Ammonia spatial distribution

Dragosits U, Sutton MA, Place CJ, Bayley AA (1998) Modelling the spatial distribution of agricultural ammonia emissions in the UK. Environ Pollut 102 195-203... 

By contrast, there is no doubt or any contradictions in literature concerning the importance of macro-kinetic factors (heat- and mass-transfer processes) in the reactions discussed in this section. It is generally realized that these processes proceed in spatially distributed systems and generate sharp gradients of parameters (temperature, pressure, density, concentrations, etc). It could be noted here a distinct similarity of alkane oxidation over Pt-group metals at short contact times and well studied and practically implemented ammonia oxidation and cyanic acid synthesis reactions, in which transfer processes play a dominant role (see Satterfield, 1970). 

A good match between experimental data (symbols) and simulations (thick lines) is evident in terms both of ammonia conversion and of NOx yield, while some deviations are present between 275 and 500 °C in terms of N2 and N2O concentration. Similar results were obtained analyzing the effect of NO2/NOX, emphasizing that the overall performance of combined SCR -I- PGM systems results from a simple superposition of the respective catalytic chemistries, which however provides different overall behaviors depending on the relative spatial distribution of the two catalyst components. 

Fig. 7.25 Spatial distribution of some of the relevant molecular orbitals in phenol with three membered ammonia cluster. (Reprinted with permission from K. Nagashima et al., J. Phys. Chem. A 116, 11167 (2012)).

Returning to the phenol ammonia system, we next show in Fig. 7.33 how the spatial distribution of the unpaired electrons evolves in time. Before the first transition (see panel (a)) the unpaired electrons are distributed on the benzene ring and the oxygen atom. After the first transition (panel (b)), some large part of the unpaired electron density moves to AMI. At time 211 fs (after the second nonadiabatic transition, panel (d)), a large component of the unpaired electron is found on AM2, through a transient state at 148 fs (panel (c)). 

The spatial distribution of acidity in acid-treated ZSM-5 zeolite is not uniform [104], the most acidic sites, and particularly Lewis sites, being located within the channel structure of the material where they are not always readily accessible to ammonia molecules at 416 K. 

Borchert R 1978 Time course and spatial distribution of phenylalanine ammonia-lyase and peroxidase activity in wounded potato tuber tissue. Plant Physiol 62 789-793... 

Based on a quadrupole ICP-MS, another technique, termed collision/reaction cell, has frequently been used to reduce polyatomic ion interferences. " These techniques provide simple, efficient, and low-cost methods in the face of many difficult interference problems. In these methods, ions to be analyzed first enter a radio-frequency-only multipole (e.g. a quadrupole, hexapole, or octapole), in which the analytes react with the collision/reaction gas, which is usually oxygen, ammonia, xenon, or methane, " to remove polyatomic interference or generate a new analyte ion of mjz showing less interference. The RP-only multipole does not separate ions like a traditional quadrupole, but it has profound influence on collisional focusing of ions, both of the energy and spatial distributions. An example of removing the polyatomic interference is shown below, which uses ammonia gas to reduce any "" Ar" " interference in the measurement of " Ca ... 

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