State-of-Art Review of NO Reduction Technologies by CO, CH4 and H2

Exploring the carbonic anhydrase-mimetic [(PMDTA)2ZnII2(OH-)2]2+ for nitric oxide monooxygenation

In biology, nitrite (NO2-) serves as a storage pool of nitric oxide (NO); however, the formation of NO2- from NO is still under investigation. Here, we report the NO monooxygenation (NOM) reaction of a ZnII-hydroxide complex (1), producing a ZnII-nitrito complex {2, (ZnII-NO2-)} + H2.

Zeolite Properties, Methods of Synthesis, and Selected Applications

Zeolites, a group of minerals with unique properties, have been known for more than 250 years. However, it was the development of methods for hydrothermal synthesis of zeolites and their large-scale industrial applications (oil processing, agriculture, production of detergents and building materials, water treatment processes, etc.) that made them one of the most important materials of the 20th century, with great practical and research significance. The orderly, homogeneous crystalline and porous structure of zeolites, their susceptibility to various modifications, and their useful physicochemical properties contribute to the continuous expansion of their practical applications in both large-volume processes (ion exchange, adsorption, separation of mixture components, catalysis) and specialized ones (sensors). The following review of the knowledge available in the literature on zeolites aims to present the most important information on the properties, synthesis methods, and selected applications of this group of aluminosilicates. Special attention is given to the use of zeolites in agriculture and environmental protection.

Noble Metal Nanoparticles Decorated Boron Nitride Nanotubes for Efficient and Selective Low-Temperature Catalytic Reduction of Nitric Oxide with Carbon Monoxide

Parallel to CO₂ emission, NO_x emission has become one of the menacing problems that seek a simple, durable, and high-efficiency deNO_x catalyst. Herein, we demonstrated simple syntheses of platinum group metal nanoparticle-decorated f-BNNT (PGM = Pd, Pt, and Rh, and f-BNNT stands for -OH-functionalized boron nitride nanotubes) as a catalyst for efficient and selective reduction of NO by CO at low-temperature conditions. PGM/f-BNNT with a low amount of noble metal nanoparticles (0.7-0.8 wt %) presents very efficient catalytic activity for NO reduction as well as CO oxidation during their removal process. The removal efficiencies of NO and CO with Pd/f-BNNT, Pt/f-BNNT, and Rh/f-BNNT catalysts were investigated under various temperatures, flow rates, and reaction times, respectively. For most cases, NO catalytic reduction with CO reaction was >99% at a temperature as low as ∼200 °C. The catalyst robustness and efficiency were also verified by presenting almost 100% conversion of NO using a Rh/f-BNNT catalyst, which was aged under humid air at 600 and 700 °C for 24 h, respectively. The synergic effect of the catalytic efficacy of the well-dispersed noble metal nanoparticles and the excellent surface properties of BNNT are reasons for the high selectivity and catalytic property at a low temperature. On the basis of this investigation, we demonstrated that the noble metal nanoparticle-decorated f-BNNT catalysts are possible to save expensive PGM catalysts, such as Pt, Pd, and Rd, as much as 100 times while presenting similar or better catalytic performance for simultaneous NO and CO removals.

Al-Decorated C2N Monolayer as a Potential Catalyst for NO Reduction with CO Molecules: A DFT Investigation

Developing efficient and economical catalysts for NO reduction is of great interest. Herein, the catalytic reduction of NO molecules on an Al-decorated C2N monolayer (Al-C2N) is systematically investigated using density functional theory (DFT) calculations. Our results reveal that the Al-C2N catalyst is highly selective for NO, more so than CO, according to the values of the adsorption energy and charge transfer. The NO reduction reaction more preferably undergoes the (NO)2 dimer reduction process instead of the NO direct decomposition process. For the (NO)2 dimer reduction process, two NO molecules initially co-adsorb to form (NO)2 dimers, followed by decomposition into N2O and Oads species. On this basis, five kinds of (NO)2 dimer structures that initiate four reaction paths are explored on the Al-C2N surface. Particularly, the cis-(NO)2 dimer structures (Dcis-N and Dcis-O) are crucial intermediates for NO reduction, where the max energy barrier along the energetically most favorable pathway (path II) is as low as 3.6 kcal/mol. The remaining Oads species on Al-C2N are then easily reduced with CO molecules, being beneficial for a new catalytic cycle. These results, combined with its low-cost nature, render Al-C2N a promising catalyst for NO reduction under mild conditions.

Investigation on Spectral Characteristics of Gliding Arc Plasma Assisted Ammonia Lean Combustion

Ammonia as a non-carbon fuel is expected to play an important role in the future, but it is difficult to be effectively utilized at this stage due to its flame retardancy and other characteristics. Therefore, we propose to use gliding arc plasma combined with a swirl burner to enhance the combustion performance of ammonia. The electrical characteristics, electron density, gas rotational temperature and the distribution of key active species in the burner were studied via optical emission spectroscopy (OES). With the increase of equivalence ratio (EQR), the width of the Hα line decreases significantly, indicating that the electron density shows a downward trend, even as the gas rotational temperature shows an upward trend. When the equivalence ratio was 0.5, the gas rotational temperature increases by about 320 K compared with the pure air condition. During pure air discharge, there will still be obvious NO emission due to the plasma reaction, but with the addition of NH3, the NO content in the emission is significantly reduced. The light intensity of O atoms in the burner gradually decreases with the increase of the equivalence ratio, the light intensity of H atoms increases first and then decreases, and the light intensity of NH shows an upward trend. The reason may be that the plasma discharge effectively strengthens NH3(E)->NH2+H, NH2+H->NH+H2 and other reactions promote the initial reaction step of NH3 which thus effectively strengthens the NH3 combustion.

Tungsten Oxide Modified V2O5-Sb2O3/TiO2 Monolithic Catalyst: NH3-SCR Activity and Sulfur Resistance

In this study, a V2O5-Sb2O3/TiO2 monolithic catalyst was modified by introducing WO3. The WO3-modified catalyst exhibited enhanced catalytic activity in the measuring temperature range of 175–320 °C. The changes in dispersion of vanadia species were investigated by ultraviolet-visible (UV-Vis) spectroscopy and H2 temperature-programmed reduction (H2-TPR). A durability test was conducted in a wet SO2-containing atmosphere at 220 °C for 25 h. The sulfate deposition was estimated by temperature-programmed decomposition (TPDC) of sulfates, thermo-gravimetric (TG) analysis, and temperature-programmed desorption (TPD) of NH3. Isothermal SO2 oxidation and temperature-programmed surface reaction (TPSR) of NH4HSO4 with NO were performed. Based on these characterizations, effects of WO3 modification on the sulfate tolerance of the catalyst were explored.