Cobalt–iridium impregnated zirconium-doped mesoporous silica as catalysts for the selective catalytic reduction of NO with ammonia

Modification of Silica with Sucrose and Ammonium Fluoride Agents: A Facile Route to Prepare Supports of Iridium Catalysts for Hydrogenation Reaction

Mesoporous silica materials were synthesized using inexpensive and environmentally friendly sucrose as a porogeneous agent. It was found that the presence of sucrose and the products of its chemical transformation during synthesis (e.g., furfural polymer) significantly affected the structure of the obtained porous silica. The influence of synthesis conditions (pH, temperature, time) on the textural properties of the final materials was determined. Samples obtained in an acidic medium, at pH = 1, and treated at room temperature, yielded products with a large surface area and a narrow pore size distribution in the range of 2-5 nm, while the synthesis at pH = 8 allowed for the formation of mesoporous systems with pores in the range of 14-20 nm. To generate acidity, the silicas were modified with an ammonium fluoride solution and then used as supports for iridium catalysts in a hydrogenation reaction, with toluene as a model hydrocarbon. The influence of parameters such as specific surface area, support acidity, and iridium dispersion on catalytic activity was determined. It was shown that modification with sucrose improved the porous structure, and NH4F modification generated acidity. These parameters favored better reducibility and dispersion of the active phase, resulting in higher activity of the catalysts in the studied hydrogenation reaction.

Studies of New Iridium Catalysts Supported on Modified Silicalite-1-Their Structure and Hydrogenating Properties

This paper investigates the catalytic properties of the iridium catalysts supported on modified silicalite-1. Post-synthesis modification of silicalite-1, with solutions of ammonium compounds (NH₄F and NH₄OH), appeared to be an efficient method to generate the acidic sites in starting support. The modification of support led not only to changes in its acidity but also its porosity-formation of additional micro- and mesopores. The novel materials were used as supports for iridium. The iridium catalysts (1 wt.% Ir) were characterized by N₂ adsorption/desorption measurements, temperature-programmed reduction with hydrogen (TPR-H₂), H₂ chemisorption, transmission electron microscopy (TEM), temperature-programmed desorption of ammonia (TPD-NH₃), X-ray photoelectron spectroscopy (XPS) and tested in the hydrogenation of toluene reaction. The catalytic activity of iridium supported on silicalite-1 treated with NH₄OH (higher porosity of support, better dispersion of active phase) was much higher than that of Ir supported on unmodified and modified with NH₄F silicalite-1.

Insights into the mechanism for the selective catalytic reduction of NOxwith NH3on (MnO)2+/ZSM-5: A DFT study

In this work, the reaction mechanisms for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with NH3on a (MnO)[Formula: see text]/ZSM-5 catalyst were investigated based on the density functional theory (DFT) method. Our calculations showed that the NH3could strongly adsorb on the (MnO)[Formula: see text]/ZSM-5 catalyst as compared to NO. The proposed reaction pathway, NH3(ads)[Formula: see text]NH[Formula: see text]H[Formula: see text]NH2(ads) [Formula: see text] NO(ads)[Formula: see text] NH2NO[Formula: see text]NHNO [Formula: see text] H[Formula: see text]N[Formula: see text]H2O, was more favorable with smaller activation barrier (1.40[Formula: see text]eV) of the rate-determining step. The compared reaction process that the adsorbed NH3reacted directly with adsorbed NO was difficult to happen for the higher activation barrier. Meanwhile, the framework oxygen participated in the oxidation process from ammonia to NH2, thereby increasing its availability for the reaction. In addition, the regeneration process of active site in the presence of NH3and NO2was explored, and the rate-limiting step possessed an activation barrier of 1.46[Formula: see text]eV. The NH2NO species was formed as the crucial intermediate and subsequently decomposed into the N2and H2O.

Catalytic oxidation of nitric oxide (NO) over different catalysts: an overview

Nitrogen oxides (mainly NO) are one of the major air pollutants that lead to a number of environmental problems such as photochemical smog, acid rain and haze.

Non-thermal plasma-treated gold catalyst for CO oxidation

Plasma under oxygen atmosphere is available for promoting the microporosity, redox properties, and the catalytic performance of gold nanoparticles.