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

Ce-Based Catalysts for the Selective Catalytic Reduction of NO_<i>x</i> in the Presence of Excess Oxygen and Simulated Diesel Engine Exhaust Conditions

A family of various cerium oxide-based catalysts were synthesized by adopting flame aerosol (FSP), coprecipitation, wet impregnation, and hydrothermal synthesis techniques. The resulting catalysts were explored for the selective catalytic reduction (SCR) of NO_<i>x</i> using NH₃ as reductant. In our studies, both the preparation method and the Ce/W ratios were found to be critical variables for successful catalyst promotion. For the industrial realization, we have scaled up the SCR activity tests. The microreactor catalytic formulations at simulated diesel engine exhaust conditions revealed that the Ce–W (1:1 atomic ratio) and Ce–W/TiO₂ catalysts showed high deNO_<i>x</i> activity, while the other catalysts’ activity was found to be rather low. Of interest is the finding that the Ce–W/TiO₂/cordierite and Ce–W (1:1 atomic ratio)/cordierite formulations show impressive deNO_<i>x</i> performance and high N₂ selectivity with respect to a commercial vanadia based reference currently used for mobile applications. To gain fundamental insights which may acquaint further improvements to the promoted Ce-based catalysts, X-ray photoelectron spectroscopy and other characterizations were executed to study the relationship between catalyst surface and NO_<i>x</i> reduction activity. Our XRD results indicate smaller lattice parameters of prepared catalysts compared to that of CeO₂ (0.540 nm). The crystal lattice contraction is attributed to the lesser ionic radius of relevant foreign metal ions (W⁶⁺ = 0.067 nm and Ti⁴⁺ = 0.074 nm) in relation to Ce⁴⁺ (0.092 nm) in the host lattice. This lattice shrinkage elucidates the formation of solid solutions. These results illustrate that the synthesis technique and various promoters could indeed influence the lattice structures and electronic state of the active components. The XPS results illustrate the higher atomic ratios of Ce³⁺/(Ce³⁺ + Ce⁴⁺) 0.30 and 0.29 in Ce–W/TiO₂ and Ce–W (1:1) coprecipitation catalysts, respectively, compared to other samples. The higher surface Ce³⁺/Ce⁴⁺ ratio in Ce–W (1:1) coprecipitation and Ce–W/TiO₂ samples indicate the enrichment in surface oxygen vacancies, which results in activation of reactive molecules and enhanced adsorption of oxygen species in SCR reaction. Interestingly, the surface atomic ratio of Ce³⁺/Ce⁴⁺ and Ce³⁺/Ce^<i>n</i>+ are interrelated to the SCR activity of the individual catalysts

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