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

Effects of the Ce and Cr Contents in Fe–Ce–Cr Ferrite Spinels on the High-Temperature Water–Gas Shift Reaction

A series of Fe–Ce–Cr ternary oxide catalysts with different Fe/Ce/Cr atomic ratios have been synthesized using a coprecipitation method. The effects of the contents of both Ce and Cr in the Fe–Ce–Cr catalyst on the high-temperature water–gas shift (HT-WGS) reaction were investigated. Among the Fe–Ce–Cr catalyst with different atomic concentrations of Ce and Cr, the catalyst with a 10:1:1 atomic ratio showed the best performance in terms of HT-WGS activity. We found a strong synergistic effect between the dopants (Ce and Cr) and Fe that contributes the highest lattice strain and lowest crystallite size in Fe–Ce–Cr with an atomic ratio of 10:1:1 compared to other compositions. The Fe/Ce/Cr atomic ratio of 10:1:1 generated the highest lattice disorder in the Fe–Ce–Cr catalyst, as determined by Raman analysis. Our H₂ TPR results confirmed that the reduction temperature of hematite (Fe₂O₃) to magnetite (Fe₃O₄) increased upon the addition of Cr. Conversely, the incorporation of Ce significantly decreased the reduction temperature for hematite-to-magnetite conversion until the Fe/Ce atomic ratio reached 10:1. The XPS results demonstrated that only Ce acts as a chemical advocate for iron oxide in the HT-WGS by facilitating the surface Fe²⁺/Fe³⁺ redox cycle through its Ce³⁺/Ce⁴⁺ redox couple. However, Cr does not chemically support the iron oxide catalyst because of its single 3+ oxidation state. The Fe²⁺/Fe³⁺ redox cycle was greatly facilitated over the surface of the catalyst at an Fe/Ce/Cr atomic ratio of 10:1:1 compared to the other investigated samples with different Fe/Ce and Fe/Cr compositions. The better HT-WGS performance of the Fe–Ce–Cr (10:1:1) catalyst compared to all of the other catalysts can be mainly ascribed to its high lattice strain or disorder and excellent surface redox properties, linked to the Fe²⁺/Fe³⁺ and Ce³⁺/Ce⁴⁺ redox pairs

A Review of Low Temperature NH₃-SCR for Removal of NO_x

The importance of the low-temperature selective catalytic reduction (LT-SCR) of NOx by NH3 is increasing due to the recent severe pollution regulations being imposed around the world. Supported and mixed transition metal oxides have been widely investigated for LT-SCR technology. However, these catalytic materials have some drawbacks, especially in terms of catalyst poisoning by H2O or/and SO2. Hence, the development of catalysts for the LT-SCR process is still under active investigation throughout seeking better performance. Extensive research efforts have been made to develop new advanced materials for this technology. This article critically reviews the recent research progress on supported transition and mixed transition metal oxide catalysts for the LT-SCR reaction. The review covered the description of the influence of operating conditions and promoters on the LT-SCR performance. The reaction mechanism, reaction intermediates, and active sites are also discussed in detail using isotopic labelling and in situ FT-IR studies

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

Superior catalytic performance of a CoOx/Sn–CeO2 hybrid material for catalytic diesel soot oxidation

The present work reports the synthesis and characterization of a ceria-based hybrid nano-catalyst composed of a Snx+ dopant incorporated in the CeO2 crystal lattice and a finely dispersed CoOx phase on its surface. Characterization studies showed that the Ce, Sn, and Co cations were present in their multivalent oxidation states. The CoOx was confirmed to be Co3O4. A HRTEM image depicted the presence of a stepped catalyst surface, which has a special importance in enhancing the heterogeneous catalytic reaction rate carried out on the solid catalyst surface. The prepared materials were subjected to diesel soot oxidation catalysis. Model soot was combusted in the presence of air under both tight and loose contact conditions of the catalyst and soot. The hybrid catalyst exhibited improved performance compared to the Sn-doped nano-CeO2 and nano-CeO2 supported CoOx catalysts. The improved catalytic activity was attributed to the existence of synergism among the multivalent cations and the stepped surface of the hybrid catalyst, which act as the potential active sites for oxidation catalysis