Selective catalytic oxidation of ammonia into nitrogen over PCH modified with copper and iron species

Textural Characterization by Using an Alternative Langmuir Isotherm and a New Thickness Function

Samples with micropores can not be adequately described by using the Langmuir isotherm. The Langmuir expression is obtained by using the monolayer assumption, which is not valid in samples with micropores. Then, we propose to include in the isotherm a corrective parameter related to the sample porosity. We show that the modified isotherm enables us to describe the experimental values for different samples (aluminas, clays, silicas, zeolites, and zirconias) in low and full relative pressure ranges. Indeed, a new thickness function for the adsorbate layer in terms of the relative pressure is proposed. Then, a better description of the external surface areas, mesopores, and micropores of the samples can be obtained with the new thickness function. The VBS model with this new thickness shows a better pore distribution description.

Enhancement Properties of Zr Modified Porous Clay Heterostructures for Adsorption of Basic-Blue 41 Dye: Equilibrium, Regeneration, and Single Batch Design Adsorber

Zirconium porous clay heterostructures (Zr-PCH) were synthesized using intercalated clay minerals by zirconium species with different contents of zirconium. The presence of zirconium and silica species was confirmed by X-ray diffraction, X-ray fluorescence, and magic-angle spinning nuclear magnetic resonance. The insertion of zirconium improved the thermal stability, the specific surface area with a maximum of 950 m²/g, and the acidity concentration of 0.993 mol of protons per g of solid. These materials were used to adsorb the basic blue-41 from aqueous solution. The adsorption efficiency was examined at different conditions, with a maximum adsorbed amount of 346 mg/g as estimated from Langmuir model. This value was dependent on zirconium content in the PCHs. The adsorption process was found to be favorable and spontaneous. The efficiency of the spent materials was maintained after five reuse cycles with a decrease by 15% of the original value for a particular Zr-PCH material with a Zr content of 6.82%. Single stage batch adsorber was suggested using the mass balance equation and Langmuir isotherm model. The amount of PCH materials required depended on the target percentage of adsorption at specific volume and initial concentration of the basic-blue-41 dye solution.

A Comparative Mini-Review on Transition Metal Oxides Applied for the Selective Catalytic Ammonia Oxidation (NH3-SCO)

The selective catalytic oxidation of NH₃ (NH₃-SCO) into N₂ and H₂O is an efficient technology for NH₃ abatement in diesel vehicles. However, the catalysts dedicated to NH₃-SCO are still under development. One of the groups of such catalysts constituted transition metal-based catalysts, including hydrotalcite-derived mixed metal oxides. This class of materials is characterized by tailored composition, homogenously dispersed mixed metal oxides, exhibiting high specific surface area and thermal stability. Thus, firstly, we give a short introduction to the structure and composition of hydrotalcite-like materials and their applications in NH₃-SCO. Secondly, an overview of other transition metal-based catalysts reported in the literature is given, following a comparison of both groups. The challenges in NH₃-SCO applications are provided, while the reaction mechanisms are discussed for particular systems.

Modified Layered Silicas as Catalysts for Conversion of Nitrogen Pollutants in Flue Gases—A Review

This paper is focused on the recent achievements in the studies of modified layered zeolites and cationic layered clay minerals. These materials are very promising catalysts in green chemistry processes, such as selective catalytic reduction of NOx with ammonia (NH3-SCR) and selective catalytic oxidation of ammonia to dinitrogen (NH3-SCO). Special attention is paid to the roles of the micro- and mesoporous structures of the catalytic materials, the type and location of deposited transition metals, as well as surface acidity in the design of effective catalysts for the NH3-SCR and NH3-SCO processes. The majority of the presented analysis is based on the authors’ research.

Zn supported on titania-doped mesoporous silicate MCM-41 as efficient catalysts for acetylene hydration

A highly efficient grafting method to synthesise Ti-doped MCM-41 mesoporous supports and their respective Zn catalysts was investigated.

Advances in selective catalytic oxidation of ammonia to dinitrogen: a review

Selective catalytic oxidation of ammonia to dinitrogen.

Catalytic ozonation of ammonia using biomass char and wood fly ash

Catalytic ozonation of gaseous ammonia was investigated at room temperature using wood fly ash (WFA) and biomass char as catalysts. WFA gave the best results, removing ammonia (11 ppmv NH(3), 45% conversion) at 23 degrees C at a residence time of 0.34 s, using 5 g of catalyst or ash at the lowest ozone concentration (62 ppmv). Assuming pseudo zero order kinetics in ozone, a power rate law of -r(NH3) = 7.2 x 10(-8) C(NH3)(0.25) (r, mol g(-1)s(-1), C(NH3)molL(-1)) was determined at 510 ppmv O(3) and 23 degrees C for WFA. Water vapor approximately doubled the oxidation rate using WFA and catalytic ozonation activity was not measured for the char without humidifying the air stream. Overall oxidation rates using the crude catalysts were lower than commercial catalysts, but the catalytic ozonation process operated at significantly lower temperatures (23 vs. 300 degrees C). Nitric oxide was not detected and the percentage of NO(2) formed from NH(3) oxidation ranged from 0.3% to 3% (v/v), with WFA resulting in the lowest NO(2) level (at low O(3) levels). However, we could not verify that N(2)O was not formed, so further research is needed to determine if N(2) is the primary end-product. Additional research is required to develop techniques to enhance the oxidation activity and industrial application of the crude, but potentially inexpensive catalysts.