Investigating catalytic reaction mechanisms could help guide the design of catalysts. Here, aimed at improving both the catalytic performance and SO 2 resistance ability of catalysts in the selective reduction of NO by NH 3 (NH 3 − SCR), an innovative CeO 2 −SiO 2 mixed oxide catalyst (CeSi2) was developed based on our understanding of both the sulfur poisoning and reaction mechanisms, which exhibited excellent SO 2 /H 2 O resistance ability even in the harsh working conditions (containing 500 ppm of SO 2 and 5% H 2 O). The strong interaction between Ce and Si (Ce−O−Si) and the abundant surface hydroxyl groups on CeSi2 not only provided fruitful surface acid sites but also significantly inhibited SO 2 adsorption. The NH 3 −SCR performance of CeSi2 was promoted by an enhanced Eley−Rideal (E−R) mechanism in which more active acid sites were preserved under the reaction conditions and gaseous NO could directly react with adsorbed NH 3 . This mechanism-enhanced process was even further promoted on sulfated CeSi2.
Para-, or 4-nitrophenol, and related nitroaromatics are broadly used compounds in industrial processes and as a result are among the most common anthropogenic pollutants in aqueous industrial effluent; this requires development of practical remediation strategies. Their catalytic reduction to the less toxic and synthetically desirable aminophenols is one strategy. However, to date, the majority of work focuses on catalysts based on precisely tailored, and often noble metal-based nanoparticles. The cost of such systems hampers practical, larger scale application. We report a facile route to bulk cobalt oxide-based materials, via a combined mechanochemical and calcination approach. Vibratory ball milling of CoCl2(H2O)6 with KOH, and subsequent calcination afforded three cobalt oxide-based materials with different combinations of CoO(OH), Co(OH)2, and Co3O4 with different crystallite domains/sizes and surface areas; Co@100, Co@350 and Co@600 (Co@###; # = calcination temp). All three prove active for the catalytic reduction of 4-nitrophenol and related aminonitrophenols. In the case of 4-nitrophenol, Co@350 proved to be the most active catalyst, therein its retention of activity over prolonged exposure to air, moisture, and reducing environments, and applicability in flow processes is demonstrated.
The development and implementation
of transition-metal-based precatalysts
have played crucial roles in modern organic synthesis. However, while
the use of such species greatly improves sustainability, their preparative
routes often rely on multiple time-, energy-, and solvent-intensive
steps. By leveraging solvent-free mechanochemical synthesis through
vibratory ball milling, we report the one-pot, one-step synthesis
of a range of first-row transition-metal bis(imino)pyridine complexes,
where both the ligand and coordination complex are assembled in situ.
Bis(imino)pyridine complexes of the first-row transition metals have
an extensive history of application as precatalysts for numerous bond-forming
transformations. The method reported herein facilitates access to
such species in a time-, solvent-, and space-saving manner which can
easily be adapted to any laboratory setting regardless of prior experience
with coordination complex synthesis.
“MoCl3(dme)” (dme = 1,2-dimethoxyethane)
is an important precursor for midvalent molybdenum chemistry, particularly
for triply Mo–Mo bonded compounds of the type Mo2X6 (X = bulky anionic ligand). However, its exact structural
identity has been obscure for more than 50 years. In search of a convenient,
large-scale synthesis, we have found that trans-MoCl4(Et2O)2 dissolved in dme can be cleanly
reduced with dimethylphenylsilane, Me2PhSiH, to provide
khaki Mo2Cl6(dme)2 in ∼90%
yield. If the reduction is performed on a small scale, single crystals
suitable for X-ray crystallography can be obtained. Two different
crystal morphologies were identified, each belonging to the P21/n space group, but with
slightly different unit cell constants. The refined structure of each
form is an edge-shared bioctahedron with overall Ci
symmetry and metal–metal separations on the order
of 2.8 Å. The bulk material is diamagnetic as determined by both
the Gouy method and SQUID magnetometry. Density functional theory
calculations suggest a σ2π2δ*2 ground state for the dimer with the diamagnetism arising
from a singlet diradical “broken symmetry” electronic
configuration. In addition to a definitive structural assignment for
“MoCl3(dme)”, this work highlights the utility
of organosilanes as easy to handle, alternative reductants for inorganic
synthesis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.