Rapid and Efficient N-tert-butoxy carbonylation of Amines Catalyzed by Sulfated Tin Oxide Under Solvent-free Condition

A straightforward, rapid, and efficient protocol for the N-tert-butoxy carbonyl (N-Boc) protection of amines (aromatic, aliphatic) using sulfated tin oxide catalyst is illustrated. N-Boc protection of various amines was carried out with (Boc)2O using sulfated tin oxide as a catalyst at room temperature under solvent-free conditions. Rapid reaction times, ease of handling, cleaner reactions, easy work-up, reusable catalyst, and excellent isolated yields are the striking features of this methodology which can be considered to be one of the better methods for the protection of amines and alcohols. DOI: http://dx.doi.org/10.17807/orbital.v10i7.115

Ce0.80M0.12Sn0.08O2−δ(M = Hf, Zr, Pr, and La) ternary oxide solid solutions with superior properties for CO oxidation

To develop efficient materials for CO oxidation, a series of co-doped CeO2 ternary oxide solid solutions (Ce0.80M0.12Sn0.08O2 d, M ¼ Hf, Zr, Pr, and La) were prepared by a simple coprecipitation method. The fundamental characteristics of the co-doped CeO2 samples were studied by X-ray diffraction, Raman spectroscopy, UV-visible diffuse reflectance spectroscopy, transmission electron microscopy, Brunauer– Emmett–Teller surface area, H2-temperature programmed reduction, X-ray photoelectron spectroscopy, and O2-temperature programmed desorption. The oxidation of CO was chosen as a model reaction to evaluate the catalytic performance of these samples. The characterization results revealed that ternary oxide solid solutions had significantly enhanced surface area, improved reducibility, increased oxygen mobility and higher quantity of surface adsorbed oxygen species and oxygen vacancies, compared to undoped CeO2. The CO oxidation performance of CeO2 was greatly improved upon co-doping due to the modification in structural, textural, and redox properties. Especially, the Ce0.80Pr0.12Sn0.08O2 d combination catalyst exhibited the highest oxidation activity among the investigated samples, which is attributed to its high specific surface area, better reducibility, superior surface active oxygen species, and oxygen vacancies among the various samples investigated

Single-step synthesis of N-doped TiO₂ by flame aerosol method and the effect of synthesis parameters

<p>We have established a novel route for the synthesis of N-doped TiO₂ by adopting flame aerosol (FSP) technique and investigated the effect of water content on the physico-chemical properties of the as-synthesized nanoparticles. The key characteristics of the developed method are to modify the precursor solution in order to incorporate nitrogen atoms into the TiO₂ lattice without altering the FSP set-up. The reduction of the flame enthalpy resulting in N-incorporation into the TiO₂ and the N-doping can be greatly enhanced further by the addition of secondary N-source (urea). Our XRD results reveal a shift of the (101) plane anatase diffraction peak to lower angles in our N-doped TiO₂ compared to undoped TiO_2, which suggest the distortion and strain in the crystal lattice prompted by the incorporation of the nitrogen atoms. The growth or expansion of crystal lattice can be attributed to the larger atomic radius of respective nitrogen atoms (<i>r</i> = 1.7 Å) compared to oxygen (<i>r</i> = 1.40 Å). Our XPS and EDX spectroscopy results elucidate that the nitrogen was effectively doped into the crystal lattice of TiO₂ in our as-synthesized N-TiO₂ catalysts predominantly in the form of interstitial nitrogen (Ti−O−N). The nitrogen atoms incorporation into the crystal lattice of titania modifies the electronic band structure of TiO₂, resulting in a new mid-gap energy state N 2<i>p</i> band formed above O 2<i>p</i> valence band. This occurrence narrows the band gap of TiO₂ (from 3.12 to ∼2.51 eV) in our N-doped TiO₂ and shifts the optical absorption to the visible region.</p> <p>Copyright © 2018 American Association for Aerosol Research</p

Flame Aerosol Synthesized Cr Incorporated TiO₂ for Visible Light Photodegradation of Gas Phase Acetonitrile

A series of Cr–TiO₂ nanoparticles with different atomic ratios of Ti to Cr have been synthesized by adopting a one-step flame aerosol synthesis technique. The photocatalytic activity of flame aerosol made TiO₂ loaded with various amounts of Cr was studied as a catalyst for gas phase photodegradation of acetonitrile (ACN) under visible light (400–800 nm). It was found that the optimal concentrations of Cr and TiO₂ exist (Ti/Cr atomic ratio = 40) for the efficient oxidation of ACN in the gas phase. XRD patterns showed a decrease in the anatase phase with increase in the amount of Cr loading. Our H₂–temperature programmed reduction (TPR) results indicate a strong interaction (Cr–O–Ti) between support and dopant in the Cr modified TiO₂ as-synthesized catalysts. Our XPS results illustrated that the relative atomic percentage value of Ti³⁺/Ti⁴⁺ characterized by XPS was significantly high for the Cr/TiO₂ nanoparticles with Ti/Cr = 40 atomic ratio (Ti³⁺/Ti⁴⁺ = 1.14, 42.1%), whereas other samples demonstrated low atomic percentage value of Ti³⁺/Ti⁴⁺ (Ti³⁺/Ti⁴⁺ = 0.18–1.05). Moreover, Cr interacts with the TiO₂ nanostructure in the interface of flame-made nanoparticles, bulk Cr oxide exists over the surface of TiO₂ nanostructure. The photodegradation ability of TiO₂/Cr catalyst with Ti/Cr atomic ratio of 40 was highly related to the existence of Cr⁶⁺ species which strongly interacted with TiO₂. The reduction peaks in Cr-doped TiO₂ shifted to much lower temperatures, due to the increase in the reduction potential of titania and chromium species. The strong interaction (formation of Cr–O–Ti bonds) is the main reason that Cr/TiO₂ is an active photocatalyst in visible light. Among all of the catalysts tested, the system with Ti/Cr atomic ratio 40 demonstrated a superior catalytic performance with the rate constant of 0.812 m³ g^–1 mol^–1 under visible light irradiation. The proposed route of the catalytic activity of the above material in visible light involves the reaction of dopant level electrons with surface Cr, which makes available valence band holes to perform oxidation reactions

Influence of SiO₂ on M/TiO₂ (M = Cu, Mn, and Ce) Formulations for Low-Temperature Selective Catalytic Reduction of NO_<i>x</i> with NH₃: Surface Properties and Key Components in Relation to the Activity of NO_<i>x</i> Reduction

A series of M/TiO₂ and M/TiO₂–SiO₂ (with M = Mn, Cu, and Ce) catalysts were prepared by adopting a wet–impregnation method and investigated for the selective catalytic reduction (SCR) of NO_<i>x</i> in the temperature range of 100–500 °C with excess (10 vol %) oxygen in the feed at industrially relevant conditions. Our X-ray diffraction (XRD) results suggest that the growth of the crystalline TiO₂ phase is strongly inhibited because of SiO₂ migration into the TiO₂ lattice. The increase of SiO₂ molar content in the TiO₂–SiO₂ support led to the decrease in the anatase phase of the titania peak intensity of the XRD spectrum and also exhibited a lower crystallinity of TiO₂ with no phase transition of anatase to rutile. Our X-ray photoelectron spectroscopy (XPS) depth profile analysis illustrated that the surface atomic ratio of Cu¹⁺/ Cu²⁺ wasgreatly enhanced with an increase in TiO₂ content in the TiO₂–SiO₂ support, and these results are consistent with the H₂-TPR results in which the additional reduction peak evolved at 200 °C for the copper-loaded titania-rich (Cu/TiO₂) catalyst. The high activity of the Cu-based TiO₂ formulations has been assigned to the enhancement in the formation of Cu¹⁺ active sites, existence of surface Cu²⁺, Cu¹⁺ species, and the increment of reduction potentials of the surface copper species. The Ce³⁺/Ce⁴⁺ and Ce³⁺/Ce^<i>n+</i> atomic ratio (1.14 and 0.53, respectively) in the Ce/TiO₂ catalyst calculated from deconvoluted XPS spectra are much higher than that of Ce/TiO₂–SiO₂ (1:1) and Ce/TiO₂–SiO₂ (3:1). The existence of the higher Ce³⁺ surface species over CeO₂/TiO₂ illustrates the increment of surface oxygen vacancies and thus facilitates the adsorption of oxygen species or activates reactants in the SCR reaction. The relative atomic percentage value of Mn⁴⁺/Mn³⁺ characterized by deconvoluted XPS was significantly high (Mn⁴⁺/Mn³⁺ = 1.98) for the Mn/TiO₂ compared to Mn/TiO₂–SiO₂ catalysts (Mn⁴⁺/Mn³⁺ = 1.23, 1.75). When ceria was supported on pure TiO₂, the low-temperature reduction peak was broad and less defined, and the reducibility in the low temperature range was much less pronounced. On the other hand, the addition of ceria to titania with strong reciprocal interaction is generally perceived as a shift in the bulk reduction temperature to lower values, to about 500–650 °C. As bigger Ce⁴⁺ ions enter the lattice structure to proxy the Ti⁴⁺ ions with smaller ionic radii (2.48 and 2.15 Å, respectively), the lattice could become highly strained. The NO_<i>x</i> conversions and the apparent kinetic constant of the catalyst <i>k</i>_ac over the Cu, Mn, Ce-loaded on different support TiO₂ and TiO₂–SiO₂ (3:1 and 1:1) catalysts measured under steady-state conditions demonstrated higher activity of the Ti-rich materials