiencing a significant transformation to provide better quality service and to match the increasing air traffic demand. This transformation requires airlines to retrofit their fleet. However, airlines implement new operating capabilities at different rates resulting in long transition periods in which aircraft with different equipage levels coexist in the same airspace. Mixed equipage environments can increase controller workload and task complexity, limit the operational benefits of new operating capabilities, and deteriorate the overall system performance. This study proposes a three dimensional approach to explore mixed equipage effects: (1) understand cognitive implications for controllers, (2) understand operational implications for users, and (3) understand system level implications. To further investigate mixed equipage effects and to illustrate the proposed approach, this study analyzed the implementation of reduced separation standards in the North Atlantic.
𝒑𝒄 𝐉 𝒑𝒄 𝑻 ) −𝟏 ), respectively.
Consequently, the parallel manipulators are said to be at an actuation singularity if 𝜅((𝐉 𝒑𝒂 𝐉 𝒑𝒂 𝑻 ) −𝟏 ) = 0 and at a constraint singularity if 𝜅((𝐉
𝒑𝒄 𝐉 𝒑𝒄 𝑻 ) −𝟏 ) = 0. It also indicates that the actuation wrench matrix and the constraint wrench matrix degenerate, respectively. On the other hand, there is a case in which the parallel manipulators are neither at the actuation singularity nor at the constraint singularity while the system is subjected to a singularity. In this case, the Jacobian matrix degenerates due to the dependency between the actuation wrench matrix and the constraint wrench matrix, hence 𝜅(𝐉 𝒑 −𝟏 ) = 0, while 𝜅((𝐉 𝒑𝒂 𝐉 𝒑𝒂 𝑻 ) −𝟏 ) ≠ 0 and 𝜅((𝐉 𝒑𝒄 𝐉 𝒑𝒄 𝑻 ) −𝟏 ) ≠ 0. This type of singularity is called a compound singularity and the moving platform gains one or more uncontrolled motion. Therefore, larger values of the condition number signify larger distances of a pose to different types of singularities.
Institute of Atmospheric Sciences and Climate (CNR), Torino, Italy
Universit´e Cˆ ote d’Azur, CNRS, LJAD, Nice, France
We study the chaoticity and the predictability of a turbulent flow on the basis of high-resolution direct numerical simulations at different Reynolds numbers. We find that the Lyapunov exponent of turbulence, which measures the exponential separation of two initially close solution of the Navier- Stokes equations, grows with the Reynolds number of the flow, with an anomalous scaling exponent, larger the one obtained on dimensional grounds. For large perturbations, the error is transferred to larger, slower scales where it grows algebraically generating an “inverse cascade” of perturbations in the inertial range. In this regime our simulations confirm the classical predictions based on closure models of turbulence. We show how to link chaoticity and predictability of a turbulent flow in terms of a finite size extension of the Lyapunov exponent.
The produced systems often feature such less desirable features as fast explosion of approximating discrete Euler schemes  in the case of positive homogeneity degrees, or extensive chattering in the operational mode in the case of discontinuous systems with non-positive homogeneity degrees. One of the methods to overcome the obstacle is to use implicit Euler schemes both in simulation and control , . The questions on the convergence and accuracy of implicit Euler schemes applied to general DIs are still to be addressed.
We conclude the paper by giving an application of Theorem 3.1. We study exit time from balls for the stable process corresponding to our semigroup. For related results we refer the reader to  or . In general, we were inspired by the approach from , for stable case see . The results in section 4 have their analogues in these papers. Observe, however, that the argument of  and  hinges on the Ahlfors-regularity of the measure, i.e. polynomial volume growth. Clearly, this excludes the homogeneous trees and hyperbolic spaces. Our contribution is to make it available for stable processes in exponential volume growth setting. Moreover, we give a proof in an abstract framework of metric measures spaces (cf. ). The interplay between (21) and (22) below may be of independent interest. In this way, we get our results for homogeneous trees and hyperbolic spaces at the same time.