Ammonia temperatures

Accordingly the enthalpy change of reaction for two gmol of ammonia temperature is given by... 

Lok, B.M., Marcus, K.K., and AngeU, C.L (1986) Characterization of zeolite addity. 11. Measurement of zeolite acidity by ammonia temperature programmed desorption and FTIR spectroscopy techniques. Zeolites, 6, 185-194. 

In the case of alkenes, 1-pentene reactions were studied over a catalyst with FAU framework (Si/Al2 = 5, ultrastable Y zeoHte in H-form USHY) in order to establish the relation between acid strength and selectivity [25]. Both fresh and selectively poisoned catalysts were used for the reactivity studies and later characterized by ammonia temperature programmed desorption (TPD). It was determined that for alkene reactions, cracking and hydride transfer required the strongest acidity. Skeletal isomerization required moderate acidity, whereas double-bond isomerization required weak acidity. Also an apparent correlation was established between the molecular weight of the hard coke and the strength of the acid sites that led to coking. 

Evidence of poisoning of acidic sites was also obtained by IR spectroscopy. The number of protons on the ferrierite surface was estimated by the intensity of the OH band at 3600 cm". After a few hours on stream, the absorbance of this OH vibration was reduced by a factor of 2.4 in contrast, the acidity of the sohd probed by ammonia temperature-programmed desorption (TPD) decreased by a larger factor (53,58). These results were considered as evidence of the poisoning of a large number of acidic sites and a partial blocking of pores, rendering some acidic sites inaccessible to the reactant. 

Figure i Idealized TPD pattern for characterizing acid sites by desorption of a simple base like ammonia. Temperature at maximum gives Information on the Intensive factor area under the curves gives quantitative Information on the extensive factor. 

Reactivity and acidity Ammonia temperature-programmed desorption (NH3TPD) Calorimetry liquid-liquid, liquid-solid and gas-solid Probe molecule microreactivity testing... 

An important consideration that affects the transport and partitioning of ammonia in the environment is that ammonia is a base. As a base, the physical and chemical properties of ammonia are pH-dependent, and thus, environmental fate processes that influence the transport and partitioning of NH3 will also be those that are pH-dependent. For some environmental fate processes, a change in pH may only affect the relative rate of a process, while for others, it could change the direction or overall result of that process. The influence of pH on the environmental fate of ammonia will be discussed where appropriate. Temperature is also an important consideration in the environmental fate of ammonia. Temperature, although to a lesser extent than pH, affects the ammonia-ammonium equilibrium. 

Ammonia temperature programmed desorption (NH3-TPD) curves were recorded by placing 1.5 g of zeolite particles (60x140 mesh) into a tube furnace and heated to 125°C. Aimnonia was supplied to the zeolite in dry air at a concentration of 1,000 mg/m (1,450 ppm) and a flow rate of 2 L/min. The aimnonia flow was terminated once the effluent concentration equaled the feed concentration, and clean air was subsequently purged through the zeohte imtil ammonia was no longer detected in the effluent. The temperature was then... 

Alternatively, can be used to calculate the activation energy of adsorption for the chemisorbed base, which is proportional to the heat of adsorption. However, determination of heats of adsorption from ammonia temperature-programmed desorption (TPD), although popular for its simplicity, may lead to inconsistent data because the experimental protocols may greatly influence the results [21]. 

Fig. 3.51 Ammonia temperature-programmed desorption from the iron (111) face with and without co-adsorbed potassium ...

Figure 4.10. Ammonia temperature-programmed desorption from clean Fe(lll) and K/Fe(lll) surfaces/ The desorption temperature of ammonia from Fe(lll) is lowered in the presence of potassium. Thus potassium lowers the adsorption energy of ammonia on the iron surface.

The studies on reaction rates and ammonia temperature-programmed desorption suggest that planes containing C7 sites, such as the Fe(211) and Fe(lll) surfaces, are being created during the water-vapor pretreatments whether aluminum oxide is present or not. However, only when aluminum oxide is present will these active surfaces remain stable and not reconvert to less active surfaces [i.e., Fe(llO) and Fe(lOO) planes]. 

Figure 5. Ammonia temperature-programmed desorption curves of various titanium oxide samples.

Type Typical Pressure kg/cm g Design t Ammonia Temperature per t Steel °C Capacity Range t ammonia Refrigeration Compressor... 

Ytterbium reacts very rapidly with cyclopentadiene at liquid ammonia temperatures or lower (Calderazzo et al, 1966 Fischer et al, 1965). After evaporation of the ammonia three compounds have been isolated by fractional sublimation of the reaction mixture YbCp3, nNH3 (deep green) YbCpz (red) perhaps contaminated with YbCp2H and a yellow product which seems to be a mixture of Yb2Cp4N2H4... 

Table 1 shows the amount loaded and the textural properties of the monoliths prepared at different conditions. On increasing the amount of added ammonia, temperature and stirring time, the amount loaded increases, as well as the total surface area and porosity of the monolith. However, the pore size decreased drastically (Fig. 2) and short whiskers appeared on the alumina pore walls (Fig. ID). These whiskers are... 

The number of acid sites on pillared montmorillonite was determined by means of ammonia temperature-programmed desorption(TPD). In each TPD experiment, a sample of 0.5 g was treated in vacuo at 673 K for 1 h and then cooled to 373 K. Ammonia was adsorbed at 373 K for 30 min and evacuated for 30 min. This sample was heated from 373 to 973 K at a rate of 10 K/min and the desorbed ammonia was monitored by thermal conductivity detector. As water was simultaneously desorbed with ammonia above 673 K, the ammonia TPD spectrum was obtained by point-by point subtraction of the water desorption spectrum obtained with the sample which had not adsorbed ammonia. 

Slurry 50 g silica gel G, 100 ml water, and 0.5 g L-aspartic acid, some drops of ammonia. Temperature 17°C... 

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